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Title: The Sea Shore
Author: Furneaux, William S.
Language: English
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*** Start of this LibraryBlog Digital Book "The Sea Shore" ***
Transcriber’s Note
Due to limitations of this format, some typographical features are not
possible. Italic and bold text is represented in this text as _italic_
and =bold=. Finally, the few superscripted characters are given
in-line, e.g. 'Ltd' or 'A1'.
The colored plates and other illustrations cannot be given here.
The approximate positions of each, including any caption text, is shown
as [Illustration: caption]. Those which are shown in the middle of
paragraphs are positioned at the nearest paragraph break.
Please consult the detailed note at the end of this text for any
corrections made, and for any other observations about the text.
THE SEA SHORE
+--------------------------------------------------------------+
| THE OUT-DOOR WORLD SERIES. |
| |
| THE OUT-DOOR WORLD; or, the Young Collector's Handbook. |
| By W. S. FURNEAUX. With 18 Plates (16 of which are |
| Coloured), and 549 Illustrations in the Text. Crown |
| 8vo, 6s. 6d. net. |
| |
| FIELD AND WOODLAND PLANTS. |
| By W. S. FURNEAUX. With 8 Plates in Colour, and numerous |
| other Illustrations by PATTEN WILSON, and from |
| Photographs. Crown 8vo, 6s. 6d. net. |
| |
| BRITISH BUTTERFLIES AND MOTHS. |
| By W. S. FURNEAUX. With 12 Coloured Plates and 241 |
| Illustrations in the Text. Crown 8vo, 6s. 6d. net. |
| |
| LIFE IN PONDS AND STREAMS. |
| By W. S. FURNEAUX. With 8 Coloured Plates and 331 |
| Illustrations in the Text. Crown 8vo, 6s. 6d. net. |
| |
| THE SEA SHORE. By W. S. FURNEAUX. |
| With 8 Coloured Plates and over 300 Illustrations in the |
| Text. Crown 8vo, 6s. 6d. net. |
| |
| BRITISH BIRDS. By W. H. HUDSON. |
| With a Chapter on Structure and Classification by FRANK E. |
| BEDDARD, F.R.S. With 16 Plates (8 of which are Coloured), |
| and 103 Illustrations in the Text. Crown 8vo, 6s. 6d. net. |
| |
| LONGMANS, GREEN & CO., 39 Paternoster Row, London, E.C.4 |
| New York, Toronto, Bombay, Calcutta and Madras. |
+--------------------------------------------------------------+
[Illustration: Plate I, A ROCK-POOL]
THE SEA SHORE
BY
W. S. FURNEAUX
AUTHOR OF
‘THE OUTDOOR WORLD’ ‘BRITISH BUTTERFLIES AND MOTHS’
‘LIFE IN PONDS AND STREAMS’ ETC.
[Illustration]
_WITH EIGHT PLATES IN COLOUR_
_AND OVER THREE HUNDRED ILLUSTRATIONS IN THE TEXT_
_NEW IMPRESSION_
LONGMANS, GREEN AND CO.
39 PATERNOSTER ROW, LONDON, E.C.4
NEW YORK, TORONTO
BOMBAY, CALCUTTA AND MADRAS
1922
All rights reserved
+------------------------------------------------+
| BIBLIOGRAPHICAL NOTE. |
| |
| _First published in September, 1903._ |
| |
| _Re-issue at Cheaper Price, July, 1911._ |
| |
| _New Impression, November, 1922._ |
| |
| |
| _Made in Great Britain_ |
| |
+------------------------------------------------+
PREFACE
To sea-side naturalists it must be a matter of great surprise that of
the inhabitants of our coast towns and villages, and of the
pleasure-seekers that swarm on various parts of the coast during the
holiday season, so few take a real interest in the natural history of
the shore. The tide flows and ebbs and the restless waves incessantly
roll on the beach without arousing a thought as to the nature and cause
of their movements. The beach itself teems with peculiar forms of life
that are scarcely noticed except when they disturb the peace of the
resting visitor. The charming vegetation of the tranquil rock-pool
receives but a passing glance, and the little world of busy creatures
that people it are scarcely observed; while the wonderful forms of life
that inhabit the sheltered nooks of the rugged rocks between the
tide-marks are almost entirely unknown except to the comparatively few
students of Nature. So general is this apparent lack of interest in the
things of the shore that he who delights in the study of littoral life
and scenes but seldom meets with a kindred spirit while following his
pursuits, even though the crowded beach of a popular resort be situated
in the immediate neighbourhood of his hunting ground. The sea-side
cottager is too accustomed to the shore to suppose that he has anything
to learn concerning it, and this familiarity leads, if not to contempt,
most certainly to a disinclination to observe closely; and the visitor
from town often considers himself to be too much in need of his
hard-earned rest to undertake anything that may seem to require energy
of either mind or body.
Let both, however, cast aside any predisposition to look upon the
naturalist’s employment as arduous and toilsome, and make up their minds
to look enquiringly into the living world around them, and they will
soon find that they are led onward from the study of one object to
another, the employment becoming more and more fascinating as they
proceed.
Our aim in writing the following pages is to encourage the observation
of the nature and life of the sea shore; to give such assistance to the
beginner as will show him where the most interesting objects are to be
found, and how he should set to work to obtain them. Practical hints are
also furnished to enable the reader to successfully establish and
maintain a salt-water aquarium for the observation of marine life at
home, and to preserve various marine objects for the purpose of forming
a study-collection of the common objects of the shore.
To have given a detailed description of all such objects would have been
impossible in a work of this size, but a large number have been
described and figured, and the broad principles of the classification of
marine animals and plants have been given such prominence that, it is
hoped, even the younger readers will find but little difficulty in
determining the approximate positions, in the scale of life, of the
various living things that come within their reach.
Of the many illustrations, which must necessarily greatly assist the
reader in understanding the structure of the selected types and in the
identification of the different species, a large number have been
prepared especially for this work.
CONTENTS
CHAPTER PAGE
I. THE GENERAL CHARACTERISTICS OF THE SEA SHORE 1
II. THE SEA-SIDE NATURALIST 21
III. SEA ANGLING 34
IV. THE MARINE AQUARIUM 51
V. THE PRESERVATION OF MARINE OBJECTS 71
VI. EXAMINATION OF MARINE OBJECTS--DISSECTION 91
VII. THE PROTOZOA OF THE SEA SHORE 102
VIII. BRITISH SPONGES 115
IX. THE COELENTERATES--JELLY-FISHES, ANEMONES, AND
THEIR ALLIES 127
X. STARFISHES, SEA URCHINS, ETC. 157
XI. MARINE WORMS 172
XII. MARINE MOLLUSCS 190
XIII. MARINE ARTHROPODS 256
XIV. MARINE VERTEBRATES 306
XV. SEA WEEDS 343
XVI. THE FLOWERING PLANTS OF THE SEA-SIDE 391
INDEX 425
LIST OF COLOURED PLATES
_Drawn by_ MR. ROBERT LILLIE _and reproduced by_
MESSRS. ANDRÉ & SLEIGH, LTD., _Bushey_.
PLATE I--_A ROCK-POOL_ _Frontispiece_
PLATE II--_SEA ANEMONES_ _To face p. 142_
1, 2, 3. _Actinia mesembryanthemum._
4. _Caryophyllia Smithii._
5. _Tealia crassicornis._
6. _Sagartia bellis._
7. _Balanophyllia regia._
8. _Actinoloba dianthus._
PLATE III--_SEA ANEMONES_ _To face p. 150_
1. _Sagartia troglodytes._
2. ” _venusta._
3. _Actinia glauca._
4. ” _chiococca._
5. _Bunodes Ballii._
6. ” _gemmacea._
7. _Anthea cereus._
8. _Sagartia rosea._
PLATE IV--_ECHINODERMS_ _To face p. 168_
1. _Asterias rubens._
2. _Goniaster equestris._
3. _Ophiothrix fragilis._
4. _Echinocardium cordatum._
5. _Echinus miliaris._
6. ” _esculentus._
PLATE V--_MOLLUSCS_ _To face p. 222_
1. _Solen ensis._
2. _Trivia europæa._
3. _Trochus umbilicatus._
4. ” _magnus._
5. _Littorina littorea._
6. ” _rudis._
7. _Haminea_ (_Bulla_) _hydatis_.
8. _Tellina._
9. _Capulus_ (_Pileopsis_) _hungaricus_.
10. _Chrysodomus_ (_Fusus_) _antiquus_.
11. _Buccinum undatum._
12, 13. _Scalaria communis._
14. _Pecten opercularis._
15. " _varius._
16. " _maximus._
PLATE VI--_CRUSTACEA._ _To face p. 290_
1. _Gonoplax angulata._
2. _Xantho florida._
3. _Portunus puber._
4. _Polybius Henslowii._
5. _Porcellana platycheles._
PLATE VII--_SEAWEEDS_ _To face p. 354_
1. _Fucus nodosus._
2. _Nitophyllum laceratum._
3. _Codium tomentosum._
4. _Padina pavonia._
5. _Porphyra laciniata_ (_vulgaris_).
PLATE VIII--_SEAWEEDS_ _To face p. 384_
1. _Chorda filum._
2. _Fucus vesiculosus._
3. ” _canaliculatus._
4. _Delesseria (_Maugeria_) sanguinea_.
5. _Rhodymenia palmata._
6. _Chondrus crispus._
7. _Ulva lactuca._
OTHER ILLUSTRATIONS
FIG. PAGE
1. CHALK CLIFF 3
2. WHITECLIFF (CHALK), DORSET 4
3. PENLEE POINT, CORNWALL 5
4. BALANUS SHELLS 6
5. A CLUSTER OF MUSSELS 7
6. BREAKERS 8
7. ILLUSTRATING THE TIDE-PRODUCING INFLUENCE OF THE MOON 10
8. ILLUSTRATING THE TIDES 11
9. SPRING TIDES AT FULL MOON 12
10. SPRING TIDES AT NEW MOON 12
11. NEAP TIDES 13
12. CHART SHOWING THE RELATIVE TIMES OF HIGH TIDE ON DIFFERENT
PARTS OF THE BRITISH COAST 16
13. THE VASCULUM 22
14. WIRE RING FOR NET 24
15. NET FRAME WITH CURVED POINT 24
16. RHOMBOIDAL FRAME FOR NET 24
17. RHOMBOIDAL NET 25
18. SEMICIRCULAR NET 25
19. THE DREDGE 25
20. THE CRAB-POT 26
21. AN OLD BIRD-CAGE USED AS A CRAB-POT 27
22. A YOUNG NATURALIST AT WORK 32
23. A GOOD HUNTING-GROUND ON THE CORNISH COAST 33
24. ROUND BEND HOOK WITH FLATTENED END 37
25. LIMERICK HOOK, EYED 37
26. METHOD OF ATTACHING SNOOD TO FLATTENED HOOK 38
27. METHOD OF ATTACHING SNOOD TO EYED HOOK 38
28. THE LUGWORM 39
29. THE RAGWORM 40
30. DIGGING FOR BAIT 41
31. METHOD OF OPENING A MUSSEL 42
32. FISHING FROM THE ROCKS 46
33. THE PATERNOSTER 48
34. SECTION OF AN AQUARIUM CONSTRUCTED WITH A MIXTURE OF
CEMENT AND SAND 54
35. CEMENT AQUARIUM WITH A GLASS PLATE IN FRONT 55
36. AQUARIUM OF WOOD WITH GLASS FRONT 56
37. HEXAGONAL AQUARIUM CONSTRUCTED OF ANGLE ZINC, WITH
GLASS SIDES 57
38. METHOD OF AERATING THE WATER OF AN AQUARIUM 65
39. AQUARIUM FITTED WITH APPARATUS FOR PERIODIC
OUTFLOW 67
40. JARS FOR PRESERVING ANATOMICAL AND BIOLOGICAL SPECIMENS 76
41. SHOWING THE DIFFERENT STAGES IN THE MAKING OF A SMALL
SPECIMEN TUBE 77
42. SMALL SPECIMEN TUBE MOUNTED ON A CARD 78
43. SMALL CRAB MOUNTED ON A CARD 82
44. SPRING FOR HOLDING TOGETHER SMALL BIVALVE SHELLS 84
45. THE TRIPLET MAGNIFIER 92
46. A SMALL DISSECTING TROUGH 93
47. CELL FOR SMALL LIVING OBJECTS 95
48. SHEET OF CORK ON THIN SHEET LEAD 99
49. WEIGHTED CORK FOR DISSECTING TROUGH 99
50. THE AMOEBA, HIGHLY MAGNIFIED 102
51. " " SHOWING CHANGES OF FORM 103
52. " " FEEDING 103
53. " " DIVIDING 104
54. A GROUP OF FORAMINIFERS, MAGNIFIED 105
55. A SPIRAL FORAMINIFER SHELL 106
56. A FORAMINIFER OUT OF ITS SHELL 106
57. THE SAME FORAMINIFER (FIG. 56) AS SEEN WHEN ALIVE 107
58. SECTION OF THE SHELL OF A COMPOUND FORAMINIFER 107
59. SECTION OF A NUMMULITE SHELL 108
60. _Globigerina bulloides_, AS SEEN WHEN ALIVE, MAGNIFIED 108
61. SECTION OF A PIECE OF NUMMULITIC LIMESTONE 109
62. A GROUP OF RADIOLARIAN SHELLS, MAGNIFIED 111
63. THREE INFUSORIANS, MAGNIFIED 113
64. A PHOSPHORESCENT MARINE INFUSORIAN (_Noctiluca_),
MAGNIFIED 114
65. SECTION OF A SIMPLE SPONGE 116
66. DIAGRAMMATIC SECTION OF A PORTION OF A COMPLEX SPONGE 117
67. HORNY NETWORK OF A SPONGE, MAGNIFIED 118
68. _Grantia compressa_ 120
69. SPICULES OF _Grantia_, MAGNIFIED 120
70. _Sycon ciliatum_ 121
71. _Leucosolenia botryoides_, WITH PORTION MAGNIFIED 121
72. _Chalina oculata_ 122
73. _Halichondria panicea_ 123
74. SPICULES OF _Halichondria_, MAGNIFIED 124
75. AN OYSTER SHELL, BORED BY _Cliona_ 124
76. SPICULES OF _Cliona_ 125
77. THREAD CELLS OF A COELENTERATE, MAGNIFIED 127
78. THE SQUIRREL'S-TAIL SEA FIR (_Sertularia argentea_),
WITH A PORTION ENLARGED 128
79. _Sertularia filicula_ 129
80. " _cupressina_ 130
81. THE HERRING-BONE POLYPE (_Halecium halecinum_) 131
82. _Tubularia indivisa_ 132
83. THE BOTTLE BRUSH (_Thuiaria thuja_) 132
84. _Antennularia antennia_ 133
85. _Aurelia aurita_ 135
86. THE EARLY STAGES OF _Aurelia_ 136
87. _Rhizostoma_ 136
88. _Chrysaora_ 136
89. _Cydippe pileus_ 137
90. SECTION OF AN ANEMONE 139
91. STINGING CELLS OF ANEMONE, HIGHLY MAGNIFIED 140
92. DIAGRAMMATIC TRANSVERSE SECTION OF AN ANEMONE 140
93. LARVA OF ANEMONE 140
94. THE TRUMPET ANEMONE (_Aiptasia Couchii_), CORNWALL;
DEEP WATER 144
95. _Peachia hastata,_ S. DEVON 145
96. _Sagartia pallida,_ DEVON AND CORNWALL 146
97. _Sagartia nivea,_ DEVON AND CORNWALL 147
98. _Corynactus viridis,_ DEVON AND CORNWALL 148
99. _Bunodes thallia,_ WEST COAST 150
100. _Bunodes gemmacea,_ WITH TENTACLES RETRACTED 151
101. _Caryophyllia cyathus_ 152
102. _Sagartia parasitica_ 153
103. THE CLOAK ANEMONE (_Adamsia palliata_) ON A WHELK
SHELL, WITH HERMIT CRAB 154
104. LARVA OF THE BRITTLE STARFISH 158
105. LARVA OF THE FEATHER STAR 160
106. THE ROSY FEATHER STAR 160
107. THE COMMON BRITTLE STAR 162
108. SECTION OF THE SPINE OF A SEA URCHIN 165
109. SEA URCHIN WITH SPINES REMOVED ON ONE SIDE 166
110. APEX OF SHELL OF SEA URCHIN 166
111. SHELL OF SEA URCHIN WITH TEETH PROTRUDING 167
112. INTERIOR OF SHELL OF SEA URCHIN 167
113. MASTICATORY APPARATUS OF SEA URCHIN 167
114. SEA URCHIN DISSECTED, SHOWING THE DIGESTIVE TUBE 168
115. THE SEA CUCUMBER 170
116. A TURBELLARIAN, MAGNIFIED 175
117. _Arenicola piscatorum_ 178
118. THE SEA MOUSE 179
119. TUBE-BUILDING WORMS: _Terebella, Serpula, Sabella_ 182
120. _Terebella_ REMOVED FROM ITS TUBE 183
121. A TUBE OF _Serpula_ ATTACHED TO A SHELL 185
122. _Serpula_ REMOVED FROM ITS TUBE 186
123. THE SEA MAT (_Flustra_) 187
124. _Flustra_ IN ITS CELL, MAGNIFIED 188
125. SEA SQUIRT 189
126. LARVÆ OF MOLLUSCS 191
127. SHELL OF THE PRICKLY COCKLE (_Cardium aculeatum_)
SHOWING UMBO AND HINGE; ALSO THE INTERIOR
SHOWING THE TEETH 192
128. INTERIOR OF BIVALVE SHELL, SHOWING MUSCULAR SCARS
AND PALLIAL LINE 193
129. DIAGRAM OF THE ANATOMY OF A LAMELLIBRANCH 194
130. _Mytilus edulis_, WITH BYSSUS 195
131. A BIVALVE SHELL (_Tapes virgineana_) 196
132. _Pholas dactylus_ 199
133. " " INTERIOR OF VALVE; AND _Pholadidea_
WITH ANIMAL 201
134. THE SHIP WORM 202
135. 1. _Teredo navalis._ 2. _Teredo norvegica_ 202
136. _Gastrochæna modiolina_ 203
137. 1. _Thracia phaseolina._ 2. _Thracia pubescens_,
SHOWING PALLIALLINE 204
138. 1. _Mya truncata._ 2. INTERIOR OF SHELL.
3. _Mya arenaria._4. _Corbula nucleus_ 205
139. _Solen siliqua_ 206
140. 1. _Solen ensis._ 2. _Cerati-solen legumen._
3. _Solecurtus candidus_ 207
141. _Tellinidæ_ 208
142. 1. _Lutraria elliptica._ 2. PART OF THE HINGE OF
_Lutraria_, SHOWING THE CARTILAGE PIT. 3. _Macra
stultorum._ 4. INTERIOR OF SAME SHOWING PALLIAL
LINE 210
143. _Veneridæ_ 211
144. _Cyprinidæ_ 213
145. _Galeomma Turtoni_ 214
146. 1. _Cardium pygmæum._ 2. _Cardium fasciatum._
3. _Cardium rusticum_ 215
147. _Cardium aculeatum_ 215
148. _Pectunculus glycimeris_, WITH PORTION OF VALVE
SHOWING TEETH, AND _Arca tetragona_ 216
149. _Mytilus edulis_ 217
150. 1. _Modiola modiolus._ 2. _Modiola tulipa._
3. _Crenella discors_ 218
151. _Dreissena polymorpha_ 219
152. _Avicula_, AND _Pinna pectinata_ 220
153. 1. _Anomia ephippium._ 2. _Pecten tigris._
3. _Pecten_, ANIMAL IN SHELL 222
154. _Terebratulina._ THE UPPER FIGURE REPRESENTS THE
INTERIOR OF THE DORSAL VALVE 224
155. UNDER SIDE OF THE SHELL OF _Natica catena_, SHOWING
THE UMBILICUS; AND OUTLINE OF THE SHELL, SHOWING THE
RIGHT-HANDED SPIRAL 225
156. SECTION OF THE SHELL OF THE WHELK, SHOWING THE
COLUMELLA 226
157. DIAGRAM OF THE ANATOMY OF THE WHELK, THE SHELL BEING
REMOVED 228
158. A PORTION OF THE LINGUAL RIBBON OF THE WHELK,
MAGNIFIED; AND A SINGLE ROW OF TEETH ON A MUCH
LARGER SCALE 229
159. EGG CASES OF THE WHELK 230
160. PTEROPODS 231
161. NUDIBRANCHS 234
162. " 235
163. SHELLS OF TECTIBRANCHS 236
164. CHITON SHELLS 238
165. SHELLS OF _Dentalium_ 238
166. _Patellidæ_ 239
167. _Calyptræa sinensis_ 241
168. _Fissurellidæ_ 241
169. _Haliotis_ 242
170. _Ianthina fragilis_ 242
171. _Trochus zizyphinus_. 2. UNDER SIDE OF SHELL.
3. _Trochus magnus._ 4. _Adeorbis subcarinatus_ 244
172. _Rissoa labiosa_ AND _Lacuna pallidula_ 244
173. SECTION OF SHELL OF _Turritella_ 245
174. _Turritella communis_ AND _Cæcum trachea_ 245
175. _Cerithium reticulatum_ AND _Aporrhais pes-pelicani_ 245
176. _Aporrhais pes-pelicani_, SHOWING BOTH SHELL AND ANIMAL 246
177. 1. _Odostomia plicata._ 2. _Eulima polita._
3. _Aclis supranitida_ 246
178. _Cypræa_ (_Trivia_) _europæa_ 247
179. 1. _Ovulum patulum_. 2. _Erato lævis_ 248
180. _Mangelia septangularis_ AND _Mangelia turricula_ 248
181. 1. _Purpura lapillus._ 2. EGG CASES OF _Purpura_.
3. _Nassa reticulata_ 249
182. _Murex erinaceus_ 249
183. OCTOPUS 251
184. _Loligo vulgaris_ AND ITS PEN 252
185. _Sepiola atlantica_ 252
186. _Sepia officinalis_ AND ITS 'BONE' 253
187. EGGS OF _Sepia_ 254
188. THE NERVE-CHAIN OF AN ARTHROPOD (LOBSTER) 257
189. SECTION THROUGH THE COMPOUND EYE OF AN ARTHROPOD 260
190. FOUR STAGES IN THE DEVELOPMENT OF THE COMMON SHORE
CRAB 261
191. THE BARNACLE 261
192. FOUR STAGES IN THE DEVELOPMENT OF THE ACORN BARNACLE 262
193. A CLUSTER OF ACORN SHELLS 263
194. SHELL OF ACORN BARNACLE (_Balanus_) 263
195. THE ACORN BARNACLE (_Balanus porcatus_) WITH APPENDAGES
PROTRUDED 264
196. A GROUP OF MARINE COPEPODS, MAGNIFIED 265
197. A GROUP OF OSTRACODE SHELLS 265
198. _Evadne_ 266
199. MARINE ISOPODS 267
200. MARINE AMPHIPODS 268
201. THE MANTIS SHRIMP (_Squilla Mantis_) 270
202. THE OPOSSUM SHRIMP (_Mysis chamæleon_) 271
203. PARTS OF LOBSTER'S SHELL, SEPARATED, AND VIEWED FROM
ABOVE 272
204. A SEGMENT OF THE ABDOMEN OF A LOBSTER 272
205. APPENDAGES OF A LOBSTER 273
206. LONGITUDINAL SECTION OF THE LOBSTER 274
207. THE SPINY LOBSTER (_Palinurus vulgaris_) 275
208. THE NORWAY LOBSTER (_Nephrops norvegicus_) 276
209. 1. THE MUD-BORER (_Gebia stellata_). 2. THE
MUD-BORROWER (_Callianassa subterranea_) 277
210. THE COMMON SHRIMP (_Crangon vulgaris_) 278
211. THE PRAWN (_Palæmon serratus_) 279
212. _Dromia vulgaris_ 282
213. THE HERMIT CRAB IN A WHELK SHELL 282
214. THE LONG-ARMED CRAB (_Corystes Cassivelaunus_) 287
215. SPIDER CRABS AT HOME 288
216. THE THORNBACK CRAB (_Maia Squinado_) 290
217. THE PEA CRAB (_Pinnotheres pisum_) 290
218. THE COMMON SHORE CRAB (_Carcinus mænas_) 291
219. THE SHORE SPIDER 294
220. THE LEG OF AN INSECT 295
221. TRACHEA OF AN INSECT, MAGNIFIED 296
222. SEA-SHORE INSECTS 298
223. MARINE BEETLES OF THE GENUS _Bembidium_ 302
224. MARINE BEETLES 303
225. TRANSVERSE SECTION THROUGH THE BONY FRAMEWORK OF A
TYPICAL VERTEBRATE ANIMAL 306
226. THE SEA LAMPREY 309
227. THE PILCHARD 310
228. THE SKELETON OF A FISH (PERCH) 315
229. THE INTERNAL ORGANS OF THE HERRING 316
230. THE EGG-CASE OF THE DOGFISH 319
231. THE SMOOTH HOUND 320
232. THE COMMON EEL 323
233. THE LESSER SAND EEL 326
234. THE THREE-BEARDED ROCKLING 327
235. THE SNAKE PIPE-FISH 328
236. THE RAINBOW WRASS (_Labrus julis_) 330
237. THE CORNISH SUCKER 330
238. THE FIFTEEN-SPINED STICKLEBACK AND NEST 331
239. THE SMOOTH BLENNY 333
240. THE BUTTERFISH 334
241. THE BLACK GOBY 335
242. THE FATHER LASHER 335
243. THE LESSER WEAVER 337
244. THE COMMON PORPOISE 341
245. _Callithamnion roseum_ 359
246. _Callithamnion tetricum_ 359
247. _Griffithsia corallina_ 361
248. _Halurus equisetifolius_ 361
249. _Pilota plumosa_ 361
250. _Ceramium diaphanum_ 363
251. _Plocamium_ 366
252. _Delesseria alata_ 368
253. _Delesseria hypoglossum_ 368
254. _Laurencia pinnatifida_ 371
255. _Laurencia obtusa_ 371
256. _Polysiphonia fastigiata_ 373
257. _Polysiphonia parasitica_ 374
258. _Polysiphonia Brodiæi_ 374
259. _Polysiphonia nigrescens_ 374
260. _Ectocarpus granulosus_ 378
261. _Ectocarpus siliculosus_ 378
262. _Ectocarpus Mertensii_ 378
263. _Sphacelaria cirrhosa_ 379
264. _Sphacelaria plumosa_ 379
265. _Sphacelaria radicans_ 380
266. _Cladostephus spongiosus_ 380
267. _Chordaria flagelliformis_ 380
268. _Laminaria bulbosa_ 384
269. _Laminaria saccharina_ 384
270. _Alaria esculenta_ 385
271. _Sporochnus pedunculatus_ 385
272. _Desmarestia ligulata_ 386
273. _Himanthalia lorea_ 387
274. _Cystoseira ericoides_ 388
275. TRANSVERSE SECTION OF THE STEM OF A MONOCOTYLEDON 391
276. LEAF OF A MONOCOTYLEDON 392
277. EXPANDED SPIKELET OF THE OAT 393
278. THE SEA LYME GRASS 395
279. _Knappia agrostidea_ 397
280. THE DOG'S-TOOTH GRASS 397
281. THE REED CANARY GRASS 397
282. MALE AND FEMALE FLOWERS OF _CAREX_, MAGNIFIED 399
283. THE SEA SEDGE 400
284. THE CURVED SEDGE 400
285. THE GREAT SEA RUSH 400
286. THE BROAD-LEAVED GRASS WRACK 401
287. THE SEA-SIDE ARROW GRASS 401
288. THE COMMON ASPARAGUS 401
289. THE SEA SPURGE 403
290. THE PURPLE SPURGE 404
291. THE SEA BUCKTHORN 404
292. _Chenopodium botryoides_ 405
293. THE FROSTED SEA ORACHE 406
294. THE PRICKLY SALT WORT 406
295. THE CREEPING GLASS WORT 407
296. THE SEA-SIDE PLANTAIN 408
297. THE SEA LAVENDER 408
298. THE DWARF CENTAURY 410
299. THE SEA SAMPHIRE 412
300. THE SEA-SIDE EVERLASTING PEA 413
301. THE SEA STORK'S-BILL 414
302. THE SEA CAMPION 416
303. THE SEA PEARL WORT 417
304. THE SHRUBBY MIGNONETTE 417
305. THE WILD CABBAGE 418
306. THE ISLE OF MAN CABBAGE 418
307. THE GREAT SEA STOCK 419
308. THE HOARY SHRUBBY STOCK 419
309. THE SCURVY GRASS 419
310. THE SEA RADISH 419
311. THE SEA ROCKET 420
312. THE SEA KALE 421
313. THE HORNED POPPY 422
THE SEA SHORE
CHAPTER I
_THE GENERAL CHARACTERISTICS OF THE SEA SHORE_
What are the attractions which so often entice us to the sea shore,
which give such charm to a ramble along the cliffs or the beach, and
which will so frequently constrain the most active wanderer to rest and
admire the scene before him? The chief of these attractions is
undoubtedly the incessant motion of the water and the constant change of
scene presented to his view. As we ramble along a beaten track at the
edge of the cliff, new and varied features of the coast are constantly
opening up before us. Each little headland passed reveals a sheltered
picturesque cove or a gentle bay with its line of yellow sands backed by
the cliffs and washed by the foaming waves; while now and again our path
slopes down to a peaceful valley with its cluster of pretty cottages,
and the rippling stream winding its way towards the sea. On the one hand
is the blue sea, full of life and motion as far as the eye can reach,
and on the other the cultivated fields or the wild and rugged downs.
The variety of these scenes is further increased by the frequent changes
in the character of the cliffs themselves. Where they are composed of
soft material we find the coast-line washed into gentle curves, and the
beach formed of a continuous stretch of fine sand; but where harder
rocks exist the scenery is wild and varied, and the beach usually strewn
with irregular masses of all sizes.
Then, when we approach the water’s edge, we find a delight in watching
the approaching waves as they roll over the sandy or pebbly beach, or
embrace an outlying rock, gently raising its olive covering of dangling
weeds.
Such attractions will allure the ordinary lover of Nature--the mere
seeker after the picturesque--but to the true naturalist there are many
others. The latter loves to read in the cliffs their past history, to
observe to what extent the general scenery of the coast is due to the
nature of the rocks, and to learn the action of the waves from the
character of the cliffs and beach, and from the changes which are known
to have taken place in the contour of the land in past years. He also
delights to study those plants and flowers which are peculiar to the
coast, and to observe how the influences of the sea have produced
interesting modifications in certain of our flowering plants, as may be
seen by comparing them with the same species from inland districts. The
sea birds, too, differing so much as they do from our other feathered
friends in structure and habit, provide a new field for study; while the
remarkably varied character of the forms of life met with on the beach
and in the shallow waters fringing the land is in itself sufficient to
supply the most active naturalist with material for prolonged and
constant work.
Let us first observe some of the general features of the coast itself,
and see how far we can account for the great diversity of character
presented to us, and for the continual changes and incessant motions
that add such a charm to the sea-side ramble.
Here we stand on the top of a cliff composed of a soft calcareous
rock--on the exposed edge of a bed of chalk that extends far inland. All
the country round is gently undulating, and devoid of any of the
features that make up a wild and romantic scene. The coast-line, too, is
wrought into a series of gentle bays, separated by inconspicuous
promontories where the rock, being slightly harder, has better withstood
the eroding action of the sea; or where a current, washing the
neighbouring shore, has been by some force deflected seaward. The cliff,
though not high, rises almost perpendicularly from the beach, and
presents to the sea a face which is but little broken, and which in
itself shows no strong evidence of the action of raging, tempestuous
seas; its chief diversity being its gradual rise and fall with each
successive undulation of the land. The same soft and gentle nature
characterises the beach below. Beyond a few small blocks of
freshly-loosened chalk, with here and there a liberated nodule of flint,
we find nothing but a continuous, fine, siliceous sand, the surface of
which is but seldom broken by the protrusion of masses from below. Such
cliffs and beaches do not in themselves suggest any violent action on
the part of the sea, and yet it is here that the ocean is enabled to
make its destructive efforts with the greatest effect. The soft rock is
gradually but surely reduced, partly by the mechanical action of the
waves and partly by the chemical action of the sea-water. The rock
being almost uniformly soft, it is uniformly worn away, thus presenting
a comparatively unbroken face. Its material is gradually dissolved in
the sea; and the calcareous matter being thus removed, we have a beach
composed of the remains of the flints which have been pulverised by the
action of the waves. Thus slowly but surely the sea gains upon the land.
Thus it is that many a famous landmark, once hundreds of yards from the
coast, now stands so near the edge of the cliff as to be threatened by
every storm; or some ancient castle, once miles from the shore, lies
entirely buried by the encroaching sea.
[Illustration: FIG. 1.--CHALK CLIFF]
The coast we have described is most certainly not the one with the
fullest attractions for the naturalist, for the cliffs lack those nooks
that provide so much shelter for bird and beast, and the rugged coves
and rock pools in which we find such a wonderful variety of marine life
are nowhere to be seen. But, although it represents a _typical_ shore
for a chalky district, yet we may find others of a very different nature
even where the same rock exists. Thus, at Flamborough in Yorkshire, and
St. Alban’s Head in Dorset, we find the hardened, exposed edge of the
chalk formation terminating in bold and majestic promontories, while
the inner edge surrounding the Weald gives rise to the famous cliffs of
Dover and the dizzy heights of Beachy Head. The hard chalk of the Isle
of Wight, too, which has so well withstood the repeated attacks of the
Atlantic waves, presents a bold barrier to the sea on the south and east
coasts, and terminates in the west with the majestic stacks of the
Needles.
[Illustration: FIG. 2.--WHITECLIFF (CHALK), DORSET]
Where this harder chalk exists the coast is rugged and irregular. Sea
birds find a home in the sheltered ledges and in the protected nooks of
its serrated edge; and the countless wave-resisting blocks of weathered
chalk that have been hurled from the heights above, together with the
many remnants of former cliffs that have at last succumbed to the
attacks of the boisterous sea, all form abundant shelter for a variety
of marine plants and animals.
[Illustration: FIG. 3.--PENLEE POINT, CORNWALL]
But it is in the west and south-west of our island that we find both
the most furious waves and the rocks that are best able to resist their
attacks. Here we are exposed to the full force of the frontal attacks of
the Atlantic, and it is here that the dashing breakers seek out the
weaker portions of the upturned and contorted strata, eating out deep
inlets, and often loosening enormous blocks of the hardest material,
hurling them on the rugged beach, where they are eventually to be
reduced to small fragments by the continual clashing and grinding action
of the smaller masses as they are thrown up by the angry sea. Here it is
that we find the most rugged and precipitous cliffs, bordering a more or
less wild and desolate country, now broken by a deep and narrow chasm
where the resonant roar of the sea ascends to the dizzy heights above,
and anon stretching seaward into a rocky headland, whose former
greatness is marked by a continuation of fantastic outliers and smaller
wave-worn masses of the harder strata. Here, too, we find that the
unyielding rocks give a permanent attachment to the red and olive weeds
which clothe them, and which provide a home for so many inhabitants of
our shallow waters. It is here, also, that we see those picturesque rock
pools of all sizes, formed by the removal of the softer material of the
rocks, and converted into so many miniature seas by the receding of the
tide.
[Illustration: FIG. 4.--BALANUS SHELLS]
A more lovely sight than the typical rock pool of the West coast one can
hardly imagine. Around lies the rugged but sea-worn rock, partly hidden
by dense patches of the conical shells of the _Balanus_, with here and
there a snug cluster of young mussels held together by their
intertwining silken byssi. The surface is further relieved by the
clinging limpet, the beautifully banded shells of the variable
dog-periwinkle, the pretty top shells, and a variety of other common but
interesting molluscs. Clusters of the common bladdery weeds are also
suspended from the dry rock, and hang gracefully into the still water
below, where the mantled cowry may be seen slowly gliding over the olive
fronds. Submerged in the peaceful pool are beautiful tufts of white and
pink corallines, among which a number of small and slender starfishes
may climb unnoticed by the casual observer; while the scene is
brightened by the numerous patches of slender green and red algæ, the
thread-like fronds of which are occasionally disturbed as the lively
little blenny darts among them to evade the intruder’s glance. Dotted
here and there are the beautiful anemones--the variously-hued animal
flowers of the sea, with expanded tentacles gently and gracefully
swaying, ready to grasp and paralyse any small living being that may
wander within their reach. Here, under a projecting ledge of the rock,
partly hidden by pale green threads, are the glaring eyes of the
voracious bullhead, eager to pounce on almost any moving object; while
above it the five-fingered starfish slowly climbs among the dangling
weeds by means of its innumerable suckers. In yonder shady corner, where
the overhanging rock cuts off all direct rays of the sun from the deeper
water of the pool, are the pink and yellow incrustations of little
sponges, some of the latter colour resembling a group of miniature
inverted volcanic cones, while on the sandy floor of the pool itself may
be seen the transparent phantom-like prawn, with its rapidly moving
spinnerets and gently-waving antennæ, suddenly darting backward when
disturbed by the incautious approach of the observer; and the spotted
sand-crab, entirely buried with the exception of its upper surface, and
so closely imitating its surroundings as to be quite invisible except on
the closest inspection. Finally, the scene is greatly enlivened by the
active movements of the hermit-crab, that appropriates to its own use
the shell which once covered the body of a mollusc, and by the erratic
excursions of its cousin crabs as they climb over the weedy banks of the
pool in search of food.
[Illustration: FIG. 5.--A CLUSTER OF MUSSELS]
Thus we may find much to admire and study on the sea shore at all times,
but there are attractions of quite another nature that call for notice
on a stormy day, especially on the wilder and more desolate western
coasts. At such times we delight to watch the distant waves as they
approach the shore, to see how they become gradually converted into the
foaming breakers that dash against the standing rocks and wash the
rattling pebbles high on the beach. The powerful effects of the sea in
wearing away the cliffs are now apparent, and we can well understand
that even the most obdurate of rocks must sooner or later break away
beneath its mighty waves.
[Illustration: FIG. 6.--BREAKERS]
The extreme mobility of the sea is displayed not only by the storm
waves, and by the soft ripples of the calm day, but is seen in the
gentle currents that almost imperceptibly wash our shores, and more
manifestly in the perpetual motions of the tides.
This last-named phenomenon is one of extreme interest to the sea-side
rambler, and also one of such great importance to the naturalist that we
cannot do better than spend a few moments in trying to understand how
the swaying of the waters of the ocean is brought about, and to see what
determines the period and intensity of its pulsations, as well as some
of the variations in the daily motions which are to be observed on our
own shores.
In doing this we shall, of course, not enter fully into the technical
theories of the tides, for which the reader should refer to
authoritative works on the subject, but merely endeavour to briefly
explain the observed oscillations of the sea and the general laws which
govern them.
The most casual observer must have noticed the close connection between
the movements of the ocean and the position of the moon, while those who
have given closer attention to the subject will have seen that the
relative heights of the tides vary regularly with the relative positions
of the sun, moon, and earth.
In the first place, then, we notice that the time of high tide in any
given place is always the same at the same period of the cycle of the
moon; that is, it is always the same at the time of new moon, full moon,
&c. Hence it becomes evident that the moon is the prime mover in the
formation of tides. Now, it is a fact that the sun, though about
ninety-three millions of miles from the earth, has a much greater
attractive influence on the earth and its oceans than the moon has,
although the distance of the latter is only about a quarter of a million
miles: but this is due to the vastly superior mass of the sun, which is
about twenty-six million times the mass of the moon. How is it, then,
that we find the tides apparently regulated by the moon rather than by
the sun?
The reason is that the tide-producing influence is due not to the actual
attractive force exerted on the earth as a whole, but to the difference
between the attraction for one side of the globe and that for the
opposite side. Now, it will be seen that the diameter of the
earth--about eight thousand miles--is an appreciable fraction of the
moon’s distance, and thus the attractive influence of the moon for the
side of the earth nearest to it will be appreciably greater than that
for the opposite side; while in the case of the sun, the earth’s
diameter is such a small fraction of the distance from the sun that the
_difference_ in the attractive force for the two opposite sides of the
earth is comparatively small.
Omitting, then, for the present the minor tide-producing influence of
the sun, let us see how the incessant rising and falling of the water of
the ocean are brought about; and, to simplify our explanation, we will
imagine the earth to be a globe entirely covered with water of uniform
depth.
The moon attracts the water on the side nearest to it with a greater
force than that exerted on the earth itself; hence the water is caused
to bulge out slightly on that side. Again, since the attractive force of
the moon for the earth as a whole is greater than that for the water on
the opposite side, the earth is pulled away, as it were, from the water
on that side, causing it to bulge out there also. Hence high tides are
produced on two opposite sides of the earth at the same time, while the
level of the water is correspondingly reduced at two other parts at
right angles with these sides.
This being the case, how are we to account for the observed changes in
the level of the sea that occur every day on our shores?
Let us first see the exact nature of these changes:--At a certain time
we find the water high on the beach; and, soon after reaching its
highest limit, a gradual descent takes place, generally extending over a
period of a little more than six hours. This is then followed by another
rise, occupying about the same time, and the oscillations are repeated
indefinitely with remarkable regularity as to time.
[Illustration: FIG. 7.--ILLUSTRATING THE TIDE-PRODUCING INFLUENCE OF
THE MOON]
Now, from what has been previously said with regard to the tidal
influence of the moon, we see that the tide must necessarily be high
under the moon, as well as on the side of the earth directly opposite
this body, and that the high tides must follow the moon in its regular
motion. But we must not forget that the earth itself is continually
turning on its axis, making a complete rotation in about twenty-four
hours; while the moon, which revolves round the earth in about
twenty-eight days, describes only a small portion of its orbit in the
same time; thus, while the tidal wave slowly follows the moon as it
travels in its orbit, the earth slips round, as it were, under the tidal
wave, causing four changes of tide in approximately the period of one
rotation. Suppose, for example, the earth to be performing its daily
rotation in the direction indicated by the arrow (fig. 8), and the tide
high at the place marked A¹, just under the moon, then, in about six
hours, this place will have been carried round to A², where the tide is
low; and, after similar intervals, to A³ and A⁴ successively, where
the tide is high and low respectively. Hence the daily changes are to a
great extent determined by the rotation of the earth.
But we have already observed that each change of tide occupies a little
more than six hours, the average time being nearly six hours and a
quarter, and so we find that the high and low tides occur nearly an hour
later every day. This is due to the fact that, owing to the revolution
of the moon round the earth in the same direction as that of the
rotation of the earth itself, the day as measured by the moon is nearly
an hour longer than the average solar day as given by the clock.
[Illustration: FIG. 8.--ILLUSTRATING THE TIDES]
There is yet another point worth noting with regard to the relation
between the moon and the tidal movements of the water, which is that the
high tides are never exactly under the moon, but always occur some time
after the moon has passed the meridian. This is due to the inertia of
the ocean, and to the resistance offered by the land to its movements.
Now, in addition to these diurnal changes of the tide, there are others,
extending over longer periods, and which must be more or less familiar
to everyone who has spent some time on the coast. On a certain day, for
instance, we observe that the high tide flows very far up the beach, and
that this is followed, a few hours later, by an unusually low ebb,
exposing rocks or sand-banks that are not frequently visible. Careful
observations of the motions of the water for some days after will show
that this great difference between the levels of high and low-water
gradually decreases until, about a week later, it is considerably
reduced, the high tide not flowing so far inland and the low-water mark
not extending so far seaward. Then, from this time, the difference
increases again, till, after about two weeks from the commencement of
our observations, we find it at the maximum again.
[Illustration: FIG. 9.--SPRING TIDES AT FULL MOON]
Here again we find that the changes exactly coincide with changes in the
position of the moon with regard to the sun and the earth. Thus, the
_spring tides_--those which rise very high and fall very low--always
occur when the moon is full or new; while the less vigorous _neap tides_
occur when the moon is in her quarters and presents only one-half of her
illuminated disc to the earth. And, as the moon passes through a
complete cycle of changes from _new_ to _first-quarter_, _full_,
_last-quarter_, and then to _new_ again in about twenty-nine days, so
the tides run through four changes from spring to neap, spring, neap,
and then to spring again in the same period.
[Illustration: FIG. 10.--SPRING TIDES AT NEW MOON]
The reason for this is not far to seek, for we have already seen that
both sun and moon exert a tide-producing influence on the earth, though
that of the moon is considerably greater than that of the sun; hence, if
the sun, earth, and moon are in a straight line, as they are when the
moon is full, at which time she and the sun are on opposite sides of the
earth, and also when new, at which time she is between the earth and
sun, the sun’s tide is added to the moon’s tide, thus producing the
well-marked spring tides; while, when the moon is in her quarters,
occupying a position at right angles from the sun as viewed from the
earth, the two bodies tend to produce high tides on different parts of
the earth at the same time, and thus we have the moon’s greater tides
reduced by the amount of the lesser tides of the sun, with the result
that the difference between high and low tides is much lessened.
[Illustration: FIG. 11.--NEAP TIDES]
Again, the difference between high and low water marks is not always
exactly the same for the same kind of tide--the spring tide for a
certain period, for example, not having the same limits as the same tide
of another time. This is due to the fact that the moon revolves round
the sun in an elliptical orbit, while the earth, at the same time,
revolves round the sun in a similar path, so that the distances of both
moon and sun from the earth vary at different times. And, since the
tide-producing influences of both these bodies must increase as their
distance from the earth diminishes, it follows that there must be
occasional appreciable variations in the vigour of the tidal movements
of the ocean.
As the earth rotates on its axis, while at the same time the tidal wave
must necessarily keep its position under the moon, this wave appears to
sweep round the earth with considerable velocity. The differences in the
level of the ocean thus produced would hardly be appreciable if the
earth were entirely covered with water; but, owing to the very irregular
distribution of the land, the movements of the tidal wave become
exceedingly complex; and, when it breaks an entrance into a gradually
narrowing channel, the water is compressed laterally, and
correspondingly increased in height. It is thus that we find a much
greater difference between the levels of high and low tides in
continental seas than are to be observed on the shores of oceanic
islands.
We have occupied so much of our time and space in explanation of the
movements of the tides not only because we think it desirable that all
who delight in sea-side rambles should understand something of the
varied motions which help to give such a charm to the sea, but also
because, as we shall observe later, these motions are a matter of great
importance to those who are interested in the observation and study of
marine life. And, seeing that we are writing more particularly for the
young naturalists of our own island, we must devote a little space to
the study of the movements of the tidal wave round Great Britain, in
order that we may understand the great diversity in the time of high
tide on any one day on different parts of the coast, and see how the
time of high tide for one part may be calculated from that of any other
locality.
Were it not for the inertia of the ocean and the resistance offered by
the irregular continents, high tide would always exist exactly under the
moon, and we should have high water at any place just at the time when
the moon is in the south and crossing the meridian of that place. But
while the inertia of the water tends to make all tides late, the
irregular distribution of the land breaks up the tidal wave into so many
wave-crests and greatly retards their progress.
Thus, the tidal wave entering the Atlantic round the Cape of Good Hope
mingles with another wave that flows round Cape Horn, and the combined
wave travels northward at the rate of several hundred miles an hour. On
reaching the British Isles it is broken up, one wave-crest travelling up
the English Channel, while another flows round Scotland and then
southwards into the North Sea.
The former branch, taking the shorter course, determines the time of
high tide along the Channel coast. Passing the Land’s End, it reaches
Plymouth in about an hour, Torquay in about an hour and a half, the Isle
of Portland in two hours and a half, Brighton in about seven hours, and
London in about nine hours and a half. The other branch, taking a much
longer course, makes its arrival in the southern part of the North Sea
about twelve hours later, thus mingling at that point with the Channel
wave of the _next_ tide. It takes about twenty hours to travel from the
south-west coast of Ireland, round Scotland, and then to the mouth of
the Thames. Where the two waves meet, the height of the tides is
considerably increased; and it will be understood that, at certain
points, where the rising of one tide coincides with the falling of
another, the two may partially or entirely neutralise each other.
Further, the flow and the ebb of the tide are subject to numerous
variations and complications in places where two distinct tidal
wave-crests arrive at different times. Thus, the ebbing of the tide may
be retarded by the approach of a second crest a few hours after the
first, so that the ebb and the flow do not occupy equal times. At
Eastbourne, for example, the water flows for about five hours, and ebbs
for about seven and a half. Or, the approach of the second wave may even
arrest the ebbing waters, and produce a second high tide during the
course of six hours, as is the case at some places along the Hampshire
and Dorset coasts.
Those who visit various places on our own coasts will probably be
interested in tracing the course of the tidal crests by the aid of the
accompanying map of the British Isles, on which the time of high tide at
several ports for the same time of day is marked. It will be seen from
this that the main tidal wave from the Atlantic approaches our islands
from the south-west, and divides into lesser waves, one of which passes
up the Channel, and another round Scotland and into the North Sea, as
previously mentioned, while minor wave-crests flow northward into the
Irish Sea and the Bristol Channel. The chart thus supplies the data by
means of which we can calculate the approximate time of high tide for
any one port from that of another.
[Illustration: FIG. 12.--CHART SHOWING THE RELATIVE TIMES OF HIGH TIDE
ON DIFFERENT PARTS OF THE BRITISH COAST
_George Philip & Son. Ltd._ _The London Geographical Institute._]
Although the time of high water varies so greatly on the same day over
such a small area of country, yet that time for any one place is always
approximately the same during the same relative positions of the sun,
earth, and moon; that is, for the same ‘age’ of the moon; so that it is
possible to determine the time of high water at any port from the moon’s
age.
The time of high tide is generally given for the current year in the
local calendars of our principal seaports, and many guide-books supply a
table from which the time may be calculated from the age of the moon.
At every port the observed high water follows the meridional passage of
the moon by a fixed interval of time, which, as we have seen, varies
considerably in places within a small area of the globe. This interval
is known as _the establishment of the port_, and provides a means by
which the time of high water may be calculated.
Before closing this short chapter on the general characteristics of the
sea shore we ought to make a few observations on the nature of the water
of the sea. Almost everyone is acquainted with the saltness while many
bathers have noticed the superior buoyancy of salt water as compared
with the fresh water of our rivers and lakes. The dissolved salts
contained in sea water give it a greater density than that of pure
water; and, since all floating bodies displace their own weight of the
liquid in which they float, it is clear that they will not sink so far
in the denser water of the sea as they would in fresh water.
If we evaporate a known weight of sea water to dryness and weigh the
solid residue of sea salt that remains, we find that this residue forms
about three and a half per cent. of the original weight. Then, supposing
that the evaporation has been conducted very slowly, the residue is
crystalline in structure, and a careful examination with the aid of a
lens will reveal crystals of various shapes, but by far the larger
number of them cubical in form. These cubical crystals consist of common
salt (sodium chloride), which constitutes about three-fourths of the
entire residue, while the remainder of the three and a half per cent.
consists principally of various salts of magnesium, calcium, and sodium.
Sea salt may be obtained ready prepared in any quantity, as it is
manufactured for the convenience of those who desire a sea bath at home;
and it will be seen from what has been said that the artificial
sea-water may be prepared, to correspond almost exactly with that of the
sea, by the addition of three and a half pounds of sea salt to about
ninety-six and a half pounds of water.
This is often a matter of no little importance to the sea-side
naturalist, who may require to keep marine animals alive for some time
at considerable distance from the sea shore, while their growth and
habits are observed. Hence we shall refer to this subject again when
dealing with the management of the salt-water aquarium.
The attractions of the sea coast are undoubtedly greater by day than at
night, especially in the summer season, when the excessive heat of the
land is tempered by the cool sea breezes, and when life, both on the
cliffs and among the rocks, is at its maximum. But the sea is grand at
night, when its gentle ripples flicker in the silvery light of the full
moon. No phenomenon of the sea, however, is more interesting than the
beautiful phosphorescence to be observed on a dark summer’s night. At
times the breaking ripples flash with a soft bluish light, and the water
in the wake of a boat is illuminated by what appears to be liquid fire.
The advancing ripples, as they embrace a standing rock, surround it with
a ring of flame; while streaks and flashes alternately appear and
disappear in the open water where there is apparently no disturbance of
any kind.
These effects are all produced by the agency of certain marine animals,
some of which display a phosphorescent light over the whole surface of
their bodies, while in others the light-giving power is restricted to
certain organs or to certain well-defined areas of the body; and in some
cases it even appears as if the creatures concerned have the power of
ejecting from their bodies a phosphorescent fluid.
It was once supposed that the phosphorescence of the sea was produced by
only a few of the lower forms of life, but it is well known now that
quite a large number of animals, belonging to widely different classes,
play a part in this phenomenon. Many of these are minute creatures,
hardly to be seen without the aid of some magnifying power, while others
are of considerable size.
Among the peculiar features of the phosphorescence of the sea are the
suddenness with which it sometimes appears and disappears, and its very
irregular variations both at different seasons and at different hours of
the same night. On certain nights the sea is apparently full of living
fire when, almost suddenly the light vanishes and hardly a trace of
phosphorescence remains; while, on other occasions, the phenomenon is
observed only on certain patches of water, the areas of which are so
well defined that one passes suddenly from or into a luminous sea.
The actual nature of the light and the manner in which it is produced
are but ill understood, but the variations and fitfulness of its
appearances can be to a certain extent conjectured from our knowledge
of some of the animals that produce it.
In our own seas the luminosity is undoubtedly caused principally by the
presence of myriads of minute floating or free-swimming organisms that
inhabit the surface waters. Of these each one has its own season, in
which it appears in vast numbers. Some appear to live entirely at or
near the surface, but others apparently remain near the surface only
during the night, or only while certain conditions favourable to their
mode of life prevail. And further, it is possible that these minute
creatures, produced as they generally are in vast numbers at about the
same time, and being more or less local, are greatly influenced by
changes of temperature, changes in the nature of the wind, and the
periodic changes in the tides; and it is probable that we are to look to
these circumstances for the explanations of the sudden changes so
frequently observed.
In warmer seas the phenomenon of phosphorescence is much more striking
than in our own, the brilliancy of the light being much stronger, and
also produced by a greater variety of living beings, some of which are
of great size, and embrace species belonging to the vertebrates and the
higher invertebrate animals.
Those interested in the investigation of this subject should make it a
rule to collect the forms of life that inhabit the water at a time when
the sea is unusually luminous. A sample of the water may be taken away
for the purpose of examination, and this should be viewed in a good
light, both with and without a magnifying lens. It is probable, too,
that a very productive haul may be obtained by drawing a fine muslin net
very slowly through the water. After some time the net should be emptied
and gently washed in a small quantity of sea water to remove the smaller
forms of life contained, and the water then examined at leisure.
Of course it must not be assumed that all the species so obtained are
concerned in any way with the phosphorescence of the sea, but any one
form turning up in abundance when collected under the conditions named
will probably have some connection with the phenomenon.
One may well ask ‘What is the use of this light-emitting power to the
animals who possess it?’ but this question is not easily answered. The
light produced by the glow-worm and other luminous insects is evidently
a signal by means of which they call their mates, and this may be the
case with many of the marine luminous animals, but it is evidently not
so with those which live in such immense numbers that they are simply
crowded together; nor can it be so with the many luminous creatures
that are hermaphrodite. It is a fact, however, that numbers of deep-sea
species possess the power of emitting light to a striking extent; and
the use of this power is in such cases obvious, for since the rays of
the sun do not penetrate to great depths in the ocean, these luminous
species are enabled to illuminate their own surroundings while in search
of food, and, in many cases at least, to quench their lights suddenly at
such times as they themselves are in danger.
CHAPTER II
_THE SEA-SIDE NATURALIST_
OUTDOOR WORK
Assuming that the reader is one who desires to become intimately
acquainted with the wonderful and varied forms of life to be met with on
the sea shore, or, hoping that he may be lured into the interesting and
profitable pastimes of the sea-side naturalist, we shall now devote a
chapter to the consideration of the appliances required for the
collection and examination of marine life, and to general instructions
as to the methods by which we may best search out the principal and most
interesting objects of the shore.
First, then, we shall describe the equipment of an enthusiastic and
all-round admirer of Nature--he who is interested in plant forms
from the flowering species down to the ‘meanest weed that grows,’ and is
always ready to learn something of any member of the animal world that
may happen to come within his reach. And this, not because we hope, or
even desire, that every reader may develop into an all-round naturalist,
but so that each may be able to select from the various appliances named
just those which would be useful for the collection and observation of
the objects which are to form his pet study.
The most generally useful of all these appliances is undoubtedly some
kind of case of the ‘hold-all’ type, a case into which specimens in
general may be placed for transmission from the hunting-ground in order
that they may be studied at leisure, and we know of nothing more
satisfactory than the botanist’s ‘vasculum.’ This is an oblong box of
japanned tin, fitted with a hinged front, and having both handle and
strap, so that it can be either carried in the hand or slung over the
shoulder. Of course almost any kind of non-collapsible box or basket
will answer the purpose, but we know of no utensils so convenient as the
one we have named. It is perfectly satisfactory for the temporary
storage of the wild flowers gathered on the cliffs, as it will keep them
moist and fresh for some considerable time; and for the reception of sea
weeds of all kinds it is all that could be desired, for it will
preserve them in splendid condition, and is so constructed that there is
no possibility of the inconvenience arising from the dripping of salt
water on the lower garments. Then, as regards marine animal-life in
general--starfishes, urchins, anemones, molluscs, crustaceans, fishes,
&c.--these may be conveyed away in it with a liberal packing of moist
weeds not only without injury, but in such a satisfactory condition that
nearly all may be turned out alive at the end of a day's work; and this
must be looked upon as a very important matter to him who aims at
becoming a naturalist rather than a mere collector, for while the latter
is content with a museum of empty shells and dried specimens, the former
will endeavour to keep many of the creatures alive for a time in some
kind of artificial rock pool in order that he may have the opportunity
of studying their development and their habits at times when he has not
the chance of visiting the sea shore for the purpose.
[Illustration: FIG. 13.--THE VASCULUM]
But although the vasculum is so generally useful for the temporary
storage and the transmission of the objects collected, yet it is not in
itself sufficient for all purposes. There are many marine animals so
small--but none the less interesting because they are small--that they
would probably be lost in a case containing a mass of sea weeds with
various larger creatures. These should be placed in small well-corked
bottles, and temporarily preserved in a little sea-water, or,
preferably, a tuft of one of the delicate weeds so common in our rock
pools. Others, again, though they may be larger, are of so fragile a
nature that they should be isolated from the general stock on that
account alone. Instead of bottles or tubes, small tin boxes may be used,
and these have the advantage of being unbreakable, though, of course,
they will not hold water. This, however, is of no consequence, as most
marine animals may be kept alive for some time in moist sea-weed quite
as well as in water.
When small animals are required for structural examination only, they
may be put into methylated spirit as they are taken, and when stored in
this way a much larger number may be put into the same receptacle; hence
the collector will often find it convenient to have a small supply of
this liquid while at his work.
A strong pocket-knife is essential for sea-side work. It serves to
remove those molluscs that adhere firmly to the rocks by suction, and
also others that fix themselves by means of a byssus of silken fibres,
as is the case with mussels. It will also be employed in the removal of
acorn barnacles, anemones, and small tufts of algæ, and may be useful in
cutting through the stouter weeds. Small sponges and other low forms of
life often form incrustations on the solid rock, and may be peeled off
with the aid of a knife. In the case of the last-named, however, as well
as with the anemones and other fixed animals, it is often far more
satisfactory to remove a small portion of the rock itself with the
animal attached, and for this purpose a small hammer will be of great
service.
A strong net of some kind is necessary in searching the rock pools, and
as suitable nets are, we believe, not to be obtained of the dealers in
naturalists’ appliances, it devolves on one to manufacture a net
according to his requirements.
The simplest form of net may be made by bending a piece of stout
galvanised iron wire into the form here shown (fig. 14), and firmly
wedging the two straight ends in a short piece of strong metal tube
which will also serve as a ferrule for the attachment of a tough handle.
Such a circular frame although satisfactory for a net to be used in
fresh-water ponds and streams, is not nearly so suitable for the
irregular rocky pools to be met with on the sea coast, for it will not
enable one to search the numerous corners and crevices into which many
marine creatures will retire on being disturbed, but it may be greatly
improved by bending the side opposite the ferrule into a moderately
sharp angle and then turning the angle slightly upward, as shown in fig.
15.
[Illustration: FIG. 14.--WIRE RING FOR NET]
[Illustration: FIG. 15.--NET FRAME WITH CURVED POINT]
Another very convenient net frame may be made by bending the wire into a
rhomboidal form (fig. 16), the ferrule being attached by means of two
short, straight ends at one of the angles. The opposite angle will serve
the purpose of searching into the crannies of the rocks, while the
straight sides will prove very useful in removing the objects that lie
on the sandy bottoms so commonly seen in rock pools. The semicircular
net shown in fig. 18 will also prove useful for working on sands or for
scraping the flatter surfaces of weed-covered rocks.
[Illustration: FIG. 16.--RHOMBOIDAL FRAME FOR NET]
The material of the net should be some kind of strong gauze, or a
loosely-woven canvas. Leno answers very well, but is somewhat easily
torn, and will have to be frequently renewed. This, however, may be
avoided to a great extent if, instead of sewing the gauze directly round
the wire, a strip of strong calico be first attached to the frame, and
the gauze then sewn to the calico; for it will be understood that any
fragile material placed round the wire will soon be worn through by
friction against the rugged surfaces of the rocks and stones. The net
itself should not be very deep, and should have no corners; and as to
the length of the handle, that will be determined by the fancy of the
collector, or by the character of the ponds to be searched, but a tough
walking-stick with a crook handle will generally answer all purposes,
the crook being itself frequently useful for removing the larger weeds
and other obstructions.
[Illustration: FIG. 17.--RHOMBOIDAL NET]
[Illustration: FIG. 18.--SEMICIRCULAR NET]
[Illustration: FIG. 19.--THE DREDGE]
Although the net, as above described, will answer the requirements of
nearly all young collectors, yet there may be some, who, not satisfied
with the exploration of the rocks and pools exposed when the tide is
out, desire to know something of the creatures that live entirely beyond
low-water mark, where the water is generally too deep for work with a
hand net. To such we recommend a small dredge that may be lowered from a
boat and then drawn along the bottom. A good form of dredge is shown in
fig. 19, and a little skill and ingenuity will enable anyone to
construct one with the help of our illustration; but, seeing that the
best work is to be done on rough bottoms, it is absolutely necessary
that both frame and net should be made of the stoutest materials that
can be conveniently employed.
[Illustration: FIG. 20.--THE CRAB-POT]
Those who have ever accompanied a fisherman while taking a pull round to
examine the contents of his crab or lobster pots will probably have
noticed what strange creatures, in addition to the edible crabs and
lobsters, sometimes find their way into the trap. These creatures are
often of great interest to a young naturalist, and it will repay him to
take an occasional trip with a fisherman in order to obtain them; or,
still better, to have a crab-pot of his own. The writer has obtained
many good specimens by means of an inexpensive trap, on the same
principle as the ordinary crab-pot, made from an old metal bird-cage of
rather small size. The bottom was removed, and a very shallow bag of
thick canvas fixed in its place; and some of the wires were cut, and
bent inwards so as to allow the easy entrance of moderately large
crustaceans and other creatures, while at the same time they served as a
barrier to their escape. Such a trap, baited with pieces of fish, and
let down to a rocky bottom, will enable the young naturalist to secure
specimens that are seldom seen between the tide-marks; and the animals
thus obtained will include not only those larger ones for which the
opening was made, but also a variety of smaller creatures that may enter
between the wires of the cage. Some of the latter may, of course, escape
by the same way as the trap is being hauled up for examination, but this
is not so likely to occur if the canvas bottom is of a material so
loosely woven that water can pass through it very freely. It will, of
course, occur to the reader that the insertion of a stone or other
weight will assist in sinking the trap; also that the ordinary door of
the cage forms a ready means by which the captives may be removed.
[Illustration: FIG. 21.--AN OLD BIRD-CAGE USED AS A CRAB-POT]
One thing more: make it a rule never to go out collecting natural
objects of any kind without a note-book and pencil. This, to the
beginner who is anxious to get to his work, with the idea only too
prevalent with the amateur that the success of his labours is to be
measured only by the number of specimens obtained, may seem quite an
unnecessary part of the equipment. But it must be remembered that there
is much to _observe_ as well as much to collect on a well-selected
coast; and that without the aid of the book and pencil a great many of
the observations made will be forgotten, and thus much interest that
would otherwise be attached to the objects permanently preserved will be
lacking.
The above appliances include the only necessary equipment of the
sea-side naturalist, with the exception of a few required for occasional
use in connection with the species of a somewhat restricted habitat, and
the outfit of the sea angler. The former will be dealt with in the
chapters where the species concerned are described, while the subject of
sea angling is of such general interest that we propose to devote a
short chapter exclusively to it.
It may seem hardly necessary to discourse on the nature of the attire
most suitable for sea-side work, since the majority will readily form
their own opinions on this matter, but perhaps a few words of advice to
the inexperienced may not be altogether out of place. First, then, make
it a rule to wear no clothing of any value. The work will lead the
enthusiast over slippery weeds, on treacherous boulders, over rocks
covered with sharp acorn shells, and among slimy and muddy stones, and
many a slip may occur in the course of a day’s work. Large pockets
specially but simply made by sewing square pieces of lining on the
inside of an old jacket are a great convenience; a cap rather than a
brimmed hat should be worn unless the latter be considered essential for
protection from a burning summer’s sun; and a pair of old shoes,
preferably with rubber soles, are just the thing for both rough and
slippery rocks, as well as for wading through shallow waters. Other
details we can safely leave to the fancy of the reader himself.
Now comes the most important question ‘Where shall we go?’ Fortunately
we are favoured with a great extent of coast-line considering the area
of our country, but the character of the coast is so diversified, both
with regard to its scenery and its life, that the naturalist will do
well to carefully select his locality according to the objects he
desires to study. The east coast of England is not generally noted
either for variety or abundance of marine life, and the same is true
both of the south-east and a large portion of the south coast. In some
places the beach is formed of an unbroken stretch of sand on which one
may walk for miles without seeing any sign of life, with the exception
of an occasional empty shell and a few fragments of dried sea-weed
washed in by the breakers during a recent storm; while at the same time
the cliffs, if such exist at all, are not very generous in their
production of the fauna and flora that are characteristic of the shore.
But even on the coasts referred to there are, here and there, isolated
spots where the uplands jut into the sea, giving rise to bold
promontories, at the foot of which are the fallen masses of rock that
afford protection to a moderate variety of truly marine life, while the
rough bottoms beyond yield numerous interesting forms that may be
secured by means of the dredge or suitable traps. Such spots are to be
found where the chalk hills abut on the sea, as at Flamborough and
Beachy Head, but it is in the neighbourhood of Weymouth that the English
coast really begins to be of great interest to the naturalist. From here
to the Land’s End almost every part of the shore will yield a great
variety of life in abundance, and the same is true of the rocky coasts
of the west, and also of the more rugged shores of the Isle of Wight.
As an ideal hunting-ground one cannot do better than to select one of
the small fishing towns or villages on the rocky coasts of Devon and
Cornwall. With such a spot as his headquarters the most enthusiastic
sea-side naturalist will find ample employment. The exposed rocks and
rock pools yield abundance of life; and if these be searched when the
tide is out, there will remain plenty of sea angling and other
employments to occupy him at other times.
We will now describe the actual work of the sea-side naturalist, giving
the necessary instructions for the observation and collection of the
various living things he will meet with.
First, then, with regard to work on the cliffs, a very few words will
suffice; for, seeing that the objects of interest to be met with here
will consist principally of the various flowers that are peculiar to or
characteristic of the sea shore, and certain insects and other creatures
more or less partial to a life on the cliffs, we may regard these as
coming within the range of the general work of the botanist,
entomologist, &c.; and since instructions for the collection and
preservation of such objects have already been given in former works of
this series, we may pass them over at once in order to deal with those
objects which are essentially marine.
It has already been hinted that the right time for collecting on the
shore is when the tide is at its lowest; and in order that the best work
may be done the collector should consult the local tide-tables, or
calculate, if necessary, the time of high tide from the establishment of
the port; and, of course, the period of spring tides should be selected
if possible. The time during which work should continue must be
regulated according to the enthusiasm of the collector or the time at
his disposal, but, as a rule, it is advisable to be on the scene of
action about three hours before the time of low tide, with a
determination to work continuously until the lowest ebb of the water.
On reaching the beach it is always advisable to start by examining the
line of miscellaneous material at high-water mark, along which may be
found quite a variety of objects, more or less interesting, which have
been washed in by the breakers, especially just after a storm, together
with numerous scavengers of the shore that perform a most useful work in
devouring the decomposing organic matter that would otherwise tend to
pollute the air.
Here we may find many useful and interesting objects of both the animal
and vegetable worlds. Among the former are the empty shells of both
univalve and bivalve molluscs, some of which are more or less worn by
the action of the waves, while others are in splendid condition for
examination and study. Here, too, are various species of sea firs and
the skeletons of sponges; the shell of the cuttle-fish, and occasionally
a cluster of the eggs of this creature--the sea-grapes of the fishermen;
also the egg-cases of the skate and the dog-fish--usually empty, but
sometimes enclosing the young animal still alive; and, lastly, we
frequently meet with portions of the skeletons of fishes in a perfect
state of preservation, the animal matter having been cleared away by the
combined action of the scavengers previously referred to. Then, as
regards the vegetable world, we often find beautiful specimens of
sea-weeds along the high-water mark, some of which are rarely met with
in the rock pools, since they are species that have been detached from
beyond the line of low water, and washed up by the breakers.
On turning over the debris thus thrown on the beach we intrude on the
privacy of numerous living creatures which immediately scamper away to
find a new hiding-place. These consist principally of sand-hoppers, but
occasionally we find members of the insect world engaged in the same
useful work in addition to the numerous flies that perform their office
of scavengers in the bright sunshine on the top of the matter that
supplies them with food.
It will be interesting to capture a few of these scavengers, and to
compare them with others of the same order obtained from different
localities. Thus, the flies may be compared with the more familiar house
fly, and the sand-hoppers of high-water mark with similar crustaceans to
be afterwards obtained lower on the beach.
Attention should now be given to the rocks left exposed by the
retreating tide, and it is here that the real work begins. Examine each
rock pool as soon as possible after it is no longer disturbed by the
waves. Remove any tufts of corallines or other weeds required for study
or preservation, and simply place them, pro tem., in the vasculum or
other receptacle provided for the purpose. These will form a useful
protective packing for other objects that are to be carried away, so
that it will be advisable to secure a moderate amount rather early, even
though they may not be required for any other purpose. Live molluscs,
crabs, small fishes, &c., may all be put in the receptacle with this
weed, and all will probably be still alive after the collecting and the
homeward journey have been completed. Probe the corners of the pool
with the point of the net, and also sweep the net upward among the weeds
to remove any creatures that seek shelter among the fronds. Tufts of
corallines and other weeds should be searched for the small and delicate
starfishes that live among them, and any stones that may cover the
bottom of the pool should be lifted. Anemones may be removed from the
rocks by means of a rather blunt knife; but, if possible, it will be
better to chip off a small piece of the rock with the anemone attached
to it, and wrap it lightly round with a tuft of soft weed previous to
placing it in the collecting case.
A number of rock pools should be searched in this manner, but those
chosen should vary as much as possible in general character. All very
small and delicate objects should be isolated from the general stock,
and placed, with the usual packing material, either in tin boxes or
small wide-mouthed bottles; and if any animals taken are not required
alive, but only for preservation, they should be preferably killed at
once and then stored in a separate case. Some creatures are easily
killed by simply dropping them into a bottle of fresh water, but others
should be covered with methylated spirit. It should be mentioned,
however, that the natural appearance of some of the crustaceans is quite
destroyed by strong spirit, which soon makes them look as if they had
been boiled. Some species are changed in this way much more readily than
others; and, until sufficient experience has been gained to enable the
young collector to distinguish between them, it will be advisable to
kill and temporarily preserve crustaceans in spirit that has been
considerably diluted with water--about two parts of water to one of
spirit, for example. Further, there are certain fragile starfishes that
have a way of breaking themselves into pieces when dropped into spirit,
or even when suddenly disturbed in almost any other manner. These must
always be handled gently, and if it is required to kill them for
preservation, the best way will be to put them in a little salt water,
and then gradually add fresh water until the desired result is obtained.
Perhaps the most productive of all sea-shore work is the turning over of
the stones of various sizes near the low-tide mark, and the examination
of the chinks and sheltered hollows of the rocks that are left uncovered
for but a short period. This work should be carried on as near the
water’s edge as possible, closely following the receding tide; and the
collector must now be prepared with a number of small bottles or tins
for the isolation of small and delicate specimens. He must also be on
the alert for numerous examples of protective resemblance, in which the
animals concerned so closely resemble their surroundings in colour and
general character of surface that they are detected only by careful
observation, while the difficulty of identification is still further
increased in instances where the creatures remain perfectly still even
when disturbed.
[Illustration: FIG. 22.--A YOUNG NATURALIST AT WORK]
Under the stones all manner of animals--fishes, crustaceans, worms,
molluscs, starfishes, anemones, &c.--will be hiding until covered by the
next tide. Some of these will be found on the ground beneath the stones,
and others attached to the under surfaces of the stones themselves;
therefore both should be carefully examined, attention being given at
first to the more active species that hurry away with all speed towards
a new shelter as soon as they find themselves exposed to the light; the
less active creatures may then be secured at leisure.
The tide will not allow the collector a great deal of time in which to
turn over the most productive stones--those close to the low-water mark,
so there is but little opportunity of observing the movements and other
interesting habits of many of the animals found; hence it is advisable
to secure a good variety of living specimens, especially of the less
familiar species, in order that they may be placed in some kind of
aquarium, temporary or otherwise, for observation at home.
[Illustration: FIG. 23.--A GOOD HUNTING-GROUND ON THE CORNISH COAST]
One thing more remains to be done while the tide is well out, and that
is to examine the weed-covered rocks near the water’s edge. Lift the
dangling weeds and carefully search the rocks for those low forms of
animal life that form incrustations on the surface, as well as for new
species of anemones, sea firs, &c. Lastly, look well into the dark and
narrow chinks of the rocks, for here several species of lowly animals
that are hardly met with elsewhere may be found, and also certain
crustaceans that delight to squeeze their bodies into the remotest
corner of a sheltered niche.
CHAPTER III
_SEA ANGLING_
We do not propose dealing with this subject from the point of view of
the angler, but rather that of the naturalist. The former is actuated
principally, if not entirely, by the mere love of sport; or, it may be,
to a great extent by the desire to obtain a supply of fish for food; and
he generally estimates the success of his expeditions not by the number
of _species_ captured, but by the total weight of his catch, no regard
being paid, as a rule, to the inedible specimens. The naturalist,
however, does not desire weight, or sweetness of flesh. He works the
greatest possible variety of habitats, with the object of determining
the number of species inhabiting the locality and of learning as much as
possible of their general form, habits, and adaptations of structure to
habits. His success is measured by the number and variety of species
caught, and he pays but little attention to superiority of size or
weight, or to the estimated market value of his haul. The element of
sport may enter more or less largely into the pleasure of his
occupation, but the main end in view is to learn as much as possible of
all the species obtainable.
Further, our remarks will not include the subject of the different kinds
of fishing usually resorted to by sea anglers, but will be confined
almost exclusively to the simple means of catching the common species
that frequent the immediate neighbourhood of the shore.
If the reader will follow the general instructions given in Chapter II.
on the outdoor work of the marine naturalist, he will undoubtedly make
the acquaintance of a considerable variety of interesting species which
may be captured in the rock pools, found under stones at low tide, or
obtained by means of a small dredge; but his knowledge of our littoral
fishes may be appreciably extended by the occasional employment of rod
and line from rocks and piers, or from a small boat in close proximity
to the shore.
The appliances required are of a very simple nature, and not at all
costly. The long, heavy rod and strong tackle of the sea angler and
professional fisherman are not at all essential to our purpose, for our
work will be confined almost exclusively to shallow water, and the fish
to be caught will be chiefly of small size. True it is that one may
occasionally find his light tackle snapped and carried away by the
unexpected run of a large fish, for cod and other large species often
approach close to the shore, and bite at baits intended for the smaller
fish that make their home among the partly submerged rocks of the coast;
but such surprises will not frequently occur, and the young naturalist
may learn all he wants to know of the fishes of our shallow waters with
the aid of a light rod of about nine or ten feet and one or two light
lines of no great length.
It must not be understood, however, that we assume the reader’s
disinclination to know anything of the inhabitants of deep water, but
rather that we consider the whole subject of deep-sea fishing quite
beyond the scope of this work. It is a fact that quite a large number of
species, the forms and habits of which are extremely interesting, live
exclusively on deep bottoms. These should undoubtedly be studied by all
who are interested in the various phases of marine life; but unless the
reader is prepared to practise sea fishing in all its branches--to put
his trust in the restless sea, supplied with all the necessary heavy
gear, and to risk those internal qualms that arise from the incessant
swaying of the boat on open waters, he should make arrangements with the
professional deep-sea fisher--preferably a trawler--for the supply of
those disreputable species that invariably form part of the haul, while
the better-known food fishes can always be obtained from dealers for
purposes of study.
On one occasion we had a rather unique and very successful interview
with a friendly trawler. She was sailing slowly towards her station in a
south-western fishing port, while two of her crew were clearing her
nets, and throwing all refuse into the sea. We rowed behind her in order
to see the nature of the rejected portion of the haul, and finding that
it included specimens of interesting fishes of ill repute, dead but
perfectly fresh, we followed her track, and collected a few for future
examination. Presently our movements were watched from aboard, and we
were invited to pull up to larboard, where a short explanation as to our
wants led to the acquisition of quite a variety of deep-sea life,
including several species of fishes not often seen on land, crabs,
shelled and shell-less molluscs, worms, star-fishes, and various lowly
organised beings, many alive and in good condition, together with
several good food fishes thrown in by way of sympathy. There is no doubt
that a naturalist can obtain much more deep-sea life with the aid of a
friendly trawler than by any amount of ‘fishing’ with ordinary tackle
from a boat; and this without the necessity of going to sea at all, if
he will only take the opportunity of examining the nets as the boats are
stranded on their return.
But now to return to our angling:--We have to provide a light rod, about
ten feet long, with a winch, and a line of twisted silk or other thin
but strong material; also a light hand line, and a supply of gut, leads,
shot, and hooks, together with one or two small floats, and a few bait
boxes.
We do not, as a rule, recommend the amateur angler to use both rod and
hand line at the same time, for the attempt to do this leads to the
neglect of both. In the end it is not likely to lead to any gain, so
many fish being lost through the inability to strike at the moment a
bite is given, and so much time having to be devoted to the baiting of
hooks rather than to the direct management of the lines. In most cases
the rod is much more convenient than the hand line. The young collector
will meet with the greatest variety of species in rocky and weedy
places, where abundant shelter exists for those fishes that prefer to
keep well under cover, and any attempt with a hand line in such spots
will certainly lead to frequent loss of hooks, and often of lead, line,
and temper. Such a line must be reserved for fishing on sandy bottoms,
while the ten-foot rod recommended will enable the angler to do good
work in the rockiest parts without much danger of fouling; and, in fact,
to fish anywhere along the coast.
The arrangement of hooks and lead must necessarily depend on the
character of the place to be worked, but in all cases we strongly
recommend no such multiplicity of hooks as is made use of by fishermen
and others who fish for food. In their case the use of so many hooks
often pays them well; but, as we have previously hinted, the naturalist
does not desire quantity of fish so much as variety of species. Further,
there is no necessity to make his work heavy and arduous. His desire is
not to spend an undue proportion of his time in baiting hooks, but to
have his line so under control that he is ready to strike at any moment,
and to be able to alter the conditions of his work as often as his ideas
or the conditions change.
In rugged and weedy places the hooks must be kept free from rocks and
weeds. This may be done by letting down the rod line with a lead at the
bottom, and one or two hooks fastened to gut at such a level as to keep
quite clear of weeds. A much better arrangement, and one which we
ourselves almost invariably employ, consists of a light lead, as a rule
not exceeding an ounce in weight, fastened at the end of the line, and
below it a few feet of gut terminating in a single hook. With such
tackle it is of course necessary to determine previously the depth of
the water, in order to adjust the line to such a length that the hook
keeps clear of rocks and weeds, and a float may be used if desired.
[Illustration: FIG. 24.--ROUND BEND HOOK WITH FLATTENED END]
We do not recommend a float for the general work of the marine
collector, for it is a decided advantage to be prepared to bring the
bait to any level from bottom to surface, especially when the water is
so clear that the fish may be seen swimming, in which case one is often
impressed with the desire to capture a specimen in order to establish
its identity, and for such work as this a float is superfluous. If,
however, a float is used, it should be a sliding one, so that it may be
adapted to the rising and falling of the tide.
[Illustration: FIG. 25.--LIMERICK HOOK, EYED]
Of hooks there is a great variety to choose from, differing in the form
both of the curve and of the end of the shank. As to the curve, those
with a decided twist are best adapted to our purpose, chiefly on account
of the fact that sea fishes generally have larger mouths than
fresh-water species of the same size, and are consequently better held
with a twisted hook. The shanks of sea hooks are either flattened or
eyed, and each is as good as the other providing the snood is firmly
attached; but some amateurs find a greater difficulty in attaching the
snood to the former than to the latter.
Gut snoods are recommended for our purpose, and fig. 26 shows one method
by which they may be fastened to a flattened shank, while fig. 27
illustrates the figure-of-eight knot by means of which the eyed shank
may be firmly secured. The gut should be soaked for some hours in cold
water previous to tying, and it may be kept soft for some considerable
time by giving it a few hours’ immersion in a solution of
glycerine--about one part of glycerine to four or five parts of
water.
[Illustration: FIG. 26.--METHOD OF ATTACHING SNOOD TO FLATTENED HOOK]
Small hooks will be most suitable for our purpose; and if the reader
finds any difficulty in attaching the snood firmly, he may purchase
suitable hooks ready mounted on gut, though, of course, these are more
expensive than the flattened or eyed hooks generally used for
sea-fishing. Such small and fragile hooks may be occasionally snapped
off by the run of a vigorous fish of moderate size, therefore it is
advisable to have a supply of larger hooks, ready fixed on strong
snoods, to be used when it is found that the shore is frequented by
larger fishes than those generally caught close to land.
[Illustration: FIG. 27.--METHOD OF ATTACHING SNOOD TO EYED HOOK]
When fishing with a rod and line from rocks, or from piers, the
foundations of which are covered with large weeds, the bait will
frequently be carried by currents among the weeds and snapped off when
endeavours are made to release the hook. This will especially be the
case when the hook is a few feet below the lead, as we have already
suggested it should be. To reduce the frequency of such mishaps, it will
be a good plan to weight the gut below the lead by means of a few split
shot. In fact, in sheltered places, where the water is not disturbed,
these shot may take the place of the lead, but little weight being
necessary for rod fishing in such localities.
The amateur sea angler is often in great doubt as to the best bait to
use; and, believing that a certain kind of bait is absolutely necessary
for his work in some particular spot, is often at a loss to obtain it.
This bait difficulty is evidently a prevailing one among amateur sea
fishers, if one may judge from the frequent questions asked as to the
best or proper bait to use, and from the very common ‘Can you oblige me
with a little bait?’
This latter question, we believe, is frequently the outcome of
carelessness or laziness on the part of the asker. He has not the
forethought, born of enthusiasm, that would lead him to procure a
suitable bait, at a convenient time, previous to starting off on his
angling expedition, but rather depends on the possibility of being able
to beg or otherwise secure sufficient for his purpose at the time; yet
there are so many good baits that are easily secured at the proper time
and place that the enthusiastic angler need never be at a loss. Some of
these may be collected by himself at low tide, others may be obtained
from local fishermen, or from the tradesmen of the town or village.
[Illustration: FIG. 28.--THE LUGWORM]
Some anglers seldom collect their own bait, either purchasing it or
employing some one to collect it for them; but we are of opinion that
the pleasure of a day’s fishing begins here, and especially so when the
angler is of the naturalist type, for he will frequently learn more of
the nature and habits of living creatures during one hour’s
bait-collecting than during three or four hours’ angling. It is true
that the work in question is often a bit laborious, particularly on a
warm day, and that it may be frequently described as dirty and odorous;
but what is that to one who is interested in his employment, and who
derives pleasure in doing his own work?
Fishermen often use lugworms for bait, and although these constitute one
of the best baits for their own fishing, they are not so suitable for
the purposes of the amateur angler, fishing with small hooks close to
shore. They may be dug out of the sand when the tide is out, and are
most abundant where the sand is mixed with mud. A spade should be used,
and this should be thrust deep into the sand, selecting those spots
where the holes or burrows of the worms most abound. Lugworms should be
used whole; and being of large size, are suitable for baiting large
hooks only. They may be kept alive in wet sand or sea-weed, preferably
the latter for convenience, and stored till required in a wooden box.
Ragworms also afford good bait, and are particularly adapted for shore
angling with small hooks. Almost all the fishes that frequent our shores
take them readily, but they are not to be found in all localities. They
are to be taken, though not usually in large numbers, on rocky shores
where numerous stones lie among the somewhat muddy deposits of the more
sheltered nooks, where they may be seen on turning over the stones. The
best situation for ragworms, however, is the more or less odoriferous
mud so frequently deposited in the estuaries of rivers and in landlocked
harbours. Here they maybe dug out in enormous numbers with a spade,
attention being directed to those spots where their burrows are most
numerous. They are best stored with a little of the mud in a shallow
wooden box provided with a sliding, perforated lid.
[Illustration: FIG. 29.--THE RAGWORM]
Failing a supply of the marine worms just mentioned, the common
earthworm may be used as a substitute, but it is decidedly less
attractive to the fishes; and the same may be said of gentles--the larvæ
or grubs of flies. The latter may be bred in large numbers by simply
placing a piece of liver in the soil with only a small portion exposed.
If this is done in the summer time, hundreds of eggs will soon be
deposited on it, and in about a week or so it will be found to be a
living mass of fat white grubs, perhaps more useful to the fresh-water
angler than to his marine counterpart.
Among the so-called shell fish of the class _mollusca_, mussels,
limpets, cockles, and whelks are all largely used for bait. The last of
these are too large for our purpose, but form a splendid bait for
deep-sea fishing, while the other three, and especially the mussels, are
well suited for shore work. Mussels, in fact, provide one of the best
possible baits for almost all kinds of shore fishing, the only drawback
being the excessive softness of their bodies, which enables them to be
easily torn from the hook. When small hooks are used, mussels of a small
size may be used whole, or the larger ones may be divided into portions
of suitable size; and in any case it will be found a good plan to tie
the bait to the hook with a short piece of cotton thread.
[Illustration: FIG. 30.--DIGGING FOR BAIT]
Mussels are not easily opened without injury, and consequently some
anglers give them a short immersion in hot water, to kill the animal and
thus cause the shell to gape. As far as our own experience goes, the
value of the bait is not deteriorated by this treatment, though some are
of opinion that it is not so attractive after scalding. Mussels are
opened, when alive, much in the same way as oysters, but the valves of
the shell fit together so closely that it seems at first almost
impossible to insert a knife between them. This, however, can be done
with ease if one valve is first made to slide a little way over the
other by pressing it with the thumb. This being accomplished, the two
valves should not be separated by the mere force of the knife, for this
would tear the animal within, and render it more or less unfit for its
purpose; but first direct the edge of the knife towards the _adductor
muscle_, by means of which the animal pulls its valves so firmly
together, and then cut through this close to the inner surface of the
upper valve. This valve can then be lifted without injury to the soft
parts, and the whole animal removed from the other valve by cutting
through the same muscle close to it.
[Illustration: FIG. 31.--METHOD OF OPENING A MUSSEL]
Between the two lobes of the _mantle_--the soft covering on both sides
of the animal that previously lined the shell--will be seen a brown,
fleshy, tongue-like body. This is the ‘foot’ of the mussel. The point of
the hook should first be run through this, and then from side to side
through the mantle, and finally through the adductor muscle previously
described. If this is carefully done, there will be little fear of the
bait becoming detached unless it is subjected to rough usage, and still
less if it is tied round the shank of the hook by means of a short piece
of cotton thread.
It is probably superfluous to mention to the reader the fact that
mussels are to be found on almost every rocky coast, where they may be
seen attached to the rocks by means of a bunch of silky fibres called
the _byssus_; and that, failing this, they are to be obtained from
almost every fisherman and fish-dealer; if, however, these molluscs are
not to be obtained, cockles may be used as a substitute, though it will
probably be found that they are appreciably inferior, except when
fishing for dabs and plaice on sandy shores, in which case they are
highly satisfactory. Cockles abound on most sandy coasts, where they
live a little below the surface; and are usually obtained by means of an
ordinary garden rake. Sometimes we meet with them in large numbers in
the estuaries of rivers, where they lie buried in the banks of mixed
sand and mud that are left exposed at low tide.
Limpets are extensively used for bait in some places, especially by
amateur anglers; and often with good results. They should always be
removed from the rocks without injury, and this is no easy matter to
those who do not know how to deal with them. If taken completely by
surprise, one sharp, but light tap on the side of the conical shell will
successfully detach them from their hold; or they may be raised by means
of the blade of a strong pocket-knife that has been thrust beneath the
cone.
For our work small limpets will prove far more satisfactory than large
ones, and these may be used whole; but if the limpets are too large for
the hooks employed, the soft, upper part of the body only need be used.
It is not an easy matter to remove fresh limpets from their shells
without destroying this soft portion of the animal, but if placed for a
minute or so in hot water they come out quite easily, and are apparently
none the less attractive as bait. Some fishermen on the Cornish coast
always collect the largest limpets for bait, remove them from their
shells by means of hot water, and arrange them on the rocks to become
partly dry. When required for bait, the soft parts only are used, but
these, having been more or less hardened by the drying process, hold
much better on the hook than when fresh.
And now, after mentioning the fact that land snails are occasionally
used, though, we believe, with no very considerable success, for sea
fishing, we will note a few baits derived from the higher head-footed
molluscs--the squid, cuttle-fish, &c. There are several species of these
peculiar molluscs, but the common squid and the common cuttle of our
seas, and especially the former, is highly prized as bait. It may be
obtained from fishermen, who frequently haul it in their nets; but if
supplied alive and fresh from the sea it must be handled very
cautiously, otherwise it may discharge the contents of its ink-bag over
one with the most unpleasant results. It is certainly best used while
fresh, though some suspend it until dry, and then store it for future
use, in which case it will require soaking in water when required. The
thin tentacles or arms are very convenient for baiting small hooks,
though other parts of the body, cut into narrow strips, will serve the
purpose of the angler equally well.
Of the crustaceans, shrimps and prawns, and various species of crabs are
used as bait. Shrimps and prawns are used whole for catching flat-fish,
but small pieces are better when fishing for smelt and other small
species of fish that swim close to shore. Little pieces of the flesh of
the crab are also well adapted for baiting hooks of small size, and will
prove very attractive to almost all kinds of fish. Small crabs, however,
may be used whole, but are of little use except when soft--that is, just
after the shedding of their shells, and before the new skin has had time
to harden. Such crabs may be found under stones and in other
hiding-places at low tide, for at such times they keep well secluded
from their numerous enemies by whom they are greedily devoured while in
this helpless and unprotected condition.
The hermit-crab, which selects the empty shell of a whelk or winkle for
its home, is probably well known to our readers. The protection afforded
by such a home is absolutely necessary to its existence, since its
abdomen has no other covering than a soft, membranous skin. This soft
abdomen is frequently used as a bait with great success, as well as the
flesh of the larger claws.
If the shell from which the hermit-crab is taken be broken, a worm,
something of the nature of the common ragworm, will almost always be
found, and this also is very serviceable as bait.
In addition to all the baits previously named there are several other
good ones, many of which are to be obtained almost everywhere. Among
these may be mentioned strips cut from the mackerel, herring, or
pilchard, preferably with a portion of the silvery skin attached; also
thin strips of tripe. Sand-eels, which may be dug out of the sand near
the water’s edge, are very useful, and may be cut into pieces for
baiting small hooks. Further, a large number of artificial baits are
employed in various kinds of sea fishing, but as these are not
essential for the work we have in hand we do not propose describing them
in detail.
Now let us suppose that we are about to try our luck at sea angling, on
some rocky coast, such as that of Devon and Cornwall, our object being
to determine, as far as possible, what species of fishes frequent the
immediate neighbourhood of the shore. And this is not all; for, when
fishing with rod and line on such a coast, it frequently happens that we
land some species of crab that has been attracted to our bait. The
ordinary angler would regard such crab as an intruder, and, we are sorry
to say, would often consider it his duty to crush the unfortunate
crustacean beneath his foot. But it is far different with the
naturalist. He favourably regards all creatures from which something may
be learnt, and is as anxious, as a rule, to gather information
concerning the habitats of one class as of another. In fact, we may go
still further, and combine crab fishing with ordinary angling, both in
one and the same expedition, by letting a small crab-pot down into deep
water among the rocks, and allowing it to remain while the angling is
proceeding.
We select a spot where there are several feet of water close to a
perpendicular rock, varied and broken by numerous holes and crevices, in
which various species of fishes and crustaceans habitually hide.
Such a situation is an ideal one for a young naturalist, for not only
does he obtain the greatest variety of species here, but the takings
will surely include some of those remarkably interesting rock-dwelling
fishes that differ from our ordinary food fishes in so many points of
structure, all of which, however, display some interesting adaptation to
the habits and habitats of the species concerned.
Our apparatus consists of nothing more than rod and line, one or two
small leads, a supply of hooks on gut snoods, a box of bait, and a
waterproof bag in which to pack the specimens we desire to preserve.
We first determine the depth of the water by means of a lead on the
_end_ of the line, and then tie the hook on the end with a small lead a
few feet above it, and fish in such a manner that the hook is just on
the bottom, or, if the bottom is covered with weeds, the hook should be
kept just clear of fouling them.
The peculiar rock fishes so common on such a coast as this on which we
are engaged need special treatment at the hands of the angler. They hide
in their holes, watching for the unwary creatures on which they feed,
and, pouncing upon them suddenly, rush back to their snug little nooks
in which they can secure themselves firmly by means of the sharp, hard
spines with which their bodies are furnished. When these fishes seize
the bait offered them--and they are not at all fastidious in the choice
of their viands--they should be hooked and pulled up with one vigorous
sweep of the rod, or they will dart into their homes, from which it is
almost impossible to dislodge them.
[Illustration: FIG. 32.--FISHING FROM THE ROCKS]
In addition to these, there will be various other species that require
gentler treatment, and may be hooked and landed much in the same manner
as fresh-water fishes, since they are free swimmers, usually keeping
well clear of the rocks and weeds.
If the day is calm, and the water clear, the sea angler will often be
able to watch various fishes as they swim, and to bring the bait gently
within their reach; and here we find the advantage of the rod as
compared with the hand line. Sometimes quite a shoal of small fishes may
be seen sporting near the surface, and, as a rule, there will be no
difficulty in obtaining one for identification and study. These are
generally best secured by means of small hooks, with but very little
bait, and will often bite freely at the tiniest fragment of worm on an
almost naked hook.
After the water has been searched at all depths, it will be well to
allow the bait to rest quite on the bottom, even at the risk of losing a
hook or two in the weeds and rocks. This may enable one to take some
fresh species of fish or to secure a crustacean or other creature that
is not often found between the tide-marks. Care should be always taken,
however, to keep the hook well clear of the weeds that grow on the sides
of the rock, and sway to and fro with every movement of the restless
waters.
Angling from piers may be pursued much in the same manner as described
above in those places where the bottom is rocky, but since the chances
of hooking large fish are greater here than close to shore, it is
necessary to be provided with stronger tackle and larger hooks. If,
however, the bottom is sandy, the rod tackle may be modified by placing
the lead at the bottom, and arranging two or three hooks above it, about
one or two feet apart, the lowest one being near the lead. With such an
arrangement the line may be cast some distance out, but for angling
close to the pier itself there is, perhaps, nothing better than the
single-hook arrangement suggested above, for with this one may fish on
the bottom and at all depths without any alteration in the tackle being
necessary.
If, however, the rod line is to be cast as suggested above, or if a hand
line is to be similarly used, the following hints may be useful as
regards the arrangement of hooks and lead.
The line itself may be of twisted silk or hemp, terminated with about a
yard of strong gut. The lead, preferably of a conical or pear-shaped
form, should be placed at the extreme end, and its weight regulated
according to the necessities of the occasion. A few ounces of lead are
quite sufficient where there are no strong currents, but it is well to
be supplied with larger sizes, to be substituted if circumstances
require it. Two hooks will be ample. One of these should be only a few
inches from the lead, and the other about eighteen or twenty inches
higher. The whole arrangement, known as a Paternoster, is represented in
fig. 33, in which the method of fixing the lead and the hook links is
also illustrated.
[Illustration: FIG. 33.--THE PATERNOSTER]
It will be seen that a swivel has been introduced in connection with the
bottom hook, the object being to show the manner in which this useful
piece of tackle is fitted. It must not be supposed, however, that
swivels are always necessary. It is often useful to insert a swivel on
the line itself, above the Paternoster, when it is of twisted material,
in order to prevent it from kinking; but its use is more frequently
serviceable on the hook links, especially when fishing where the
currents are strong. When the bait used is one that presents two flat
surfaces to the water, as would be the case with a strip of mackerel, a
strong current will set it spinning round and round, thus causing the
hook link to kink if it has not been fitted with a swivel, and the same
effect is often produced by the spinning of a fish on the hook.
The employment of a suitable ground bait will often make a wonderful
difference in the angler’s haul. It frequently attracts large numbers,
keeping them near at hand for some considerable time, and apparently
sharpens their appetite. It may be often observed, too, that a fish will
bite freely at the angler’s bait when in the neighbourhood of the ground
bait, while the former is viewed with suspicion in the absence of the
latter.
When fishing on the bottom only, the ground bait should be weighted if
it is of such a nature that it does not sink readily or if it is liable
to be carried away by currents; but it will often be found more
convenient to secure it on the end of a string, tied up in a muslin bag
if necessary, so that it may be adjusted to any desired depth.
Among the attractive viands suitable for this purpose we may mention
mussels, crushed crabs, pounded liver, the guts of any oily fish, and
the offal of almost any animal.
Along the east coast, and in some of the sandy bays of Devon and
Cornwall, fishing from the beach is practised, but we can hardly
recommend this as of much value to the amateur whose object is to obtain
as great a variety as possible of fishes for study. Some good food
fishes are often caught by this means, but the methods employed are
often very primitive, and would lack all interest to those who love good
sport.
On the east coast a long line, fitted with many hooks, is slung out as
far as possible by means of a pole, and the home end either held in the
hand of the fisher or fastened to the top of a flexible stick driven
into the sand. The latter plan becomes necessary when more than one line
is owned by the same individual, and he is made aware of the bite of a
large fish--and a large fish only, since the hooks are placed beyond a
heavy lead--by the bending of the stick.
The naturalist, however, is as much interested in the small fish as the
large ones, and, even for beach fishing, a rod and line, fitted with one
or two hooks only, and a lead no heavier than is absolutely essential,
will be preferable. A little practice will of course be necessary in
order that one may become expert in the casting of the rod line, but
with large rings on the rod, and a reel without a check, or a check that
can be thrown off when desired, the necessary proficiency in casting
ought to be acquired without much difficulty.
In some of the sandy bays of the south-west, long lines with a heavy
lead at both ends and baited hooks at short intervals throughout the
whole length, are placed on the sand at low tide close to the water’s
edge, and left unwatched until the next tide is out. As far as our
observations go this primitive mode of fishing is usually anything but
successful, the receding of the tide generally revealing a long row of
clean hooks, with, perhaps, one or two dead or half-dead fish; and it is
probable that most of the bait is devoured by crabs and other
crustaceans before the water becomes sufficiently deep to allow the
desired fishes to reach it.
There is one other method of fishing on which we may make a few remarks,
although it hardly comes under the heading of shore fishing. We refer to
a method of catching surface fishes from a moving boat, which method is
known as whiffing. The line is weighted with a lead which must be
regulated according to the speed of the boat. If the boat is an ordinary
rowing-boat, kept going at only a moderate speed, a few ounces of lead
will be sufficient, but a whiffing line trailing behind a sailing boat
travelling in a good breeze will require a pound or two of lead to keep
the bait only a little below the surface.
Beyond the lead we have three or four yards of gimp or strong gut, at
the end of which is a single hook fitted with a spinner, or baited with
some attractive natural or artificial bait. Whatever be the bait used,
there will certainly be more or less spinning caused by the resistance
offered by the water, hence it will be necessary to have a swivel beyond
the lead.
When whiffing near the shore, care must be taken to avoid outlying rocks
that approach the surface of the water, or a sudden snapping of the line
will give you an unwelcome warning of their existence. Further, we
should note that the fishes which are to be caught when whiffing do not
always swim at the same depth, thus it will be advisable to fish at
different distances from the surface by varying either the weight of the
lead or the speed of the boat.
CHAPTER IV
_THE MARINE AQUARIUM_
We have already advised our readers to take home their specimens alive
for the purpose of studying their growth and habits. Now, although there
may be some difficulties in the way of keeping marine animals and plants
alive for any considerable time, yet we are inclined to emphasise the
importance of this matter, knowing that the pleasure and instruction
that may be obtained from even a moderately successful attempt to carry
this out will far more than compensate for the amount of trouble
entailed. There are very many marine objects that are exceedingly pretty
and also very instructive, even when studied apart from the life with
which they were associated in the sea. Thus, a well-preserved sea-weed
may retain much of its original beauty of form and colour, the shells of
numerous molluscs and crustaceans exhibit a most interesting variety of
features well worthy of study, and a number of the soft-bodied animals
may be preserved in such a manner as to closely resemble their living
forms. This being the case, we can hardly say anything to discourage
those who gather sea-side objects merely for the purpose of making a
collection of pretty and interesting things to be observed and admired.
Such objects must necessarily afford much pleasure and instruction, and
the time spent in the collection and preparation will certainly cause
the collector to stray to the haunts of the living things, where he is
certain to acquire, though it may be to a great extent unconsciously, a
certain amount of knowledge concerning their habits and mode of life.
Moreover, sea-side collecting is one of the most healthy and
invigorating of all out-door occupations, and for this reason alone
should be encouraged.
Yet it must be observed that he whose sea-side occupation is merely that
of a collector, and whose work at home is simply the mounting and
arranging of the objects obtained, can hardly be considered a
naturalist. Natural history is a living study, and its devotee is one
who delights in observing the growth and development of living things,
watching their habits, and noting their wonderful adaptation to their
environments; and it is to encourage such observation that we so
strongly recommend the young collector to keep his creatures alive as
far as it is possible to do so.
The first thing to settle, then, is the nature of the vessel or vessels
that are to serve the purpose of aquaria for the work of the young
naturalist.
As long as the outdoor work is in progress temporary aquaria will be
very useful as a means by which the objects collected may be sorted and
stored until a final selection is made for the permanent tank. These
temporary aquaria may consist of jars or earthenware pans of any kind,
each containing a few small tufts of weed, preferably attached to pieces
of rock, and a layer of sand or gravel from the beach.
As such temporary aquaria will, as a rule, be within a convenient
distance from the sea-side where the collecting is being done, there
will be, we presume, no great difficulty in the way of obtaining the
frequent changes of water necessary to keep the animals and plants in a
healthy condition, so that we need do no more now than urge the
importance of avoiding overcrowding, and of renewing the water
frequently for the purpose of supplying the air required for the
respiration of the inmates.
When it is desired to isolate small species in such a manner that their
movements may be conveniently observed, glass jars answer well; but
whatever be the form or size of the vessels used, care must be taken to
avoid excess of both light and heat. They should be kept in a cool
place, quite out of the way of direct sunshine, and the glass vessels
used should be provided with a movable casing of brown paper to exclude
all light except that which penetrates from above.
Even temporary aquaria, used merely for the purpose suggested above,
should be carefully watched, for a single day’s neglect will sometimes
result in the loss of several valuable captives. A dead animal should be
removed as soon as it is discovered to avoid the unpleasant results
arising from the putrefaction of its body. The appearance of a scum or
film on the surface of the water should always be regarded with
suspicion. Such a scum should be removed with the aid of absorbent
paper, since it tends to prevent the absorption of oxygen from the air;
and, should the water be tainted in the slightest degree, it should be
changed at once, or, if this is not practicable, air should be driven
into it for some time by means of a syringe with a very fine nozzle.
Such precautions, however, are not so urgently needed when the aquarium
contains crustaceans only, for the majority of these creatures suffer
less than others in the tainted sea water, some even being apparently
quite as comfortable in this as in a supply fresh from the sea.
Sea-weeds exhibiting the slightest tendency to decay must be removed at
once; and, as regards the feeding of the animals, one must be careful to
introduce only as much food as is required for immediate use, so that
there be no excess of dead organic matter left to putrefy. Some of the
marine animals obtained from our shores feed entirely on the minute and
invisible organisms that are always present in the sea water, and others
subsist principally on certain of the weeds. Many, however, of a more
predaceous disposition, capture and devour living prey, while some, and
more especially the crustaceans, are partial to carrion. If, therefore,
the observer desires to study the ways in which the various creatures
secure and devour their food, he should introduce into his aquaria live
marine worms and other small animals, and also small pieces of fish or
flesh.
We will now pass on to the more serious undertaking of the construction
and management of a permanent salt-water aquarium.
The first point to decide is, perhaps, the size of the proposed vessel,
and this will in many cases be determined partly by a consideration of
the space at one’s disposal, and of the apartment it is intended to
occupy. If it is to be placed in a drawing-room or other ordinary
apartment of a dwelling-house, preference should be given to a window
facing the north in order to avoid the direct rays of the sun, but
perhaps no situation is more suitable than a cool conservatory in the
shady part of a garden; and in either case a strong table or other
support should be provided, of a form and size adapted to those of the
aquarium to be constructed.
Various materials may be used in the construction of such an indoor
aquarium, and we shall deal with two or three different types, so that
the reader may make his selection according to his fancy, or to his
mechanical ability, if he intends that it shall be of his own
construction.
We will begin with an aquarium constructed entirely of a mixture of
cement and fine sand, this being the most inexpensive and certainly the
easiest to make; and although it may not be regarded as the most
ornamental--but opinions will differ on this point--yet it has the
decided advantage of being the nearest approach to the natural rock
pool. Though somewhat heavy and cumbersome, even when empty, the amount
of material used in its construction may be varied according to the
taste and convenience of the maker. Further, this form of aquarium is
one that will readily admit of structural alterations at any future
period. It may be deepened at any time; lateral additions or extensions
may be made, or a portion may at any time be shut off for the purpose of
isolating certain of the animals procured.
[Illustration: FIG. 34.--SECTION OF AN AQUARIUM CONSTRUCTED WITH A
MIXTURE OF CEMENT AND SAND]
The first thing to do is to prepare a flat, strong slab of hard wood or
stone, the exact shape and size of the desired artificial pool, and then
cover this, if of wood, with a mixture of fine sand and cement, mixed to
a convenient consistency with water, to the depth of about one inch. The
banks or walls of the pool must then be built up on all sides, and this
is best done by the gradual addition of soft pellets of cement, applied
in such a manner as to produce an irregular surface. Unless the walls of
the aquarium be very thick and massive the cement will soon show a
tendency to fall from its place as the height increases, but this may be
avoided by doing the work in instalments, allowing each portion to set
before further additions are made to the structure.
Since some marine animals like to occupy snug and shady niches in deep
water while others prefer full exposure to the light in shallows,
arrangements should be made for all by varying the depth of the bed, and
providing several little tunnels and caverns. This may be accomplished
either by working the cement itself into suitable form, or by means of
piled stones obtained from the sea beach; and if the latter plan is
adopted, the stones should not be obtained until the aquarium is quite
ready for its living contents; for then a selection of stones and rock
fragments with weeds, anemones, sponges, and other fixed forms of life
attached to them, may be made. The natural appearance of a rock pool is
thus more nearly approached, and in a shorter time than if the sedentary
life were required to develop on an artificial ground.
Objection may be raised to the form of aquarium just described on the
ground that no life within it is visible except when viewed from above.
But is not this also the case with a rock pool on the sea shore? And has
any admirer of nature ever been heard to complain of the beauties of
such a pool because he was unable to look at them through the sides?
Further, it may be urged that the inmates of our aquarium will be living
under more natural conditions than those of the more popular glass-sided
aquaria, _because_ they receive light from above only.
[Illustration: FIG. 35.--CEMENT AQUARIUM WITH A GLASS PLATE IN FRONT]
However, should the reader require a glass front to his cement tank, the
matter is easily accomplished. Three sides are built up as before
described. A sheet of thick glass--plate glass by preference--is then
cut to the size and shape of the remaining space, and this is fixed by
means of cement pressed well against its edges, both inside and outside.
Water should not be put into the tank until it is quite dry; and, if one
side is made of glass, not until the cement surrounding the edge of the
glass has been liberally painted with marine glue, hot pitch, or some
other suitable waterproof material.
If any pipes are required in connection with the water supply of the
aquarium, according to either of the suggestions in a later portion of
this chapter, such pipes may be fixed in their proper places as the
cement sides are being built up.
The next type of aquarium we have to describe is of low cost as far as
the materials are concerned, and one that may be made by any one who has
had a little experience in woodwork; and although the tank itself is of
a simple rectangular form, yet it may be made to look very pretty with a
suitable adjustment of rocks and weeds.
It consists of a rectangular box, the bottom, ends, and back of which
are of hard wood, firmly dovetailed together, and the front of plate
glass let into grooves in the bottom and ends. All the joints and
grooves are caulked with marine glue, but no paint should be used in the
interior.
This form of tank may be vastly improved by the substitution of slabs of
slate for the wood, though, of course, this change entails a much
greater expenditure of both time and cash; but supposing the work to be
well done, the result is everything that could be desired as far as
strength and durability are concerned.
[Illustration: FIG. 36.--AQUARIUM OF WOOD WITH GLASS FRONT]
In either of the rectangular tanks just described glass may be used for
two sides instead of one only; and since this is not a matter of very
great importance, the choice may well be left to the fancy of the one
who constructs it.
Some prefer an aquarium with glass on all sides, and where this is the
case the framework may be made of angle zinc with all the joints
strongly soldered. Such an aquarium may be made in the form of any
regular polygon, for it is no more difficult to construct one of six or
eight sides than of four. It is more difficult, however, to make such an
aquarium perfectly watertight, for the glass, instead of being in
grooves, has to be securely fastened to the metal frame by means of a
cement on one side only, and this cement has to serve the double purpose
of holding the glass and keeping in the water.
Various mixtures have been suggested for this purpose, and among them
the following are perfectly satisfactory:--
1. Litharge 2 parts
Fine sand 2 "
Plaster of Paris 2 "
Powdered resin 1 part
Mix into a very thick paste with boiled linseed oil and a little driers.
2. Red lead 3 parts
Fine sand 3 ”
Powdered resin 1 part
Mix with boiled linseed oil as above.
Both these cements should be applied very liberally, and the aquarium
then allowed to remain quite undisturbed for at least two weeks before
any water is introduced.
[Illustration: FIG. 37.--HEXAGONAL AQUARIUM CONSTRUCTED OF ANGLE ZINC,
WITH GLASS SIDES]
When ready for the water, the bottom of the aquarium should be covered
with a moderately thick layer of fine sand from the sea shore, and
stones then piled in such a manner as to form little tunnels and caves
to serve as hiding-places for those creatures that prefer to be under
cover. As to the selection of stones, we have already suggested that
some may have weeds rooted to them, and that pieces of rock with
anemones, sponges, and other forms of life attached may be chipped off.
Further, on many of our rocky coasts we may find, near low-water mark, a
number of stones covered with a layer of vegetable growth, amongst which
many small animals live, often more or less concealed by their
protective colouring. Some of these stones placed on the bed of the
salt-water aquarium would add greatly to the natural appearance, as well
as give greater variety to the living objects. Shells bearing the
calcareous, snakelike tubes of the common serpula (p. 121), preferably
with the living animals enclosed, will also enhance the general
appearance and interest of the aquarium.
In making preparations previous to the introduction of animal life, due
regard should be paid to the peculiar requirements of the creatures it
is intended to obtain. We have already referred to the advisability of
arranging the bed of the tank in such a manner that the water may vary
considerably in depth, so that both deep and shallow water may be found
by the animals as required, and to the provision of dark holes for
crustaceans and other creatures that shun the light. Very fine sand
should be provided for shrimps, prawns, and other animals that like to
lie on it; and this sand must be deep in places if it is intended to
introduce any of the burrowing molluscs and marine worms.
The water used may be taken from the sea or be artificially prepared.
The former is certainly to be preferred whenever it can be conveniently
obtained, and at the present time few will find much difficulty in
securing a supply, for not only are we favoured with the means of
obtaining any desired quantity by rail at a cheap rate from almost any
seaport, but there are companies in various ports who undertake the
supply of sea water to any part of the kingdom. If the water is to be
conveyed from the coast without the aid of the regular dealers in this
commodity, great care must be taken to see that the barrel or other
receptacle used for the purpose is perfectly clean. Nothing is more
convenient than an ordinary beer or wine barrel, but it should be
previously cleansed by filling it several times with water--not
necessarily sea water--and allowing each refill to remain in it some
time before emptying. This must be repeated as long as the water shows
the slightest colouration after standing for some time in the barrel.
Should any difficulty arise in the way of getting the salt water direct
from the sea, it may be made artificially by dissolving ‘sea salt’ in
the proper proportion of fresh water, or even by purchasing the
different salts contained in the sea separately, and then adding them to
fresh water in proportionate quantities.
The composition of sea water is as follows:--
Water 96·47 per cent.
Sodium chloride 2·70 ”
Magnesium chloride ·36 ”
Magnesium sulphate (Epsom salts) ·23 ”
Calcium sulphate ·14 ”
Potassium chloride ·07 ”
Traces of other substances ·03 ”
100·00
and it will be seen from this table that artificial sea water may be
made by adding about three and a half pounds of sea salt, obtained from
the sea by the simple process of evaporation, to every ninety-six and a
half pounds of fresh water used. In making it there may be some
difficulty in determining the weight of the large volume of water
required to fill an aquarium of moderate dimensions, but this will
probably disappear if it be remembered that one gallon of water weighs
just ten pounds, and, therefore, one pint weighs twenty ounces.
If the sea salt cannot be readily obtained, the following mixture may be
made, the different salts being purchased separately:--
Water 96-1/2 lbs.
Sodium chloride (common salt) 43-1/4 ozs.
Magnesium chloride 5-3/4 ”
Epsom salts 3-3/4 ”
Powdered gypsum (calcium sulphate) 2-1/4 ”
Although in this mixture the substances contained in the sea in very
small quantities have been entirely omitted, yet it will answer its
purpose apparently as well as the artificial sea water prepared from the
true sea salt, and may therefore be used whenever neither sea salt nor
the natural sea water is procurable.
Assuming, now, that the aquarium has been filled with sea water, it
remains to introduce the animal and vegetable life for which it is
intended; and here it will be necessary to say something with regard to
the amount of life that may be safely installed, and the main conditions
that determine the proportion in which the animal and vegetable life
should be present in order to insure the greatest success.
Concerning the first of these we must caution the reader against the
common error of overcrowding the aquarium with animals. It must be
remembered that almost all marine animals obtain the oxygen gas required
for purposes of respiration from the air dissolved in the water. Now,
atmospheric air is only very slightly soluble in water, and hence we can
never have an abundant supply in the water of an aquarium at any one
time. If a number of animals be placed in any ordinary indoor aquarium,
they very soon use up the dissolved oxygen; and, if no means have been
taken to replace the loss, the animals die, and their dead bodies soon
begin to putrefy and saturate the water with the poisonous products of
decomposition.
It is probably well known to the reader that a large proportion of the
oxygen absorbed by the respiratory organs of animals is converted by
combination of carbon into carbonic acid gas within their bodies, and
that this gas is given back into the water where it dissolves, thus
taking the place of the oxygen used in its formation.
If, then, an aquarium of any kind is to be a success, some means must be
taken to keep the water constantly supplied with fresh oxygen quite as
rapidly as it is consumed, and this can be done satisfactorily by the
introduction of a proportionate quantity of suitable living weeds,
providing there is not too much animal life present.
The majority of living plants require carbonic acid gas as a food, and,
under the influence of light, decompose this gas, liberating the oxygen
it contained. This is true of many of our common sea-weeds, and thus it
is possible to establish in a salt-water aquarium such a balance of
animal and vegetable life that the water is maintained in its normal
condition, the carbonic acid gas being absorbed by the plants as fast as
it is excreted by animals, and oxygen supplied by the plants as rapidly
as it is consumed by the animals.
This condition, however, is more difficult to obtain in a salt-water
aquarium than in one containing fresh-water life, partly because,
generally speaking, the sea-weeds do not supply oxygen to the water as
rapidly as do the plants of our ponds and streams, and partly because of
the difficulties attending the successful growth of sea-weeds in
artificial aquaria. Thus it is usually necessary to adopt some means of
mechanically aërating the water; but, for the present, we shall consider
the sea-weeds only, leaving the mechanical methods of aërating the water
for a later portion of this chapter.
In the first place, let us advise the amateur to confine his attention
to the smaller species of weeds that are commonly found in small and
shallow rock pools, for the successful growth of the larger purple and
olive weeds will probably be beyond his power, even though his tank be
one of considerable capacity. The best plan is that we have already
suggested--namely, to chip off small pieces of rock with tufts of weed
attached, and to fix them amongst the rockery of the aquarium, being
careful to place those that grew in shallow water with full exposure to
the light, and those which occupied sheltered and shady places in the
rock pool, respectively, in similar situations in the artificial pool.
For the purposes of aëration we have to rely principally on the bright
green weeds, and preference should be given to any of these that
exhibit, in their natural habitat, a multitude of minute air-bubbles on
the surface of their fronds, for the bubbles consist principally of
oxygen that is being liberated by the plant, and denote that the species
in question are those that are most valuable for maintaining the desired
condition of the water in an aquarium.
Any small sea-weed may be tried at first, but experience will soon show
that some are much more easily kept alive than others. In this
experimental stage, however, a constant watch should be maintained for
the purpose of detecting signs of decay in the marine garden. A plant
should always be removed as soon as it presents any change from the
natural colour, or exhibits the smallest amount of slimy growths on the
surface, for decomposing plants, as well as decaying animals, will soon
convert an aquarium into a vessel of putrid and poisonous water.
It seems almost unnecessary to name a selection of sea-weeds for small
aquaria, seeing that our rock pools produce so many extremely beautiful
species, most of which may be successfully kept alive in a well-managed
tank; but the common Sea Grass (_Enteromorpha compressa_), and the Sea
Lettuce (_Ulva latissima_), also known locally as the Green Laver or
Sloke, are particularly useful for the aëration of the water; while the
Common Coralline (_Corallina officinalis_), the Dulse (_Schizymenia
edulis_), the Peacock’s tail (Padina pavonia), the Irish or Carrageen
Moss (_Chondrus crispus_), _Callithamnion_, _Griffithsia setacea_,
_Plocamium plumosium_, _Rhodymenia palmata_, _Rhodophyllis bifida_, and
_Ceramium rubrum_ are all beautiful plants that ought to give no trouble
to the aquarium-keeper.
It is not advisable to introduce animal life into the aquarium
immediately it is filled, on account of the possibility of the water
being contaminated by contact with the cement that has been used to make
it water-tight. It is safer to allow the first water to stand for a few
weeks, the weeds and all other objects being _in situ_, and the
necessary means employed for perfect aëration during this interval, and
then, immediately before the animals are placed in their new home, to
syphon off the whole of the water, and refill with a fresh supply.
In the selection of animals due regard should be paid to two important
points--first, the danger of overcrowding, and, secondly, the
destructive habits of some of the more predaceous species.
No more than two or three animals should, as a rule, be reckoned for
each gallon of water; and the proportion of animals should be even less
than this when any of them are of considerable size.
As regards the destructive species, these are intended to include both
those that are voracious vegetable feeders and also those whose habit it
is to kill and prey on other creatures.
It must be understood that the weeds are to serve two distinct
purposes:--They are to supply at least some of the oxygen required for
the respiration of the animal inmates, and also to serve as food for
them. Some marine fishes and molluscs feed on the fronds of the weeds,
and among these the common periwinkle may be mentioned as one of the
most voracious. If many such animals are housed in the aquarium, it will
be necessary to replace at intervals those species of weeds that suffer
most from their ravages. The zoospores thrown off by the weeds,
particularly in the autumn, are also valuable as food for some of the
animals.
Notwithstanding the destructive character of the periwinkle just
referred to, it has one redeeming feature, for it is certainly useful in
the aquarium as a scavenger, as it greedily devours the low forms of
vegetable life that cover the glass and rocks, thus helping to keep them
clean; and the same is true of the common limpet and other creeping
molluscs. Some of these are even more to be valued on account of their
partiality for _decaying_ vegetable matter, by devouring which they
reduce the amount of the products of decomposition passing into the
water.
Other details concerning the selection of animal and vegetable life for
the indoor aquarium must be left to the discretion and experience of the
keeper, for it is impossible by written instructions and advice to cover
all the various sources of loss and trouble that may from time to time
arise. If, however, the general hints for the management of the marine
aquarium here given be faithfully followed, there ought to be no further
losses than must accrue from the injudicious selection of animal
species, and these will decrease as experience has been acquired
respecting the habits of the creatures introduced.
We must now pass on to matters pertaining to the maintenance of the
healthy condition of an aquarium which, we will suppose, has been
established with due regard to scientific principles. Under this head we
shall consider, (1) the aëration of the water, (2) the repair of loss
due to evaporation, and (3) the regulation of light and temperature.
It has already been shown that the marine aquarium can hardly be
maintained in a satisfactory condition as regards its air supply by
leaving the aëration of the water entirely to the action of plant life;
and herein this form of aquarium differs from that employed for the
animal and vegetable life derived from ponds and streams. Fresh-water
weeds develop and multiply with such rapidity, and are such ready
generators of oxygen gas that it is a very easy matter to establish a
fresh-water aquarium that will remain in good condition for years with
but little attention; it is therefore important that we should point out
the difference in treatment necessary to those of our readers who are
already acquainted with the comparative ease with which the fresh-water
aquarium may be kept in good order, lest they expect the same
self-aërating condition in the marine tank.
It is never a good plan to leave the renovation of the water of the
aquarium until there are visible signs within that something is going
wrong. It is true that an unsatisfactory condition of the water,
revealed by a slight taint in the odour, or a general turbidity, or the
formation of a slight scum on the surface, may sometimes be rectified by
the prompt application of some method of artificial aëration, but the
aim of the aquarium-keeper should be not the rectification of
unsatisfactory conditions, but the establishment of such a method of
aëration that the unsatisfactory condition becomes an impossibility. We
do not wish to discourage anyone who has the slightest desire to start a
marine aquarium. Our aim is to point out any difficulties that lie in
the way in order that the aquarium may be a success; and thus, having
stated that the difficulties attending it are somewhat greater than
those connected with the management of a fresh-water aquarium, we should
like to add that these practically disappear when one is prepared to
devote a short time at regular intervals in order to see that the
process of aëration is properly carried out.
Some recommend the occasional injection of air by a syringe as one means
of aërating the water; but, although this may be all very well as a
_temporary_ purifier of the slightly tainted aquarium, it is hardly
suitable as a means of maintaining a good, healthy condition. It must be
remembered that oxygen gas--the gas of the atmosphere so essential to
animal life--is only very slightly soluble in water. By this we mean not
only that water dissolves oxygen very slowly, but also that it can never
hold a large supply of the gas at any one time. This being the case, it
is clear that the use of a syringe for a short time, though it
discharges an enormous total volume of air into the water, will result
in the actual solution of only a small quantity. No method of aëration
is perfect that allows the admission of air for a short time only at
comparatively long intervals; the most perfect system is that in which
air is slowly but _continuously_ passed into solution.
Since air is slightly soluble in water, it is clear that it must be
continuously passing into any body of water that has its surface freely
exposed to it; hence a wide and shallow aquarium is much more likely to
keep in good order than one that is narrower and deeper. But, with
marine aquaria, the simple absorption from the air at the surface is not
in itself sufficient, as a rule, to maintain a healthy condition. Yet it
will be advisable to remember this matter when constructing a tank for
marine life.
One of the prettiest, and certainly one of the most effectual, methods
of supplying air to an aquarium is by means of a small fountain with a
very fine spray. The water need seldom be changed, but the fountain may
be fed by water from the aquarium, and as the fine spray passes through
the air it will absorb oxygen and carry it in solution to the tank.
The accompanying diagram illustrates the manner in which this can be
accomplished. The aquarium (A) is supplied with an outlet (O) about an
inch from the top by means of which the water is prevented from
overflowing, and the outlet pipe leads to a vessel (V) of considerable
capacity which, for the sake of convenience and appearance, may be
concealed beneath the table on which the aquarium stands. Some feet
above the level of the aquarium is another vessel (C), supported on a
shelf, having about the same capacity as V, and supplied with a small
compo pipe that passes down into the aquarium, and then, hidden as much
as possible by the rockery, terminates in a very fine jet just above the
level of the water in the centre. The upper vessel should also be
provided at the top with a loose covering of muslin to serve as a
strainer, and this should be replaced at intervals as it becomes clogged
with sedimentary matter.
In order that this arrangement may give perfect satisfaction the two
vessels (C and V) must each be of at least half the capacity of the
aquarium itself, and the total quantity of salt water sufficient to fill
the aquarium together with one of them. It should also be remembered
that since the pressure of water depends not on its quantity, but on its
height measured perpendicularly, it follows that the height to which the
fountain will play is determined by the height of the vessel C above the
level of the jet.
[Illustration: FIG. 38.--METHOD OF AËRATING THE WATER OF AN AQUARIUM
A, aquarium with fountain; C, cistern to supply the fountain;
O, pipe for overflow; V, vessel for overflow]
Let us now suppose that the aquarium and the upper vessel have both been
filled with sea water. The fine jet from the pipe plays into the air and
returns with a supply of oxygen to the aquarium, while the excess above
the level of O passes into the concealed vessel below the table. If the
two vessels are as large as we recommend, and the jet a very fine one,
the fountain may continue to play for hours before C is empty, the
animals of the tank being favoured all this time with a continuous
supply of air. And when the supply from above is exhausted, the contents
of the bottom vessel are transferred to the top one, and at the same
time so effectually strained by the layer of muslin that no sedimentary
matter passes down to choke the fine jet of the fountain. One great
advantage this method possesses is that the living creatures derive the
benefit of a much larger quantity of water than the aquarium alone could
contain; and thus, apart from the aërating effects of the fountain, the
result is the same as if a much larger tank were employed.
In our next illustration (fig. 39) we give a modified arrangement based
on the same principle which may commend itself by preference to some of
our readers. Here the supply pipe to the fountain passes through a hole
in the bottom of the aquarium instead of into the top, and the outlet
pipe is bent downward within so as to form a syphon.
Those who are acquainted with the principle of the syphon will
understand at once the working of such an arrangement as this. Let us
suppose the vessel _c_ to be full of water, and the fountain started,
while the water in the aquarium stands no higher than the level _l_. The
water slowly rises until the level _h_ of the bend of the outlet tube
has been reached, and during the whole of this time no water escapes
through the exit. As soon, however, as the latter level has been
attained, the water flows away into the lower vessel, into which it
continues to run until the lower level is reached, and then the outflow
ceases, not to commence again until the fountain causes the water to
rise to the upper level.
From what has been said the reader will see that the total quantity of
water required in this instance need not exceed the capacity of the
aquarium; also that each of the vessels connected with water supply and
waste should have a capacity equivalent to the volume of water contained
in the aquarium between the two levels _h_ and _l_.
The alternate rising and falling of the water produced in the manner
just described represents in miniature the flow and ebb of the tides,
but perhaps this is in itself of no great advantage in the aquarium
except from the fact that it allows those creatures that prefer to be
occasionally out of the water for a time a better opportunity of
indulging in such a habit. And further, with regard to both the
arrangements for aëration above described, it should be noted that
earthenware vessels are much to be preferred to those made of metal for
the holding of sea water, since the dissolved salts corrode metallic
substances rather rapidly, and often produce, by their chemical action,
soluble products that render the water more or less poisonous.
[Illustration: FIG. 39.--AQUARIUM FITTED WITH APPARATUS FOR PERIODIC
OUTFLOW]
Other methods of aërating the water of aquaria are practised, but these,
as a rule, are only practicable in the case of the large tanks of public
aquaria and biological laboratories, as the mechanical appliances
necessary to carry them out successfully are beyond the means of an
ordinary amateur.
In such large tanks as those referred to it is common to force a fine
jet of air into the water by machinery. Sometimes this air is driven
downward from a jet just below the surface, and with such force that a
multitude of minute bubbles penetrate to a considerable depth before
they commence to rise, but in others the air is made to enter at the
bottom and must therefore pass right through the water.
Of course the amateur aquarium-keeper may carry out this method of
aëration with every hope of success providing he has some self-acting
apparatus for the purpose, or can depend on being able himself to attend
to a non-automatic arrangement at fairly regular intervals, always
remembering that a single day’s neglect, especially in the case of a
small tank with a proportionately large amount of animal life, may lead
to a loss of valuable specimens.
We have already mentioned the use of a syringe as a means by which an
aquarium may be temporarily restored to a satisfactory condition
providing it has not been neglected too long, and some recommend forcing
air, or, still better, pure oxygen gas, from an india-rubber bag into
the water. We have used, for the same purpose, a stream of oxygen from a
steel cylinder of the compressed gas with very satisfactory results; and
since oxygen may be now obtained, ready compressed, at a very low
price--about twopence a cubic foot--there is much to be said in favour
of this method as an auxiliary in the hands of the owner of a small
tank, though we hardly recommend it as a prime means of aëration to take
the place of the fountain.
In any case, where a stream of air or oxygen is employed, an exceedingly
fine jet should be used, in order that the expelled gas may take the
form of a stream of minute bubbles; for, as previously stated, the water
can absorb the gas only very slowly, so that there must necessarily be a
considerable waste when the gas issues rapidly. Further, the smaller the
bubbles passing through the water, the greater is the total surface of
gas in contact with the liquid, the volume of the supply being the same,
and hence the more effectually will the solution of the gas proceed.
Again, another advantage of the fine stream of minute bubbles lies in
the fact that the smaller these bubbles are the more slowly they rise to
the surface of the water, and thus the longer is the time in which the
gas may be absorbed during its ascent.
A fine jet, well suited to the purpose here defined, may be made very
easily by holding the middle of a piece of glass tubing in a gas flame
until it is _very_ soft, and then, immediately on removing it, pulling
it out rather quickly. A slight cut made with a small triangular file
will then enable the operator to sever the tube at any desired point.
Yet another method of maintaining the air supply of aquaria is adopted
in the case of some of the large tanks of public aquaria and biological
laboratories situated close to the sea, and this consists in renewing
the water at every high tide by means of pumps.
It must not be supposed that an indoor aquarium, even when well
established, and supplied with the best possible system of aëration,
requires no further care and attention. In the first place there is a
continual loss of water by evaporation, especially in warm and dry
weather, and this must be rectified occasionally. Now, when water
containing salts in solution evaporates, the water passing away into the
air is perfectly free from the saline matter, and thus the percentage of
salt in the residue becomes higher than before. It is evident,
therefore, that the loss by evaporation in a marine aquarium must be
replaced by the addition of _fresh_ water, which should either be
distilled, or from the domestic supply, providing it is soft and
moderately free from dissolved material.
But the question may be asked, ‘Do not the marine animals and plants
utilise a certain amount of the saline matter contained in the salt
water?’ The answer to this is certainly in the affirmative, for all
sea-weeds require and abstract small proportions of certain salts, the
nature of which varies considerably in the case of different species;
and, further, all the shelled crustaceans and molluscs require the salts
of lime for the development of their external coverings, and fishes for
the growth of their bony skeletons. Hence the above suggestion as to the
replenishment of loss by evaporation with pure water is not perfectly
satisfactory. It will answer quite satisfactorily, however, providing
the sea water is _occasionally_ changed for an entirely new supply.
Again, since carbonate of lime is removed from sea water more than any
other salt, being such an essential constituent of both the external and
internal skeletons of so many marine animals, as well as of the
calcareous framework of the coralline weeds, we suggest that the
aquarium may always contain a clean piece of some variety of carbonate
of lime, such as chalk, limestone, or marble, which will slowly dissolve
and replace that which has been absorbed.
Water is rendered denser, and consequently more buoyant, by the presence
of dissolved salts; and, since the density increases with the proportion
of dissolved material, we are enabled to determine the degree of
salinity by finding the density of the solution. We can apply this
principle to the aquarium, as a means of determining whether the water
contains the correct amount of sea salt, also for testing any artificial
salt water that has been prepared for the aquarium.
Probably some of our readers are acquainted with some form of
hydrometer--an instrument used for finding the density of any liquid;
but we will describe a simple substitute that may be of use to the owner
of a marine aquarium, especially if the salt water for the same is
artificially prepared. Melt a little bees-wax, and mix it with fine,
clean sand. Then, remembering that the wax is lighter than water, and
consequently floats, while sand is considerably heavier, and sinks,
adjust the above mixture until a solid ball of it is just heavy enough
to sink _very slowly_ in sea water. Now make two such balls, and then
cover one of them with a light coating of pure wax. We have now two
balls, one of which will float in sea water, and the other sink, and
these may be used at any time to test the density of the water in, or
prepared for, the aquarium. If the water is only a little too salt, both
balls will float; while, if not sufficiently rich in saline matter, both
will sink.
We must conclude this chapter by making a few remarks on the important
matter of the regulation of light and temperature. Direct sunlight
should always be avoided, except for short and occasional intervals, not
only because it is liable to raise the temperature to a higher degree
than is suitable for the inmates of the aquarium, but also because an
excess of light and heat tends to produce a rapid decomposition of
organic matter, and a consequent putrid condition of the water, and this
dangerous state is most likely to occur when both light and temperature
are high at the same time.
The water should always be cold; and as it is not always easy to
estimate the temperature, even approximately, by the sensation produced
on immersing the fingers, it is a good plan to have a small thermometer
always at hand, or placed permanently in the aquarium. In the summer
time the water should be kept down to fifty-five degrees or lower, and
in winter should never be allowed to cool much below forty. There may be
some difficulty in maintaining a temperature sufficiently low in summer,
but a small piece of ice thrown in occasionally to replace the loss due
to evaporation, especially on very hot days, will help to keep it down.
CHAPTER V
_THE PRESERVATION OF MARINE OBJECTS_
The sea-side naturalist, in the course of his ramblings and searchings
on the coast, will certainly come across many objects, dead or alive,
that he will desire to set aside for future study or identification in
his leisure moments at home. Some of these will be required for
temporary purposes only, while, most probably, a large proportion will
be retained permanently for the establishment of a private museum, that
shall serve not only as a pleasant reminder of the many enjoyable hours
spent on the shore, but also as a means of reference for the study of
the classification of natural objects and of their distribution and
habitats.
We will first deal with those specimens that are required for temporary
purposes only--those of which the collector desires to study the general
characters, as well as, perhaps, something of the internal structure;
but before doing so we cannot refrain from impressing on the reader the
advisability of learning as much as possible of the external features
and mode of growth of the different living creatures while still alive,
for it must be remembered that it is impossible to preserve many of them
without more or less destruction of their natural colouring and
distortion of their characteristic forms.
In those cases where it is possible to keep the creatures alive for a
short time only, it is a good plan to make notes of their movements and
all observed changes in form, and their methods of feeding, and also to
illustrate these notes by sketches drawn from life. This may seem quite
an unnecessary procedure to many beginners in the study of natural
objects, and may even, as far as the sketches are concerned, present
difficulties that at first appear to be insurmountable; but the power to
sketch from nature will surely be acquired to a greater or less degree
by constant practice, and illustrated notes prepared for the purpose we
suggest will undoubtedly be of great value to the student. Further,
though it may often be necessary to set specimens aside in a
preservative fluid until one has the leisure to examine their structure,
it should always be remembered that they never improve by keeping, also
that they are rarely in such good condition for dissection after
saturation with the preservative as when perfectly fresh.
One of the most convenient preservatives for general use is undoubtedly
methylated spirit. This is alcohol that has been adulterated in order to
render it undrinkable, so that it may be sold free from duty for use in
the various arts and manufactures without any danger of its being
employed for the concoction of beverages. It may be used just as
purchased--that is, in its strongest condition--for many purposes, but
in this state it has a powerful affinity for water, and will rapidly
abstract water from animal and vegetable objects, causing the softer
ones to become hard, shrunken, and shrivelled, often to such an extent
that they are almost beyond recognition.
By diluting the spirit, however, we satisfy to a great extent its
affinity for water, and thus prevent, or, at least, reduce the action
just mentioned. A mixture of equal quantities of spirit and water is
quite strong enough. Unfortunately the common methylated spirit of the
shops produces a fine white precipitate, that gives the whole mass a
milky appearance, when it is diluted. This is due to the presence of
mineral naphtha, which is added in a certain fixed proportion in
accordance with the Government regulations. But it _is_ possible, by
special application, to obtain the ‘non-mineralised’ or ‘ordinary’
methylated spirit of former years, though not in small quantities, and
this liquid dissolves in water without the formation of a precipitate.
It should be noted, however, that the use of the spirit as a
preservative is in no way interfered with by the presence of the mineral
naphtha, the only disadvantage of this impurity lying in the fact that
the milkiness consequent on dilution prevents the objects in a specimen
jar from being observed without removal.
We have just referred to the hardening action of strong spirit as a
disadvantage, and so it is when it is required to preserve soft
structures with as little as possible of change in general form and
appearance; but there are times when it becomes necessary to harden
these soft structures in order that sections may be made for the purpose
of examining internal structure with or without the aid of the
microscope, and for such purposes strong spirit is one of the best
hardening agents that can be employed.
Formaldehyde is another very good preservative. It is a colourless
liquid, and should be considerably diluted for use, a two per cent.
solution being quite strong enough for all ordinary purposes. It
possesses some distinct advantages as compared with spirit. In the first
place, it does not destroy the natural colours of objects to the extent
that spirit does; and, although a hardening agent as well as a
preservative, it does not harden soft structures by the extraction of
the water they contain, and therefore does not cause them to become
shrivelled or otherwise distorted. It will also occur to the reader
that, since a small bulk of formaline represents a large volume of the
diluted preservative, it is very conveniently stored, and a very small
bottle of it taken for outdoor work may, on dilution with water, be made
to yield all that is required for the preservation of the takings of a
successful day, or even of a longer period. Formaldehyde is usually sold
in solution of about forty per cent. strength, and for the preparation
of a two per cent. solution it will be found convenient to provide a
glass measure graduated either into cubic centimetres or fluid ounces
and drams. One hundred volumes of the original solution contain forty of
pure formaldehyde, and if water be added to make this up to two thousand
volumes, a two per cent. solution is obtained. Thus, one hundred cubic
centimetres of the original solution is sufficient to prepare two litres
(three and a half pints) of suitable preservative.
A very good preservative liquid may be made by dissolving two ounces of
common salt, one ounce of alum, and two or three grains of corrosive
sublimate (a deadly poison) in one quart of water, and then, after
allowing all sedimentary matter to settle to the bottom, decanting off
the clear solution. This mixture is known as Goadby’s fluid, and is
well adapted for the preservation of both animal and vegetable
structures. It does not cause any undue contraction of soft tissues,
and, as a rule, does not destroy the natural colours of the objects kept
in it.
Glycerine is valuable as a preservative for both animal and vegetable
objects, and especially for the soft-bodied marine animals that form
such a large percentage of the fauna of our shores. It maintains the
tissues in a soft condition, and preserves the natural tints as well as
any liquid.
An inexpensive preservative may also be made by dissolving chloride of
zinc--about one ounce to the pint of water. This is considered by some
to be one of the best fluids for keeping animal structures in good
condition.
Now, although the different fluids here mentioned are described in
connection with the _temporary_ preservation of natural objects, it must
be remembered that they are equally adapted for the permanent
preservation of the animals and plants that are to figure in the museum
of the sea-side naturalist; and, although some marine objects may be
preserved in a dry state in a manner to be hereafter described, yet
there are many species of animals, and also some plants, that can be
satisfactorily preserved only by immersion in a suitable fluid.
This method may be applied to all soft-bodied animals, such as anemones,
jelly-fishes, marine worms, shell-less molluscs (sea slugs, cephalopods,
&c.), the soft parts of shelled molluscs, fishes, &c.; and most sponges
retain their natural appearance much better in a preservative fluid than
in a dry condition. Many sea-weeds also, which are practically destroyed
by the most careful drying process, are most perfectly preserved in
fluid.
But the puzzled amateur will probably be inclined to ask: ‘Which is the
best preservative liquid for this or that specimen?’ No satisfactory
general rule can be given in answer to such a question, and a great deal
will have to be determined by his own experiments and observations.
Whenever he has two or three specimens of the same object, as many
different fluids should be employed, and the results compared and noted.
In this way a very great deal of useful information will be obtained and
by the best possible means. However, it may be mentioned that all the
fluids alluded to above may be safely used for almost every animal or
vegetable specimen with the following reservations: strong spirit should
not be employed for _any_ very soft animal, nor should it be used for
delicate green plants, since it will dissolve out the green colouring
matter (_chlorophyll_), leaving them white or almost colourless.
Further, the greatest care should be exercised in dealing with sea
anemones and jelly-fishes. If spirit is used for preserving these
creatures, it should be very dilute, at least at first, but may with
advantage be increased in strength afterwards, though this should be
done gradually.
Whatever be the preservative used, it is sure to be more or less charged
with sedimentary and coloured matter extracted from the object immersed
in it; hence, if the specimen concerned is to form part of a museum
collection, it will be necessary to transfer it to a fresh solution
after a time, and a second, and even further changes may be necessary
before the object ceases to discolour the fluid or render it turbid.
Considerable difficulty will sometimes be found in the attempts to
preserve a soft-bodied animal in its natural attitude. Thus, when a sea
anemone is removed from its native element, it generally withdraws its
tentacles, and, contracting the upper part of its cylindrical body,
entirely conceals these appendages, together with the mouth they
surround; and a mollusc similarly treated will generally pull itself
together within its shell, leaving little or no trace of the living body
inhabiting the lifeless case. Then, if these animals are transferred to
any fluid other than sea water, or placed anywhere under unnatural
conditions, they usually remain in their closed or unexpanded form.
Thus, almost every attempt to kill them for preservation deprives them
of just the characteristics they should retain as museum specimens.
Some such animals may be dealt with satisfactorily as follows: Transfer
them to a vessel of fresh sea water, and leave them perfectly
undisturbed until they assume the desired form or attitude. Then add a
_solution_ of corrosive sublimate very gradually--a drop or two at
intervals of some minutes. In this way the bodies of anemones may be
obtained ready for preservation with expanded tentacles, tube-secreting
worms with their heads and slender processes protruding from their limy
or sandy cases, molluscs with their ‘feet’ or their mantles and gills
protruding from their shells, and barnacles with their plume-like
appendages projecting beyond the opening of their conical shells.
The specimens thus prepared may be placed at first in very dilute
spirit, and then, after a time, finally stored in a stronger solution of
spirit in water; or they may be transferred to one of the other
preservative solutions previously mentioned.
All specimens permanently preserved in fluid for a museum should be
placed in jars, bottles, or tubes of suitable size, each vessel
containing, as a rule, only one. Where expense is no object, stoppered
jars made expressly for biological and anatomical specimens may be used
for all but the smallest objects; or, failing this, ordinary
wide-mouthed bottles of white glass, fitted with good corks or glass
stoppers.
For very small specimens nothing is more suitable than glass tubes, but
it must be remembered that wherever corks are used, even if they are of
the best quality procurable, it will be necessary to look over the
specimens occasionally to see if the preserving fluid has disappeared to
any extent either by leakage or evaporation; for such loss is always
liable to occur, although it may be very slow, and especially when
methylated spirit is the liquid employed.
[Illustration: FIG. 40.--JARS FOR PRESERVING ANATOMICAL AND BIOLOGICAL
SPECIMENS]
The writer has preserved many hundreds of small marine and other objects
in glass tubes of dilute spirit that have been hermetically sealed, thus
rendering the slightest loss absolutely impossible, while the perfect
exclusion of air prevents the development of fungoid growths that
sometimes make their appearance in imperfectly preserved specimens. The
making and closing of such tubes, though a more or less difficult
operation at first to those who have had no previous experience in
glass-working, become exceedingly simple after a little practice; and
believing it probable that many of our readers would like to try their
hand at this most perfect method of preserving and protecting small
objects, we will give a description of the manner in which it is done.
The apparatus and materials required for this work are:--Lengths of
‘soft’ glass tubing, varying from about one quarter to a little over
half an inch in internal diameter; a supply of diluted spirit--about
half spirit and half water; a Herapath blowpipe, preferably with
foot-bellows; and a small triangular file.
The glass tubing may be cut into convenient lengths by giving a single
sharp stroke with the file, and then pulling it apart with, at the same
time, a slight bending _from_ the cut made.
[Illustration: FIG. 41.--SHOWING THE DIFFERENT STAGES IN THE MAKING OF
A SMALL SPECIMEN TUBE]
Cut a piece of tubing about eight or nine inches long, heat it in the
blowpipe flame, turning it round and round all the time, until it is
quite soft, then remove it from the flame and immediately pull it out
_slowly_ until the diameter in the middle is reduced to about a
sixteenth of an inch (fig. 41, 2). Make a slight scratch with the file
at the narrowest part, and divide the tube at this point (fig. 41, 3).
Now heat one of these pieces of tubing as before just at the point where
the diameter of the drawn part begins to decrease; and, when very soft,
pull it out rather quickly while it is _still in the flame_. The part
pulled now becomes completely separated, and the tube is closed, but
pointed. Continue to heat the closed end, directing the flame to the
point rather than to the sides, until the melted glass forms a rather
thick and flattened end; and then, immediately on removing it from the
flame, blow gently into the open end until the melted glass is nicely
rounded like the bottom of a test-tube (fig. 41, 4). When the tube is
cold, the specimen that it is to contain, and which has already been
stored for a time in dilute spirit, is dropped into it. The tube is now
heated about an inch above the top of the specimen, drawn out as shown
in fig. 41, 5, and again allowed to cool. When cold, the fresh spirit is
poured into the open end of the tube, but the middle part is so narrow
that the spirit will not run down freely. If, however, suction be
applied to the open end, air from the bottom will bubble through the
spirit, and then, on the cessation of the suction, the spirit will pass
down to take the place of the air that was withdrawn. This may be
repeated if necessary to entirely cover the specimen with the fluid. Any
excess of spirit is then thrown from the upper part of the tube, and the
latter cut off. Nothing is now left but to close the tube hermetically.
This is done by heating the lower part of the narrow neck, and then
drawing it out _in the flame_, taking great care that the tube is
withdrawn from the flame the moment it is closed. The tube must also be
kept in an upright position until it has cooled. The appearance of the
finished tube is shown in fig. 41, 6.
[Illustration: FIG. 42.--SMALL SPECIMEN TUBE MOUNTED ON A CARD]
All preserved specimens should have a label attached on which is written
the name of the specimen, the class and order to which it belongs, the
locality in which it was found, together with any brief remarks that the
owner desires to remember concerning its habits &c.
The bottles or tubes that are too small to have a label attached to them
in the ordinary way may be mounted on a card, as represented in fig. 42,
and the desired particulars then written on the card.
When soft or delicate specimens are preserved in a bottle of fluid they
frequently require some kind of support to keep them in proper form and
to display them better for observation. Perhaps the best way to support
them is to fasten them to a very thin plate of mica of suitable size by
means of a needle and very fine thread. The mica is so transparent that
it is invisible in the fluid, and the few stitches are also hardly
perceptible, thus making it appear as if the specimen floats freely in
the fluid.
We will now pass on to consider those objects of the shore that are
usually preserved in a dry condition, commencing with
STARFISHES AND SEA URCHINS
Starfishes are commonly preserved by simply allowing them to dry in an
airy place, with or without direct exposure to the sun’s rays, and this
method is fairly satisfactory when the drying proceeds rapidly; but care
should be taken to maintain the natural roughness of the exterior as
well as to have the numerous suckers of the under surface as prominent
as possible. If the starfish is simply laid out on some surface to dry,
the side on which it rests is often more or less flattened by the weight
of the specimen itself, which therefore becomes adapted for the future
examination of one surface only; but a better result, as regards both
the rapidity of drying and the after appearance of the specimen, may be
obtained by suspending it on a piece of fine net or by threads. A still
better plan is to put the dead starfish into _strong_ spirit, which will
rapidly extract the greater part of the moisture that its body
contained. After allowing it to remain in this for a day or two to
harden it, put it out to dry as before mentioned. The spirit, being very
volatile, will soon evaporate, so that the specimen will shortly be
ready for storing away.
It is most important to observe that dried specimens--not starfishes
only, but all animal and vegetable objects--should never be placed in
the cabinet or other store-case until _perfectly_ dry, for a very small
amount of moisture left in them will often encourage the development of
moulds, not only on themselves, but on other specimens stored with them.
Very small and delicate starfishes, when preserved in a dry condition,
may be protected from injury by fastening them on a card by means of a
little gum, or by keeping them permanently stored on cotton wool in
glass-topped boxes.
Sea urchins, or sea eggs, as they are commonly called, may be preserved
exactly in the same way as starfishes, though it is more essential in
the case of these to soak them in strong spirit previous to drying,
otherwise the soft animal matter within the shell will decompose before
the drying is complete. Here, however, it is possible to remove the
whole interior with the aid of a piece of bent wire, and to thoroughly
clean the inner surface of the shell before drying it.
Some of the shells should be preserved with the spines all intact, and
others with these removed in order to show the arrangement of the
plates which compose the shell, as well as the perforations, and the
rounded processes to which the spines are articulated.
The majority of sea urchins are provided with a most complicated and
beautiful arrangement of teeth which are well worthy of study. These
should be removed from a moderately large specimen, the soft surrounding
structures carefully dissected away, and then cleaned by means of an old
tooth-brush without disarranging them.
It will be found that dried sea urchins will require care when preserved
with spines attached, for these appendages are usually very brittle and
are easily dislocated at their bases where they are united to the shell
by ball-and-socket joints.
It may be mentioned here that corrosive sublimate is very valuable for
preventing the development of mould on the surfaces of starfishes, sea
urchins, and museum specimens generally. It is best supplied in the form
of an alcoholic solution made by dissolving a few grains in about half a
pint of methylated spirit; the advantage of this over an aqueous
solution being the rapidity with which it dries. In most cases it is
simply necessary to apply the solution to the object by means of a soft
brush, but, as regards starfishes and urchins it is far better to
dissolve a few grains of the corrosive sublimate in the spirit in which
the objects are placed previous to drying.
CRUSTACEANS
The preservation of crustaceans by the dry method often requires some
care and demands a certain amount of time; but the process is never
really difficult, and the satisfaction of having produced a good
specimen for a permanent collection well repays one for the trouble
taken and time spent.
Some of our crustaceans are only partially protected by a firm outer
covering, and almost every attempt to preserve these as dry objects
results in such a shrivelling of the soft tissues that the natural
appearance is quite destroyed. This is the case with some of the
barnacles, and the abdominal portion of the bodies of hermit crabs,
which are, therefore, far better preserved in fluid. Dilute spirit is
quite satisfactory for most of these as far as the preservation of the
soft structures is concerned, but it has the disadvantage that it turns
the shells of some crustaceans red, making them appear as if they had
been boiled.
Other crustaceans are so small, or are hardened externally to such a
slight extent, that they also are not adapted for the dry method of
preservation. Speaking generally, such crustaceans as shrimps and
sand-hoppers are best preserved in fluid, while the different species of
crabs and lobsters are more conveniently preserved dry unless it is
desired to study any of their soft structures.
It is quite impossible to remove the soft parts from small crabs and
lobsters previous to drying them, hence the drying should be conducted
as rapidly as possible, so that no decomposition may set in. Where the
process goes on very slowly, as is the case when the air is damp, or
when the specimens are not set out in an airy spot, a decay of the soft
structures soon proceeds, and the products of this decay will generally
saturate the whole specimen, giving rise to most objectionable odours,
and destroying the natural colour of the shell.
If it has been found that the species in question are not reddened by
the action of methylated spirit, they should be allowed to remain in
this fluid, with a few grains of dissolved corrosive sublimate, for at
least a few hours, and then they will dry rapidly without any signs of
putrefaction; and even those species that _are_ reddened by spirit may
be treated to a shorter immersion in this fluid with advantage.
The specimens should always be set out in some natural attitude to dry,
unless it is desired to spread out the various appendages in some manner
that is more convenient for the study of their structure. A sheet of
blotting-paper may be placed on cork or soft wood, the specimens placed
on this, and the appendages kept in the desired positions when necessary
by means of pins placed beside, but not thrust through them. When more
than one specimen of the same species has been collected, one should be
set in such a manner as to exhibit the under side; and, further, in
instances where the male and female of the same crustacean differ in
structure, as is commonly the case, two of each should be preserved, one
displaying the upper, and the other the under surface.
When perfectly dry, all small crustaceans should be mounted on cards
with the aid of a little gum, and the name and other particulars to be
remembered then written on the card.
The question may well be asked: ‘Which is the best gum to use?’ In
answer to this we may say that gum tragacanth is certainly as good as
any. It holds well, and leaves no visible stain on a white card. A small
quantity of the solid gum should be put into a bottle with water in
which a grain or so of corrosive sublimate has been dissolved. It
absorbs much water, becoming a very soft, jelly-like mass. Any excess of
water may be poured off, and the gum is then ready for use.
The larger crabs and lobsters contain such an amount of soft tissue
within that it becomes absolutely necessary to clear them in order to
avoid the unpleasant and destructive effects of decomposition.
[Illustration: FIG. 43.--SMALL CRAB MOUNTED ON A CARD]
In the case of lobsters the abdomen should be removed from the large
cephalo-thorax by cutting through the connecting membrane with a sharp
knife. The soft portions of both halves of the body are then raked out
by means of a piece of wire flattened and bent at one end, and the
interior cleaned with the aid of a rather stiff bottle-brush. The large
claws are then removed by cutting through the membrane that unites them
with the legs, and these are cleared in a similar manner. The different
parts are next laid out to dry on blotting-paper, with the various
appendages attached to the body arranged just as in life; and, finally,
when all parts are quite dry, both within and without, the separated
parts are reattached by means of some kind of cement. For this purpose a
solution of gelatine in acetic acid is much better than gum tragacanth,
as it has a far greater holding power, and this is necessary when we
require to unite rather large structures with but small surfaces in
contact.
Large crabs are to be dealt with much in the same manner, but, instead
of removing the abdomen only, which, in the crab, is usually very small
and doubled under the thorax, the whole carapace--the large shell that
covers the entire upper surface of the body--should be lifted off, and
replaced again after the specimen has been cleaned and dried.
MARINE SHELLS &C.
We have previously dealt with the preservation of the shell-less
molluscs, and the soft bodies of the shelled species when such are
required, so we will now see what should be done with the shells.
Numerous shells are often to be found on the sea beach--shells that have
been washed in by the breakers, and from which the animal contents have
disappeared, either by the natural process of decay, aided by the action
of the waves, or by the ravages of the voracious or carrion-eating
denizens of the sea; and although these shells are rarely perfect,
having been tossed about among the other material of the beach, yet we
occasionally find here the most perfect specimens of both univalve and
bivalve shells in such a condition that they are ready for the cabinet,
and these often include species that are seldom found between the
tide-marks, or that are otherwise difficult to obtain.
However, the shell-collector must not rely on such specimens as these
for the purpose of making up his stock, but must search out the living
molluscs in their habitats and prepare the shells as required.
The molluscs collected for this purpose are immersed in boiling water
for a short time, and the animal then removed from the shell. In the
case of bivalves it will generally be found that the hot water has
caused the muscles of the animal to separate from the valves to which
they were attached, or, if not, they have been so far softened that they
are easily detached, while it does not destroy the ligament by means of
which the valves are held together at the hinge; but the univalve
molluscs must be removed from their shells by means of a bent pin or
wire. In the latter instance care must be taken to extract the whole of
the body of the animal, otherwise the remaining portion will decompose
within the shell, giving rise to the noxious products of natural decay.
The univalves have now simply to be placed mouth downwards on
blotting-paper to drain and dry, when they are ready for the cabinet.
If, however, they include those species, like the periwinkles and
whelks, that close their shells by means of a horny lid (_operculum_)
when they draw in their bodies, these lids should be removed from the
animal and attached to their proper places in the mouth of the shell.
The best way to accomplish this is to pack the dry shells with cotton
wool, and then fasten the opercula to the wool by means of a little gum
tragacanth or acetic glue.
Bivalve shells should, as a rule, be closed while the ligament is still
supple, and kept closed until it is quite dry, when the valves will
remain together just in the position they assume when pulled together by
the living animal. The shells of the larger species may be conveniently
kept closed during the drying of the ligament by means of thread tied
round them, but the very small ones are best held together by means of a
delicate spring made by bending fine brass wire into the form shown in
fig. 44.
[Illustration: FIG. 44.--SPRING FOR HOLDING TOGETHER SMALL BIVALVE
SHELLS]
There are many features connected with the internal structure and
surface of the shells of molluscs that are quite as interesting and
instructive as those exhibited externally; hence a collection of the
shells intended for future study should display internal as well as
external characteristics. Thus, some of the spiral univalve shells may
be ground down on an ordinary grindstone in order to display the central
pillar (the _columella_) and the winding cavity that surrounds it, while
others, such as the cowries, may be ground transversely to show the
widely different character of the interior. Bivalve shells, too, may be
arranged with the valves wide open for the study of the pearly layer,
the lines of growth, the scars which mark the positions of the muscles
that were attached to the shell, and the teeth which are so wonderfully
formed in some species.
Some collectors make it a rule to thoroughly clean all the shells in
their collection, but this, we think, is a great mistake; for when this
is done many of the specimens display an aspect that is but seldom
observed in nature. Many shells, and especially those usually obtained
in deep water, are almost always covered with various forms of both
animal and vegetable growth, and it is advisable to display these in a
collection, not only because they determine the general natural
appearance, but also because these growths are in themselves very
interesting objects. Further, it is a most interesting study to inquire
into the possible advantages of these external growths to the
inhabitants of the shells, and _vice versâ_--a study to which we shall
refer again in certain chapters devoted to the description of the
animals concerned.
But there is no reason whatever why some of the _duplicate_ specimens
should not be cleaned by means of a suitable brush, with or without the
use of dilute hydrochloric acid (spirits of salt), or even polished, in
some few cases, to show the beautiful colours so often exhibited when
the surface layer has been removed. This, however, should be done
somewhat sparingly, thus giving the greater prominence to the exhibition
of those appearances most commonly displayed by the shells as we find
them on the beach or dredge them from the sea.
Very small and delicate shells may be mounted on cards, as suggested for
other objects; but, as a rule, the specimens are best displayed by
simply placing them on a layer of cotton wool in shallow boxes of
convenient size.
The number of insects that may be described as truly marine is so small
that their preservation is not likely to form an important part of the
work of the sea-side naturalist; and even though a considerable number
of species exhibit a decided partiality for the coast, living either on
the beach or the cliffs, the study of these is more generally the work
of the entomologist. For this reason, and partly because we have already
given full instructions for the setting and mounting of insects in a
former work of this series, we consider a repetition inadmissible here.
The subject of the preservation of fishes, also, will require but few
words. There is no satisfactory method of preserving these in a dry
state, though we often meet with certain thin-bodied species, such as
the pipe-fish, that have been preserved by simply drying them in the
sun. Fishes should be placed in dilute spirit, or in one of the other
liquids recommended, but a change of fluid will always be necessary
after a time, and also frequently the gentle application of a brush to
remove coagulated slime from the surface of the scales.
The great drawbacks in the way of preserving a collection of fishes are
the expense of the specimen jars, and the large amount of space required
for storing the specimens. Of course the former difficulty can be
overcome by substituting ordinary wide-mouthed bottles in the place of
the anatomical jars, while the latter can be avoided to a considerable
extent by limiting the collection to small species, and to small
specimens of the larger species. If this is done, it is surprising what
a large number of fishes can be satisfactorily stored in bottles of only
a few ounces’ capacity.
FLOWERS AND SEA WEEDS
The apparatus required for the preservation of the wild flowers of our
cliffs, and the sea weeds, consists of a quantity of blotting paper or
other thick absorbent paper cut to a convenient size, a few thin boards
and a few pieces of calico of the same size, some heavy weights, and
several sheets of drawing paper.
The wild flowers are arranged on the sheets of absorbent paper while
still fresh, care being taken to display the principal parts to the best
advantage. They are then placed in a single pile, with a few extra
sheets of absorbent paper between each two specimens to facilitate the
drying, boards at the bottom and top as well as at equal distances in
the midst of the pile, and the weights on the top of the whole.
The natural colours of leaves and flowers are not very often preserved
satisfactorily, but the best results are obtained when the drying
process proceeds most rapidly. Hence, if the press contains any
specimens of a succulent or sappy nature, they should be taken out after
the first day or two, and then replaced with a fresh supply of dry
paper.
The flowers must be left in the press until quite dry, and they may then
be mounted on sheets of drawing paper, by fixing them with a little gum
tragacanth, or by narrow strips of gummed paper passing over their
stems.
Some collectors prefer simply placing their botanical specimens inside
double sheets of drawing paper, not fastening them at all, and there is
much to be said in favour of this, especially as it allows the specimens
to be examined on both sides; and even when they _are_ fastened to the
paper double sheets are much to be preferred, for the specimens are not
then so liable to be damaged by friction when being turned over,
especially when the names are written on the outside of each sheet.
The larger sea-weeds may be dried in the same manner, though it is a
good plan to absorb the greater part of the moisture they contain by
pressing them between pieces of calico previous to placing them in the
ordinary press. It should be observed, however, that many sea-weeds
exude a certain amount of glutinous substance that makes them adhere to
the paper between which they are dried, while they do not so freely
adhere to calico. These should be partially dried in the calico press,
and then laid on the paper on which they are to be finally mounted, and
re-pressed with a piece of dry calico on the top of each specimen.
Many of the smaller weeds may be treated in the manner just described,
but the more delicate species require to be dealt with as
follows:--Place each in a large, shallow vessel of water, and move it
about, if necessary, to cause its delicate fronds to assume that
graceful form so characteristic of the algæ of our rock pools. Then
immerse the sheet of paper on which the weed is to be finally mounted,
and slowly raise the specimen out of the water, on the paper, without
disturbing the arrangement of the fronds. If it is found necessary to
rearrange any of the fronds, it may be done by means of a wet camel-hair
brush. Now lay the specimen on calico or absorbent paper, placed on a
sloping board, to drain; and, after the greater part of the moisture has
disappeared by draining and evaporation, transfer the specimen to the
press with a piece of dry calico immediately over it. All are dealt with
in turn in the manner described, and allowed to remain in the press
until perfectly dry, when it will be found that the majority of them
have become firmly attached to the mount, and require nothing but the
label to fit them for the herbarium.
Sea-weed collectors often make the great mistake of pressing tufts that
are far too dense to admit of the structural characters being
satisfactorily examined. To avoid this fault, it will often be necessary
to divide the clusters collected so that the forms of their fronds may
be more readily observed.
The calcareous corallines may be pressed in the same way as the other
algæ, but very pretty tufts of these, having much the appearance of the
living plant, may be obtained by simply suspending them until thoroughly
dry; though, of course, specimens so prepared must not be submitted to
pressure after they are dry, being then so brittle that they are easily
broken to pieces.
The hard framework of these interesting corallines is composed
principally of carbonate of lime, a mineral substance that dissolves
freely in hydrochloric acid (spirits of salt). Thus, if we place a tuft
of coralline in this acid, which should be considerably diluted with
water, the calcareous skeleton immediately begins to dissolve, with the
evolution of minute bubbles of carbonic acid gas; and after a short
time, the end of which is denoted by the absence of any further
bubbling, nothing remains but the vegetable matter, now rendered soft
and pliant. A decalcified specimen of coralline may be pressed and
dried, and then mounted beside the plant in its natural condition for
comparison; and the true appearance of the vegetable structure may also
be retained, and in a far more satisfactory manner, by preserving a
portion of the specimen in dilute spirit.
Finally, it may be observed that many sea-weeds, like wild flowers, do
not retain their natural forms and colours when preserved dry. They are
spoilt by the pressure applied, or become so shrivelled and discoloured
in the drying as to be but sorry representatives of the beautifully
tinted and graceful clothing of the rocks of the coast. But many of
those that suffer most in appearance when dried may be made to retain
all their natural beauty by preserving them in a fluid; and it is most
important that this should be remembered by all who desire to study the
weeds at home, and particularly by those who possess a microscope, and
wish to search into the minute structure of marine algæ. Our own plan is
to keep not only the dried specimens for the purpose of studying the
general characters and classification of the algæ, but also to keep a
few large bottles--stock bottles--filled with weeds of all kinds in a
preservative fluid. These latter are exceedingly useful at times, and
are frequently brought into requisition for close inspection, with or
without the microscope. Small pieces may be detached for microscopic
examination when required, and sections may be cut either for temporary
or permanent mounting just as well as from living specimens, such
sections showing all the details of structure exhibited by the living
plant.
THE MUSEUM
One of the greatest difficulties besetting the young collector lies in
the choice and construction of the cabinet or other store-house for the
accommodation of the specimens that accumulate as time advances.
Of course, when expense is a matter of no great consideration, a visit
to the nearest public or private museum to see the manner in which the
specimens are housed, followed by an order to a cabinet-maker, will set
the matter right in a short time; but it is probable that the majority
of our readers are unable to fit up their museum in this luxurious
style, and will either have to construct their own cabinets and
store-boxes or to purchase cheap substitutes for them.
Where one has the mechanical ability, and the time to spare, the
construction of a cabinet with the required number of drawers may be
undertaken, and there is no better form of store than this. The whole
should be made of well-seasoned wood, and the drawers should vary in
depth according to the size of the specimens they are to contain. Some
of these drawers may be lined with sheet cork, and the cork covered with
white paper or a thin layer of cotton wool. This will enable some of the
specimens to be fixed in their places by means of pins. As a rule,
however, no pins will be required, and the specimens will be most
conveniently arranged in shallow cardboard boxes, placed in rows in the
drawer, a little cotton wool covering the bottom of each.
Failing the usual cabinet, the specimens may be stored in shallow trays
or boxes, or even in the little cardboard cabinets so often sold for
storing stationery &c. The best and cheapest things of this kind we have
ever met with are the little cabinets, each containing either six or
twelve drawers, made by Macdonald & Co., of Temple Row, Birmingham. By
the use of such as these the specimens may be neatly stored away, and
additions to match may always be made as the collection increases in
magnitude.
The specimens should all be classified according to their positions in
the animal or vegetable world, and accompanied by labels giving the name
of species and genus, together with localities, habitats, &c. The
outlines of classification may be studied from the later chapters of
this work, in which the common objects of the sea shore are described in
their scientific order, beginning with the lowest sub-kingdoms and
classes; and further, it will be observed that the sub-kingdoms are
divided into classes, the classes into orders, orders into families,
families into genera, and that the genera contain a smaller or larger
number of closely allied species.
The collection must be kept in a perfectly dry place, otherwise many of
the specimens will be liable to develop moulds, and this will, of
course, quite spoil their appearance. It is almost sure to be attacked
by mites and other animal pests unless some means be taken to prevent
their intrusion.
As regards the latter, it is well to know that it is far easier to
prevent the intrusion of small animal pests than it is to exterminate
them after they have once found an entrance; and so, from the very
commencement of the formation of the collection, all drawers and boxes
should be charged with some substance that is objectionable, if not
fatal, to them. Small lumps of naphthaline (albo-carbon) put into the
various compartments, and renewed occasionally as they disappear by
evaporation, will generally suffice to prevent the entrance of all
pests, but this substance is not effectual as an insecticide for the
purpose of killing them after they are in.
Perhaps the best of all insecticides is the corrosive sublimate already
mentioned, and this may be applied to any animal or vegetable object
that is capable of providing food for museum pests, and it is difficult
to find such an object on which they will not feed.
Many of the specimens that find a place in a museum have been
temporarily preserved in spirit previous to being dried, and if a little
corrosive sublimate was dissolved in this spirit, the specimens will
have been rendered perfectly free from all attacks of marauders, since
the spirit will have saturated the whole object, carrying with it the
dissolved poison.
Most of the specimens that have not been treated by the above method
would not suffer from a short immersion in spirit containing the
corrosive sublimate; but in cases where it is considered inexpedient to
do this, the same liquid may be applied to them by means of a soft
brush. In this way even the dried botanical specimens may be rendered
perfectly secure from attacks.
CHAPTER VI
_EXAMINATION OF MARINE OBJECTS--DISSECTION_
An enthusiastic observer of nature will learn much concerning the
structure of natural objects with the unaided eye, but there are times
when he will desire some kind of magnifier to reveal more perfectly the
structure of minute parts, or to enable him to observe the small
creatures that are invisible to the naked eye. Further, one may learn
many interesting and instructive facts relating to animal and plant life
by cutting sections for close examination, or by making such simple
dissections as will enable one to observe the more salient features of
internal structure; we therefore propose in the present chapter to make
a few remarks and suggestions regarding work of this kind.
A pocket magnifier is of great value to the young naturalist, both for
the inspection of natural objects while engaged in out-door work, and
for the subsequent examination of the specimens collected for study. It
is often necessary to enable one to identify and classify small animals
and plants, and will be in constant demand for the purpose of studying
the less conspicuous external features. Such an instrument should be
regarded as an essential companion of the naturalist, and should
accompany him on every ramble.
There are several different forms of pocket lenses, but for general work
there is, perhaps, nothing more convenient and serviceable than the
‘triplet’ magnifier. It is a combination of three lenses, enclosed in a
pocket case, and so arranged that they may be used separately or in
combination, thus supplying a variety of powers. The three lenses of the
triplet are themselves of different magnifying powers, and these powers
may be increased by combining two or all of them.
For work at home a ‘dissecting microscope’ is very useful. This consists
of a magnifying lens, mounted on a support over a surface on which small
objects may be examined and dissected, the height of the lens being, of
course, adjusted according to its focal distance. Lenses ready mounted
on adjustable stands may be purchased for this purpose, but no one ought
to experience much difficulty in designing and constructing some simple
stand that will give every satisfaction.
The arrangement just described is, of course, suitable for the
dissection of only small objects, and these are placed on a material
adapted to the nature of the work to be done. Thus it is sometimes
convenient to place the object to be examined on a small sheet of cork,
in order that it may be secured by means of pins while the dissection
proceeds, while at other times it is essential that it be laid on a hard
and unyielding surface, such as that of a slip of glass. But whatever be
the nature of the substance on which the dissection is made, its colour
may be regulated according to that of the object. If, for example, we
are dissecting a small white flower on a piece of cork, we should
naturally blacken the cork, or cover it with a piece of dead black
paper; or, if we are to dissect a small, light-coloured object on a
glass surface, we lay the glass on black paper.
[Illustration: FIG. 45--THE TRIPLET MAGNIFIER]
The advantage of dissecting objects under water does not seem to be
generally appreciated by beginners, who often allow their specimens to
become dry and shrivelled, almost beyond recognition, during the
progress of their examination. This mode of dissection is certainly not
necessary with all objects, but may be generally recommended for soft
and succulent vegetable structures, as well as for almost all animal
dissections.
This being the case, arrangements should certainly be made to provide a
miniature dissecting trough as an accessory to the dissecting
microscope, and the following instructions will enable the reader to
construct a highly satisfactory and inexpensive one:--
Procure the flat lid of a cylindrical tin box, or the lid of a glass or
porcelain pomade pot, such lid to be about two inches in diameter and
about half an inch in depth. Cement the flat side of this lid to a small
slab of hard wood, or to a square piece of sheet lead, by means of
acetic glue--ordinary glue or gelatine dissolved in glacial acetic
acid--to give it the necessary steadiness during the dissection. When
the cement is quite hard, pour into the lid some melted paraffin
(paraffin wax) which has been blackened by the admixture of a small
quantity of lamp-black in the form of a fine powder. The paraffin should
be melted by putting it into a beaker or wide-mouthed bottle, and
standing it in hot water, and the lamp-black should be added, with
stirring, as soon as it is entirely liquefied. The quantity of the
mixture used must be sufficient to half fill the lid, thus leaving a
space to contain water to the depth of about a quarter of an inch. The
blackened wax provides a good background on which to work, and provides
a hold for pins when these are necessary in order to fix the object
under examination.
[Illustration: FIG. 46.--A SMALL DISSECTING TROUGH]
The complete trough is represented in fig. 46; and will be found to
answer its purpose admirably, except that it occasionally displays one
fault, but one that is easily remedied. The wax contracts on cooling,
and may, therefore, detach itself from the trough; and, being lighter
than water, will float instead of remaining submerged. This may be
prevented by securing the disc of wax in its place by means of a ring of
brass wire, or by weighting the wax with two or three small pieces of
lead pushed down into it while it is yet soft.
With such a dissecting microscope and trough as we have described one
may do a great deal of exceedingly useful work, both hands being quite
free to manipulate the object under examination.
The dissection may be conducted with the aid of a small scalpel or other
very sharp knife, the parts being arranged or adjusted by means of a
needle, mounted in a handle, and held in the left hand. Sometimes,
however, the object to be dissected is so minute that even a small
scalpel is too large for the purpose, and in such cases nothing is
better than little dissecting instruments made by mounting large sewing
needles in suitable handles, and then grinding down the points of the
needles on two opposite sides, on a hone, so as to produce little
pointed, two-edged blades. Bent needles are often useful, too, and these
may be prepared by heating the points to redness in a gas-flame, bending
them as desired while hot, and then hardening them by suddenly thrusting
them, at a red heat, into cold water.
The compound microscope will often prove useful for the examination of
very minute objects, as well as for the study of the structure of the
principal tissues of the larger species; but since detailed instructions
for the management of the microscope, and for the preparation of objects
for microscopic examination would occupy much more space than we can
spare, we shall content ourselves with nothing more than a few general
hints on this portion of the young naturalist’s work, dealing more
particularly with those points which commonly present difficulties to
the amateur.
If it is desired to examine some minute living object, such as a
protozoon, place the object in a drop of the water in which it lived
just in the middle of a clean glass slip, and cover it with a
cover-glass. The quantity of water should be just sufficient to fill the
space between the two glasses. If less than this has been used, a little
more applied to the edge of the cover by means of a glass rod will
immediately run in between the glasses; while if an excessive amount was
employed, the surplus may be removed by the application of a strip of
blotting paper. Place the glass slip on the stage of the microscope, and
reflect light through it from the mirror below.
Examine it first with a low power; and, after having observed as much as
possible of the creature’s movements and structure with this aid, repeat
with a higher power. This rule applies not only to such small objects as
we have now under consideration, but to all objects, and parts of them,
in which minute details are to be observed.
Beginners with the microscope often find prolonged examination very
tiring to the eyes, but this, we believe, would seldom be the case if
right methods were followed. Both eyes should always be open, and the
microscopist should train himself to use both eyes equally for the
actual observation.
The higher the magnifying power used, the nearer must the objective (the
lower combination of lenses) be brought to the object itself, and it is
no uncommon thing for the amateur, in his attempts to focus his object,
to lower the body of the microscope beyond its proper position, causing
the objective to crush the object, break the thin cover-glass, and
become wetted with the liquid, if any, in which the object was being
examined. All this may be avoided by lowering the body of the microscope
until it nearly touches the cover-glass before attempting to view the
object through it, and then, with the eye above the object-glass, to
gradually raise the body until the object is in focus.
[Illustration: FIG. 47.--CELL FOR SMALL LIVING OBJECTS]
The top of the cover-glass should always be perfectly dry; and if by any
chance the objective becomes wet it should be wiped perfectly dry with a
piece of old silk or with chamois leather. Also, if permanent mounting
is attempted, and the preservative liquid is allowed to come in contact
with the objective, such liquid must, of course, be washed off with some
suitable solvent before any attempt is made to wipe the lens dry.
If the object under examination is of such dimensions that the
cover-glass has a tendency to rock on it, or if it is a living object of
such a size that it is unable to move freely in the exceedingly thin
film of water between the cover and the slip, it should be placed in a
cell. The cell may be made by cementing a ring of glass or vulcanite to
the middle of a slip, or it may be a little circular cavity prepared in
the slip itself. In either case the cell must be quite full of water
before the cover-glass is applied, so that no air-bubbles are included.
Hitherto we have spoken only of mounting small objects in water, and
this is advisable when the object is moist, whether it be animal or
vegetable, alive or dead. But dry objects may be examined in the dry
state, in which case they need not be covered. If they are composed of
transparent material they are to be dealt with in the manner recommended
before, as far as the management of the light is considered; that is, a
moderately strong light is sent through them by the reflector below the
stage; but opaque objects are best examined on a dead black ground, the
light being directed on to them by means of a condensing lens placed
between them and the source of light.
A collector who has done only a few days’ work on the sea shore will
probably find himself the possessor of a host of interesting objects
that will afford much pleasure and instruction when placed under the
microscope--objects, many of which have been somewhat hastily deposited
in a bottle of spirit or other preservative for study in his future
leisure moments. These objects, if small, may be examined as above
described, simply placing them under a cover-glass, or in a cell, with a
clear drop of the same liquid in which they have been kept.
The general characters of the larger objects may also be observed by
means of some kind of hand lens, but even these are generally best
examined under water or other suitable liquid.
A great deal may be learnt of natural objects by preparing very thin
sections for microscopic examination; and although special works should
be consulted if one desires to become proficient in the different
methods of cutting and preparing such sections, yet a great amount of
good work may be done with the aid of a sharp razor, manipulated with
nothing more than ordinary skill.
Some objects, especially certain of those of the vegetable world, are of
such a nature that suitable sections may be cut, either from the fresh
or preserved specimen, without any preliminary preparation. All that is
required is to hold the object firmly between the finger and thumb of
the left hand, previously securing it in some kind of holder if
necessary, and pare off the thinnest possible slices with a horizontal
movement of the razor, both razor and object being kept very wet during
the process. As the sections are cut they may be allowed to drop into a
shallow vessel of water; and, the thinnest then selected for examination
in water as previously described.
Other objects are so soft that the cutting of sections becomes
impossible without previously hardening them. Methylated spirit is a
good hardening reagent, and many of the soft structures that have been
preserved in this fluid, especially if it has been used undiluted, will
be found sufficiently hard for cutting thin sections. Among the other
hardening reagents used by microscopists may be mentioned a solution of
chromic acid--one part by weight of the solid acid dissolved in from one
hundred to two hundred parts of water, and a solution of bichromate of
potash--one part of the bichromate to about forty parts of water. In
either case the hardening of the object takes place slowly, and it
should be examined from day to day until the necessary consistence has
been obtained.
The structures of many soft animals can never be satisfactorily hardened
for section-cutting by either of the above reagents, and thus it becomes
necessary either to freeze or to imbed them. In the former case the
object is first soaked in gum water--a thin solution of gum arabic--and
then frozen by an ether spray or by a mixture of ice and salt. The
sections should be cut with a razor just as the object is beginning to
thaw, and they may then be examined under a cover-glass, in a drop of
the gum water.
The other method is conducted as follows:--The soft object is first
soaked in absolute alcohol to extract all the water it contains, and is
then transferred to paraffin that has been heated just to its
melting-point by standing it in warm water. After the object is
thoroughly permeated with the paraffin, the whole is cooled quickly by
immersion in cold water. Sections are now cut, the paraffin being sliced
away with the substance it contains. These sections are placed in warm
turpentine, where they are allowed to remain until the whole of the wax
has dissolved, and they may then be mounted in a drop of turpentine, and
covered with a cover-glass.
We have given brief instructions for temporary mounting only, but most
amateur microscopists would undoubtedly prefer mounting their objects
permanently, so that they may be set aside for study at any future
period. Hence we append a few directions to this end, advising the
reader, however, to consult a work dealing especially with this subject
if he desires to become proficient in the preparation of microscopic
slides.
Moist objects, including those which have been preserved in dilute
spirit, may be soaked in water, then transferred direct to the glass
slip, and covered with a drop of glycerine. Any excess of the glycerine
should then be absorbed from around the cover-glass by means of a strip
of blotting-paper, and the edge of the cover cemented by gold size
applied with a small camel-hair brush.
Glycerine jelly is also a valuable mountant for permanent work. When
this is used the object should first be soaked in glycerine, and then in
the melted jelly. It is then transferred to a drop of melted jelly which
has been placed on a _warm_ slide, and covered as before. The jelly soon
solidifies, so that a ring of cement is not absolutely necessary, though
it is advisable, as a rule, to cement the cover-glass all round with
gold size or black varnish.
Sections cut while frozen are best mounted in glycerine, to which they
may be transferred direct.
Canada balsam is one of the best media for permanent mounting; and, as
it becomes very hard after a time, it serves the purposes of both
preservative and cement. When this is used the object must be entirely
freed from water by soaking it in absolute alcohol. It is then put into
turpentine for a minute or two, transferred to a warm slide, and covered
with a drop of the prepared balsam. Sections that have been imbedded in
paraffin may be mounted in this way, the turpentine acting as a solvent
for the paraffin in which it was cut.
Although the compound microscope is absolutely necessary for the study
of the minutest forms of life and of the minute structure of the various
tissues of larger beings, yet the young naturalist will find that a vast
amount of good work may be done without its aid. Thus the general
structure of the larger species may be made out by means of simple
dissections requiring no extraordinary skill on the part of the worker,
and with appliances that may be obtained at a low cost. Certain of the
marine animals, however, require special treatment that can hardly be
described in a short chapter devoted to general instructions only, but
hints with regards to these will be given in future chapters in which
the animals referred to are described.
The appliances referred to above include nothing more than a simple form
of dissecting trough, a few dissecting instruments, and one or two minor
accessories that may always be found at hand as required.
The dissection of animals is always best performed under water, for by
this method the object examined may not only be kept clean as the work
proceeds, but the parts, having a tendency to float, readily separate
from one another and therefore become more distinctly visible when
submerged.
[Illustration: FIG. 48.--SHEET OF CORK ON THIN SHEET LEAD]
A very convenient form of trough may be made by taking any kind of
rectangular, flat-bottomed dish, one made of zinc being, perhaps, the
best of all, and covering the bottom with a slab of good cork carpet
which has been weighted with sufficient lead to prevent it from
floating. Or, instead of cork carpet, a sheet of cork may be used. In
either case, a piece of thin sheet lead, a little larger than the slab,
should be cut, the corners of which are then snipped off as shown in
fig. 48, and the edges finally turned over as represented in the next
illustration. The size of the trough must be regulated according to the
nature of the work to be done, but one measuring ten inches long, seven
wide, and two inches deep will answer most purposes.
[Illustration: FIG. 49.--WEIGHTED CORK FOR DISSECTING TROUGH]
The object to be dissected is placed in the trough, secured in position
by means of a few ordinary pins, and then completely covered with
water.
We need hardly impress upon the reader the great importance of
thoroughly examining all external characters--all those structures that
are visible without actual dissection--before attempting to remove
anything; and we have already insisted on the importance of carefully
examining all creatures while alive before anything else is done. The
value of this latter stipulation can hardly be overestimated, for in
many instances it is almost impossible to detect the use of an organ
unless it has been observed in action; and the enthusiastic student will
go even further than this, for he will make it an invariable rule to
sketch everything he sees, and to make full notes on all his
observations.
When pins are used to fix the object under examination--and it is
generally essential that the object be fixed--their heads should be
turned outwards; for then the object will not slip from its position,
nor will the pins tend to get in the way of the work.
Some objects are of such a nature that they are not easily secured by
means of pins, and yet require to be fixed in some way or other. Thus,
one may desire to examine the structure and appendages of a prawn or
small crab, or to investigate the nature of a chiton. In such instances
as these it is a good plan to make a cake of paraffin wax of suitable
size by pouring the melted substance into a mould, then secure the
object in proper position in the wax while still fluid, and pin the
latter to the cork of the dissecting trough.
It is often necessary to trace the courses of internal passages that
open on the surface of the body, or of tubes that are revealed during
the progress of dissection, and this may be done by means of a little
instrument called a seeker. It is simply a blunted needle, bent into a
large angle, and mounted in a handle; or, it may consist of nothing but
a moderately long and stiff bristle, rendered blunt at one end by
tipping it with melted sealing wax. This is not always sufficient,
however, for it frequently happens that certain tubes and passages in
animal forms are disposed in such a complicated manner that it is
impossible to send even the most flexible seeker through them. For
instance, suppose one desires to trace the course of the digestive tube
of some large bivalve mollusc with its many reflections, the seeker is
useless except that it will penetrate to the first sharp bend. The
arrangement of such a tube must be traced by dissecting along its
course, but this may be aided considerably by first filling it with some
coloured substance to enable its direction to be more easily followed.
In fact, the injection of some brightly coloured fluid, forced through
the tube by means of a fine-nozzled glass syringe will often enable the
course of such a tube to be seen without any dissection at all, the
colour of the fluid used being detected through the semi-transparent
tissues surrounding it. A mixture of Berlin blue and water, or a mixture
of plaster of Paris and water coloured with carmine is well adapted to
this purpose; and if the latter is employed it may be allowed to set,
and thus produce a permanent cast from the tube that is being dissected.
Perhaps it should be mentioned that if either of the injection mixtures
be used for this purpose it must be previously strained through muslin,
and that, in the case of the plaster, the mixing and straining should
occupy as little time as possible, or it may begin to set before the
injection has been completed.
A very considerable insight into the structure of animals may be
frequently obtained by cutting sections through the body with all its
organs _in situ_, but, generally speaking, they are too soft to allow of
this without danger of the displacement of those very parts, the
relations of which we desire to determine. To avoid this the body should
be previously hardened by a somewhat prolonged soaking in methylated
spirit, or in a solution of chromic acid prepared as before directed.
Then, with the aid of a good razor, very interesting sections may be
prepared with the greatest of ease, and the true relations of the
various organs throughout the body may be exactly determined by cutting
a succession of slices, not necessarily very thin, from end to end, or,
transversely, from side to side.
Even those crustaceans that are protected by a hard, calcareous
exo-skeleton, and the molluscs that cannot be removed from their stony
shells without injury to their soft structures, may be studied in the
manner just described, and this may be done by first soaking them in
dilute hydrochloric acid, renewed as often as may be necessary, until
all the mineral matter has been dissolved completely, and then hardening
the softer tissues in one of the reagents mentioned above. Hydrochloric
acid may also be used to dissolve the calcareous shells of foraminifers,
the vegetable corallines, and other small forms of life, previous to
microscopic examination of the soft parts.
CHAPTER VII
_THE PROTOZOA OF THE SEA SHORE_
We shall now study the principal forms of animal life to be found on the
sea shore; and, in order that the reader may thoroughly understand the
broader principles of classification, so as to be able to locate each
creature observed in its approximate position in the scale of life, we
shall consider each group in its zoological order, commencing with the
lowest forms, and noting, as we proceed, the distinguishing
characteristics of each division.
The present chapter will be devoted to the _Protozoa_--the sub-kingdom
that includes the simplest of all animal beings.
Each animal in this division consists of a minute mass of a jelly-like
substance called _protoplasm_, exhibiting little or no differentiation
in structure. There is no true body-cavity, no special organs for the
performance of distinct functions, and no nervous system.
Perhaps we can best understand the nature of a protozoon by selecting
and examining a typical example:
Remove a small quantity of the green thread-like algous weed so commonly
seen attached to the banks of both fresh and salt water pools, or
surrounding floating objects, and place it in a glass with a little of
the water in which it grew. This weed probably shelters numerous
protozoons, among which we are almost sure to find some _amœbæ_ if we
examine a drop of the water under the high power of a microscope.
[Illustration: FIG. 50.--THE AMŒBA, HIGHLY MAGNIFIED]
The amœba is observed to be a minute mass of protoplasm with an
average diameter of about one-hundredth of an inch, endowed with a power
of motion and locomotion. Its body is not uniformly clear, for the
interior portion is seen to contain a number of minute granules,
representing the undigested portions of the animal’s food. There is a
small mass of denser protoplasm near the centre, termed the _nucleus_,
and also a clear space filled with fluid. This latter is called the
_vacuole_, and is probably connected with the processes of respiration
and excretion, for it may be seen to contract at irregular intervals,
and occasionally to collapse and expel its contents.
As we watch the amœba we see that it is continually changing its
shape, sending out temporary prolongations (_pseudopodia_) of its
gelatinous substance from any part, and sometimes using these extended
portions for the purpose of dragging itself along.
Its method of feeding is as remarkable as it is simple. On coming in
contact with any desired morsel, it sends out two pseudopods, one on
each side of the food. These two pseudopods gradually extend round the
food, till, at last, they meet and coalesce on the opposite side of it,
thus completely enclosing it within the body. Any part of the body of
the amœba may thus be converted into a temporary mouth; and, there
being no special cavity to serve the purpose of a stomach, the process
of digestion will proceed equally well in any part of the body except in
the superficial layer, where the protoplasm is of a slightly firmer
consistence than that of the interior. Further, the process of digestion
being over, any portion of the superficial layer may be converted into a
temporary opening to admit of the discharge of indigestible matter.
[Illustration: FIG. 51.--THE AMŒBA, SHOWING CHANGES OF FORM]
[Illustration: FIG. 52.--THE AMŒBA, FEEDING]
The amœba is an omnivorous feeder, but subsists mainly on vegetable
organisms, especially on diatoms and other minute algæ; and the
siliceous skeletons of the former may often be seen within the body of
the animal, under the high power of a microscope.
The multiplication of the amœba is brought about by a process of
fission or division. At first the nucleus divides into two, and then the
softer protoplasm contracts in the middle, and finally divides into two
portions, each of which contains one of the nuclei. The two distinct
animals thus produced both grow until they reach the dimensions of
their common progenitor.
[Illustration: FIG. 53.--THE AMŒBA, DIVIDING]
All the protozoons resemble the amœba in general structure and
function; but while some are even simpler in organisation, others are
more highly specialised. Some, like the amœba, are unicellular
animals; that is, they consist of a single, simple speck of protoplasm;
but others live in colonies, each newly formed cell remaining attached
to its parent cell, until at last a comparatively large compound
protozoon is formed.
The sub-kingdom is divided into several classes, the principal of which,
together with their leading characteristics, are shown in the following
table:--
1. _Rhizopods:_--Body uniform in consistence.
Pseudopods protruded from any point.
2. _Protoplasta:_--Outer protoplasm slightly firmer in consistence.
Pseudopods protruded from any point.
(Often grouped with the _Rhizopods_.)
3. _Radiolaria:_--Possessing a central membranous capsule.
Usually supported by a flinty skeleton.
4. _Infusoria:_--Outer protoplasm firmer and denser; therefore
of more definite shape.
Possess permanent threadlike extensions of protoplasm
instead of pseudopods.
We shall now observe the principal marine members of the protozoa,
commencing with the lowest forms, and dealing with each in its proper
zoological order as expressed in the above table.
MARINE RHIZOPODS
When we stand on a beach of fine sand on a very calm day watching the
progress of the ripples over the sand as the tide recedes we frequently
observe whitish lines marking the limits reached by the successive
ripples as they advance toward the shore. If, now, we scrape up a little
of the surface sand, following the exact course of one of these whitish
streaks, and examine the material obtained by the aid of a good lens, we
shall in all probability discover a number of minute shells among the
grains of sand.
These shells are of various shapes--little spheres, discs, rods,
spirals, &c.; but all resemble each other in that they are perforated
with a number of minute holes or _foramina_. They are the skeletons of
protozoons, belonging to the class _Rhizopoda_, and they exist in
enormous quantities on the beds of certain seas.
[Illustration: FIG. 54.--A GROUP OF FORAMINIFERS, MAGNIFIED]
We will first examine the shells, and then study the nature of the
little animals that inhabit them.
The shells vary very much in general appearance as well as in shape.
Some are of an opaque, dead white, the surface somewhat resembling that
of a piece of unglazed porcelain; others more nearly resemble glazed
porcelain, while some present quite a vitreous appearance, much after
the nature of opal. In all cases, however, the material is the same, all
the shells consisting of carbonate of lime, having thus the same
chemical composition as chalk, limestones, and marble.
If hydrochloric acid be added to some of these shells, they are
immediately attacked by the acid and are dissolved in a very short time,
the solution being accompanied by an effervescence due to the escape of
carbonic acid gas.
The shells vary in size from about one-twelfth to one three-hundredth of
an inch, and consist either of a single chamber, or of many chambers
separated from each other by perforated partitions of the same material.
Sometimes these chambers are arranged in a straight line, but more
frequently in the form of a single or double spiral. In some cases,
however, the arrangement of chambers is very complex.
We have already referred to the fact that the shells present a number of
perforations on the exterior, in addition to those which pierce the
partitions within, and it is this characteristic which has led to the
application of the name Foraminifera (hole-bearing) to the little beings
we are considering.
[Illustration: FIG. 55.--A SPIRAL FORAMINIFER SHELL]
[Illustration: FIG. 56.--A FORAMINIFER OUT OF ITS SHELL]
The animal inhabiting the shell is exceedingly simple in structure, even
more so than the amœba. It is merely a speck of protoplasm,
exhibiting hardly any differentiation--nothing, in fact, save a
contractile cavity (the _vacuole_), and numerous granules that probably
represent the indigestible fragments of its food.
The protoplasm fills the shell, and also forms a complete gelatinous
covering on the outside, when the animal is alive; and the vacuole and
granules circulate somewhat freely within the semi-solid mass. Further,
the protoplasm itself is highly contractile, as may be proved by
witnessing the rapidity with which the animal can change its form.
When the foraminifer is alive, it floats freely in the sea, with a
comparatively long and slender thread of its substance protruded through
each hole in the shell. These threads correspond exactly in function
with the blunt pseudopodia of the amœba. Should they come in contact
with a particle of suitable food-material, they immediately surround
it, and rapidly retracting, draw the particle to the surface of the
body. The threads then completely envelop the food, coalescing as soon
as they touch, thus bringing it within the animal.
[Illustration: FIG. 57.--THE SAME FORAMINIFER (FIG. 56) AS SEEN WHEN
ALIVE]
[Illustration: FIG. 58.--SECTION OF THE SHELL OF A COMPOUND
FORAMINIFER]
The foraminifer multiplies by fission, or by a process of budding. In
some species the division of the protoplasm is complete, as in the case
of amœbæ, so that each animal has its own shell which encloses a
single chamber, but in most cases the ‘bud’ remains attached to a parent
cell, and develops a shell that is also fixed to the shell of its
progenitor. The younger animal thus produced from the bud gives rise to
another, which develops in the same manner; and this process continues,
the new bud being always produced on the newest end, till, at last, a
kind of colony of protozoons is formed, their shells remaining attached
to one another, thus producing a compound shell, composed of several
chambers, arranged in the form of a line or spiral, and communicating by
means of their perforated partitions. It will now be seen that each
‘cell’ of the compound protozoon feeds not only for itself, but for all
the members of its colony, since the nourishment imbibed by any one is
capable of diffusion into the surrounding chambers, the protoplasm of
the whole forming one continuous mass by means of the perforated
partitions of the complex skeleton.
[Illustration: FIG. 59.--SECTION OF A NUMMULITE SHELL]
Some of the simplest foraminifers possess only one hole in the shell,
and, consequently, are enabled to throw off pseudopods from one side of
the body only. In others, of a much more complex nature, the new
chambers form a spiral in such a manner that they overlap and entirely
conceal those previously built; and the development may proceed until a
comparatively large discoid shell is the result. This is the case with
_Nummulites_, so called on account of the fancied resemblance to coins.
Further, some species of foraminifera produce a skeleton that is horny
in character, instead of being calcareous, while others are protected
merely by grains of sand or particles of other solid matter that adhere
to the surface of their glutinous bodies.
[Illustration: FIG. 60.--_Globigerina bulloides_, AS SEEN WHEN ALIVE,
MAGNIFIED]
We have spoken of foraminifera as floating freely about in the sea
water, but while it is certain that many of them live at or near the
surface, some are known to thrive at considerable depths; and those who
desire to study the various forms of these interesting creatures should
search among dredgings whenever an opportunity occurs. Living specimens,
whenever obtained, should be examined in sea water, in order that the
motions of their pseudopods may be seen.
[Illustration: FIG. 61.--SECTION OF A PIECE OF NUMMULITIC LIMESTONE]
If we brush off fragments from the surface of a freshly broken piece of
chalk, and allow them to fall into a vessel of water, and then examine
the sediment under the microscope, we shall observe that this sediment
consists of minute shells, and fragments of shells, of foraminifers. In
fact, our chalk beds, as well as the beds of certain limestones, consist
mainly of vast deposits of the shells of extinct foraminifera that at
one time covered the floor of the sea. Such deposits are still being
formed, notably that which now covers a vast area of the bed of the
Atlantic Ocean at a depth varying from about 300 to 3,000 fathoms. This
deposit consists mainly of the shells of a foraminifer called
_Globigerina bulloides_, a figure of which is given on the opposite
page.
The structure of chalk may be beautifully revealed by soaking a small
piece of the rock for some time in a solution of Canada balsam, allowing
it to become thoroughly dry, and then grinding it down till a very thin
section is obtained. Such a section, when viewed under the low power of
a compound microscope, will be seen to consist very largely of minute
shells; though, of course, the shells themselves will be seen in
section only.
The extensive beds of nummulitic limestones found in various parts of
South Europe and North Africa are also composed largely of foraminifer
shells, the most conspicuous of which are those already referred to as
nummulites--disc-shaped shells of a spiral form, in which the older
chambers overlap and hide those that enclose the earlier portion of the
colony.
Before concluding our brief account of these interesting marine
protozoons, it may be well to point out that, although the foraminifera
belong to the lowest class of the lowest sub-kingdom of animals, yet
there are some rhizopods--the _Monera_, which are even simpler in
structure. These are mere specks of undifferentiated protoplasm, not
protected by any shell, and not even possessing a nucleus, and are the
simplest of all animal beings.
The second division of the Protozoa--the class _Protoplasta_--has
already received a small share of attention, inasmuch as the amœba,
which was briefly described as a type of the whole sub-kingdom, belongs
to it.
The study of the amœba is usually pursued by means of specimens
obtained from fresh-water pools, and reference has been made to it in a
former work dealing particularly with the life of ponds and streams; but
it should be observed that the amœba inhabits salt water also, and
will be frequently met with by those who search for the microscopic life
of the sea, especially when the water examined has been taken from those
sheltered nooks of a rocky coast that are protected from the direct
action of the waves, or from the little pools that are so far from the
reach of the tides as to be only occasionally disturbed. Here the
amœba may be seen creeping slowly over the slender green threads of
the confervæ that surround the margin of the pool.
The third class--_Radiolaria_--is of great interest to the student of
marine life, on account of the great beauty of the shells; but, as with
the other members of this sub-kingdom, a compound microscope is
necessary for the study of them.
The animals of this group resemble the foraminifers in that they throw
out fine thread-like pseudopods, but they are distinguished from them by
the possession of a membranous capsule in the centre of the body,
surrounding the nucleus, and perforated in order to preserve the
continuity of the deeper with the surrounding protoplasm. They have
often a central contractile cavity, and further show their claim to a
higher position in the animal scale than the preceding classes by the
possession of little masses of cells and a certain amount of fatty and
colouring matter.
[Illustration: FIG. 62.--A GROUP OF RADIOLARIAN SHELLS, MAGNIFIED]
Some of the radiolarians live at or near the surface of the ocean, while
others thrive only at the bottom. The former, in some cases, appear to
avoid the light, rising to the surface after sunset; and it is supposed
that the phosphorescence of the sea is due in part to the presence of
these animals. The latter may be obtained from all depths, down to
several thousand fathoms.
The beauty of the radiolarians as a class lies in the wonderful shells
that protect the great majority of them. These shells are composed not
of carbonate of lime, as is the case with foraminifers, but of silex or
silica, a substance that is not acted on by the strongest mineral acids.
They are of the most exquisite shapes, and exhibit a great variety of
forms. Some resemble beautifully sculptured spheres, boxes, bells, cups,
&c.; while others may be likened to baskets of various ornamental
design. In every case the siliceous framework consists of a number of
clusters of radiating rods, all united by slender intertwining threads.
It is not all the radiolarians, however, that produce these beautiful
siliceous shells. A few have no skeleton of any kind, while others are
supported by a framework composed of a horny material, but yet
transparent and glassy in appearance.
The sizes of the shells vary from about one five-hundredth to one half
of an inch; but, of course, the larger shells are those of colonies of
radiolarians, and not of single individuals, just as we observed was the
case with the foraminifers.
Those in search of radiolaria for examination and study should, whenever
possible, obtain small quantities of the dredgings from deep water.
Material brought up by the trawl will often afford specimens; but,
failing these sources of supply, the muddy deposit from deep niches
between the rocks at low-water mark will often provide a very
interesting variety.
Place the mud in a glass vessel, and pour on it some nitric acid
(aqua-fortis). This will soon dissolve all calcareous matter present,
and also destroy any organic material. A process of very careful washing
is now necessary. Fill up the vessel with water, and allow some time for
sedimentary matter to settle. Now decant off the greater part of the
water, and repeat the process several times. By this means we get rid of
the greater part of the organic material, as well as of the mineral
matter that has been attacked by the acid; and if we examine the final
sediment under the microscope, preferably in a drop of water, and
covered with a cover-glass, any radiolarians present will soon reveal
themselves.
It is often possible to obtain radiolarian shells, as well as other
siliceous skeletons, through the agency of certain marine animals. The
bivalve molluscs, for example, feed almost entirely on microscopic
organisms; and, by removing such animals from their shells, and then
destroying their bodies with aqua-fortis, we may frequently obtain a
sediment composed partly of the skeletons referred to.
There remains one other class of protozoons to be considered, viz. the
_Infusorians_--the highest class of the sub-kingdom. In this group we
observe a distinct advance in organisation; for, in the first place, the
infusorians are enclosed in a firm cuticle or skin, which forms an
almost complete protective layer. Within this is a layer of moderately
firm protoplasm, containing one or more cavities that contract at
intervals like a heart. Then, in the interior, there is a mass of softer
material with cavities filled with fluid, two solid bodies, and numerous
granules.
[Illustration: FIG. 63.--THREE INFUSORIANS MAGNIFIED]
In these creatures we find, too, a distinct and permanent mouth, usually
funnel-shaped, leading to the soft, interior substance, in which the
food material becomes embedded while the process of digestion proceeds.
Here, then, for the first time, we meet with a special portion of the
body set apart for the performance of the work of a stomach; and,
further, the process of digestion being over, the indigestible matter is
ejected through a second permanent opening in the exterior cuticle.
Again, the infusorian does not move by means of temporary pseudopods, as
is the case with the lower protozoons, but by means of minute hair-like
processes which permanently cover either the whole of the body, or are
restricted to certain portions only. These little processes, which are
called _cilia_, move to and fro with such rapidity that they are hardly
visible; and, by means of them the little infusorian is enabled to move
about in its watery home with considerable speed.
In some species a few of the cilia are much larger than the others, and
formed of a firmer material. These often serve the purpose of feet, and
are also used as a means by which the little animal can anchor itself to
solid substances.
As with the lower protozoons, the infusoria multiply by division; but,
in addition to this, the nucleus may sometimes be seen to divide up into
a number of minute egg-like bodies, each of which, when set free, is
capable of developing into a new animal. Should the water in which
infusorians have been living evaporate to dryness, the little bodies
just mentioned become so many dust particles that may be carried away by
air currents; but, although dry, they retain their vitality, and develop
almost immediately on being carried into a suitable environment.
Infusorians are so called because they develop rapidly in infusions of
various vegetable substances; and those who desire to study their
structure and movements with the aid of a microscope cannot do much
better than make an infusion by pouring boiling water on fragments of
dried grass, and leaving it exposed for a few days to the warm summer
atmosphere. The numerous germs floating in the air will soon give rise
to abundance of life, including several different species of infusoria,
varying from 1/30 to 1/2000 of an inch in length.
Fresh-water pools and marshes provide such an abundance of infusoria
that the animals are generally obtained for study from these sources,
and a few of the common and most interesting species inhabiting fresh
water have already been described in a former work. Nevertheless, the
sea is abundantly supplied with representatives of the class, and it is
certain that the beautiful phosphorescence sometimes observed in the sea
at night is in part due to the presence of luminous infusoria, some of
which appear to have an aversion to sunlight, retiring to a depth during
the day, but rising to the surface again after sunset.
[Illustration: FIG. 64.--A PHOSPHORESCENT MARINE INFUSORIAN
(_Noctiluca_), MAGNIFIED]
CHAPTER VIII
_BRITISH SPONGES_
It seems to be the popular opinion that sponges are essentially natives
of the warmer seas, and it will probably be a surprise to many young
amateur naturalists to learn that there are about three hundred species
of this sub-kingdom of the animal world to be found on our own shores.
It must not be thought, however, that they are all comparable with the
well-known toilet sponges in regard to either size or general form and
structure, for some of them are very small objects, no larger than about
one-twentieth of an inch in diameter, and some form mere incrustations
of various dimensions on the surfaces of rocks and weeds, often of such
general appearance that they would hardly be regarded as animal
structures by those who have not studied the peculiarities of the group.
Sponges are known collectively as the _Porifera_ or _Polystomata_, and
constitute a separate sub-kingdom of animals of such distinct features
that they are not readily confused with the creatures of any other
group. Their principal characteristic is expressed by both the group
names just given, the former of which signifies ‘hole-bearing,’ and the
latter ‘many openings’; for in all the members of the sub-kingdom there
are a number of holes or pores providing a means of communication
between the body cavity or cavities and the surrounding water. Most of
these holes are very small, but there is always at least one opening of
a larger size at the anterior end.
It will be seen from what we have just stated that sponges exhibit a
distinctly higher organisation than the _protozoa_ described in the last
chapter, inasmuch as they possess a permanent body-cavity that
communicates with the exterior; but in addition to this there are many
points of differentiation of structure that denote a superior position
in the scale of life.
In order to ascertain the general features of a sponge we cannot do
better than select one of the simplest forms from our own shores. If we
place the live animal in a glass vessel of sea water, and examine it
with a suitable magnifying power, we observe a number of minute pores
scattered over its whole surface; and a much larger opening at the free
end. The animal is motionless, and exhibits no signs of life except that
it may contract slightly when touched. The water surrounding the sponge
also appears to be perfectly still, but if we introduce some fine
insoluble powder, such as precipitated chalk, or a drop of a soluble
dye, the motion of the suspended or soluble material will show that the
water is passing into the sponge through all the small pores, and that
it is ejected through the larger opening.
On touching the sponge we observe that it is of a soft, gelatinous
consistence throughout, or if, as is often the case, the body is
supported by a skeleton of greater or less firmness, a gentle
application of the finger will still show that this framework is
surrounded by material of a jelly-like nature. This gelatinous
substance is the animal itself, and a microscopic examination will show
that its body-wall is made up of two distinct layers, the inner
consisting of cells, many of which possess a cilium or whip-like
filament that protrudes from a kind of collar, its free extremity
extending into the body-cavity.
[Illustration: FIG. 65.--SECTION OF A SIMPLE SPONGE]
These minute cilia are the means by which the water currents just
described are set up. By a constant lashing movement they urge the fluid
contained in the body-cavity towards the larger hole, thus causing the
water to flow in through the numerous small pores. This circulation of
sea water through the body-cavity of the sponge is the means by which
the animal is supplied with air and food. Air is, of course, absorbed
from the water by the soft material of the external layer of the body,
but the constant flow of fresh water through the body-cavity enables
this process of respiration to go on with equal freedom in the interior.
The mode of feeding of the sponge is very similar to that of the
_protozoa_. Organic particles that are carried into the body-cavity, on
coming in contact with the cells of the internal layer, are absorbed
into their protoplasm by which they are digested. Thus the sponge may be
compared to a mass of protozoon cells, all united into a common colony
by a more or less perfect coalescing of the cell-substance, some of the
units being modified in structure for the performance of definite
functions. The air and food absorbed by any one cell may pass readily
into the surrounding cells, and thus each one may be said to work for
the common weal.
[Illustration: FIG. 66.--DIAGRAMMATIC SECTION OF A PORTION OF A
COMPLEX SPONGE]
The description just given applies only to the simplest of the sponges,
and we have now to learn that in the higher members of the group the
structure is much more complicated. In these the surface-pores are the
extremities of very narrow tubes which perforate both layers of the
body-wall and then communicate with wider tubes or spaces within, some
of which are lined with the ciliated cells above described. These
spaces, which are sometimes nearly globular in form, and often arranged
in groups with a common cavity, communicate with wider tubes which join
together until, finally, they terminate in a large opening seen on the
exterior of the sponge. Hence it will be seen that the water entering
the minute pores of the surface has to circulate through a complicated
system of channels and spaces, some of which are lined with the ciliated
cells that urge the current onwards before it is expelled through the
large hole. Further, imagine a number of such structures as we have
described growing side by side, their masses coalescing into one whole,
their inner tubes and spaces united into one complex system by numerous
inter-communications, and having several large holes for the exit of the
circulating water, and you then have some idea of the general nature of
many of the more complex sponges to be found on our shores (see fig.
66).
[Illustration: FIG. 67.--HORNY NETWORK OF A SPONGE, MAGNIFIED]
But even this is not all, for as yet we have been regarding the sponges
as consisting of animal matter only, whereas nearly all of them possess
some kind of internal skeleton for the support of the soft, gelatinous
animal substance. The skeleton consists of matter secreted by certain
cells from material in the water and food, and is either horny,
calcareous, or siliceous. The horny skeleton is formed of a network of
fibres of a somewhat silky character, and often, as in the case of the
toilet sponges, highly elastic; but it is sometimes so brittle that the
sponge mass is easily broken when bent. The fibres of this framework
support not only the outer wall of the sponge, but also the walls of all
the internal tubes and spaces, which are often of so soft a nature that
they would collapse without its aid.
The other forms of skeletons consist of minute bodies of carbonate of
lime or of silica, respectively, which assume certain definite shapes,
resembling stars, anchors, hooks, pins, spindles, &c., and are known as
_spicules_. Such spicules are usually present in those sponges that have
horny skeletons, but in others they form the entire skeleton.
Sponges sometimes increase by division, a part being separated from the
parent mass and then developing into a complete colony; and they may be
reproduced artificially to almost any extent by this method, each piece
cut off, however small, producing a new sponge. They also increase by a
process of ‘budding,’ the buds produced sometimes remaining attached to
the original colony, thus increasing its size, but on other occasions
becoming detached for the formation of new colonies on a different site.
In addition to these methods of reproduction there are special cells in
a sponge that possess the function of producing eggs which are ejected
through the larger holes. The eggs are usually developed in the autumn,
and, after being ejected, swim about freely for a time, after which they
become fixed to rocks or weeds, and produce sponges in the following
year. The eggs may often be seen towards the end of the summer by
cutting through a sponge, or by carefully pulling it asunder. They are
little rounded or oval bodies, of a yellowish or brownish colour,
distinctly visible to the naked eye, occupying cavities in the interior.
Sponges are classified according to the composition of the skeleton and
the forms of the spicules, the chief divisions being:--
1. The CALCAREOUS Sponges (_Calcarea_). Skeleton consisting of
spicules of carbonate of lime in the form of needles and
three-or four-rayed stars.
2. The SIX-RAYED SPONGES (_Hexactinellida_). Skeleton of six-rayed
glassy spicules.
3. COMMON SPONGES (_Demospongia_). Skeleton horny, flinty, or
entirely absent.
The first of these divisions contains about a dozen known British
species, which are to be found on the rockiest shores, attached to
stones, weeds, or shells, generally hidden in very secluded holes or
crevices, or sheltered from the light by the pendulous weeds. They
should be searched for at the lowest spring tide, particular attention
being given to the under surfaces of large stones, narrow, dark
crevices, and the roofs of small, sheltered caves. They may be readily
recognised as sponges by the numerous pores on the surface, though these
are often hardly visible without a lens, and the calcareous nature of
the skeleton may be proved by dropping a specimen into dilute
hydrochloric acid, when the carbonate of lime will speedily dissolve,
the action being accompanied by the evolution of bubbles of carbonic
acid gas.
If calcareous sponges are to be preserved for future reference, they may
be placed in diluted spirit, in which case the animal matter, as well
as the mineral substance, will be preserved with but little alteration
in the natural appearance and structure. A specimen which has been
decalcified by means of acid, as above described, may also be preserved
in the same manner; and small portions of this will serve for the
microscopic study of the animal portion of the sponge. If the skeleton
only is required, the sponge is simply allowed to dry, when the soft
animal substance, on losing its contained water, will leave hardly any
residue; or, better, allow the calcareous sponge to macerate in water
for some days for the animal substance to decompose, and then, after a
few minutes in running water, set it aside to dry.
[Illustration: FIG. 68.--_Grantia compressa_]
[Illustration: FIG. 69.--SPICULES OF _Grantia_, MAGNIFIED]
Small portions of the skeleton, examined under the microscope, will show
the nature of the calcareous spicules of which it is composed. These
consist of minute needles and stars, the latter having generally either
three or four rays.
We give figures of three of the calcareous sponges of our shores, the
first of which (_Grantia compressa_) resembles little oval, flattened
bags, which hang pendulous from rocks and weeds, sometimes solitary, but
often in clusters. The smaller openings are thickly scattered over the
flat sides of the bag, and the larger ones, through which the water is
expelled, around the margin. When the sponge is out of the water and
inactive, the two opposite sides of the bag are practically in contact,
but, when active, the cavity is filled with water by means of the
whip-cells that line it, and the sides of the sponge are then more or
less convex.
[Illustration: FIG. 70.--_Sycon ciliatum_]
The ciliated sycon (_Sycon ciliatum_), fig. 70, though of a very
different appearance externally, is similar in structure to _Grantia_.
It is also found in similar situations, and is not uncommon on many
parts of the South Coast, from Weymouth westwards. The other example,
_Leucosolenia botryoides_, shown in fig. 71, is a branching calcareous
sponge, consisting of a number of tubes, all united to form one common
cavity which is lined throughout with whip-cells. It is usually found
attached to weeds.
[Illustration: FIG. 71.--_Leucosolenia botryoides_, WITH PORTION
MAGNIFIED]
Nearly all our British sponges belong to the group _Demospongia_--common
sponges; but the members of this group present a great variety of form
and structure. Most of them have a skeleton consisting of siliceous
spicules, but some have a horny skeleton, somewhat after the nature of
that of the toilet sponges; and others, again, have fleshy bodies
entirely, or almost entirely, unsupported by harder structures. They are
sometimes known collectively as the _Silicia_, for the greater number of
them have skeletons consisting exclusively of siliceous matter, while
the so-called horny sponges usually have spicules of silica
intermingled with the horny substance, and even those which are
described as having no skeleton at all sometimes contain scattered
spicules of silex.
[Illustration: FIG. 72.--_Chalina oculata_]
As the spicules of sponges are in themselves beautiful objects, and are
important to the naturalist, inasmuch as they form a basis for the
classification of sponges, it is well to know by what means they may be
separated from the animal for microscopic examination. The separation is
based on the fact that nitric acid (aqua-fortis) will destroy organic
matter while it has not the slightest action on silica. In some of our
common horny sponges the fibres are so transparent that, when teased out
and placed under the microscope, the siliceous spicules may be seen
embedded within them, but the spicules, both in these and the fleshy
sponges, may be separated completely from the animal matter by putting a
fragment of the sponge in a test-tube, covering it with nitric acid, and
boiling it for a short time. The tube should then be filled up with
water and allowed to stand undisturbed for a time, after which the
liquid is poured off gently from the sediment. If the sediment is then
put under the microscope on a slip of glass, it will be seen to consist
of grains of sand, of which there is always a considerable amount in the
pores and cavities of a sponge, and the siliceous spicules.
Among the common objects of the sea shore is the horny skeleton of the
sponge _Chalina oculata_, which is frequently washed on the beach by
the waves, especially after storms. This sponge is not likely to be seen
between the tide-marks except at the lowest spring tide, when it may be
found suspended in a sheltered crevice or cave. The skeleton consists of
a fine network of horny fibres, in the centre of which lie the spicules,
imbedded in the horny material. The spicules are short and straight,
tapering at both ends.
[Illustration: FIG. 73.--_Halichondria panicea_]
The Bread-crumb sponge (_Halichondria panicea_) is even more common, for
it is to be found on every rocky coast, encrusting weeds and rocks,
often considerably above low-water mark. It is of a yellowish or pale
greenish colour, and forms an incrustation varying in thickness from
one-twentieth of an inch to half an inch or more; and, like most
sponges, should be looked for in narrow crevices, under heavy growths of
weeds, or in other situations where it is protected from the light.
Sometimes its free surface is unbroken, except, of course, by the minute
pores, and, here and there, the larger openings that serve for the
outgoing currents; but when it is found encrusting a rock in patches of
considerable size, the larger holes all occupy the summit of a little
cone resembling a miniature volcano with its crater. This sponge is
easily removed from the rock with the aid of a blunt broad-bladed knife,
and retains its natural appearance to perfection if preserved in
methylated spirit. Its horny skeleton is of a very compact nature, and
the spicules are minute siliceous needles pointed at both ends.
Rambling on the sea beach we frequently meet with old oyster and other
shells perforated by a number of circular holes about the size of a
pin’s head or less, and chalk and limestone rocks also are seen
similarly bored. On breaking into or grinding down the substance we find
that the openings are the ends of channels that form a network of canals
and chambers, some of which are so near the surface that they are
covered by an exceedingly thin layer of the calcareous substance. These
canals and chambers form the home of the Boring Sponge (_Cliona_),
which, although a very soft-bodied animal, has itself excavated them.
[Illustration: FIG. 74.--SPICULES OF _Halichondria_, MAGNIFIED]
[Illustration: FIG. 75.--AN OYSTER SHELL BORED BY _Cliona_]
The manner in which the _Cliona_ excavates such a complicated system of
passages in so hard a material has naturally raised a considerable
amount of curiosity, and those who have studied the matter are divided
in opinion as to whether the work is done by chemical or by mechanical
action.
Some of those who advocate the chemical theory suppose that an acid
fluid is secreted by the sponge, and that the carbonate of lime forming
the shell or stone is thereby dissolved; but such advocates have, as
yet, failed to detect the presence of any acid substance in the body of
the animal. Others ascribe the action to the solvent power of carbonic
acid gas. This gas certainly has the power of dissolving carbonate of
lime, as may be proved by a very simple experiment: Pour a little lime
water into a glass, and blow into it through a glass tube. The lime
water speedily becomes milky in appearance, the lime having been
converted into particles of chalk or carbonate of lime by union with the
carbonic acid gas from the lungs. Continue to blow into the liquid for
some time, and the carbonate of lime will slowly disappear, being
gradually dissolved by the excess of the gas--the gas over and above
that required for the formation of the carbonate. Thus, it has been
said, the carbonic acid gas evolved as a product of the respiration of
the sponge is the agent by which the channels are excavated. Whatever be
the acid to which this power is ascribed, whether it be the carbonic
acid or a special acid fluid secreted for the purpose, there is still
this difficulty in the way of accepting the theory, namely, that an
acid, though it has the power of dissolving the mineral matter of a
shell--the carbonate of lime--has no action on the laminæ of animal
substance that form part of the structure. If we put the shell of a
mollusc in hydrochloric or _dilute_ nitric acid, we obtain, after the
complete solution of the carbonate of lime, a substantial residue of
animal matter which the acid does not touch, but in the case of _Cliona_
both animal and mineral substances yield to its power.
[Illustration: FIG. 76.--SPICULES OF _Cliona_]
Those who favour the mechanical theory assert that the material is worn
away by siliceous particles developed by the sponge, and kept in
constant motion as long as the animal lives; and the theory is supported
by the statement that, in addition to the spicules of silica, which are
pin-shaped, and occupy the interior of the animal, there are little
siliceous granules scattered on the surface of the sponge which are kept
in constant motion resembling that of cilia; and the minute particles of
carbonate of lime that form a dusty deposit within the galleries are
supposed to be the product of the rasping or drilling action of these
granules.
The pin-shaped spicules of _Cliona_ may be obtained for microscopic
examination by breaking any old oyster shell that has formed its home,
and brushing out the dust from the galleries; or, a part of the shell
may be dissolved in acid, and the sediment examined for spicules on a
slip of glass.
CHAPTER IX
_THE CŒLENTERATES--JELLY-FISHES, ANEMONES,
AND THEIR ALLIES_
One of the most interesting groups of marine life is that including
jelly-fishes and anemones. In it are the pretty little sea firs, so
often mistaken for sea-weeds by the youthful admirers of these plants,
who almost always include them in their collection of marine _algæ_; the
transparent, bell-shaped jelly-fishes, which may often be seen in
thousands during the summer, carried by the tides, and swimming gently
by graceful contractions of their bells; and, most beautiful of all, the
lovely anemones--the ‘sea flowers’ of the older naturalists, by whom
they were regarded as forms of vegetable life.
[Illustration: FIG. 77.--THREAD CELLS OF A CŒLENTERATE, MAGNIFIED
1. Thread retracted 2. Thread protruded]
The simplest animals of this group are minute jelly-like creatures, of a
more or less cylindrical form, usually fixed at one end, and having a
mouth at the other. The body is a simple hollow cylinder, the wall of
which is made up of two distinct layers, while the cavity within serves
the purpose of a stomach. The mouth is surrounded by a circle of arms or
tentacles by means of which the creature is enabled to capture its prey.
These arms are capable of free movement in every direction, and can be
readily retracted when the animal is disturbed. They are also armed with
minute oval, hollow cells, each of which has a slender filament coiled
up into a spiral within its cavity. Each filament is capable of being
suddenly protruded, thus becoming a free whip-like appendage, and these
are so numerous as to be very effectual in seizing and holding the
living beings on which the animal feeds. This would undoubtedly be the
case even if they were capable of mechanical action only, but, in many
instances at least, they seem to be aided by the presence of some
violent irritant, judging from the rapidity with which the struggling
prey is paralysed when seized, especially in the case of some of the
larger members of the group.
The simple forms referred to increase by a process of budding, the buds
appearing first as simple swellings on the side of the parent creature,
and afterwards developing a mouth and tentacles, thus becoming exactly
like the adult form. Clusters of eggs also are developed in the outer
layer of the body-wall, and these are set free at intervals, and
produce new individuals. These animals possess no blood system of any
kind, and have no special organs for respiration, but the nutrient
matter absorbed from the body-cavity permeates the soft structures of
the flower-like body, and the oxygen required for respiratory purposes
is readily absorbed from the surrounding water.
[Illustration: FIG. 78.--THE SQUIRREL’S-TAIL SEA FIR (_Sertularia
argentea_), WITH A PORTION ENLARGED]
The higher cœlenterates differ in certain particulars from the lower
forms just referred to. Thus, they frequently have a large number of
tentacles around the mouth, often arranged in several distinct whorls.
They have also a stomach separate from the general body-cavity, but
communicating with the latter below; and the body-cavity is divided into
compartments by a number of radiating partitions. Some, also, develop a
hard, stony skeleton by secreting carbonate of lime obtained from the
water in which they live.
[Illustration: FIG. 79.--_Sertularia filicula_]
We often see, when collecting on the beaches of rocky coasts, and
especially after storms, a number of vegetable-like growths, of a
greyish or brownish colour, each consisting of one or more main stalks
bearing a number of delicate branches. Some of them, by their peculiar
mode of growth, have suggested the name of sea firs, and a few of these,
together with other animals of the same group, may readily be recognised
by the accompanying illustrations. They are the objects already referred
to as being commonly included in collections of sea-weeds by young
naturalists, but they are in reality the horny skeletons of colonies of
cœlenterates of the simplest type, belonging to the division
_Hydrozoa_.
[Illustration: FIG. 80.--_Sertularia cupressina_]
If we examine them with a lens we find that there are little cup-like
bodies projecting from each portion or branch of the stem-like
structure, and that the stem itself is hollow, with a communicating pore
at the base of each cup. This constitutes the skeleton only of the
colony--the dead matter, so to speak, which persists after the living
creatures have perished; but if the specimens collected have been
obtained fresh from the sea, placed in a glass of sea water, and then
examined with the aid of a lens, little jelly-like _hydroids_ or
_polypites_ will be seen to protrude from the cups, and extend their
short arms in search of food.
[Illustration: FIG. 81.--THE HERRING-BONE POLYPE (_Halecium
halecinum_)]
Each of the little creatures has a tubular stalk which passes through
the hole at the base of the cup, and is continuous with a tube of
gelatinous material in the interior of the horny stem, and thus each
member of the colony is directly connected with all the others, so that
any nutrient matter collected and digested by one member may be absorbed
into the central tube for the nourishment of the entire company of
little socialists, the activity of the one being thus made to compensate
for the laziness or incompetency of others. And this provision seems to
be absolutely necessary for the well-being of the colony as a whole, for
a close examination will often show that a kind of division of labour
has been established, since it includes two or three distinct kinds of
polypites, each adapted for the performance of a certain function. Thus,
in addition to the feeding or nutritive members of the community, there
are some mouthless individuals whose sole function seems to be the
production of eggs for the propagation of the species, while others,
also mouthless, develop an enormous number of stinging cells, probably
for the protection of the whole community against its enemies, and these
must therefore be provided, as we have seen they are, with a means by
which they may derive nourishment through the agency of the feeding
polypites.
[Illustration: FIG. 82.--_Tubularia indivisa_]
[Illustration: FIG. 83.--THE BOTTLE BRUSH (_Thuiaria thuja_)]
When the eggs are liberated from what we may call the reproductive
members, they are carried away by the currents or tides, and soon
develop into little _larvæ_ which are very unlike the parent, since they
are covered with minute vibratile cilia by means of which they can swim
freely. This they do for a period, and then settle down, lose their
cilia, become stalked, and thus constitute the foundation of a new
colony. A tubular stalk grows upward from its root, new members are
added as outgrowths or buds from their progenitor, and so the growth
proceeds until an extensive colony of hundreds of individuals has been
formed.
We have spoken of the hydroid communities as being washed up on the
beaches of our rocky coasts, but the collector of these interesting
objects should not depend on such specimens for purposes of study. It is
undoubtedly true that splendid examples of the sea firs and their allies
are frequently washed up by the waves, including some species that
inhabit deep water, and which are, consequently, not to be found by the
ordinary collector in their proper habitat, and that these may often be
secured with the polypites still alive; but several species are to be
obtained between the tide-marks, especially at extreme low water,
growing on rocks, weeds, and shells; and we have often met with good
specimens, still alive, attached to the shells of whelks, scallops, &c.,
in fishmongers’ stores, even in inland towns.
[Illustration: FIG. 84.--_Antennularia antennia_]
Sometimes individual polypites become detached from a colony, and
develop into little umbrella-shaped jelly-fishes, about a fifth of an
inch in diameter; and these float about freely, keeping themselves near
the surface by rhythmic contractions of their ‘bells,’ the margins of
which are fringed by numerous fine tentacles. The mouth is situated
centrally on the under side, and is surrounded by a circular canal from
which proceed radiating tubes; and pigmented spots, supposed to be
rudimentary eyes, are formed round the edge. These little bodies are
called _Medusoids_, and may frequently be seen floating round our coasts
towards the end of the summer. In the water they are almost invisible on
account of the extreme transparency of their bodies; but if a muslin
net be drawn through the water from the stern of a boat, and the net
then gently turned inside out in a vessel of sea water, a number of
medusoids may be obtained for examination. These creatures produce eggs
which yield small ciliated larvæ that swim about freely for a time, and
then settle down and establish stalked colonies as previously described.
The larger jelly-fishes or _Medusæ_ so frequently seen floating in
enormous numbers near the surface of the sea during the summer months
are allied to the medusoids. Their bodies are so soft that it is a
difficult matter to remove them from the water without injury, and when
removed their graceful forms are completely destroyed by the pressure of
their own weight. When left stranded on the beach, as is often the case,
they seem to dissolve almost completely away, so readily does the soft
animal tissue disintegrate in the large proportion of water, which forms
about 95 per cent. of the weight of the whole body.
Those who desire to examine the nature and movements of the medusæ will
find it necessary to observe them in water. The creatures may be lifted
out of the sea in a vessel placed below them, and then transferred to a
glass tank or a still rock pool by submerging the vessel and allowing
them to float out. It will then be observed that the mouth is situated
at the summit of a tube that projects from the middle of the under side
of the ‘bell,’ and is surrounded by lobed or frilled lips. Marginal
tentacles also generally fringe the edge of the bell, projecting
downwards into the water. Round the circumference of the body may be
seen a circular canal, from which several tubes converge towards, and
communicate with, the cavity of the stomach.
When a medusa is inactive, its body gradually sinks to the bottom, being
usually slightly heavier than the water in which it lives; but it is
enabled to keep afloat by those rhythmic contractions of the bell with
which we are so familiar. It seems that the medusæ are very sensitive to
various external conditions, for they frequently disappear
simultaneously from the surface water, and as suddenly reappear in
shoals when the conditions are more favourable; but it is difficult to
understand the causes which give rise to these remarkable movements.
The medusæ are often termed the _Acalephæ_--a word which signifies
‘nettles,’ and they are popularly known as sea nettles. They all possess
stinging cells, which are distributed most thickly in the tentacles, and
some of the larger species are undoubtedly able to produce an
impression on the bodies of unwary bathers, while almost all have the
power of paralysing the living prey on which they feed.
By far the commonest of the jelly-fishes of our seas is the beautiful
blue medusa--_Aurelia aurita_. This species appears in enormous shoals
during the summer, and large numbers are washed upon flat, sandy
beaches. They vary in size from two or three inches to nearly a foot in
diameter, and may be recognised from our illustration. The ‘bell’ is
umbrella-shaped, and is so transparent that the stomach with its
radiating canals may be seen through its substance. Around the margin
there are little pigment spots which are supposed to be rudimentary
eyes, and little cavities, containing a clear fluid, that are thought to
serve the purpose of ears.
[Illustration: FIG. 85.--_Aurelia aurita_]
On the under surface may be seen the square mouth, furnished with four
long and graceful frilled lips, which are richly supplied with stinging
cells; also the four ovaries or egg-producing organs, rendered
conspicuous by their violet colouring.
The life history of _Aurelia_ is most interesting. The eggs are produced
in pouches that communicate directly with the stomach-cavity, and these
give rise to little ciliated larvæ that are ejected through the mouth,
and then swim about freely in the water for a time. After this they
settle at the bottom, lose their cilia, and become little cylindrical
jelly-fishes, fixed by a short stalk-like foot to rocks or weeds.
Numerous tentacles develop as the creatures increase in size, and a
number of transverse furrows appear at the surface. The furrows
gradually increase in depth until, at last, the body is broken up into
several star-like discs, each of which floats away and develops into a
new medusa.
[Illustration: FIG. 86.--THE EARLY STAGES OF _Aurelia_]
Other jelly-fishes, some of which are considerably larger than
_Aurelia_, frequent our seas, and are often to be seen stranded on the
beach. Two of these--_Rhizostoma_ and _Chrysaora_--are figured. Although
they differ considerably in form from the blue aurelia, they closely
resemble it in general structure and habits.
[Illustration: FIG. 87.--_Rhizostoma_]
[Illustration: FIG. 88.--_Chrysaora_]
When strolling on flat, sandy beaches, especially in the spring and
early summer, we commonly see what appear to be little balls of
exceedingly transparent and glassy jelly, no larger than an ordinary
marble. If picked up and examined, we observe that they are not quite
spherical, but oval in form, with a little tubercle at one end, and
eight equidistant bands running from this to the opposite end, like the
meridians on a globe.
This extremely beautiful little creature is one of the cœlenterates,
belonging to the division _Ctenophora_, or comb-bearing jelly-fishes, so
called because they possess comb-like ciliated plates, and is called the
Globular Beroe (_Cydippe pileus_).
The ctenophores are very active creatures, swimming freely in the open
seas by means of their numerous cilia; and, although of such delicate
structure, are very predaceous, devouring small crustaceans and other
marine animals. They are usually globular in form, but some are like
long ribbons, and almost all are remarkable for their wonderful
transparency, which renders them nearly invisible when floating in
water. They have not the power of stinging or paralysing their prey, as
the medusæ have, but their fringed arms are provided with adhesive cells
by which they hold their prey tenaciously.
[Illustration: FIG. 89.--_Cydippe pileus_]
In order to observe the form and habits of the Beroe we transfer it to a
vessel of sea water, when it immediately displays its regular spheroid
form, and its eight rows of comb-like plates which form the meridians
before alluded to. Its mouth is situated on the little tubercle at what
we may call the lower pole, for it is the habit of the Beroe to swim in
an inverted position, and the digestive cavity may be seen through its
glassy body.
At first no appendages of any kind are visible, but soon the animal
protrudes two long and exceedingly slender arms, fringed with slender
gelatinous threads, from two cavities, at opposite sides of the body,
into which they can be withdrawn. A close examination will also reveal
the rapid movements of the cilia of its combs, and it is remarkable that
these do not always work together, the animal being able to move any of
its plates independently, and to reverse their motion when occasion
requires. It has no tentacles corresponding with those of jelly-fishes
and anemones, but is assisted in the capture of its prey by its two long
arms, the chief use of which, however, seems to be that of a rudder for
steering.
If the Beroe is left out of water for some time, the water which forms
such a large proportion of its body evaporates, leaving an almost
imperceptible residue of solid matter; and if left in water after it is
dead, its substance rapidly dissolves away, leaving not the slightest
trace of its presence. There seems to be no satisfactory way of
preserving this beautiful form of animal life. If placed in strong
spirit the water is rapidly extracted from its body, and its animal
substance shrivelled to a minute, shapeless mass; while in weak spirit
and in other fluid preservatives it becomes more or less distorted, and
deprived of its beautiful transparency, or else it disappears
altogether.
We now come to the great favourites among the cœlenterates--the
beautiful anemones-the animated flowers of the ocean, remarkable not
only for their lovely flower-like forms, but also for the great variety
of colour and of habits which they display. These, together with the
corals, form the division of the cœlenterates known as the
_Zoantharia_, characterised by the possession of simple tentacles, the
number of which is a multiple of either five or six. The latter differ
from the former mainly in the power of secreting a calcareous skeleton
which remains attached by its base after the animal substance has
decayed.
The expanded anemone exhibits a more or less cylindrical body, attached
by a suctorial base to a rock or some other object, and a broad circular
disc above. In the centre of this disc is the mouth, surrounded by the
tentacles, often very numerous, and arranged in one or more whorls. When
the animal is inactive the tentacles are usually completely withdrawn,
and the body contracted into a semiglobular or pear-shaped mass which is
very firm to the touch.
The general internal structure of an anemone may be made out by simple
dissections, and the examination conducted with the specimen submerged
in water. A longitudinal section will show that the body is a double
tube, the outer being formed by the body-wall, and the inner by the
wall of the stomach. Thus there is a body-cavity distinct from that of
the stomach, but the two will be seen to communicate below, since the
stomach-wall does not extend as far down as the base. It will be seen,
too, that the body-wall is made up of two distinct layers--an outer
one, that is continued inward at the mouth to form the inner wall of the
stomach, and an inner one that lines the whole of the body-cavity. The
latter contains the muscular elements that enable the anemone to
contract its body.
When the animal is expanded, the whole interior is filled with sea
water, as are also the tentacles, which are hollow tubes, really
extensions of the body-cavity, and formed by prolongations of the same
two layers that constitute the body-wall. As it contracts this water is
expelled, partly through the mouth, and partly through small openings
that exist at the tips of the tentacles.
[Illustration: FIG. 90.--SECTION OF AN ANEMONE
_t_, tentacles; _m_, mouth; _s_, stomach; _b c_, body-cavity
_p_, mesentery; _o_, egg-producing organ]
The outer layer of the body-wall is provided with stinging cells which
serve not only to protect the anemone from its enemies, but also to aid
it in the capture of its prey, for which latter purpose they are
distributed in much greater abundance in the tentacles.
The body-cavity is divided into a number of communicating compartments
by means of vertical partitions running from the body-wall and
converging towards the centre of the cavity. These are called
mesenteries, and are extensions of the inner layer of the body-wall.
Five or six of these are larger than the others, extending from disc to
base, and are called _primary mesenteries_. Between these are an equal
number of smaller _secondary mesenteries_; and, sometimes, a third set
of still smaller _tertiary mesenteries_.
These internal partitions are best displayed in a transverse section of
the body, which shows the double tube formed by the walls of the body
and the stomach, together with the wheel-like arrangement of the
mesenteries. At one time all animals that had a radial symmetry--the
regular arrangement of parts round a common centre--were grouped
together under the title of _Radiata_; but it has since been recognised
that the creatures of this group exhibited such a great diversity of
structure that they have been re-classified into two main divisions, one
of which constitutes the cœlenterates which we are at present
considering, and the other containing such creatures as star fishes and
sea urchins.
[Illustration: FIG. 91.--STINGING CELLS OF ANEMONE, HIGHLY MAGNIFIED
_a_ and _c_, with thread protruded; _b_, with cell retracted]
[Illustration: FIG. 92.--DIAGRAMMATIC TRANSVERSE SECTION OF AN ANEMONE
_S_, stomach; _bc_, body-cavity; _m′_, _m″_, _m‴_, primary,
secondary, and tertiary mesenteries]
[Illustration: FIG. 93.--LARVA OF ANEMONE]
On the surface of the mesenteries of the anemone may be seen the ovaries
or egg-producing organs. These discharge the ova into the general
body-cavity, after which they are ejected through the mouth. The embryos
are minute jelly-like creatures that have an active existence, swimming
about freely in the ocean by means of vibrating cilia, but after this
period of activity they settle down and fix themselves, gradually
assuming the adult form common to the species.
The habits of sea anemones are particularly interesting, and it will
well repay anyone to make a study of these animals in their natural
haunts as well as in the aquarium. The gentle swinging of the tentacles
when searching for food, the capture and disposal of the prey, the
peculiar modes of locomotion, and the development of the young, are
among the chief points of interest. As regards locomotion, the usual
method of moving from place to place is by an exceedingly slow gliding
of the base or ‘foot’; and while some anemones are almost constantly on
the move, others hardly ever stir from the secluded niche in which they
have taken up their abode.
Sometimes an anemone will detach itself from the rock, and drag itself
along, but very slowly, by means of its tentacles, sometimes inverting
its body and walking on its head, as it were, and though one may never
have the opportunity of witnessing this manœuvre on the shore, we have
found it far from an uncommon occurrence in the aquarium.
The natural food of anemones consists of small crustaceans, such as
shrimps, and crabs, molluscs, small fishes, and in fact almost every
kind of animal diet, and there need never be any difficulty in finding
suitable viands for species kept in captivity. It is really astonishing
to see what large morsels they can dispose of with the assistance of
their extensile mouths and stomachs. It is not even necessary, indeed,
that the morsel be so small as to be entirely enclosed by the walls of
its digestive cavity, for the anemone will digest one portion while the
other remains projecting beyond its mouth. Further, it will even attack
bodies which it cannot swallow at all, by protruding its stomach so as
to partially envelope them, and then digesting the portion enclosed.
Indigestible portions of its food, such as the shells of small molluscs,
are ejected through the mouth after the process of digestion has been
completed.
We have already referred to the reproduction of sea anemones by means of
eggs, but it is interesting to note that they may also increase by a
division of the body into two or more parts, and that this division may
be either natural or artificial.
If an anemone be cut into halves longitudinally, each half will develop
into a complete animal. If cut transversely, the upper portion will
almost always develop a new suctorial disc, and produce a new individual
complete in every respect; and it has been stated that the basal portion
of the divided animal will also, occasionally, produce a new disc and
tentacles.
The natural division of the anemone has frequently been spoken of as by
no means an uncommon occurrence, but, as far as our experience of
captive anemones go, this mode of multiplication does not seem to take
place except as the result of some mechanical force applied, or as a
means by which the animal may relieve itself of a solid body that it is
unable to eject. Thus, on one occasion, when a stone had slipped so that
its narrow edge rested across the middle of the disc of a large
_Mesembryanthemum_, the animal, apparently unable to free itself from
the burden, simply withdrew its tentacles and awaited results. In a few
days two individuals were to be seen, one on either side of the stone,
both undoubtedly produced as the result of the pressure applied. This
instance seems to be exactly akin to artificial division, for it is far
more likely that the animal was severed by the simple pressure of the
stone than that it divided itself to be relieved of its burden.
On another occasion an anemone that had almost entirely surrounded a
mussel on which it had been feeding, gradually released itself of the
shell by a longitudinal division of its body; but here, again, it is
probable that the fission was the result of pressure applied rather than
of any power on the part of the animal.
A few of the British sea anemones are shown on Plates II. and III., and
although the coloured illustrations will probably suffice for purposes
of identification, yet a short description of each one represented may
be acceptable.
The most common and most widely distributed species is undoubtedly the
familiar Beadlet (_Actinia mesembryanthemum_--Plate II., figs. 1, 2, 3),
which is to be found on every bit of rocky coast around the British
Isles, and even on some stony beaches where there are no standing rocks
between the tide-marks.
The colour of this species is exceedingly variable, but the most
abundant variety is of a liver-brown colour, with crimson disc and
tentacles, brilliant blue spots round the margin of the disc, and a line
of bright blue around the base. In others the prevailing colour is deep
crimson, orange, yellowish brown, or green. Fig. 1 represents a variety
commonly known as the Strawberry Beadlet (_Fragacea_), which is
distinguished by its superior size, and in which the dark-red ground is
often conspicuously spotted with green.
Two members of the same genus are also shown on Plate III. One of
these--_A. glauca_ (fig. 3)--is of a bluish-green colour; while the
other--_A. chiococca_ (fig. 4)--is bright scarlet, with deep crimson
disc and white spots round the disc.
[Illustration: PLATE II.
SEA ANEMONES
1, 2, 3, Actinia mesembryanthemum.
4. Caryophyllia Smithii.
5. Tealia crassicornis.
6. Sagartia bellis.
7. Balanophyllia regia.
8. Actinoloba dianthus.]
The general form of this genus is that of an expanded flower on a
short column; the name Beadlet is applied on account of the little
bead-like projections on the margin of the disc. The tentacles number
nearly two hundred in a fully grown individual, and are arranged in
several rows; but when the animal is disturbed and the tentacles
retracted, its form is almost hemispherical.
It is interesting to note that _A. mesembryanthemum_ not only exists in
varieties distinguished by distinct colours, but that the same
individual will sometimes change its tint, as may be observed when it is
kept in the aquarium; and it may be mentioned, by the way, that it is
very easily reared in captivity, either in the natural or the artificial
salt water, for not only may the same individuals be kept alive for
years with only a moderate amount of attention, but their offspring may
be reared without difficulty.
On Plate II. (fig. 8) are two illustrations of the beautiful _Actinoloba
dianthus_, which grows to a length of five or six inches, and is easily
distinguished by its expanded and frilled disc, its very numerous short
and slender tentacles, and its tall, pillar-like body. Its colour is
somewhat variable, being either salmon, flesh-colour, cream, white, red,
orange, or brownish; but whatever be the tint of the body and tentacles,
the margin of the mouth is always red or orange. When young it may
easily be mistaken for another species, as its disc is not then frilled,
and the tentacles are much fewer in number.
This pretty anemone usually inhabits deep water, and is frequently
brought in, attached to shells and stones, by trawlers, but it may be
commonly observed in the dark crevices of rocks, a little above
low-water mark, where it is usually seen contracted into a ball, or even
so much flattened that it looks like a mere pulpy incrustation of the
rock. It is very common on the rocky coasts of Dorset, Devon, and
Cornwall, as well as in many parts of Scotland and Ireland.
Like the Beadlet, it is easily kept alive in the aquarium, where it
commonly multiplies by natural division; but as it does not generally
expand in full daylight, its beauty is often better observed at night by
artificial light.
On Plate II. (fig. 5) we have an illustration of the beautiful Dahlia
Wartlet (_Tealia crassicornis_), which may be readily recognised by its
thick, banded, horn-like tentacles, and the numerous little adhesive
warts that almost cover the surface of its body.
This species is as abundant as it is beautiful, for it is to be found in
plenty on almost every rocky coast, where it may be seen in the rock
pools and in the crevices of rocks near low-water mark. The diameter of
its cylindrical body often reaches two or three inches, while the
expanded tentacles embrace a circle of four or five inches. Specimens
even much larger than this are sometimes obtained by dredging in deep
water.
The ‘Dahlia’ is not so frequently seen by sea-side collectors as its
abundance would lead one to expect, and this is principally due to the
fact that it not only conceals itself in narrow and out-of-the-way
crevices and angles of rocks, but also that, on the retreat of the tide,
it generally covers itself with small stones, fragments of shells, &c.,
held fast to its body by means of its numerous suckers. In this manner
it conceals its beauty so well that the sense of touch, as well as that
of sight, is necessary in determining its whereabouts. As a rule,
however, it does not resort to this method of concealment when it
inhabits deep water, or even a permanent rock pool between the
tide-marks, and thus it is in the latter home where one may expect to
see this sea flower in all its glory, for when permanently covered with
water it will seldom hide its crown, except when alarmed, or when in the
act of swallowing its food.
[Illustration: FIG. 95.--_Peachia hastata_, S. DEVON]
It should be noted, too, that the rock pool is the right place in which
to study the habits of this anemone, for it is not nearly so easy to
rear in the artificial aquarium as the species previously described,
and, moreover, it requires a great deal of food. We have found it live
longest in running water, kept cool, and frequently renewed by supplies
fresh from the sea. It may be fed on almost any, if not every, form of
animal life inhabiting a rock pool. A small fish or a prawn is perfectly
helpless when once it is seized by the creature’s tentacles. Mussels,
winkles, limpets, &c., are eagerly swallowed, and the indigestible
shells disgorged after the animal substance has been dissolved by the
digestive fluid. Even the active shore crab, armed as it is with a coat
of mail and powerful pincers, is no match for its powerfully adhesive
tentacles; nor do the sharp spines of the prickly urchin preserve it
from so voracious a creature.
The rocky coasts of Devon and Cornwall are the chief haunts of the
pretty ‘Daisy Anemone’ (_Sagartia bellis_), and here it is very abundant
in places. This species lives in holes and crevices of the rocks, its
body usually entirely hidden from view, but its dark brown disc,
intersected by bright red radiating lines, and fringed with numerous
small tentacles, fully exposed to view as long as it is submerged. The
length of its body is always adapted to the depth of the hole or crevice
in which the animal lives, and may vary from half an inch to two or
three inches, the diameter of the columns being greatest where the
length is least.
[Illustration: FIG. 96.--_Sagartia pallida_, DEVON AND CORNWALL]
Sometimes the ‘Daisy’ may be seen living a solitary life, having settled
down in a hole just large enough to accommodate it, but more commonly it
is seen in company with several others of its species, occupying a
crevice in a rock pool, and often so closely packed together that the
tentacles of each individual are intermingled with those of its
neighbours, thus exhibiting a more or less continuous cluster or line of
‘flowers,’ each disc being from one to two or three inches in diameter
when fully expanded.
On account of the peculiar positions selected by this species, it is not
easily removed without injury, and hammer and chisel are almost always
necessary for its removal; but if it is obtained without injury, and
transferred to the indoor aquarium, but little difficulty will be found
in keeping it alive and in health. It is also very prolific, and a
single specimen placed in the indoor tank will frequently produce a
large number of young.
The colour of _S. bellis_, like that of many of our anemones, is very
variable, but the species may easily be recognised by the radiating
lines of the disc, and the numerous small tentacles. One variety,
however, deviates considerably in form, colour, and habit from the
normal. It (Plate II., fig. 6) is of a dull yellow colour, and has a
much less graceful form; and, instead of living in the holes and
crevices of rocky coasts, where it would be washed by fresh sea water at
every tide, it inhabits the muddy and fœtid waters of narrow inlets of
the sea in the neighbourhood of Weymouth.
[Illustration: FIG. 97.--_Sagartia nivea_, DEVON AND CORNWALL]
Three other species of the same genus are represented on Plate III. The
first of these--_Sagartia troglodytes_, sometimes called the
Cave-dweller (fig. 1)--though very variable in colour, may be known by
its barred tentacles, each with a black B-like mark near its base. It
lives in sheltered, sandy, or muddy hollows between the rocks on most
rugged coasts, often with its body entirely buried beneath the sediment;
or, if only partially buried, the projecting portion of the column
concealed by particles that adhere to its suckers.
The column is usually of an olive colour, striped longitudinally with a
paler tint, and sometimes reaches a length of two inches, while the
diameter of the expanded ‘flower’ may even exceed this length.
This anemone is not a very conspicuous object of the shore, since the
exposed portion of its column is usually more or less covered by
sedimentary matter, and the tentacles are generally of a tint closely
resembling that of the surrounding surface. Thus the anemone is
protected from its enemies by its peculiar habit and colouring, while at
the same time the spreading tentacles constitute an unseen but deadly
snare for the unwary victims that come within their range.
[Illustration: FIG. 98.--_Corynactus viridis_, DEVON AND CORNWALL]
This species is often difficult to secure without injury on account of
its preference for narrow chinks in awkward situations, but we have
found that it is sometimes easily removed by first clearing away the
surrounding débris, and then gently pushing it from its hold by means of
the finger-nail. It seems, in fact, that its base is occasionally quite
free from the underlying rock, being simply imbedded in sand or mud. In
other cases hammer and chisel are necessary to remove it from its snug
hole.
If placed in the aquarium it should be allowed to get a foot-hold in a
suitable hole or crevice, which should be afterwards partially filled
with sand. It is not difficult to keep, and although not a showy
species, and having a decided preference for shady places, yet its
habits will be found interesting.
The Orange-disked Anemone (_Sagartia venusta_) is represented in fig. 2
of the same plate. It may be easily distinguished by its brilliant
orange-coloured disc, surrounded by white tentacles, which, when fully
expanded, commands a circle of from one to one and a half inches.
South-west Wales is said to be the headquarters of this pretty sea
flower, but we have found it abundant on parts of the north Devon coast,
especially in places between Ilfracombe and Lynton. Like the last
species, it may be termed a cave-dweller, for it delights to hide in
corners and crevices that are so overhung with rocks and weeds that the
light is never strong.
Yet another species of this genus (_S. rosea_) is depicted in Plate
III., fig. 8. It has been termed the Rosy Anemone, from the brilliant
rosy tint of its numerous tentacles. The column is generally of a dull
brown colour, with suckers scattered over the upper portion, and the
flower reaches a diameter of an inch or more. This anemone may be seen
at rest on overhanging rocks near low-water mark when the tide is out,
its disc only partially hidden, and the tips of its bright tentacles
just exposed. It may be seen on many parts of the Devon coast, and is,
or, at least, was, abundant in localities near Brixham and Shaldon.
On the same plate is an illustration (fig. 7) of one of the most
abundant and most interesting of our anemones. It is commonly known as
the Opelet, and its scientific name is _Anthea cereus_. Almost everyone
who has done a little collecting on the rocky shores of the south-west
of England, or on the shores of Scotland or Ireland, must have seen this
species, easily distinguished by its long, slender, smooth tentacles,
all of about equal length, and presenting a waxy appearance. These
appendages are usually green and tipped with pink, but sometimes pale
yellow or red, and are of such a length that they cover a circle of five
or six inches.
This species is decidedly of social disposition, for a number may
generally be seen in a cluster, crowded closely together; and when we
see them, as we often do, occupying a little tide pool that contains
scarcely sufficient water to enable them to give free play to their
tentacles, and exposed for hours to the full blaze of the summer sun, we
naturally form the opinion that they ought to require no special care in
the indoor aquarium. And this is actually the case, for they thrive well
with but little trouble.
Perhaps the chief interest attached to this anemone is the deadly nature
of its grip. The numerous long tentacles have considerable clinging
power throughout their length, and their paralysing power is very
considerable compared with that of many other species of the same size.
Even the human skin is more or less affected by the irritating influence
of this species, a sensation approaching to a sting being sometimes
produced, and the skin showing visible signs of the injury done. The
grip, too, is so tenacious that tentacles are sometimes torn off when
the hand is quickly withdrawn from their hold.
Our next example is the Red-specked Pimplet (_Bunodes Ballii_), shown in
fig. 5 of Plate III., which has received its popular name on account of
the numerous longitudinal rows of red-specked warts that run down its
short yellow column, and other red spots on the column itself, between
the rows. Its tentacles are usually pale yellow or white, but sometimes
grey or greenish, and often tinged with pink.
[Illustration: FIG. 99.--_Bunodes thallia_, WEST COAST]
This anemone is common on some parts of the coasts of Hampshire, Dorset,
Devon, and Cornwall, as well as on the south coast of the Isle of Wight,
and may be found in secluded crevices of the rocks, or under the large
stones that are scattered on the beach.
The Gem Pimplet (_Bunodes gemmacea_) is shown on the same plate (fig.
6). It is easily distinguished by the six conspicuous longitudinal rows
of large white warts, between which are several other rows of smaller
ones. The column is pink or brownish, and the thick tentacles are
conspicuously marked by light-coloured roundish spots. It is not
uncommon on the south-west coast of England, where it may be seen in the
rock pools and on the surfaces of rocks between the tide-marks. Both of
the species of _Bunodes_ above mentioned may be kept in the aquarium
without much trouble.
[Illustration: PLATE III.
SEA ANEMONES
1. Sagartia troglodytes
2. Sagartia venusta
3. Actinia glauca
4. Actinia chiococca
5. Bunodes Ballii
6. Bunodes gemmacea
7. Anthea cereus
8. Sagartia rosea]
All the anemones so far briefly described are quite devoid of any kind
of skeleton, the whole body being of a pulpy or leathery consistence,
but some of our British species develop an internal calcareous skeleton,
consisting of a hollow cylinder of carbonate of lime secreted by the
body-wall, and attached to the rock by means of a similar deposit formed
in the base, and also, within the cylinder, of a number of thin plates
attached to the skeleton of the body-wall and projecting inwards towards
the axis, thus resembling, in fact, the skeletons of a number of the
tropical corals with which we are familiar. The animals in question are
often collectively spoken of as British corals.
[Illustration: FIG. 100.--_Bunodes gemmacea_, WITH TENTACLES
RETRACTED]
One of the finest of these corals is the Devon Cup-Coral (_Caryophyllia
Smithii_), figured on Plate II. It may be found in many parts of Devon
and Cornwall, attached to the rocks between the tide-marks, often in
very exposed places, but is much more abundant in deep water.
Its skeleton is white or pale pink, and very hard, and is in itself a
beautiful object. The animal surrounding this stony structure is of a
pale fawn colour, with a white disc relieved by a deep brown circle
round the mouth. The tentacles are conical, almost colourless and
transparent, with the exception of the deep-brown warts scattered
irregularly over them, and are tipped by rounded white heads.
Of course a hammer and chisel are necessary for the removal of these
corals, but they are hardy creatures, and may be kept for a considerable
time in captivity. Their habits, too, are particularly interesting, and
two or more may sometimes be found with skeletons attached, suggesting
that branched arrangement so common in many of the corals from warmer
seas.
Another of these stony corals (_Balanophyllia regia_) is shown on the
same plate. It is much smaller than the last species, but exceedingly
pretty. It is also much less abundant, being confined almost exclusively
to the coast of North Devon, and is seldom seen far above the lowest ebb
of the tide.
[Illustration: FIG. 101.--_Caryophyllia cyathus_]
Our few brief descriptions of British anemones and corals have been
confined to those species which appear in our coloured plates, but we
have interspersed here and there between the text a few illustrations
which will assist in the identification of other species and also help
to show what a rich variety of form is exhibited by these beautiful
creatures. Some of these inhabit deep water only and are consequently
beyond the reach of most sea-side observers during the ordinary course
of their work; yet they may often be seen in fishing villages,
especially in the south-west, where they are frequently brought in among
the haul of the trawlers, attached either to shells or stones; and live
specimens of these deep-sea anemones may even be seen on the shells of
whelks and bivalve molluscs in the fishdealers' shops of London and
other large towns.
[Illustration: FIG. 102.--_Sagartia parasitica_]
One of the species in question--the Parasitic Anemone (_Sagartia
parasitica_) is generally found on the shell of the whelk or some other
univalve; and, if removed from its chosen spot, it will again transfer
itself to a similar shell when an opportunity occurs. This interesting
anemone is usually seen among the dredgings of the trawler, but may be
occasionally met with on the rocky coasts of the south-west, at extreme
low-water mark. Though sometimes seen attached to stones, shells may
undoubtedly be regarded as constituting the natural home of the species,
and many regard the former position as accidental or merely temporary,
and denoting that the animal had been disturbed and removed from its
favourite spot, or that circumstances had recently rendered a change of
lodgings necessary or desirable. Further, the shell selected by this
anemone is almost always one that is inhabited by a hermit crab; and
this is so generally the case that the occasional exceptions to the rule
probably point to instances in which the occupant of the shell had been
roughly ejected during the dredging operations.
[Illustration: FIG. 103.--THE CLOAK ANEMONE (_Adamsia palliata_) ON A
WHELK SHELL, WITH HERMIT CRAB]
The peculiar habit of the anemone just referred to makes it an
interesting pet for the aquarium, for if removed from its natural home,
and placed in the aquarium with a hermit crab, it will, sooner or later,
as the opportunity occurs, glide from its hole on the stone or rock, and
transfer itself to its favourite moving home.
It may be difficult at first to see what advantage can accrue to the
anemone by the selection of such a situation; and, moreover, it becomes
an interesting question as to whether the advantage is a mutual one.
Close observations may, and already have, thrown some light on this
matter, though it is probable that there still remains something to be
learnt concerning the relations which exist between the inside and
outside occupants of the portable house.
It may be noticed that the anemone almost invariably takes up a position
on the same portion of the shell, and that, when fully expanded, its
mouth is usually turned towards that of the crab. This seems to be a
very favourable position for the anemone, since it is one that will
enable it to catch the waste morsels from the crab’s jaws by its
expanded tentacles. But it is, perhaps, not so easy to suggest a means
by which the anemone can make an adequate return for free board thus
obtained. It is well to remember, however, that crabs are regarded as
such delicate morsels by fishes that we have already spoken of the value
of these crustaceans as bait; while the fact that sea anemones remain
perfectly unmolested in rock pools inhabited by most voracious fishes,
coupled with the fisherman’s experience as to the absolute worthlessness
of anemones as bait, is sufficient in itself to justify the conclusion
that these creatures are very distasteful to fishes. This being the
case, it is possible that the hermit crab is amply repaid by the anemone
for its liberal board not only by partially hiding the crab from the
view of its enemies, and thereby rendering it less conspicuous, but also
by associating its own distasteful substance with that which would
otherwise be eagerly devoured.
When the hermit grows too large to live comfortably in its shell, a
change of home becomes necessary, and it is interesting to observe that
the anemone living on the outside of the shell transfers itself at the
same time; and this is a matter of vital importance to the crab, since
it usually changes its lodging at the moulting period, at which time its
body is covered by a soft skin, and is then even more acceptable as prey
to the fishes. Thus the anemone accompanies its host, affording it
continued protection during the period of its greatest danger.
Before leaving the cœlenterates we must refer to one other form which,
though not often having its habitat between the tide-marks, is
nevertheless a very common object in the neighbourhood of fishing
villages, where the refuse from the nets used in deep water has been
thrown on the beach. We refer to the peculiar animal known to fishermen
as ‘Dead Men’s Fingers,’ and to the naturalist as the _Alcyonium_.
When seen out of water it is not by any means an inviting object, but is
apparently a mass of gristly matter, of a dirty yellowish or brownish
colour, sometimes flattened and shapeless, and sometimes lobed in such a
manner as to suggest the popular name so commonly applied. It is always
attached to some hard object, such as a stone or a shell, and is so
frequently associated with oyster shells that it is by no means an
uncommon object in the fishmonger’s shop, from which we have often
obtained live specimens for the aquarium.
When placed in sea water it gradually imbibes the fluid surrounding it,
becoming much swollen. Then little star-like openings appear, the
circumference of each of which protrudes so as to form a little
projecting tube. Finally, a crown of eight little tentacles is
protruded, and the mass, so uninteresting at first sight, reveals itself
as a colony of pretty polyps.
In general structure the Alcyonium resembles the sea anemone, but the
firm body-wall of the colony is supported and protected to some extent
by the presence of minute spicules of carbonate of lime; and it is
interesting to note that while the tentacles of anemones and corals make
up a number that is a multiple of either five or six, those of the
Alcyonaria and the allied ‘Sea pens’ are always in multiples of four.
CHAPTER X
_STARFISHES, SEA URCHINS, ETC._
Still passing up the scale of animal life, we now come to the
_Echinodermata_--the other sub-kingdom which we have already referred to
as forming, with the Cœlenterates, the old division of Radiata. The
term _Echinoderm_ signifies ‘hedgehog skin,’ and is applied to the group
on account of the fact that the majority of its species possess a skin
that is either distinctly spiny, or exhibits numerous more or less
defined prominences. This skin is also supported and hardened by the
deposit of little plates or spicules of carbonate of lime, all joined
together so as to form a kind of scaffolding or ‘test’ for the
protection of the animal; and this secretion of carbonate of lime is not
always confined to the outer skin, for, in some cases, it occurs in the
walls of the internal organs as well.
Most of the animals of this sub-kingdom display a regular radiate
symmetry; that is, the parts of their bodies are arranged regularly
round a common axis, and the arrangement is usually a five-fold one, as
may be observed in the case of the common Five-fingered Starfish of our
coasts (see Plate IV.), and it is worthy of note that this radiate
disposition of parts is not merely external, but that, as in the case of
anemones and jelly-fishes, it also obtains within, and determines the
arrangement of the internal organs. Further, although this radiate
symmetry characterises the adult animals of the group we are
considering, yet some show a tendency towards bilateral symmetry (parts
arranged equally on two opposite sides of a common axis), while this is
the rule, rather than the exception, with the early stages or _larvæ_ of
these creatures. Observe, for instance, the larva of the common Brittle
Starfish, the adult of which species exhibits an almost perfect radiate
symmetry, and we see something more than a mere trace of a two-sided
disposition.
We have not to look far into the structure of any typical echinoderm to
see that it is a distinct advance on the anemones in the matter of
organisation. To begin with its digestive system--this consists of a
tube having no communication with the general body-cavity, but remaining
quite distinct throughout its length, with both ends communicating
directly with the exterior. Its nervous system also is more highly
developed, for it has a well-formed ring of nerve matter round the
mouth, from which pass two or three systems of nerve fibres, each system
having its own special function to perform. The sense organs, however,
do not appear to be well developed, though there exist certain ‘pigment
spots,’ in which nerve fibres terminate, and which are supposed to serve
the purpose of eyes.
[Illustration: FIG. 104.--LARVA OF THE BRITTLE STARFISH]
One of the most interesting features in connection with the echinoderms
is undoubtedly the structure and function of the apparatus for
locomotion. Examine a live sea urchin, or the common five-rayed
starfish, in a rock pool or aquarium, and it will be seen to possess a
large number of soft, flexible, and protrusible processes, each of which
terminates in a little sucking-disc that enables the animal to obtain a
good ‘foot-hold;’ and, having fixed itself on one side by means of a
number of these little ‘feet,’ it is enabled, by the contraction of
certain muscles, to pull itself along.
The little feet we are examining are really tubes filled with water, and
capable of being inflated by the injection of water into them from
within the body of the animal. Each one communicates with a water tube,
several of which (usually five) radiate from a circular canal of water
that surrounds the mouth. This circular canal does not communicate with
the mouth, but with a tube, known as the ‘stone canal’ because of the
carbonate of lime deposited within its walls, that opens at the surface
of the body on the opposite side, and is guarded at the orifice by one
or more perforated plates through which water gains admission. Thus the
animal can fill its ‘water system’ direct from the sea, and, by the
contraction of muscles that surround the main canals, force this water
into the little ‘tube-feet,’ causing them to protrude and present their
sucking-discs to any solid object over which it desires to creep. We may
observe, however, that some of the little protrusible tubes have no
sucking-discs, and probably serve the purpose of feelers only; also,
that while these tube-feet are the principal means of locomotion in
certain species, in others the movements of the body are performed
almost exclusively by the five or more rays that extend from the centre
of the animal, and which are readily curved into any desired position by
the action of well-developed muscles.
All the echinoderms come within the domain of the marine naturalist, for
no members of the sub-kingdom are inhabitants of fresh water; and it is
interesting to observe that, unlike the animals previously described,
none of them live in colonies.
A general examination of the various starfishes to be found in our seas
will show that they may be divided into three distinct groups. One of
these contains the pretty Feather Stars, which are distinguished by
their long and slender ‘arms,’ usually ten or more in number, each of
which bears a number of pinnules that give it quite a feathered
appearance. The second includes the Brittle Stars, possessing five
slender arms that are jointed to the small, flattened, central disc, and
which are so named on account of the readiness with which the animal
falls to pieces when alarmed or disturbed; and the third is formed by
the remaining five-rayed stars, the arms of which, instead of being
jointed to, are continuous with, the centre of the body.
All these starfishes have a leathery skin, supported and hardened by a
framework of calcareous plates, and presenting a number of hard ridges
or spines. In addition to the system of water tubes already mentioned as
characteristic of the echinoderms, they also possess a second circular
vessel round the mouth, from which a number of vessels are distributed
to the walls of the digestive tube. These, however, are bloodvessels,
and are directly concerned with the nutrition of the body. Some, also,
have imperfectly developed eyes at the ends of the arms or rays.
Contrary to what one would expect after watching the somewhat sluggish
movements of starfishes, they are really very voracious creatures,
attacking and devouring molluscs and small crustaceans, sometimes even
protruding their stomachs to surround their prey when too large to be
passed completely through the mouth; and they are also valuable as
scavengers, since they greedily devour dead fishes and other
decomposible animal matter.
[Illustration: FIG. 105.--LARVA OF THE FEATHER STAR]
Feather Stars differ from other starfishes in that they are stalked or
rooted during one portion of their early life. At first they are little
free-swimming creatures, feeding on foraminifers and other minute
organisms that float about in the sea. Then they settle down and become
rooted to the bottom, usually in deep water, at which stage they are
like little stalked flowers, and closely resemble the fossil encrinites
or stone lilies so common in some of our rock beds, and to which they
are, indeed, very closely allied. After a period of this sedentary
existence, during which they have to subsist on whatever food happens to
come within their reach, they become free again, lose their stalks, and
creep about by means of their arms to hunt for their prey.
[Illustration: FIG. 106.--THE ROSY FEATHER STAR]
The commonest British species of these starfishes is the Rosy Feather
Star (_Antedon rosaceus_); and as this creature may be kept alive in an
aquarium for some considerable time without much difficulty, it will
repay one to secure a specimen for the observation of its habits. It is
not often, however, that the Feather Star is to be found above low-water
mark, its home being the rugged bottom under a considerable depth of
water, where a number usually live in company; but there is no
difficulty in obtaining this and many other species of interesting
starfishes in fishing towns and villages where trawlers are stationed,
for they are being continually found among the contents of the net.
Although the Feather Star can hardly be described as an active creature,
yet it will cover a considerable amount of ground in the course of a
day, creeping over rocks and weeds by means of its arms, which are
raised, extended, and again depressed in succession, each one thus in
turn serving the purpose of a foot. These arms are capable of being
moved freely in any direction, as are also the little more or less rigid
pinnules appended to them. The latter are bent backwards on an extended
arm that is being used to pull the animal along, so that they form so
many grappling hooks that hold on the bottom; and then the arm in
question is bent into a curve by the contraction of its muscles, thus
dragging the body forward. The arms on the opposite side of the body are
also used to assist the movement by pushing it in the same direction,
and this is accomplished by first bending the arms, and then, after
curving the pinnules in a direction from the body, again extending them.
Other movements of the feather star are equally interesting. Thus, the
manner in which it will suddenly extend its arms and apply its pinnules
to the surface on which it rests in order to obtain a good hold when
alarmed, and the way in which it apparently resents interference when
one of the arms is touched, are worthy of observation. The arms
themselves are readily broken, and will continue to move for some time
after being severed from the body, but the loss to the animal is only
temporary, for a new arm grows in the place of each one that has been
broken off.
This tendency to break into pieces is much greater in the Brittle Stars,
as might be expected from their popular name; and is, in fact, such a
marked characteristic of the group that it is not by any means an easy
matter to obtain a collection of perfect specimens. They will often snap
off all their arms, as if by their own power of will, when disturbed or
alarmed, and even when removed from their hold without injury, they will
frequently break themselves into pieces if dropped into spirit or in any
way subjected to a sudden change of conditions.
The tube-feet of Brittle Stars are very small and are not provided with
suckers, but are very sensitive, serving the purpose of feelers; also,
having thin, permeable walls, they probably play a large part in the
process of respiration. Both arms and disc are hardened by a dense
scaffolding of calcareous plates; and not only are the former attached
to the latter by a well-formed joint, but the arms themselves are
constructed of a number of segments that are held together by a kind of
‘tongue and groove’ joint. Round the mouth are a number of tentacles
that are kept in constant motion with the object of carrying the food
towards it, and of holding the larger morsels while the act of
swallowing is progressing.
[Illustration: FIG. 107.--THE COMMON BRITTLE STAR]
The various species of Brittle Stars live among the rocks and weeds,
chiefly in deep water, where they move about by means of the muscular
contraction of their arms, the disc being raised on the curved arms as
the animal proceeds. Some species are to be found between the
tide-marks, and especially abundant on the south-west coast are two
small species that live among the tufts of coralline weeds, sometimes so
crowded together that dozens may be taken from a little patch of
coralline only two or three inches square. These have such small discs,
and such slender arms, and are, moreover, so well concealed by their
colouring, which closely resembles that of the weed-tuft they inhabit,
that they are only to be detected by close inspection.
The remaining division of the starfishes, sometimes distinguished by the
name of Common Stars, possess five arms or rays, which may be either
long or short, and which are not jointed with the central disc, but
continuous with it; that is, there is no sharp line of demarcation
between arm and disc. One or two species are well known to all
frequenters of the sea-side, but the majority of them inhabit deep
water, where they creep about over the rocks and weeds, obtaining their
food from the bed below them.
If we examine the common five-finger star that is so often stranded on
the beach, and so frequently found in rock pools between the tide-marks,
we see that each arm has a large and conspicuous groove running along
its centre on the under side, and on each side of these are the rows of
tube-feet, arranged in such a manner that they have suggested the
appearance of an avenue of trees on each side of a garden walk, and have
consequently earned the name of _ambulacrum_. These tube-feet may be
protruded for some distance; and, being provided with suckers that
possess considerable clinging power, they form the principal means of
locomotion.
Put the starfish in the aquarium, or in a tidepool by the sea, and you
will find it very interesting to observe how the animal progresses,
while some idea of the clinging power of the tube-feet may be
ascertained by allowing the animal to creep over the submerged hand.
The movements of the tube-feet may also be seen to advantage when the
starfish is laid upside down in a pool, and, what is still more
interesting, the manner in which the animal turns itself over. To do
this it will first bend the tips of one or two of its arms so as to
bring the suckers against the ground; and then, aided by the pulling
action of these, it will gradually bring other suckers into a similar
position till, at last, the whole body has been turned over. Some of our
common starfishes have rays so short that they may be termed angles
rather than arms, and these are unable to turn their inverted bodies by
the gradual method just described. They generally raise their bodies on
the tips of three or four of the rays, assuming somewhat the form of a
three-or four-legged stool, and then, bending the remaining one or two
arms over the body, they alter the position of the centre of gravity
till eventually the body topples over to the desired position.
Some of the common five-rayed stars have no suckers on their tube-feet,
and consequently have to creep by means of the muscular contractions of
their arms; and several of them are like the brittle stars in breaking
up their bodies when irritated or seized. This latter peculiarity will
account for the frequency with which we come across animals with one or
more rays smaller than the others, the smaller rays being new ones that
have been produced in the place of those lost. Again, we sometimes meet
with such monstrosities as a five-rayed star with six or more rays, some
smaller than others, the smaller ones representing two or more that have
grown in the place of one that has been lost; or a starfish with
branched or forked arm, illustrating the tendency to produce a new arm
even when the original one has been only partially severed.
A close observation of a starfish in water may enable us to detect a
number of little transparent processes standing out between the
prominences of the rough skin of the upper surface. These are little
bags filled with fluid, formed of such thin walls that gases can readily
pass through them, and are undoubtedly connected with the process of
respiration. Also, on the upturned extremity of each arm a red spot may
be seen; and this from the nature of its structure, and from its
association with the nervous system, has been regarded as a rudimentary
eye.
On the upper side of the disc one may also observe a more or less
conspicuous spot of variable colour, on one side of the centre. It is a
plate, finely perforated, covering the outer extremity of a short canal
which communicates with the system of water tubes that were described in
the earlier part of this chapter. It is, in fact, the entrance through
which water is admitted into the central ring round the mouth, and from
this into the radial water tubes that run through each arm of the
starfish to supply the tube-feet. The short tube referred to is always
filled with sand, and thus the water that enters into the water-vascular
system is filtered before it reaches the circular vessel. It is
interesting to note, in this connection, that here is one respect in
which the radiate symmetry of the starfish is broken, there being only
one entrance, and that not a central one, by which water is distributed
into the five rays.
Of course, when the ray of a starfish has been broken off the water
vessel or vessels that it contained are destroyed, as is also the
prolongation of the stomach, in the form of a long, blind tube, that
extended into it. But no inconvenience attaches itself to this loss, for
the starfish has the power of reproducing even its lost viscera, as well
as any of the five rays of the body that may be broken off.
We must briefly refer to one other feature of the common star, viz. the
possession of small prehensile organs around the mouth. These are little
spines, the extremities of which are movable, and take the form of
little pincers by means of which the animal can hold its prey.
When it is desired to preserve starfishes for future study, immersion in
diluted spirit or a solution of formaldehyde will answer all purposes,
the soft parts being thus preserved as well as the harder structures;
but it is usual to preserve them in a dry state when they are required
merely for purposes of identification, as is usually the case with the
specimens in an ordinary museum collection. In the latter case it is
advisable to put the starfishes in strong spirit for a few days,
changing the spirit if several specimens are put together, and then
drying them as quickly as possible in the open air.
[Illustration: FIG. 108.--SECTION OF THE SPINE OF A SEA URCHIN]
We have now to consider the Sea Urchins or Sea Eggs, which are readily
known by the hedgehog-like covering of hard spines. Externally they
appear as globular or heart-shaped bodies, the surface entirely hidden
by spines except, perhaps, the mouth on the under side, which is
provided with an apparatus for mastication. If alive, and in the water,
one may notice that the animal creeps along the bottom, mouth downwards,
moving itself either by means of its moveable spines, or by soft
tube-feet resembling those of starfishes, that are protruded between the
spines, or by both combined; and the movements of its masticating organ
may be seen by observing the animal through the side or bottom of a
glass vessel of sea water. The last-named organ is surrounded by an area
of soft skin, and is not present in all species.
A closer examination of the common globular urchin will show that it is
wonderfully constructed. Even the spines, which are in themselves
uninteresting objects to the naked eye, are most beautifully formed, a
transverse section revealing a radiate or reticulated structure when
viewed through the microscope. Each spine has a concave base which fits
on a little tubercle of the calcareous shell or test that covers the
body of the animal, forming a perfect ball-and-socket joint, and is
capable of being moved in any direction by means of small muscular
bands.
[Illustration: FIG. 109.--SEA URCHIN WITH SPINES REMOVED ON ONE SIDE]
On removing the spines the shell is seen to completely enclose the
animal with the exception of the mouth, with its masticatory apparatus,
and the small area around it which is covered by the uncalcified skin
just referred to.
At the very top of the shell, exactly opposite the mouth, there is a
small plate perforated by the extremity of the digestive tube. Round
this are five angular plates, each perforated by the ducts of the
ovaries or egg-producing glands, but one of these is enlarged and
further perforated, that it may serve the second purpose of allowing
water to enter the system of water tubes that supply the tube-feet, and
thus corresponds exactly with the plate already noticed on the upper
surface of the starfish. Between these are five smaller plates, each
with a rudimentary eye that receives a fine nerve-thread.
[Illustration: FIG. 110.--APEX OF SHELL OF SEA URCHIN]
The remaining and greater portion of the shell of the urchin is composed
of ten radiating segments, each of which is made up of two rows of flat
angular plates united at their edges. Five of these segments, arranged
alternately with the others, are perforated by numerous holes, through
which the tube-feet of the urchin are protruded, while the remainder
are imperforate; and all ten plates bear the little hemispherical
processes to which the spines are jointed.
[Illustration: FIG. 111.--SHELL OF SEA URCHIN WITH TEETH PROTRUDING]
One of the most interesting features of this urchin is undoubtedly its
complex and wonderful masticating system. There are five teeth,
symmetrically arranged, and all pointing towards the centre of the
mouth. Each is attached to a wedge-shape jaw, made up of several
pieces, and the whole apparatus is attached by ligaments to loops in the
interior of the shell, and is moved by no less than thirty distinct
muscles. The complete system may be readily dissected out, and is well
worthy of study and preservation. (The harder portions of the system may
often be found in the interior of the empty shell of an urchin after the
softer structures of the body have decayed away.)
[Illustration: FIG. 112.--INTERIOR OF SHELL OR SEA URCHIN]
[Illustration: FIG. 113.--MASTICATORY APPARATUS OF SEA URCHIN]
An interesting dissection of the globular urchin may also be made by
cutting completely round the shell with a pair of sharp-pointed
scissors midway between the mouth and the apex, and then separating the
upper and lower halves, as shown in fig. 114. In this way the whole of
the digestive tube, with its numerous curves, may be traced from the
mouth to the anus at the opposite pole. The water-vessels that supply
the tube-feet in the regions of the five perforated plates may also be
seen, as well as the ovaries or egg-producing organs and the bases of
the five jaws with their complicated system of muscles.
A little acquaintance with the commonest of the British sea urchins will
show that they may be divided into two well-defined groups, one
containing the globular or subglobular forms, of which the common sea
urchin or sea egg (_Echinus sphæra_) above described, is a type, as well
as the pretty little Green Pea Urchin (_Echinocyamus pusillus_), and the
little Purple-tipped Urchin (_Echinus miliaris_), which is found
principally on the west coast of Scotland; while the second group is
formed by the less symmetrical Heart Urchins, which differ from the
others in several interesting particulars of structure and habit.
[Illustration: FIG. 114.--SEA URCHIN DISSECTED, SHOWING THE DIGESTIVE
TUBE]
These heart urchins (Plate IV., fig. 4) are covered with short, delicate
spines which are not much used for purposes of locomotion, the animals
moving from place to place almost entirely by means of their tube-feet,
while the globular urchins travel principally by their spines, which are
stouter and more freely moved on well-formed ball-and-socket joints.
Also, while in the globular species the perforated plates that admit of
the protrusion of the feet are arranged with a perfect radiate symmetry,
those of the heart urchins are confined to one side of the shell; and
the digestive tube, which in the former terminates in the pole opposite
the mouth, in the latter ends close to the mouth itself. Further, the
heart urchins do not possess any kind of dental apparatus.
[Illustration: PLATE IV
ECHINODERMS
1. Asterias rubens
2. Goniaster equestris
3. Ophiothrix fragilis
4. Echinocardium cordatum
5. Echinus miliaris
6. Echinus esculentus]
The habits of sea urchins are interesting, and may be watched in the
aquarium, where the movements of the spines and of the tube-feet may
be seen perfectly. Some species are very inactive, living in holes and
crevices, or under stones, and seldom move from their hiding-places,
while others travel considerable distances. The former have generally no
eyes, and, instead of seeking their food, simply depend for their
subsistence on the material carried to them by the movements of the
water; while the latter possess visual organs similar to those observed
in certain starfishes. Some species also protect themselves from their
enemies when in the open by covering their bodies with sand, small
stones, shells, or weeds, and thus so perfectly imitate their
surroundings that they are not easily detected. The feet that are used
for purposes of locomotion terminate in suckers resembling those of the
common five-fingered starfish, and have considerable clinging power, but
some have either very imperfectly developed suckers or none at all, and
are probably used as feelers only.
Sea urchins, like their allies the starfishes, generally inhabit deep
water beyond low-water mark, where they often exist in enormous numbers,
feeding on both animal and vegetable substances; but some species are
often to be met with between the tide-marks, where they may be seen
under stones, and frequently half hidden in mud. The globular species
occur principally on rocky coasts, but the heart urchins are more
commonly dredged from banks of sand or mud that are always submerged.
The life-history of urchins closely resembles that of starfishes, for
the young are free-swimming creatures of an easel-like form, and during
this early larval existence their bodies are supported by a calcareous
skeleton.
We will conclude our short account of the British echinoderms with a
description of the peculiar Sea Cucumbers, which belong to the division
_Holothuroidea_. These creatures are so unlike starfishes and urchins in
general appearance that the uninitiated would hardly regard them as
close relatives. The body is, as the popular name implies,
cucumber-shaped, with the mouth at one end, and the general aspect is
wormlike. There is, however, a radiate symmetry--a five-fold arrangement
of parts, though not so regular as in most echinoderms. Running
lengthwise along the body are five rows of tube-feet, but only two of
these are well developed and terminate in functional suckers; and, as
might be expected, the animal crawls with these two rows beneath it. The
feet are outgrowths of a system of water tubes similar to that of the
urchin, there being a circular tube round the mouth, from which branch
five radial tubes, one for each row.
The mouth of the sea cucumber is surrounded by plumed tentacles which
can be retracted at will, and which are used in capturing the smaller
living things that form its food. Like the earthworm, it will often
swallow large quantities of sand, from which it digests the organic
matter contained.
The body-wall of the _Holothuroidea_ is strong and muscular, and is
strengthened by the presence of numerous spicules of carbonate of lime,
often in the form of little anchors, wheels, and crosses, while the
outer surface is rough and slimy, and often of a colour so closely
resembling the surroundings of these animals that they are not easily
observed. This feature is one of great value to the creatures, since
they have no means of defence from their enemies, and seem to owe their
safety entirely to their protective colouring.
[Illustration: FIG. 115.--THE SEA CUCUMBER]
There are several species of sea cucumbers on our coasts, but all
inhabit deep water and are seldom to be seen above low-water level. They
are, as a rule, easily obtained from fishermen, who will bring them in
when requested to do so. Live specimens may be kept for a considerable
time in the indoor aquarium, and seem to prefer a rocky bottom on which
they can hide under stones at times, and a bed of sand on which they
will occasionally crawl. They will readily devour small molluscs and
crustaceans, and will partake of dead organic matter in a partially
decomposed state.
The following tabular summary of the classification of Echinoderms may
possibly be of use for reference:--
SUB-KINGDOM _ECHINODERMATA_
+-------------------------------------------+-------------+--------------+
|Body star-shaped. |Body glob- |Body |
+------------+------------------------------+ ular, sub- | elongated, |
|Body |Body not stalked. | globular, | and covered |
| stalked, |Tube-feet used for locomotion.| or heart- | with a |
| at least |=Class:= _Stelleridæ._ | shaped, | soft skin |
| during +--------------+---------------+ and cov- | containing |
| early |Arms jointed |Arms contin- | ered with | calcareous |
| stage. | to disc, and | uous | a con- | spicules. |
| Feet not | not contain- | with disc, | tinuous | |
| used for | ing prolong- | and contain- | shell. |=Class:= |
| loco- | -tions of the| ing processes | | _Holothu- |
| motion. | internal | of the |=Class:= | roidea_ |
| | organs | viscera. | _Echinoidea_| (Sea |
|=Class:= | | | (Sea Ur- | Cucumbers). |
| _Crinoidea_|=Order:= |=Order:= | chins). | |
| (Feather | _Ophiuroidea_| _Asteroidea_ | | |
| Star). | (Brittle | (Common | | |
| | Stars). | Stars). | | |
+------------+--------------+---------------+-------------+--------------+
CHAPTER XI
_MARINE WORMS_
Some groups of animals are so well defined that the individual species
contained in them can be assigned their proper place without any
difficulty, the main characteristics by which the group is distinguished
running with more or less precision throughout the series; but,
unfortunately this is not the case with the ‘worms,’ which constitute
the sub-kingdom _Vermes_. Here we have a most heterogeneous assemblage
of animals, collectively exhibiting exceedingly wide variations in both
form and structure.
We have already referred to the sea cucumber as wormlike in form, and
this creature is only one of a large number of wormlike animals that are
not worms; and it is also a fact that a considerable number of the worms
are not wormlike. It appears as if the sub-kingdom Vermes were a kind of
receptacle into which we may throw almost any invertebrate animal that
does not readily fall in line with the general characteristics of the
other important groups; for in it we have such a varied assemblage of
creatures that, speaking of them collectively as worms, it becomes most
difficult, if not absolutely impossible, to say exactly what a worm is;
and it is a question whether the sub-kingdom ought not to be divided
into at least two or three groups of the same standing.
This being the case we can hardly give a satisfactory summary of the
characteristics of the group, and therefore it must be understood that
in our attempt to do so we unavoidably exclude some forms that belong to
it according to our present system of classification. This being
remembered, we will define worms as soft-bodied and elongated animals,
exhibiting a bilateral symmetry (that is, having appendages and organs
arranged symmetrically on each side of a plane extending from the dorsal
to the ventral surface through the centre of the body), and with the
body usually divided into a succession of segments, each of which
resembles the one preceding and following it. Though many of the worms
are generally looked upon as uninteresting creatures, of such an
unattractive appearance and with such depraved habits that they are
beneath respect, yet a study of the sub-kingdom will prove that not only
does it include a number of wonderful forms with the most marvellous
life histories, but that some of them are very beautiful objects; and
this last remark refers more particularly to many of the marine worms,
which come directly within the scope of our work.
Before passing on to the special study and classification of the marine
species, however, we must say a few words concerning the worms in
general, reminding the reader that all our statements regarding the
anatomy of the creatures may be readily verified by simple dissections
of one or two typical species, such as the common earthworm, the
fisherman's lugworm, the sea mouse, or the common horse-leech of our
fresh-water ponds. With this object in view, the animal may be killed by
immersion in spirit, then pinned out in the dissecting tray under water,
and the body-wall opened by means of a pair of sharp-pointed scissors.
The digestive tube of a worm runs completely through the length of the
body, and though there is no distinct head, there is always a mouth, and
this is often provided with horny jaws, and sometimes also with horny
teeth, with which the animal is enabled to inflict wounds on its prey.
Like the preceding sub-kingdom--the _Echinodermata_--worms possess a
system of water tubes; this system, however, is not in any way connected
with the function of locomotion, but is, in many cases at least, if not
in all, intimately associated with the process of respiration. It
consists of a series of tubes, arranged in pairs in the successive
segments, communicating with the body-cavity internally, and opening at
the exterior by means of pores in the cuticle. In some there is a highly
organised system of bloodvessels, containing blood that is usually
either colourless, red, or green, but the colour of the blood is never
due to the presence of corpuscles, as is the case with higher animals,
the tint being due to the plasma or fluid portion of the blood; and
though worms cannot be said to possess a true heart, yet they often have
one or more contractile bloodvessels which serve the purpose of
propelling the blood.
Most worms possess a nervous system, and, where this is present, it
consists of a chain of ganglia, placed along the ventral side of the
body, beneath the digestive tube, all united by means of a nerve cord,
and distributing nerves in pairs to various parts of the body; and it
may be well to note here one very important point of distinction between
the general arrangement of the central portion of the nervous system in
the worms and higher invertebrates, as compared with that of the
corresponding structure in the vertebrates:--In the former the main axis
of the system, consisting, as we have seen, of a chain of ganglia
connected by a nerve cord, is invariably placed along the _ventral_
portion of the body-cavity--the surface on which the animal crawls;
while in the vertebrates the axis of the nervous system lies along the
upper or dorsal part of the body; and, instead of lying in the general
body-cavity, in company with the organs of digestion and circulation, is
enclosed in the bony canal formed by the vertebral column. It will be
seen from this that when it is desired to examine the nervous system of
the invertebrate animal, the body-wall should be opened along the middle
of the ventral surface, while, in the vertebrate, the central axis
should be exposed from above.
Many of the vermes are parasitic, either attaching themselves to the
exterior of other animals, and deriving nourishment by sucking their
blood, or they are internal parasites, living in the digestive canal of
their hosts and partaking of the digested food with which they are
almost perpetually surrounded, or burrowing into the tissues and
imbibing the nutritive fluids which they contain; and it is interesting
to study even these degraded members of the group, if only to observe
how their physical organisation degenerates in accordance with their
depraved mode of living. In them we find no digestive system with the
exception of the simplest sac from which the fluids they swallow may be
absorbed, for their food is taken in a condition ready for direct
assimilation; and the food so obtained being readily absorbed into all
parts of their soft bodies, and being sufficiently charged with oxygen
gas by the respiration of their hosts, they require no special organs
for circulation or respiration, nor, indeed, do we find any. Further, we
find that the nervous system is often undeveloped; for since the
parasites, and especially the internal ones, are so plentifully
surrounded with all the necessaries of existence, their bodies are so
simple in construction that no complex nervous system is required to
promote or control either locomotion or internal functions. Even the
general body-cavity often disappears in these degraded creatures, the
internal organisation being of such a low type that there is no
necessity for it; and all the abundant nourishment absorbed over and
above that required for the sustenance of their simple bodies is
utilised in the reproduction of the species; consequently we find, as a
rule, the reproductive organs well represented, and the species
concerned very prolific.
It is an interesting fact, too, that these parasites, in their earliest
stage, possess organs which are present in the higher worms, but which
degenerate as they approach the adult form, thus indicating that they
have descended from more respectable members of the animal world, and
that the low physical development which they ultimately attain is the
natural result of their base mode of living.
The young marine naturalist, working on our coasts, will not be brought
into intimate contact with parasitic worms to any large extent, yet we
have said this little on parasitism to show that these degenerate
creatures are not really devoid of interest, and that they will repay
study whenever they are found. They will be more frequently met with
during the examination of the animals--usually higher types--that become
their hosts, and thus they hardly come within the scope of this work.
[Illustration: FIG. 116.--A TURBELLARIAN, MAGNIFIED
_a_, mouth; _b_, cavity of mouth; _c_, gullet; _d_, stomach; _e_,
branches of stomach; _f_, nerve ganglion; _g_ to _m_, reproductive
organs.]
The simplest of the worms are those forming the class _Turbellaria_, so
designated on account of the commotion they produce in the water
surrounding them by means of the vibratile cilia that fringe their
bodies--a characteristic that is also expressed by their popular name of
Whirl Worms. They are usually small creatures, with soft, flattened,
unsegmented bodies, though some of the larger species are really
wormlike in form, and are more or less distinctly divided into a chain
of segments. Many of them are marine, and may be seen gliding over
stones left uncovered by the receding tide with a smooth slug-like
motion, and when disturbed in a rock pool, occasionally swimming with a
similar smooth motion by the aid of their cilia. They avoid bright
light, and are consequently generally found on the under surfaces of
stones, especially in rather muddy situations, and where the stones are
covered with a slimy deposit of low forms of life. In these
turbellarians the mouth is situated on the under surface, thus enabling
the animal to obtain its nourishment from the slimy surface over which
it moves, and it is also provided with an extensile proboscis that aids
it in the collection of its food. The digestive tube is generally very
complex in form, extending its branches into every part of the soft
body; and, there being no special organs of respiration, the animal
derives all the oxygen required by direct absorption from the water
through the soft integument.
When searching for turbellarians on the sea shore one must be prepared
to meet with interesting examples of protective colouring that will
render a close examination of rocks and stones absolutely necessary.
Some of these worms are of a dull greyish or brownish colour, so closely
resembling that of the surface over which they glide that they are not
easily distinguished; and the thin bodies of others are so transparent
that the colour of the stone beneath is visible through them, thus
preventing them from being clearly observed.
Overturned stones should be examined for their flattened bodies gliding
along rapidly in close contact with the surface. They may be removed
without injury by placing a wet frond of a sea weed close to the stone,
in front of one end of the body, and then urging them to glide on to it
by gently touching the opposite end. Sometimes, however, the
turbellarians remain perfectly still when exposed to the light, in which
case they are even more difficult to detect, but a little practice will
soon enable one to distinguish them with readiness.
Allied to the turbellarians are the Spoon Worms or Squirt Worms, some
species of which inhabit deep water round our shores, where they burrow
into the sand or mud of the bed of the sea. These form the class
_Gephyrea_, and consist of creatures with sac-like or cylindrical and
elongated bodies, and a protrusible proboscis, which is often of great
length. Their bodies are not distinctly segmented, nor do they bear any
appendages. The skin is tough and horny, and the body-wall, which is
very thick and muscular, is often contracted when the animal is
disturbed, thus causing a jet of water to be forcibly ejected.
All the most interesting of the marine worms belong to the _Annelida_ or
_Chætopoda_, popularly known as the Bristle-footed worms, because their
locomotion is aided more or less by the presence of stiff bristles that
project beyond the surface of the skin. These are all highly organised
worms, mostly with very elongated bodies that are distinctly segmented
exteriorly by a number of transverse grooves, while the interior is
correspondingly divided into a number of compartments by means of a
series of _septa_.
In addition to the bristles already mentioned, there are often numerous
appendages, but these must be distinguished from the more perfect
appendages of the arthropods, to be hereafter described; for while the
latter are distinctly jointed to the body, and are themselves made up of
parts that are jointed together, the former are mere outgrowths of the
body-wall. The digestive and circulatory systems are well developed, as
is also the system of water tubes that connect the body-cavity with the
exterior, while the body-cavity itself is full of fluid.
This group of worms is subdivided into two divisions, the many bristled
(_Polychæta_) and the sparsely bristled (_Oligochæta_) worms. The latter
contain the common earthworms and some less known species, while the
former include a number of interesting and even beautiful worms, all of
which are marine, and many of them among the commonest objects of the
sea shore.
These Polychætes exhibit a great variety of habit as well as of
appearance. Some live in crevices of the rocks or under stones and
weeds, or make burrows in the sand or mud of the bed of the sea, and
roam about freely at times in search of food. They are continually
coming within the ken of the sea-side collector, being revealed by
almost every overturned stone near the low-water mark, and are often
seen crawling over the wet rocks just left uncovered by the receding
tide; while their burrows are often so numerous that hundreds may be
counted in every few square feet. But many are sedentary species, and
these are not so generally known to young sea-side naturalists, who
frequently observe, and even preserve, the interesting homes they
construct, while less attention is given to the architects that build
them.
It is very interesting to observe some of the general differences
between the roving and the sedentary species--differences which
illustrate the principle of adaptation of structure to habit. The roving
species are provided with a lobe that overhangs the mouth, bearing
feelers and eyes, and are thus enabled to seek out any desired path and
to search for their food. They are provided with bristles and other
appendages by means of which they can travel freely over the surfaces of
solid objects, and are able to swim well either by undulations of the
body, or by fringed appendages, or both. The carnivorous species, too,
are provided with strong, horny jaws, and sharp, curved teeth, by means
of which they can capture and hold their prey. The sedentary species, on
the other hand, unable to move about in search of food, are supplied
with a number of appendages by means of which they can set up water
currents towards their mouths, and which also serve the purpose of
special breathing organs, and, having no means of pursuing and devouring
animals of any size, they do not possess the horny jaws and curved teeth
so common in the rovers. Their eyes, too, are less perfectly developed,
and the tactile proboscis of their free-moving relatives is absent.
[Illustration: FIG. 117.--_Arenicola piscatorum_]
Of the roving worms, perhaps, the Lugworm or Sandworm (_Arenicola
piscatorum_) is the best known. Its burrows may be seen on almost every
low sandy or muddy shore, and, being so highly valued as a bait, its
general appearance is well known to all professional and amateur sea
fishers. It reaches a length of eight inches or more, and varies in
colour according to the sand or mud in which it lives. The segments of
this worm are very different in structure in different parts of the
body. Those in the front of the body have a few tufts of bristles
arranged in pairs, while the middle portion of the body has large
brush-like tufts of filamentous gills placed rather close together; and
the hindmost part has no bristles or appendages of any kind, and is so
well filled with the sand or mud that it is quite hard and firm to the
touch. As is the case with our common earthworms, the sand or mud is
swallowed in enormous quantities, and this is not only the means by
which the lugworm derives its food, but also assists it considerably in
making its burrows; the extent to which this creature carries on its
work of excavation may be estimated by the thousands of little
contorted, worm-like heaps of sand that lie on the surface at every
period of low water. These little heaps are known as ‘castings,’ and
consist of the sand that passed through the worm’s body as the burrowing
proceeded.
The Ragworm is another species that is highly valued as bait. It burrows
into the odorous mud that is so commonly deposited in harbours and the
mouths of sluggish rivers. In this species the segments are similar
throughout the length of the body, and the numerous flattened appendages
give it the ragged appearance that has suggested its popular name. Quite
a number of marine worms closely allied to the common ragworm, and
resembling it in general form, are to be found on our shores. Many of
these may be seen by turning over stones that are left exposed at low
tide, while others hide themselves in snug little crevices of the rock,
or in the empty shells of the acorn barnacle and various molluscs; and
some species, including one of a bright-green colour, creep freely over
the wet rocks in search of food or home, often exposing themselves to
the rays of a fierce summer sun.
[Illustration: FIG. 118.--THE SEA MOUSE]
The Sea Mouse (_Aphrodita aculeata_) is certainly one of the most
interesting of the roving marine worms, and, though seldom seen above
low-water line, may often be obtained by the sea-side collector with the
aid of friendly fishermen, who sometimes find it plentifully among the
contents of their trawl nets. Failing such aid, it may be looked for
among the encrusted stones that are exposed only at the lowest spring
tides, especially in places where a certain amount of mud has been
deposited under the shelter of outlying rocks; and the chances of
success are much greater if the search is made immediately after a
storm, for at such times much of the life that exists in deep water will
have been driven shoreward by the force of the waves.
At first sight the sea mouse would hardly be associated with the worms;
for, instead of having the elongated and cylindrical form that is
usually regarded as characteristic of these creatures, it is broad and
slug-like in shape, the under surface, on which it crawls, being flat,
while the upper side is convex. The segmentation of the body, too, is
not readily seen in the upper surface on account of the thick felt-like
covering of hairs, but is at once apparent when the creature has been
turned over to expose the ventral side.
When seen for the first time in its natural haunt one naturally wonders
what the moving mass may be. Crawling sluggishly over incrusted stones,
or remaining perfectly still in a muddy puddle that has been exposed by
overturning a stone, it looks like a little mound of mud itself, about
four or five inches long, and its general colour and surface so closely
resembles that of its surroundings that an inexperienced collector may
never even suspect that the mass is a living animal form. But take the
creature and wash it in the nearest rock pool, and it will be recognised
as a broad segmental worm, thickly covered with fine hairs above, and
its sides adorned by bristles that display a most beautiful iridescence.
It is not easy to see the value of this gorgeous colouring to the
animal, and it is doubtful whether, on account of the muddy nature of
the creature’s home, such colouring is often displayed to the view of
other inhabitants of the sea; but it is well known, on the other hand,
that sea mice are readily devoured by fishes, even though they possess
an armature of stiff and sharp spines, and that they must therefore be
often preserved from destruction by the close resemblance of the general
colour to that of their surroundings.
The gills of the sea mouse are not prominent appendages, as with most
marine worms, but are soft fleshy structures situated beneath the
overlapping scales that lie hidden below the thick hair of the upper
surface.
As it is most probable that the reader may desire to preserve a sea
mouse at some time or other, a few words concerning the best methods of
doing this may be of value. If it is to be preserved in fluid, it should
be thoroughly washed to remove all the mud that normally covers its
body, and then placed in spirit or formaldehyde, both of which fluids
have no destructive effects on the iridescent colouring of the bristles.
If, however, it is desired to keep the specimen in a dry state, it
should first be put into strong spirit containing a few grains of
corrosive sublimate, for a few days. It should then be put under
considerable pressure between several thicknesses of absorbent paper to
expel the fluid it contains, as well as all the softer internal
structures. By this means it will have been squeezed quite flat, so that
it presents anything but a natural appearance; but the skin may be blown
out to the normal shape by means of a glass tube inserted into the
mouth, and then set aside to dry. As the water it originally contained
has been extracted by the strong spirit, the drying takes place very
quickly; and the small amount of corrosive sublimate that has penetrated
into its substance will be sufficient to protect it from the invasion of
those pests that commonly attack our museum specimens.
Passing now to the sedentary or fixed worms, we meet with some that are
very interesting and beautiful creatures, even when considered apart
from the wonderful homes they construct. The several species of the
genus _Terebella_ form a soft and flexible tube by binding together
particles of sand, shells, or mud with a sticky substance that exudes
from their own bodies. These tubes are to be found in abundance between
the tide-marks on almost every low, sandy shore, the nature of the tubes
varying, of course, with the character of the materials at the disposal
of the builder.
In some cases the tubes are exposed throughout the greater part of their
length, but very frequently they are more or less buried in the sand or
other material of the beach, so that one has to dig to a moderate depth
in order to extricate them. In either case, however, the tube of
Terebella may be known by the free tufts of sandy threads that form a
deep fringe around its mouth.
These worms almost invariably select a sheltered situation for their
abode, and should be searched for at the foot of rocks, or under stones,
and it is no easy matter to move the buried tube with its occupant
intact.
When turning over the stones of a sandy or muddy beach one frequently
discovers the slender, thread-like tentacles of the Terebella, together
with the sandy filaments that surround the mouth of the tube, the
remainder of the tube and its occupant being beneath the surface, and
the ground is often so hard and stony that a strong tool is necessary
to dig it out; but the work entailed will be amply repaid if a perfect
specimen be obtained and placed for observation in the aquarium.
[Illustration: FIG. 119.--TUBE-BUILDING WORMS: _Terebella_ (LEFT),
_Serpula_ (MIDDLE), _Sabella_ (RIGHT)]
The reader may possibly be acquainted with the tubes or cases that are
constructed by the larvæ of caddis flies in fresh-water ponds and
streams, and perhaps has noticed the ease with which these creatures may
be made to construct new homes after having been turned out of doors.
Similar experiments may be performed with Terebella; for when the worm
has been extricated from its tube without injury--a work that requires
great care on account of the soft and slender nature of the creature’s
body--and placed in the aquarium with a bed of suitable material, it
will build itself a new dwelling. As with the caddis larvæ, the
different species may be known by the materials they select to construct
their tubes, but in captivity they may be compelled to employ other than
their favourite substance for this purpose. It is unfortunate, however,
that Terebella is a nocturnal builder, and thus its movements are not so
easily observed.
When removed from its tube its first movements suggest a resentment at
the untimely ejection. This being over, it seeks a sheltered situation
beneath the edge of a stone, and, at nightfall, commences the slow
process of the construction of a fresh home. The particles of material
at hand are seized by the tentacles, placed in position round the body,
where they are held together by the sticky secretion already mentioned.
[Illustration: FIG. 120.--_Terebella_ REMOVED FROM ITS TUBE]
The tentacles are employed in two distinct ways:--They may be flattened
into slender ribbon-like structures, which, by being folded
longitudinally at any point, may be made to grasp a particle of sand;
and, in addition to this, the tip of the tentacle may be converted into
a minute cup-shaped sucker by the withdrawal of the fluid it contains
into the body.
Some species of Terebella build their tubes of ordinary sand, while
others select fragments of shells. Some employ mud only, and
occasionally we meet with tubes constructed of the silky secretion of
the body with hardly any foreign matter.
We sometimes see edges of rocks, on low, sandy shores, covered with what
appears to be large masses of consolidated sand, full of holes a little
more than an eighth of an inch in diameter; and these masses are often
so extensive and so firm that they seem to form the greater part of the
rock itself. Such masses are particularly abundant on the south coasts
of Devon and Cornwall, but are more or less plentiful on most sandy
shores of Great Britain. They consist of the tubes of a species of the
marine worm _Sabella_, which have been built up much in the same manner
as those of Terebella, but usually exist in such numbers in the same
spot that, together with the sand that has been washed between them,
they form the dense masses just described.
A cluster of some dozens of these tubes may be detached with the aid of
a hammer and chisel; or, in some instances, where the mass of tubes is
not held so firmly together, by the mere pressure of the hand; and it
will then be observed that each tube consists of a flexible membrane, of
a somewhat leathery nature, formed by a sticky secretion from the body
of the worm, with its outer surface covered with grains of sand. The
tubes may be easily opened, and the occupants extracted for examination,
when it will be observed that the front or upper portion of the worm is
short and thick, while the hindmost portion is much thinner, and is
doubled forwards in the tube. The body is also provided with numerous
bristles, by means of which the worm is enabled to grasp the membranous
lining of the tube, and thus secure a firm hold within its home.
A cluster of these tubes should be placed in a rock pool, or in the
marine aquarium, when the worms may be seen to protrude gradually, and
expose a large number of feathered tentacles, which, by their incessant
motion, keep up the constant circulation of the water for the purpose of
respiration as well as to bring food particles towards the mouths of the
worms.
It is possible to keep these worms alive for some time in the aquarium,
but special care is required for the reason that it is a very difficult
matter to secure a cluster of tubes without injury to a certain number
which are sure to be broken or otherwise damaged; and these, dying and
decomposing within their homes, speedily pollute the water. Hence it is
necessary to keep a sharp watch for dead specimens, which should, of
course, be removed at once. The presence of a putrefying worm may often
be detected by the appearance of a whitish fungoid growth round the
mouth of what appears to be an empty tube; and if, through neglect, the
water of the aquarium has been allowed to become contaminated by the
products of decomposition, it will often happen that some of the living
worms will come entirely out from their tubes, as if to seek a more
sanitary situation. Thus, the exit of worms from their homes may always
be looked upon as pointing to a suspicious condition of the water which,
if not corrected immediately, may lead to the death of all.
The species we have briefly described is by far the commonest of the
genus Sabella, but there are several others to be found on our shores.
Some are of a solitary nature, and construct a sandy tube so much like
that of a certain species of Terebella that they may be mistaken for
that genus. Another solitary species builds a hard stony tube of
carbonate of lime that has been extracted from the sea water; and
although it is hardly possible to take the live worm from this
calcareous tube without injury, the animal may be obtained intact for
examination or preservation by dissolving away the tube in dilute
hydrochloric acid.
[Illustration: FIG. 121.--A TUBE OF _Serpula_ ATTACHED TO A SHELL]
While engaged in collecting specimens on the sea shore we are
continually meeting with stones and shells that are more or less covered
with white, limy tubes twisted into all manner of serpentine forms.
These are the tubes of other marine worms known as the _Serpulæ_, which,
like the species previously mentioned, are interesting objects for the
aquarium.
The tubes themselves are worthy of study and preservation, more
especially as they vary in form, and may, to some extent, provide a
means by which the different species may be identified. They are
composed of fine layers of calcareous matter secreted by the body of the
worm within, and lined by a thin leathery membrane which may be easily
exposed by dissolving away the mineral matter as just described. Some
are triangular in section, and often distinctly keeled, while others are
cylindrical, and flattened more or less on the lower side. The
triangular tubes are attached to stones or shells throughout their
length, but the cylindrical ones are often elevated above the surface in
the wider and newer part.
If a cluster of these tubes, freshly gathered from between the
tide-marks, be placed in the aquarium, the worms will soon protrude the
foremost portion of their bodies, exposing beautiful fan-like gills,
often brilliantly coloured in shades of scarlet, blue, or purple, which
are kept in motion in such a manner as to convey water, and consequently
also food, towards the mouth. The gills are of course, richly supplied
with blood, for their main function is to aërate that liquid by exposing
it to the water in order to absorb oxygen gas. The body of the worm is
provided also with little cilia, which, by their constant vibratory
motion, keep up a circulation of water through the tube; and this not
only keeps the tubular home free from excrement and other sedimentary
matter, but also probably assists in the function of respiration by
bringing fresh supplies of water in contact with the animal’s soft and
absorbent skin.
[Illustration: FIG. 122.--_Serpula_ REMOVED FROM ITS TUBE]
When the worms are disturbed they immediately withdraw themselves within
the tubes, this being done by the aid of the numerous minute hooklets on
the surface of the body that enable the worms to cling firmly to the
membranous linings of their homes; and it will then be observed that the
mouth of each tube is closed by a lid (_operculum_), which hangs as by a
hinge when not in use. These operculi vary much in character, and supply
another aid in the identification of the various species. They differ
much in shape, and may be either membranous, horny, or calcareous.
Little calcareous tubes, somewhat similar to those of the _Serpulæ_, but
always in the form of a spiral, may often be seen on stones and shells,
and the fronds of sea weeds, sometimes so closely packed together as to
almost entirely cover the surface. The average diameter of these spirals
is only about a sixteenth of an inch, and many are so small that a lens
is necessary to discern their shape. In general form they closely
resemble some of the small species of _Planorbis_ shells that are so
common in our ponds and streams, but these latter are the shells of
freely moving _molluscs_, and are generally of a brownish colour.
[Illustration: FIG. 123.--THE SEA MAT (_Flustra_)]
The minute worms that live within the tubes in question belong to the
genus _Spirorbis_, and are very similar to those of the _Serpulæ_, and
their pretty plumed gills may be seen with a lens when a cluster of the
tubes is placed in a shallow vessel of sea water. A sharp tap on the
table on which the vessel rests will cause the little creatures to
suddenly retire into their homes, the entrances to which may then be
seen to be closed by an operculum.
There is an interesting group of animals known collectively as the
_Bryozoa_ or _Polyzoa_, or, popularly, as the Moss Polyps, that are
often classed with the worms, though they are not, according to the
general idea, wormlike in appearance. They live in pretty colonies, many
of which are certainly familiar objects to all who ramble along the sea
shore. Some form pretty lacelike patches on the fronds of sea weeds,
while others are built up into flat, frond-like, branching objects that
are often mistaken for sea weeds by young collectors. Among the latter
is the Sea Mat (_Flustra_), that is so commonly washed up on the shore
in great abundance. An examination with a lens will show that, in both
instances, the mass consists of very many minute cells, with horny or
calcareous walls, the mouth of each cell being close by an operculum.
On placing the colony in sea water, however, we find that each little
cell is the home of a small animal, that protrudes from the cell,
exposing a mouth that is surrounded by a crown of tentacles. A
moderately high magnifying power will also show that the tentacles are
covered with minute vibratile cilia, by means of which currents of water
are set in motion towards the mouth to supply the animal with food.
Some, too, have a lip by means of which the mouth may be closed.
[Illustration: FIG. 124.--_Flustra_ IN ITS CELL, MAGNIFIED]
In addition to the colonies just briefly described, there are other moss
polyps that build up little, branching, tree-like clusters which closely
resemble some of the sea firs, and many of these are to be found in the
sheltered crevices of rocks, or attached to the under sides of stones
between the tide-marks.
While searching the surfaces of rocks and weeds at low tide, one’s
fingers will be constantly coming in contact with fixed, soft-bodied
animals that suddenly eject a fine stream of water as they are touched.
These are the Sea Squirts, sometimes spoken of as the Tunicate Worms.
They are semi-transparent creatures of oval or elongated form, and
usually of a pale yellow, brown, or pink colour; and derive their
popular name from the fact that they are covered externally by a
continuous tunic or wall of tough structure.
Although the tunicates resemble worms in many points of structure, it is
interesting to note that in their young or larval state the body
consists of two cavities, one of which contains the internal organs,
while in the other the central portion of the nervous system is
developed, in which respects they resemble the vertebrate or back-boned
animals--fishes, amphibians, reptiles, birds, and mammals. At this
stage, too, the creatures possess a tail that is supported by a rod of
gristle similar to that which gives place to the backbone in the
developing vertebrate. These features, though only transitory, are
regarded as a mark of relationship to the higher forms of animal life,
and thus the tunicates have been separated from the sub-kingdom Vermes
by some zoologists, and given an exalted place at the top of the
invertebrate scale, where they form a sub-kingdom of their own, and are
looked upon as a link connecting the invertebrates with the vertebrates.
[Illustration: FIG. 125.--SEA SQUIRT]
Before passing on to the next sub-kingdom, we should observe that the
interesting Rotifers or Wheel Animals also belong to the Vermes; but
although many of these minute creatures are to be found in sea water,
their principal home is the stagnant water of fresh-water ponds and
ditches, and thus we may be excused for neglecting them here.
CHAPTER XII
_MARINE MOLLUSCS_
The sub-kingdom _Mollusca_ includes a great variety of soft-bodied
animals which differ from the members of the last division in the fact
that they are never segmented, and in the possession of a thick outer
covering, of a leathery nature, which completely envelops the body, and
which usually secretes a calcareous shell of one or more parts. A
general idea of the extent of the group may be formed when we state that
it contains the Octopus and the Cuttlefish; all Snails and Slugs, and
animals of a similar nature; and all those numerous ‘bivalves’ which are
represented by the well-known Oysters, Mussels, Scallops, &c.
By far the greater number of the molluscs are aquatic in habit; and of
these such a large proportion are marine that the group provides plenty
of occupation for the sea-side naturalist. This being the case, we shall
devote the present chapter to a description of the general
characteristics of these animals, and to the principles of their
classification, illustrating our remarks by a few selections from all
the chief divisions.
Although, as we have already hinted, the body of a mollusc generally
bears but little resemblance to that of the typical elongated and
segmented worm, yet the study of the earliest stages of the former shows
that a certain relationship exists between the two sub-kingdoms, the
newly hatched mollusc being often a minute free-swimming creature with
expanded lobes fringed with cilia, and bearing a resemblance to certain
of the Rotifers, Moss Polyps, and other animals that are included among
the _Vermes_. But in the adult molluscs this resemblance is lost, these
creatures being generally easily distinguished from all others by
certain well-marked external features, as well as by internal characters
that are peculiar to them and fairly constant throughout the group.
The external shell, where it exists, is usually composed of one or of
two parts, and therefore we speak of univalve and bivalve molluscs; and
no internal skeleton of any kind is to be found except in the division
containing the Cuttlefishes, the ‘bone’ of which is one of the common
objects washed up on our shores by the breakers.
In all the molluscs there is a well-formed digestive tube, and often a
complex arrangement of small teeth which sever the food by a rasp-like
action. There is also a well-formed heart, consisting of two or more
cavities, by means of which the blood is forced through the body; but,
as a rule, blood vessels are either few or absent, the blood being
driven through spaces between the tissues that serve the same purpose.
[Illustration: FIG. 126.--LARVÆ OF MOLLUSCS
_v_, ciliated ‘velum’; _f_, rudimental foot]
The nervous system consists of a few masses of nerve substance
(_ganglia_), connected by nerve cords, and sending off fibres to various
parts of the body, the principal ganglion being one situated close to
the mouth, and often surrounding the first portion of the digestive
tube.
The animals of this sub-kingdom are grouped into three principal and
well-marked divisions--the _Lamellibranchs_, or Plate-gilled molluscs,
the gills of which are composed of plate-like layers, and the headless
bodies enclosed in a bivalve shell; the _Cephalophora_, or head-bearing
molluscs, protected by a univalve shell; and the _Cephalopoda_, or
Head-footed molluscs, so called because the mouth is surrounded by
tentacles or arms by which the animal can cling to objects or seize its
prey.
We shall deal with these three divisions in the above order, taking
first the bivalves, the shells of which are found in great variety along
our shores.
The general nature of a lamellibranch is easily made out by the
examination of one of the common species that may be obtained alive on
any part of the coast, such as the Edible Mussel, the Cockle, or the
Oyster, and the reader will do well to secure a few specimens and
examine them with the aid of the following description of the principal
distinguishing features.
The shell is formed of two valves, united by a hinge which is sometimes
of the simplest possible description, but which often exhibits a
beautiful arrangement of interlocking teeth. A _ligament_ of flexible
and elastic substance often holds the two valves together.
[Illustration: FIG. 127.--SHELL OF THE PRICKLY COCKLE (_Cardium
aculeatum_) SHOWING UMBO AND HINGE; ALSO THE INTERIOR SHOWING THE
TEETH]
The reader has probably observed that the valves of a dead lamellibranch
usually gape. This is due either to the pull exerted by a ligament that
is attached to the valves outside the hinge, or to the pressure of an
internal cartilage which unites the valves within, and which is
compressed when the shell is closed. When the animal is alive, it has
the power of closing its shell by the contraction of the adductor
muscles, to be presently described, and when the valves are brought
together by this means the external ligament is more or less stretched,
or the cartilage within, which is also an elastic material, is
compressed.
Examining the shell from the exterior we observe that each valve has a
nucleus (the _umbo_) close to the hinge, round which are usually a
number of more or less distinct concentric lines, extending to the lower
or ventral margin. This nucleus represents the whole shell of the young
mollusc, and the lines are the lines of growth, each one marking the
extreme limit of the valve at a particular period of the animal’s
existence. Further it will be observed that the lines of growth are
often wider apart in some directions than in others, thus denoting the
unequal rate of growth that determined the form of the adult shell.
[Illustration: FIG. 128.--INTERIOR OF BIVALVE SHELL, SHOWING MUSCULAR
SCARS AND PALLIAL LINE]
The shell of a bivalve is often made up of two very distinct layers, the
outer one called the prismatic layer because, when examined
microscopically, it is seen to consist of minute vertical prisms of
calcareous matter; and the inner one presenting a beautiful pearly
iridescence, due to the fact that it is made up of a number of extremely
thin and finely waved layers of calcareous substance that have the power
of decomposing light. This latter layer is secreted by the whole surface
of the mantle that lies in contact with it, while the outer, prismatic
portion of the shell is formed only by the free edge of the mantle; and
we often find a distinct line (the _pallial line_), some little distance
from the ventral margin that marks the junction of the muscle of the
mantle with the shell. The shape of this line is a very important
feature of the shell, since it is of great value in the determination of
relationships.
Further, the inner surface of each valve is marked by the impressions or
scars of other muscles, the number and position of which vary
considerably in different species. They include the _adductor_ muscle or
muscles (one or two in number) that pull the valve together; the muscle
or muscles that withdraw the foot, called the _retractor pedis_, and the
_protractor pedis_ that pulls the foot out. Not only are these scars
often very distinct in themselves, but we may frequently observe lines
running tangentially from their circumferences towards the umbo, to
which they all converge. These lines enclose the areas previously
occupied by the muscular impressions; in other words, they show the
directions in which the muscles named above shifted their positions as
the animal grew.
[Illustration: FIG. 129.--DIAGRAM OF THE ANATOMY OF A LAMELLIBRANCH
_f_, mouth, with labial palps; _g_, stomach; _i_, intestine,
surrounded by the liver; _a_, anus; _r_, posterior adductor muscle;
_e_, anterior adductor muscle; _c_, heart; _d_, nerve ganglion;
_m_, mantle (the right lobe has been removed); _s_, siphons; _h_,
gills; _ft_, foot]
Now let us obtain a few species of live lamellibranchs, put them in a
vessel of sea water, and observe them after they have been left
undisturbed for a time. The shell will be seen to gape slightly,
exposing the edges of the two lobes of the mantle which lie closely on
the inner surface of the valves, thus completely enveloping the body of
the animal; and at one end, usually the narrower end in the case of
irregular shells, we shall observe two openings--the _siphons_,
sometimes enclosed within a tube formed by a prolongation of the united
mantle lobes, and protruding from between the valves, and sometimes
formed by the mere contact of the mantle lobes at two adjacent points.
If now we introduce a little carmine or other colouring matter by means
of a glass tube, setting it free near the lower siphon--the one more
remote from the umbo of the shell, we observe that it enters the body of
the mollusc through this opening, and reappears shortly afterwards
through the upper or dorsal siphon. Thus we see that water currents are
incessantly circulating in the body of the animal, entering by the
_inhalent_ or _ventral siphon_, and leaving by the _exhalent_ or _dorsal
siphon_. These currents are maintained by the vibratile action of
thousands of minute cilia belonging to cells that line the cavities of
the body, and serve to supply the animal with both air and food; for
lamellibranchs, being gill-breathers, derive the oxygen necessary for
respiration from the air held in solution by the water, and their food
consists entirely of the minute living creatures that always abound in
natural waters.
Again, we shall find that some of our live bivalves have protruded a
thick, conical, fleshy mass--the _foot_, from the opposite end of the
body. This organ is the means of locomotion in the case of the burrowing
and other free-moving bivalves, but is developed to a less extent in
those species that lead a sedentary life. Thus, the common Edible Mussel
secretes a tuft of strong silky fibres (_byssus_) by means of which it
fixes itself to a rock or other body, and therefore does not need the
assistance of a muscular foot; and an examination of its body will show
that the foot is very small in proportion to the size of the animal, as
compared with that of the wandering and burrowing species. The same is
true of the oyster, which lies fixed on its side, the lower valve being
attached to the surface on which it rests.
[Illustration: FIG. 130.--_Mytilus edulis_, WITH BYSSUS]
We have made use of the terms _dorsal_ and _ventral_ in speaking of the
shell of a bivalve, and it is important that these and a few other
similar terms be well understood by those who are about to read the
descriptions of the animals, or who may desire to describe them
themselves. To do this, take a bivalve in your hand, and hold it before
you in such a position that the hinge is uppermost, and the siphons
turned towards you. The foot of the animal is now pointing in the
direction you are looking, and the mouth, situated at the base of the
foot, is also directed the same way. You have now placed the shell, and,
of course, also the animal, in such a position that its _dorsal_ side is
uppermost, the _ventral_ side below, the _anterior_ end turned from you,
the _posterior_ (often narrower) end towards you, the _right valve_ on
your right, and the _left valve_ on your left. Knowing the exact uses of
these few terms you are in a better position to understand the
descriptions of bivalves, and to locate the exact situations of the
various internal organs named in such descriptions.
A great deal of the internal anatomy of a bivalve mollusc may be made
out by easy dissections, and although the structure of the different
species varies in several details, the general characteristics of the
group are practically the same in all and may be gathered by the
examination of a few specimens.
[Illustration: FIG. 131.--A BIVALVE SHELL (_Tapes virgineana_)
_a_, anterior; _p_, posterior; _l_, left valve; _r_, right valve;
_u_, umbo, on dorsal side]
For this purpose the shell should be prised open by means of some
flattened but blunt implement, such as the handle of a scalpel, and
then, after inserting a piece of cork to keep the valves apart, gently
remove the mantle lobe from the valve which is held uppermost with the
same implement, being careful to separate it from the shell without
doing any damage to the soft structures. Separating the mantle from the
shell in this way we meet with one or more hard masses of muscle that
are joined very firmly to the latter. These are the adductor muscles
that pass directly from valve to valve, and on cutting them through
close to the uppermost valve, the latter can be raised so as to expose
the body of the animal, mostly hidden by the overlying mantle lobe.
Before raising the upper mantle lobe we observe the heart, on the dorsal
margin of the body, near the hinge of the shell, situated in a
transparent cavity (the _pericardium_) containing a colourless fluid. It
consists of at least two cavities--a thick-walled ventricle and a
thin-walled auricle, and its slow pulsations may be watched with or
without the use of a hand lens. On opening the pericardium the heart is
still better seen, and if we carefully cut into the thick-walled
ventricle we find a tube running completely through its cavity. This is
the _rectum_--the last part of the digestive tube, that commences at the
mouth, and terminates in a cavity at the posterior end communicating
with the exhalent siphon.
After noting the nature and position of the one or two adductor muscles
previously cut through, we turn the upper mantle lobe upwards, laying
it back over the hinge of the shell, cutting it through at the bases of
the siphons if we find it is united with the opposite lobe at those
points; or, if not united, we observe two points at which the lobes
touch each other in order to form the siphonal openings.
Several organs are now exposed to view. The lower mantle lobe is seen in
close contact with the valve below it, and if we touch its edge we shall
probably observe that it is retracted slightly by the contraction of its
own muscular fibres. The tip of the foot is also seen projecting towards
the anterior end, its base being hidden between the two sets of
plate-like gills that extend along the length of the body. On touching
the tip of the foot we find it retract by the contraction of the
muscular fibres of which it is composed, aided, perhaps, by the action
of one or more _retractor pedis muscles_ with which it is supplied. On
raising the upper gill-plates we may observe the dark colour of the
digestive gland (liver) at the base of the foot, and also see two or
more _tentacles_ or _labial palpi_ on the anterior side of the same.
Between the labial palpi is the mouth, which leads into the stomach by a
short, wide tube, and then into a convoluted tube which finally passes
through the heart, and terminates near the exhalent siphon as above
described. The whole length of this tube may be followed by careful
dissection, its direction being determined at short intervals by probing
it with a bristle that has been tipped with a little melted sealing wax.
It will be seen to wind through the base of the foot, surrounded through
the greater part of its course by the digestive gland, from which a
digestive fluid enters it through small ducts.
The diagram on p. 194 shows the general internal anatomy of a
lamellibranch, parts of which have been removed to reveal the underlying
structures. The animal lies in its left valve, the right valve, the
right mantle lobe, and the right set of gill-plates having been
completely dissected away. The whole course of the digestive tube has
also been exposed, and the positions of the three nerve ganglia, with
their connecting nerve cords, constituting the central portion of the
nervous system, are also indicated.
It will be interesting, finally, to learn the direction taken by the
water currents which supply the animal with air and food in their course
through the system. Passing in through the inhalent siphon, the water
immediately enters a large cavity between the mantle lobes. This cavity
(the _branchial cavity_) contains gills, as we have already seen, and
also extends to the mouth. The water, urged on by the motion of myriads
of minute ciliated cells in the walls of the cavity, passes in part
through the digestive tube, and in part around, between, and through the
gill plates, which are perforated by numerous holes. After thus
completely bathing the gills, and supplying the oxygen necessary for
respiration, this latter current passes into a second cavity above the
gills, and thence into the exhalent siphon, where it mingles with the
fluid from the digestive tube as well as with other excretory matter.
Lamellibranchs are, as a rule, exceedingly prolific, a single individual
of some species discharging more than a million ova in one season. The
larvæ swim freely in the water, and are provided with eyes that enable
them to search for their food, but the eyes always disappear when the
young settle down to a more sedentary life. It is true that adult
bivalves sometimes possess visual organs, often in the form of
conspicuous coloured spots on the edge of the mantle, these, however,
are not the same that existed during the larval stage, but are of a more
recent development.
Lamellibranchs are classified in various ways by different authorities,
the arrangement being based principally on the number and position of
the adductor muscles, or on the nature of the gills. For our present
purpose we shall look upon them as consisting of two main divisions--the
_Asiphonida_ and the _Siphonida_, the former including those species
which do not possess true tubular siphons, the inhalent and exhalent
openings being formed merely by the touching of the mantle lobes; and
the latter those in which the mantle lobes are more or less united and
tubular siphons formed. Each of these divisions contains a number of
families, most of which have representatives that inhabit the sea; and
we shall now note the principal characteristics by which the more
important families are distinguished, and take a few examples of each,
starting with the _Siphonida_.
Examining the rocks that are left exposed at low tide we frequently find
them drilled with holes that run vertically from the surface, seldom
communicating with each other within, and varying in diameter from less
than a quarter of an inch to half an inch or more. Some of these holes
are the empty burrows of a boring mollusc, while others still contain
the living animal _in situ_.
The molluscs in question belong to the family _Pholadidæ_, which
contains a number of species that exhibit very remarkable features both
as regards structure and habit. The shell is very thin and fragile, but
yet composed of hard material, and its surface is relieved by a series
of prominent concentric ridges that bear a number of little rasp-like
teeth. It gapes at both ends, has neither true hinge nor ligament, and
is often strengthened externally by two or more extra or accessory
valves. The _hinge-plate_ is a very peculiar structure, for it is
reflected over the exterior of the umbones, above which they are
supported by about ten thin shelly plates, the whole thus forming a
series of chambers. The accessory valves are supported by these bridged
structures, and a long, straight, calcareous plate also fills the space
along the dorsal side of the shell in some species. The muscular scars
and the pallial line are distinctly seen on the inner surface, and a
peculiar curved shelly plate projects from under the umbo of each valve.
[Illustration: FIG. 132.--_Pholas dactylus_
1, ventral aspect, with animal; 2, dorsal side of shell showing
accessory valves]
The animal inhabiting the shell is somewhat wormlike in general form,
and the mantle lobes are united in front--that is at the lower end of
the shell as it lies in the burrow--except that an opening is left for
the protrusion of the short foot. The siphons are united and much
elongated, so that they protrude beyond the mouth of the burrow when the
animal is active; the gills are narrow, and extend into the exhalent
siphon; and the anterior adductor muscle, being very near the umbones,
serves the double purpose of adductor and ligament.
Such are the general distinguishing features of this family, all the
species of which burrow into stone or other material. Those more
commonly met with on our coasts belong principally to the genus
_Pholas_, and are popularly known as Piddocks.
It was long a puzzle as to how the fragile piddocks could excavate the
tubular burrows in which they live, and, since their shells are so thin
that it seemed almost impossible for hard stones to be ground away by
them, it was suggested that the rocks were excavated by the action of an
acid secretion. This, however, would not account for the formation of
holes in sandstone and other materials which are insoluble in acids;
and, as a matter of fact, no such acid secretion has ever been
discovered. The boring is undoubtedly done by the mechanical action of
the rasp-like shell, which is rotated backwards and forwards, somewhat
after the manner of a brad-awl, though very slowly, by the muscular
action of the foot of the animal.
Piddocks are found principally in chalk and limestones, though, as
before hinted, they are to be seen in sandstones and other rocks, the
material in any case being, of course, softer than the shell that bores
it. The largest holes and the largest specimens are to be found in chalk
and other soft rocks; while the piddocks that burrow into harder
material are unable to excavate to the same extent and are, as a
consequence, more stunted in their growth. The burrowing is continued as
long as the animal grows, the hole being always kept at such a depth
that the shell is completely enclosed; and not only this, for when the
rock is soft, and the surface is worn down by the sea, the piddock has
to keep pace with this action, as well as to allow for its increase in
size.
As a result of the rasping action of the pholas shell on the surrounding
rock the space hollowed out becomes more or less clogged with débris.
This is ejected at intervals by the sudden contraction of the foot of
the animal, which brings the shell quite to the bottom of the burrow,
thus causing the water with its sediment to shoot upwards,
It is not usually an easy matter to obtain perfect specimens of the
pholas by simply pulling them from their burrows, the shells being so
thin and fragile, and the mouth of the burrow being often narrower than
the widest part of the shell. The best plan is to chip away the rock
with the aid of a mallet and chisel, or to break it into pieces with a
hammer, thus laying open the burrows so that the molluscs fall from
their places.
The Common Piddock (_Pholas dactylus_) may be identified by the
illustrations, and the other members of the family may be recognised at
once by the similarity in structure and habit. The principal species are
the Little Piddock (_P. parva_), the shell of which is wider in
proportion to the length, with only one accessory valve; and the White
Piddock (_P. candida_), also with a single accessory. In all the above
the foot is remarkable for its ice-like transparency.
[Illustration: FIG. 133.--_Pholas dactylus_, INTERIOR OF VALVE; AND
_Pholadidea_ WITH ANIMAL]
There is another genus--the _Pholadidea_--the species of which are very
similar to _pholas_ both in structure and habit. The shells are,
however, more globular in form, and are marked by a transverse furrow.
The gape at the anterior (lower) end is also very wide, and covered over
with a hardened plate in the adult. Also, at the posterior (upper) end
of the shell is a horny cup through which the siphons protrude, and the
latter, which are combined throughout their length, terminate in a disc
that is surrounded by a fringe of little radiating appendages.
In the same family are the molluscs popularly known as ship worms, which
are so destructive to the woodwork of piers and jetties, or which burrow
into masses of floating timber. Some of these, belonging to the genus
_Xylophaga_--a word that signifies ‘wood eaters’--have globular shells
with a wide gape in front, and burrow into floating wood, nearly always
in a direction across the grain. The burrows are about an inch deep, and
are lined with a calcareous deposit. The siphons, combined except at the
ends, are slender and retractile; and the foot, which is thick, is
capable of considerable extension.
[Illustration: FIG. 134.--THE SHIP WORM]
[Illustration: FIG. 135.--1. _Teredo navalis._ 2. _Teredo norvegica_]
Other ship worms belong to the genus _Teredo_, and are very similar in
general characters. The shell is small and globular, with a wide gape at
both ends, and consists of two three-lobed valves with concentric
furrows. It is so small in proportion to the size of the animal that it
encloses but a small portion of the body, and lies at the bottom of the
burrow, which is of considerable length--often from one to two feet. The
animal is very wormlike in form; and although the shell is so small, yet
all the internal organs are enclosed by it. The mantle lobes are united
in front, except where the sucker-like foot passes through them; the
gills are long and narrow, and extend into the siphonal tube; and the
two very long siphons are united almost throughout their length. It is
also interesting to note that in these animals the rectum does not pass
through the heart, as it does in nearly all molluscs, and that a pair of
horny or calcareous 'styles' or 'pallets' project from the place where
the two siphonal tubes begin to diverge.
Several species of _Teredo_ are to be met with on our coasts, but they
are so similar in general structure that the above brief description
applies almost equally well to all.
Other boring molluscs frequent the British shores, but they belong to
quite a distinct family called the _Gastrochænidæ_ because their shells
gape widely on the ventral side. Their valves are equal in size and very
thin, the hinge has no teeth and the pallial line is sinuated. The
margins of the mantle lobes are thickened and united except where a
small aperture is left for the protrusion of the finger-like foot. The
siphons are very long and retractile, and the gills extend into the
inhalent tube. These animals burrow into mud, shells, or stone, often
dwelling together in such numbers that their galleries cross one another
and form a most intricate network, and the different species are to be
found from low-water mark to a depth of a hundred fathoms or more.
[Illustration: FIG. 136.--_Gastrochæna modiolina_
1, Animal in shell; 2, shell; 3, cell]
The British species belong to two genera--the typical genus
_Gastrochæna_, and the _Saxicava_ or stone-borers.
The former contains the Common Flask shell (_G. modiolina_) which
burrows into limestone and shells, in the latter case passing generally
through the shells into the ground below, and completing its home by
cementing together any fragments of hard material that come in its way
into a flask-shaped cell. The opening of the burrow is shaped like an
hour-glass, the two expansions serving for the protrusion of the
siphonal tubes, and the neck of the flask-shaped abode is usually
lined with a calcareous layer that projects slightly to afford further
protection to the extended siphons. Although this species is very common
on some parts of our coast, it is seldom obtained without the aid of a
dredge, for it usually lives at a depth of from five to ten fathoms; and
when found it is generally no easy matter to extricate them from their
holes, to the sides of which they often cement their shells.
The genus _Saxicava_ contains a few species that drill holes, often
several inches deep, in shells and stone, and frequently do great damage
to breakwaters and other artificial structures. The foot is usually
provided with a byssus by which the animal fixes itself to a little
projection on the side of its burrow. The species are to be found from
low-water mark to a depth of one hundred fathoms or more.
The next family, named _Anatinidæ_, contains a number of molluscs that
burrow in mud or sand or live in seclusion in the crevices of rocks.
Their shells are thin, with a granulated outer surface, and the valves
are united by a thin external ligament. The inner surface is pearly, the
pallial line usually sinuated, and both valves are pitted for the
reception of the somewhat stout internal cartilage. The mantle lobes are
united, as are also the siphons to a greater or lesser extent; and there
is only one gill on each side.
[Illustration: FIG. 137.--1. _Thracia phaseolina._ 2. _Thracia
pubescens_, SHOWING PALLIAL LINE]
Some of the common species of this family are popularly known as Lantern
shells, and perhaps the most familiar of these is _Thracia phaseolina_,
the specific name of which is given on account of a fancied resemblance
of the shell to a bean. The shell is very fragile, and although large
numbers may often be seen stranded on sandy beaches, but few of them are
perfect specimens.
The family _Myacidæ_ may be recognised by the thick, strong, opaque
shells, usually gaping at the posterior end; the wrinkled epidermis
which covers the whole or part of the shell; and the united siphons,
which are more or less retractile. The mantle cavity is also closed with
the exception of a small hole left for the protrusion of the small foot.
The pallial line of the shell is sinuated.
[Illustration: FIG. 138.--1. _Mya truncata._ 2. INTERIOR OF SHELL.
3. _Mya arenaria._ 4. _Corbula nucleus_]
In the above illustration we represent the Common Gaper (_Mya
arenaria_), which burrows to a considerable depth in the sand or mud,
especially in the estuaries of rivers, from between the tide-marks to a
depth of twenty fathoms or more. It may be readily distinguished, in
common with the other species of the same genus, by the characteristic
wrinkled, membranous tube that encloses its fringed siphons, the
membrane being a continuation of the epidermis that extends over the
shell. Another characteristic feature of the genus is the large, flat
process inside the left valve for the attachment of the internal
cartilage. An allied species, _Mya truncata_, is often found abundantly
in company with the above, and may be known by the abruptly squared
posterior end.
Other species of the _Myacidæ_ inhabit our shores, including the little
Basket shell (_Corbula nucleus_), the left valve of which is much
smaller than the right, which overlaps it. The latter, also, is covered
with epidermis, while the former, which is flat, is quite naked.
[Illustration: FIG. 139.--_Solen siliqua_
The valves have been separated and the mantle divided to expose the
large foot]
We now come to the interesting family of Razor shells (_Solenidæ_),
specimens of which are washed up on almost every sandy beach, while the
living molluscs may be dug out of their burrows at low-water mark. The
shells are elongated, gaping at both ends with an external ligament; and
the hinge has usually two teeth in one valve and three in the other. The
foot of the animal is cylindrical, large and powerful; and the siphons
are short and united in the long species, but longer and only partially
united in the shorter ones. The gills are long and narrow, and are
prolonged into the inhalent siphon.
These molluscs lie vertically in their deep burrows at low-water mark,
the opening of the burrow having a form resembling that of a keyhole.
While covered with water they occupy the upper portion of their abode,
but sink to a depth of a foot or more when the tide goes out. As we walk
along the water’s edge at extreme low tide we may observe jets of water
that are shot into the air before us. These are produced by the sudden
retreat of the ‘Razor-fish’ to the bottom of its burrow when alarmed by
the approaching footsteps. Owing to this wariness on the part of the
mollusc, and to the considerable depth of its burrow, specimens cannot
be obtained by digging without much labour; but if a little salt or some
other irritant be dropped into the hole, the animal will soon rise to
eject it, and may then be shut out from the lower part of the burrow by
sharply driving a spade below it. This is undoubtedly the best method of
securing perfect specimens for study or preservation, but fishermen
often obtain large numbers, either for food or for bait, by suddenly
thrusting a long hook down into the gaping shells, and then pulling them
out. This method always does injury to the soft body of the animal, and
often damages the shell, but answers the fisherman’s purpose exactly.
We give illustrations of two shells belonging to the typical genus
(_Solen_), including one on Plate V.; also a British representative of
each of two other genera of the family--_Cerati-solen_ and _Solecurtus_,
the latter of which, as the name implies, contains shorter species.
[Illustration: FIG. 140.--1. _Solen ensis._ 2. _Cerati-solen legumen._
3. _Solecurtus candidus_]
The next family--the _Tellinidæ_--contains a number of well-known
molluscs that burrow into sand or mud, and are enclosed in shells that
are often very prettily marked; and although the family includes several
genera, all may be recognised by the following general features. The
shell is compressed, composed of two equal valves, with little or no
gape, and the ligament situated on the shortest side. The central or
_cardinal_ teeth never exceed two in number in each valve, and the
adductor impressions are round and polished. The mantle is quite open at
the anterior end, and its margins are fringed; the foot is flattened and
tongue-shaped; and the siphons, which are quite separate, are generally
long and slender.
In the typical genus (_Tellina_), of which we represent two very common
British species, the ligament is very prominent, and the slender siphons
are often much longer than the shell. The members of this group move
very freely, travelling about by means of a broad, flattened foot.
[Illustration: FIG. 141.--_Tellinidæ_
1. _Psammobia ferroensis._ 2. _Donax anatinus._ 3. _Tellina
crassa._ 4. _Tellina tenuis._ 5. _Donax politus_]
The shells of the genus _Psammobia_ are popularly known as Sunset
shells, being prettily marked with radiating bands of pink or other
tint, reminding one of the beams of the sun when setting in a cloudy
sky. In these, too, the ligament is very prominent, and the shell gapes
slightly at both ends.
The same family contains the pretty little Wedge shells, which are so
called on account of their triangular form, and constitute the genus
_Donax_. These shells, which are seldom much over an inch long, are very
common on some of our sandy beaches, being washed up in considerable
numbers after the animals have died, but the specimens are seldom
perfect. The molluscs themselves are burrowers, and live in the sand, at
and just below low-water mark; and, as they usually burrow to a depth of
only a few inches, are easily obtained alive.
The shells are rather thin, closed at both ends, blunt and rounded at
the anterior end, but straight and more pointed at the shorter
posterior end; and the margins of the valves are very finely grooved in
such a manner as to resemble the milling of a coin. Each valve has two
central hinge teeth, with one long lateral tooth on each side; and the
ligament is external and prominent. The lobes of the mantle are fringed;
the siphons are separate and diverging, but shorter and thicker than in
most of the other _Tellinidæ_, and the foot is comparatively large,
flattened, and pointed.
The genus contains many species, the commonest being, perhaps, _D.
anatinus_, the colour of which is yellowish, banded with brown, and
marked by a number of radiating white lines. This colour, however, is
due entirely to the thin, shining epidermis that completely covers the
valves; and if this is rubbed off the shell itself will exhibit a pale
pinkish tint. Another common species (_D. politus_) may be recognised by
the broad patch of white running from the hinge to the margin, on the
posterior side of the middle of each valve.
The family _Mactridæ_ contains some British shells popularly known as
Trough shells, and the family name itself is derived from the word
_mactra_, which signifies a kneading trough. In this group the shells
are all more or less triangular in form, with the valves equal, and are
either closed or very slightly gaping. The ligament, perhaps more
correctly designated the cartilage, is generally internal, and contained
in a deep triangular hollow; and the shell is covered with epidermis.
The mantle of the animal is open in front, and the siphonal tubes are
united and fringed. The foot is usually large and flattened.
The typical genus, _Mactra_, contains some common molluscs that bury
themselves just beneath the surface of sandy beaches; and these are so
abundant in some parts of Great Britain that they are used largely for
feeding pigs. Some of the mactras are remarkable for the great power and
extensibility of the foot, which, in some cases, is used so vigorously
that the animal turns itself quickly over, or even leaps on the ground.
Our example of this genus is _M. stultorum_, which is a very common
object of the shore. Its colour is very variable, usually some shade of
grey or brown, and marked by radiating white lines.
The Otter shells (_Lutraria_), of which we figure one species, are much
like the _Mactræ_ in structure, and are usually included in the same
family, but in some respects they resemble the _Myacidæ_ or Gapers. The
shell is oblong rather than triangular, and gapes at both ends; and the
animal buries itself deep in sand or mud, principally in the estuaries
of rivers, from low-water mark to a depth of about ten fathoms. The
shells are not very common objects of the shore, for they are found only
in muddy places, and those of the commonest species (_L. elliptica_) are
too large and heavy to be washed ashore in the sheltered estuaries where
they abound.
[Illustration: FIG. 142.--1. _Lutraria elliptica._
2. PART OF THE HINGE OF _Lutraria_, SHOWING THE CARTILAGE PIT.
3. _Macra stultorum._ 4. INTERIOR OF SAME SHOWING PALLIAL LINE]
We now leave the burrowers, to consider a family of molluscs that move
about somewhat freely by means of a flattened tongue-shaped foot, and
which only rarely fix themselves in any way. The shells of the group are
popularly known as Venus shells, probably on account of the beauty of
some of the species, and the family in question as the _Veneridæ_.
The shells of the various species are usually of a graceful oval or
oblong form, frequently marked by chevron-shaped lines in pretty
colours, and distinctly grooved along the lines of growth. The ligament
is external, the hinge has usually three diverging teeth in each valve,
and the pallial line is sinuated.
The principal genus is _Venus_, in which the shells are ovate in form,
thick, and smooth, and the margins of the valves are minutely
crenulated. The genus is a very large one, and contains several British
species, two of which we represent in the accompanying illustrations.
Allied to these is the larger but pretty shell _Cytherea chione_, which
inhabits deep water off the southern coasts, to about one hundred and
fifty fathoms. It is much like the _Venus_ shells in form, but the
margins are not crenulated.
[Illustration: FIG. 143.--_Veneridæ_
1. _Venus fasciata._ 2. _Venus striatula._ 3. _Tapes virgineana._
4. _Tapes aurea_]
The same family (_Veneridæ_) contains the large genus _Tapes_, so called
because many of its shells are marked in such a manner as to recall the
patterns of tapestry. The general form of these shells is oblong, and
the margins are quite smooth. They are frequently washed up on the
beach, especially during storms, but the animals may be found alive at
low water, buried in sand, or hiding in the crevices of rocks or among
the roots of the larger sea weeds. The mantle is open at the anterior
end, and the siphons are either quite distinct or only partly united.
Some of the shells are very prettily coloured. One (_T. aurea_) receives
its name from the yellow ground, which is variously marked by deeper
tints; another (_T. decussata_) is so called on account of the cross
grooves with which the shell is sculptured; and a third (_T.
virgineana_), which inhabits the muddy bottoms of deep water, is
prettily marked by radiating bands that run from the umbones to the
ventral margins.
We now come to the family _Cyprinidæ_, in which the shell is regular in
form, oval or elongated; and the valves, which are equal in size, are
thick and solid, and fit closely. The teeth are beautifully formed, the
central ones numbering from one to three in each valve, and the pallial
line is not sinuated. The mantle lobes are united on the posterior side
by means of a kind of curtain that is pierced by two siphonal openings.
There are two gills on each side, united posteriorly, and the foot is
tongue-shaped and thick.
The typical genus--_Cyprina_--contains a large mollusc (_C. islandica_),
which is moderately common round our shores, especially in the north,
but is not often seen above low-water mark, except when washed up by
storms. The shell is oval and thick, with the umbones prominent and
turned towards the posterior side, and the ligament is strong and
prominent. It is entirely covered with a thick epidermis, of a rich
brown colour, often exhibiting a fine silky gloss, especially near the
margins. The interior of the shell is white, and the adductor
impressions oval and polished.
The same family includes some smaller shells that inhabit deep water,
and are therefore not commonly seen on the beach. Among these are two
species of the genus _Astarte_, one of which is deeply furrowed in a
direction parallel with the margins; also _Circe minima_, which seldom
exceeds half an inch in length. Although so small compared with
_Cyprina_, these shells may be identified by their clothing of
epidermis, together with the family characteristics given above.
The _Cyprinidæ_ also contains the interesting Heart Cockle (_Isocardia
cor_), the form of which is so characteristic that identification is
easy. The heart-shaped shell is thick and strong, and is swollen out in
such a manner that the umbones are wide apart. These latter are also
curved into a spiral form, and the ligament between them is prominent.
The colour of the shell is variable, the epidermis being of any shade
from a yellow to a dark brown. The foot is small and pointed, and the
siphons fringed.
The Heart Cockle burrows in sand by means of its foot, going down just
far enough to bury the whole of its shell, and always leaving its
siphons exposed at the surface. It inhabits deep water, and is not
likely to be obtained without the use of the dredge or trawl.
[Illustration: FIG. 144.--_Cyprinidæ_
1. _Cyprina islandica._ 2. _Teeth of Cyprina._ 3. _Astarte
compressa._ 4. _Circe minima._ 5. _Isocardia cor_]
The molluscs of the family _Lucinidæ_ are found principally in tropical
and sub-tropical seas, ranging from the shore to a very great depth, but
a few are moderately common in our own waters. They are closely allied
to the _Cyprinidæ_, but the shell is round rather than oval, and is
obliquely grooved inside. The mantle lobes of the animal are not united
on the ventral side, but at the posterior end they are continuous,
except where they form one or two siphonal openings. The foot is long
and of almost the same thickness throughout when extended; and the
gills, numbering either one or two on each side, are large and thick. In
all the members of this family, as in the last, the pallial line of the
shell is simple. None of the shells are really common objects of our
shores, since the animals inhabit deep water, some of them moving about
freely on the bottom, while others moor themselves by means of a byssus.
We shall take only one example of the family--_Galeomma Turtoni_--the
generic name of which means ‘weasel eye.’ This pretty little mollusc may
be found on our southern coasts, where it often moors itself to the
rocks or weeds by means of its silken byssus; or, having broken itself
away from its temporary place of rest, creeps freely on the bottom by a
long, flattened foot, applied closely to the surface over which it
travels, and used much in the same way as the broad foot of a snail or
whelk, its valves being all the time spread out nearly in the same
plane.
[Illustration: FIG. 145.--_Galeomma Turtoni_]
The shell itself is oval, with central umbones, and is covered with a
thick epidermis. The mantle lobes are united behind, where they form a
single siphonal opening; and the margins are double, with a row of
eye-like spots on the inner edge of each.
The true Cockles, some few species of which are known to almost every
one, constitute the family _Cardiadæ_, so called on account of the
cordate or heart-shaped form of the shell as viewed from the anterior or
posterior side. The shell is regular, or nearly so, and the valves,
which are equal, are ornamented with prominent rays that run from the
umbones to the margin. The ligament is short, strong and prominent, and
the valves fit closely by the interlocking of their crenulated margins,
or gape slightly on the posterior side. There are two central teeth in
each valve, and a long lateral tooth both on the anterior and posterior
sides. The mantle lobes are open in front, with the margins plaited, and
the siphons, which are usually short, are provided with a number of
little tentacles. The foot is large and powerful, and is usually curved
into the form of a sickle.
Although the general nature of the common edible cockle (_Cardium
edule_) is so well known even to the inhabitants of inland towns that a
description may seem out of place here, yet it is possible that but few
of our readers have ever taken the trouble to place the animal in a
vessel of sea water, either obtained direct from the sea or artificially
prepared, for the purpose of studying its movements or other habits;
and it will be well to remember that this and several other species of
edible molluscs which reach our towns alive may be very conveniently
studied at home, and often at times and seasons when work at the
sea-side is undesirable or impossible.
[Illustration: FIG. 146.--1. _Cardium pygmæum._ 2. _Cardium fasciatum._
3. _Cardium rusticum_]
The edible species referred to lives in banks of sand or mud, buried
just below the surface, and frequently in spots that are exposed for
several hours between the tides. They are usually obtained by means of a
rake similar to that used in our gardens.
[Illustration: FIG. 147.--_Cardium aculeatum_]
On the coasts of Devon and Cornwall we find a much larger species, also
valued as an article of diet, and known locally as the Prickly Cockle
(_C. aculeatum_). Its shell is beautifully formed, the rays being very
prominent, each bearing a number of calcareous spines arranged in a
single row. We give an illustration of this species, together with two
sketches to show the nature of the teeth of the shell.
In addition to the two species named, we have the red-footed, _C.
rusticum_, which can suddenly turn itself over by the action of its
powerful pedal organ; the Banded Cockle (_C. fasciatum_), a very small
species distinguished by the brown bands of the shell; and a still
smaller one (_C. pygmæum_), with a triangular shell, occurring on the
Dorset and Devon coasts (fig. 146).
Passing now to the _Asiphonida_, we deal first with the family _Arcadæ_.
These include a number of shells which, though very variable in general
form and appearance, may all be recognised by the long row of similar
comb-like teeth that form the hinge. The shells of this group are
regular in form, with equal valves, and are covered with epidermis. The
mantle of the animal is open, the gills are united by a membrane behind,
and the foot is large, curved, and grooved.
[Illustration: FIG. 148.--_Pectunculus glycimeris_, WITH PORTION OF
VALVE SHOWING TEETH, AND _Arca tetragona_]
One of the prettiest shells in the family is _Pectunculus glycimeris_,
which reaches a length of about two inches. The shell is grooved in the
direction of the lines of growth, and there are also very delicate
striations running radially from umbones to margin; and the ground
colour of white or pale yellowish is beautifully mottled with reddish
brown. We give a figure of this species, together with a drawing of the
peculiar and characteristic teeth, but a more typical shell of this
family may be seen in the Noah’s Ark (_Arca tetragona_). This shell is
almost quadrate in form, swollen, and strongly ribbed. The hinge is
straight, with many comb-like teeth--increasing in number with the age
of the shell; and the umbones are separated by a diamond-shaped
ligament. The foot of the animal is heeled--that is, it has a creeping
surface that extends backwards as well as forwards; the mantle is
furnished with minute eyes (_ocelli_), and the animal has two distinct
hearts. We give a figure of this peculiar shell, and the other British
members of the same genus, though varying more or less in form, may be
recognised at once by the same general characteristics.
In the same family we have the small nutshells (genus _Nucula_), which
are often dredged up from deep water in large numbers; and the elongated
shells of the genus _Leda_, also inhabitants of deep water; and, as
before stated, the affinities of all may be readily established by the
characteristic nature of the teeth.
We now pass on to the family of Mussels (_Mytilidæ_), of which the
common Edible Mussel (_Mytilus edulis_) is a typical species. In this
interesting group the shell is oval or elongated, with equal valves, and
is covered with a dark-coloured epidermis which is often distinctly
fibrous in structure. The umbones are at the anterior end of the shell,
which end is usually very narrow and pointed, while the posterior is
broad and rounded. The hinge has small teeth or none, and the ligament,
which is long, is internal. The shells of mussels consist of two
distinct layers; on the inner, which is often of a most beautiful pearly
lustre, may be traced the simple pallial line and the impressions of the
small anterior and the large posterior muscles.
The mantle lobes of the animal are united only at a point between the
two siphonal openings. There are two elongated gills on either side, and
the foot is thick and more or less grooved.
[Illustration: FIG. 149.--_Mytilus edulis_]
Mussels inhabit salt, brackish, and fresh waters, generally attaching
themselves by means of a silken byssus, but sometimes concealing
themselves in ready-made holes, or in burrows of their own; and some
even hide themselves in a nest which they prepare by binding together
fragments of shells or sand.
The edible mussel, which forms such an important article of diet,
especially among the poorer classes in our large towns, may be easily
distinguished from similar species of another genus by the very pointed
umbones, and the coarse and strong fibrous byssus by which it clings to
any solid object. It is found most abundantly on muddy coasts, and on
mud banks in the estuaries of rivers, generally in such situations as
are uncovered at low tide. The fry abound just below low-water level,
and grow so rapidly that they reach their full size in a single year.
It is well known that a diet of mussels occasionally produces very
unpleasant and even dangerous symptoms in the consumer, and this result
has been attributed to the action of a particular organ of the animal
which has not been carefully removed before eating. This, however, is
not the case, as proved by the fact that the eating of these edibles is
usually perfectly safe when no such precautions have been taken. It is
highly probable that the deleterious character referred to is due to a
disease which sometimes attacks the mussels themselves, but the exact
nature of this has not been thoroughly made out.
[Illustration: FIG. 150.--1. _Modiola modiolus._ 2. _Modiola tulipa._
3. _Crenella discors_]
There is another genus (_Modiola_) containing several species commonly
known as Horse Mussels, and these may be distinguished from _Mytilus_ by
their habit of burrowing, or of constructing a nest by spinning together
various fragments. The shell, also, is more oblong in form, and much
swollen near the anterior end; and the umbones are not so pointed. The
epidermis covering the shell is of fibrous structure, and often extends
beyond the edges of the valves in the form of a fringe.
Several species of Horse Mussels inhabit our shores, from low-water mark
to a depth of fifty fathoms, but none of them is used for food. The
commonest species is _Modiola modiolus_, which has a particularly strong
byssus, and its fibres generally bind together such a number of stones
&c. that the shell is completely hidden in the entangled mass. Other
British species include _M. barbata_, so called on account of the
peculiar fringed threads of the epidermis; _M. phaseolina_, in which
the epidermis threads are not fringed; and _M. tulipa_, named from the
streaks of crimson or purple that radiate from the umbones of the shell
and remind us of the colouring of the tulip flower.
An allied sub-genus (_Crenella_) includes a few small British molluscs
the shells of which are crenulated on the dorsal margin behind the
ligament. The shells are short and swollen, and lined by a brilliant
pearly layer. One species (_C. discors_) is pale green, with radiating
lines from umbo to margin. It is common on many of our shores, but is
not easily found, as it hides at or below low water mark, in a nest
formed by binding together small stones. Other species, one of which is
black, are less abundant, and are not readily obtained except by the use
of the dredge.
Before leaving this family we must refer to the remarkable _Dreissena
polymorpha_, sometimes called the Chambered Mussel, on account of the
chamber which is formed in the beak of the shell by means of a pearly
plate that stretches across it. This animal is not indigenous to
Britain, but was introduced from the East by trading vessels, either
attached by its silken byssus to timber that had been left floating in
water previous to being shipped, or to the bottoms of the ships. It
seems to thrive almost equally well in salt, brackish, and fresh waters,
and has spread very rapidly since its introduction. It is more commonly
found, however, in docks, canals, and rivers, and is on that account
usually described with the fresh-water species.
[Illustration: FIG. 151.--_Dreissena polymorpha_]
The form of the shell is very similar to that of _Mytilus_, but has no
internal pearly layer, and the valves are bluntly keeled. The mantle is
closed, the siphons short, and the foot small.
Our next family--the _Aviculidæ_--contains those shells that are
distinguished by peculiar flat processes on each side of the umbones,
one of which, the posterior, is generally wing-like in form. They are
popularly known as Wing Shells, and the family includes the so-called
Pearl Oysters. Most of the species are natives of tropical seas, but
several are common on our own shores.
[Illustration: FIG. 152.--_Avicula_, AND _Pinna pectinata_]
One species of the typical genus is sometimes found off the coasts of
Cornwall and Devon. The shell is very oblique, and the valves are
unequal, the right one, on which the animal rests, being somewhat
smaller than the left; and the epidermis is very scanty. The hinge is
long and straight, without teeth, and the cartilage is contained in
grooves. The interior of the shell is pearly. The posterior adductor
impression is large, and not far from the middle of the shell, while the
anterior, which is small, is close to the umbones. The mantle of the
animal is open, and the margins of the lobes fringed; and the small foot
spins a powerful byssus.
Most of the British species of the family belong to the genus _Pinna_,
so called on account of the fins or wings on the dorsal side of the
shell. In this group the shell is more or less wedge-shaped, with equal
valves, and the umbones are quite at the anterior end, while it is
blunted and gaping at the other end. The hinge has no teeth. The margins
of the mantle are doubly fringed, and the byssus is extremely powerful.
The Common Pinna (_P. pectinata_) is a very large mollusc, sometimes
measuring a foot in length, and is very abundant off the south-west
coast, where it moors itself vertically at the bottom of the water with
the pointed end buried, and the broad end gaping widely so as to expose
its body. It has been stated that fishes are frequently tempted to
intrude into the open shell for the purpose of devouring the animal
within, and that they are immediately crushed by the sudden closing of
the valves, which are pulled together by two large and powerful
adductors.
We have already referred to the little Pea Crab that inherits the shell
of the Pinna, living permanently in the mantle cavity of the animal.
The last family of the Lamellibranchs is the _Ostreidæ_ or Oysters, of
which the edible oyster may be taken as a type. In this group the shells
are frequently unequal, and they lie on one side either free or adherent
to the surface below them; the hinge is usually without teeth. The
mantle is quite open, the gills number two on each side, and the foot is
either small or absent.
The Edible Oyster is a type of the typical genus _Ostrea_, its
scientific name being _Ostrea edulis_; and as this mollusc may be
readily obtained at any time, it is a convenient species for the study
of the general characteristics of its family. Its shell is irregular in
form, and the animal always rests on its left valve, which is convex,
while the upper or right valve is either flat or concave. The lower
valve is also thicker and laminated in structure, and is attached to the
surface on which it rests. On examining the interior we find that the
shell is somewhat pearly in appearance, and that the edges of the mantle
lobes are finely fringed. The gills, too, are united with each other and
with the mantle on the posterior side, thus forming a distinct branchial
chamber.
Oysters are found on banks at the depth of several fathoms, where they
spawn in early summer, and the fry or spats are collected in large
numbers and transferred to artificial beds or tanks, where they are kept
in very shallow water so as to be easily obtainable when required for
food. It is interesting to note, however, that their growth is slow on
these artificial grounds, the full size being attained in about seven
years, while, in the natural beds, they are full grown in a little more
than half that time.
Native oysters--those that are reared on artificial beds--are of course
removed as soon as they are ready for the market, but those that live on
natural banks are often left undisturbed till their shells are thick
with age. The latter, too, are often destroyed in large numbers by the
boring sponge (p. 124), which so completely undermines the substance of
the shell that it finally breaks to pieces.
In the genus _Anomia_ the lower valve is concave, and perforated with a
large oval hole very near the hinge, while the upper one is very convex,
but the shell is very variable in shape, since the animal sometimes
clings permanently to an object, and the shell, during its growth,
accommodates itself to the surface of that object. The use of the hole
is to allow of the protrusion of a set of muscles which proceed from the
upper valve, and give attachment to a plug or button, more or less
calcified, by which the animal clings.
[Illustration: FIG. 153.--1. _Anomia ephippium._ 2. _Pecten tigris._
3. _Pecten_,
ANIMAL IN SHELL]
One species (_A. ephippium_), known as the Saddle Oyster, is common on
some parts of our coast. It is seldom found on the beach at low water,
but the empty shells are often washed up by the waves.
The same family includes the Scallops, which constitute the genus
_Pecten_. In these the shell is nearly round, with ears on each side of
the umbones, those on the anterior side being generally much more
prominent than the others, and both valves are ornamented by prominent
radiating ribs. The shell is often very prettily coloured, and the
animal rests on the right valve, which may be distinguished from the
left by its greater convexity, and by the presence of a notch under
the anterior ear. The hinge is straight, with a very narrow ligament,
and the internal cartilage is situated in a central pit.
[Illustration: PLATE V.
MOLLUSCS
1. Solen ensis
2. Trivia Europæa
3. Trochus umbilicatus
4. Trochus magnus
5. Littorina littorea
6. Littorina rudis
7. Haminea (Bulla) hydatis
8. Tellina
9. Capulus hungaricus
10. Chrysodomus antiquus
11. Buccinum undatum
12 & 13 Scalaria communis
14. Pecten opercularis
15. Pecten varius
16. Pecten maximus]
The mantle of the animal is free, with double margins, the inner of
which forms a finely fringed curtain all round, and on this curtain are
a number of black eyes surrounded by very fine tentacles. The gills are
in the form of very thin crescents, and the foot is shaped like a
finger.
Although the majority of scallops are inhabitants of tropical seas,
several species are to be found off our coasts, where they range from
depths of about four to forty fathoms, and the empty shells, often in
the most perfect condition, are frequently found on the beach.
The Common Scallop (_P. maximus_) is largely used as food, and is
therefore a common object in the fishmonger’s shop. Its colour is very
variable, and the shell has equal ears and about twenty radiating ribs.
The Quin (_P. opercularis_) is also an important article of diet in some
parts.
Perhaps the prettiest of the British species is the Variable Scallop
(_P. varius_), so called on account of the very variable colour of the
shell, the ground tint of which may be almost anything between a very
pale yellow and a dark reddish brown, and this is irregularly patched
with some lighter colour. The chief distinguishing features of the
species are the spiny projections of the numerous ribs, most prominent
near the margin of the valves, and the presence of a permanent byssus,
which, in other species, occurs only in the young. Three of the species
named above are shown on Plate V.
We may also mention the Tiger Scallop (_P. tigrinus_), the radiating
ribs of which are sometimes slightly formed, and which has only one ear
in each valve; and _P. pusio_, in which the adult shell is often greatly
altered in form.
It may be noted, in conclusion, that all the species of this genus have
the power of swimming rapidly by flapping their valves--a mode of
locomotion very common among the bivalves especially during an early
stage of their existence.
Before passing on to the univalve molluscs, we must refer briefly to a
group of animals that are enclosed in bivalve shells, and which were
once included with the Mollusca, but are now made to form quite a
distinct group by themselves. We refer to the Brachiopods, at one time
very abundant, as proved by the immense number of fossil shells embedded
in various stratified rocks, but now represented by only a few living
species.
The shells of these animals are commonly known as Lamp Shells, on
account of their resemblance to an antique lamp; and although at first
sight they bear a general likeness to certain bivalve shells of
lamellibranchs, a close examination will show that not only the shell,
but also the animal residing within it, are both of a nature very
different from that of the molluscs with which they were at one time
supposed to be closely related.
[Illustration: FIG. 154.--_Terebratulina._ THE UPPER FIGURE REPRESENTS
THE INTERIOR OF THE DORSAL VALVE]
The valves of the shell are unequal, and are not placed respectively on
the right and left sides of the body of the animal, but rather on the
dorsal and ventral or upper and lower sides. The ventral shell is the
larger, and is produced into a beak which sometimes has a round hole
corresponding in position with the hole for the wick of an antique lamp,
and the dorsal or smaller valve is always imperforate. The hinge is a
perfect one, the junction of the two valves being so well secured by it
that it is impossible to separate them without injury. It is formed by
two curved teeth on the margin of the ventral valve that fit into
corresponding sockets on the dorsal. A few brachiopods, however, have no
hinge, the valves being secured by means of numerous muscles. The hole
in the shell serves for the protrusion of a pedicel or foot by means of
which the animal is enabled to attach itself.
Two long arms, covered with vibratile cilia, and capable of being folded
or coiled, are attached at the sides of the mouth. They are practically
processes of the lips, mounted on muscular stalks, and attached to a
delicate calcareous loop on the dorsal valve; and serve not only to
produce water currents for the conveyance of food to the mouth, but also
answer the purpose of gills.
The digestive system of a brachiopod includes an œsophagus that leads
into a simply formed stomach round which is a large digestive gland. The
heart has only one cavity, but the animal is provided with two smaller
and separate organs that assist in the propulsion of the blood, which
circulates through numerous blood spaces in the bristly mantle.
About two thousand fossil species of brachiopods are known, extending
over a vast range of time; and the living species, numbering less than a
hundred, are found from shallow water to the greatest habitable depths.
Since the reader is hardly likely to form any extensive acquaintance
with the Brachiopods, we shall illustrate our remarks by the
introduction of only one species--the Serpent’s Head Terebratula
(_Terebratulina caput-serpentis_), which is found in deep water in the
North Sea. The interior of the dorsal valve, showing the calcareous loop
above referred to, is represented in fig. 154, as is also the exterior
of the shell, which is finely striated. The latter represents the dorsal
aspect of the shell in order to show the hole in the upturned beak of
the ventral valve.
[Illustration: FIG. 155.--UNDER SIDE OF THE SHELL OF _Natica catena_,
SHOWING THE UMBILICUS; AND OUTLINE OF THE SHELL,
SHOWING THE RIGHT HANDED SPIRAL]
We have now to consider the large group of head-bearing molluscs
(_Cephalophora_), the study of which forms a very important part of the
work of the sea-side naturalist; and while we deal with the general
characteristics of this group, the reader will do well to have before
him a few living typical species in order that he may be able to verify
as many as possible of the descriptions here given by actual
observation. These types may include such creatures as the whelk,
periwinkle, and limpet; or if marine species are not at hand at the
time, the garden snail, fresh-water snail, and slug will serve the
purpose fairly well.
By far the large majority of Cephalopods are enclosed in a single shell,
though a few have a rudimentary shell or none at all.
As is the case with the lamellibranchs, the shell is composed of both
animal and mineral substance, the latter being a calcareous deposit
secreted by the mantle of the animal. The shell is usually spiral in
form, as in the whelk, but sometimes conical (limpet) or tubular.
Spiral shells are nearly always _dextral_ or right-handed; that is, if
we trace the direction of the spiral from the apex to the mouth, we
find that its turns or whorls run in the same direction as the hands of
a watch. A few, however, are _sinistral_, or left-handed, and
occasionally we meet with left-handed varieties of those species that
are normally of the right-handed type. The cavity of the shell is a
single spiral chamber which winds round a central pillar, and each whorl
of the shell generally overlaps the preceding one, the two being
separated externally by a spiral depression called the _suture_.
Sometimes the coils of a shell are not close together internally, so
that the central column of the spiral is hollow, and opens to the
exterior at the base of the shell. In this case the shell is said to be
_umbilicated_, and the opening referred to is the _umbilicus_. In others
the spiral winds round a solid central pillar which is spoken of as the
_columella_.
[Illustration: FIG. 156.--SECTION OF THE SHELL OF THE WHELK, SHOWING
THE COLUMELLA]
The apex of the shell, sometimes called the _nucleus_, is the oldest
part, and represents what was once the whole. It is generally directed
backwards as the animal crawls, and in adult shells is often more or
less worn away by constant friction. We speak of the whorls as first,
second, third, &c., taking them in the order of their growth, and it
will generally be found that the last whorl is much larger than the
others, so much so that it contains the greater part of the body of the
animal; hence this one is commonly spoken of as the _body-whorl_, and
the others make up the _spire_ of the shell.
The mouth of the shell is of different forms in different species, but
in the herbivorous kinds it is usually simple, while in the carnivorous
species it is notched or produced. The edge of the mouth (_peristome_)
is formed by an _outer lip_ which is usually sharp in young shells and
either thickened, reflected (turned outward), or inflected (turned
inward) in adults; also it may be considerably expanded, or ornamented
by a fringed margin. The _inner lip_ is that side of the peristome
adjacent to the central pillar of the shell.
If we examine the external surface of several different shells, we find
that they are usually more or less distinctly furrowed or sculptured,
and that they are often marked by lines or bands of a colour different
from that of the ground tint. These furrows, lines, or bands sometimes
pass directly from the apex, across the various whorls, to the base of
the shell, in which case they are said to be _longitudinal_. If they
follow the course of the whorls, they are described as spiral; and if
parallel with the peristome, so that they mark the former positions of
the mouth of the shell, thus denoting the _lines of growth_, they are
said to be _transverse_.
Most univalve shells are covered with epidermis, but in some instances
the animal, when extended, surrounds the exterior of the shell with its
mantle, as do the cowries, and then the outside of the shell is always
glazed. Other species keep their shells covered with the mantle, and in
these the shell is always colourless.
The body of the head-bearing mollusc is attached to the shell internally
by one or more muscles, and if we examine the interior surface we are
generally able to distinguish the impressions or scars denoting the
points of attachment.
The reader will have observed that the periwinkle, whelk, and other
univalves close their shells by a kind of lid when they retract their
bodies. This lid is called the _operculum_, and is constructed of a
horny material, often more or less calcified on the exterior, and is
attached to the hinder part of the foot. It sometimes fits accurately
into the mouth of the shell, but in some species it only partially
closes the aperture. The operculum, like the shell itself, often
exhibits distinct lines of growth which display the manner in which it
was built up. If these lines are concentric we know that the operculum
grew by additions on all sides; but if its nucleus is at one edge, and
the lines of growth widest apart at the opposite side, the growth must
have taken place on one side only. Some, even, are of a spiral form,
denoting that the additions were made continuously at one edge, and such
opercula may be right-handed or left-handed spirals.
It will be noticed that in the above general description of univalve
shells we have introduced a number of technical terms which are printed
in italics, and this we have done advisedly, for the employment of these
terms is a very great convenience when giving descriptions of individual
shells, and we shall use them somewhat liberally in noting the
distinguishing characteristics of the families and genera; but before
entering into this portion of our work we must briefly note the general
features of the bodies of the _Cephalophora_.
[Illustration: FIG. 157.--DIAGRAM OF THE ANATOMY OF THE WHELK, THE
SHELL BEING REMOVED
_c_, stomach; _e_, end of intestine; _g_, gills; _h_, ventricle of
the heart; _a_, auricle; _f_, nerve ganglia; _b_, digestive gland;
_ft_, foot; _o_, operculum; _d_, liver]
Sometimes these bodies are bilaterally symmetrical, as we have observed
is the case with the worms, but more commonly the organs on one side are
aborted, while the growth proceeds apace on the opposite side. Thus the
animal assumes a spiral form, being coiled towards the aborted side,
with the gills and other organs developed on that side only. As a rule
this curvature is such that the body takes the form of a right-handed or
dextral spiral, as we have already observed in the shells which cover
them, the mouth being thus thrown to the right, but sometimes it takes
the opposite direction.
When one of these animals is extended and creeping, we observe that it
has a distinct head, furnished with a mouth below, and tentacles and
eyes above; also, if an aquatic species, the gills are more or less
prominent. Further, the exposed portion of the body is covered with a
leathery mantle, and the animal creeps on a broad, flattened surface
which is called the foot.
The tentacles or feelers are usually retractile, and, when retracted,
are turned outside-in. Each one is provided with a muscle that runs from
the body internally to the tip; and, by the contraction of this muscle
the tentacle is involuted just in the same way as the finger of a glove
could be by pulling a string attached to the tip inside. In addition to
these tentacles, and the eyes and mouth previously mentioned, the head
is furnished with ear-sacs, which are little cavities, filled with fluid
containing solid particles, with nerve filaments distributed in the
walls.
On the floor of the mouth there is a ribbon, supported on a base of
gristle, and covered with numerous minute teeth arranged regularly in
rows. The gristle is moved backwards and forwards by means of muscles in
such a manner that this 'lingual ribbon' acts like a rasp, and is
employed in scraping or tearing away portions of the substance on which
the animal is feeding. By this action the teeth are gradually worn away
in front, but this is of no consequence, for the lingual ribbon is
always growing forwards, the worn material being replaced by new growth
behind.
[Illustration: FIG. 158.--A PORTION OF THE LINGUAL RIBBON OF THE WHELK,
MAGNIFIED; AND A SINGLE ROW OF TEETH ON A MUCH LARGER SCALE
_b_, medial teeth; _a_ and _c_, lateral teeth]
The arrangement and form of the teeth are characteristic and important;
and since they afford one of the means by which we may trace the natural
affinities of similar species, they will be frequently referred to when
dealing with the principles of classification. For this reason the
student should be prepared to examine the lingual ribbons of molluscs
with the aid of a compound microscope as occasion requires. As a rule
the ribbon is easily stripped away from the floor of the mouth; and, if
placed in a drop of water and covered with a cover-glass, the teeth are
readily observed. Until a little experience has been gained the
observations may be confined to some of the larger species, in which the
ribbon is both large and easily obtained. In the common whelk, for
example, it often measures more than an inch in length.
It is difficult to understand how the univalve mollusc manages to glide
along so rapidly and gracefully on its expanded foot when we observe it
from above, but the difficulty is cleared away when we see it creeping
on the side of a glass aquarium, or when we place it on a sheet of glass
and observe its movements from the other side. We then see that the foot
is in complete contact with the glass, and that a steady but rapid
undulatory movement is produced by the successive expansions and
contractions of the disc, brought about, of course, by the action of
muscular fibres.
A few of the univalves are viviparous--that is, they produce their young
alive; but the majority lay eggs. The eggs are often enclosed in horny
cases, some of which may be commonly seen washed up on the beach, or
attached to rocks and weeds between the tide-marks. The larvæ are always
enclosed in a shell, though they are sometimes wholly or partially
concealed by the mantle. The shell is usually closed by an operculum;
but as the animal advances in age the shell sometimes disappears
altogether, or is reduced to a mere shelly plate, as is the case with
the land and marine slugs and sea lemons. The young of the
water-breathers always swim about freely by means of a pair of ciliated
lobes or fins, but these remain only for a brief period, after which the
animal settles to the bottom for a more or less sedentary existence.
[Illustration: FIG. 159.--EGG CASES OF THE WHELK]
The Cephalophora fall naturally into two fairly well-defined groups,
which we may describe as the air-breathers and the water-breathers. The
former breathe air direct from the atmosphere through an aperture on the
right side of the body, the air passing into a pulmonary organ or lung,
in the walls of which the bloodvessels ramify, and they include all the
land snails and slugs. The latter breathe by gills which are more or
less prominent on the sides of the body, and include all the fresh-water
snails, as well as the marine species which fall within our special
province.
We shall first consider the class _Pteropoda_ or Wing-footed Molluscs,
so called from the wing-like appendages that are attached to the side of
the mouth, or to the upper side of the foot, which is either very small
or altogether wanting.
These Pteropods are in many respects lowly organised as compared with
the higher molluscs; and as they spend the whole of their existence in
the open sea, they can hardly be considered as falling within the scope
of the sea-side naturalist’s work. Yet since their shells are
occasionally drifted on to the shore, and because a knowledge of them is
essential to the student of the mollusca, we shall briefly note their
principal characteristics.
The pteropods are extremely abundant in some seas, occurring in such
vast numbers that they discolour the water for miles. They swim about by
flapping the pair of wings already referred to. They are known to form
an important article of the diet of the whale, and are also devoured in
enormous numbers by various sea birds; and they are themselves
carnivorous, feeding on various smaller creatures that inhabit the open
waters.
[Illustration: FIG. 160.--PTEROPODS]
In appearance they much resemble the young of higher species of
molluscs. The nervous system consists of a single ganglion situated
below the gullet, and the eyes and tentacles are either rudimentary or
absent. The digestive system includes a muscular gizzard provided with
teeth for the mastication of food, and a digestive gland or liver for
the preparation of a digestive fluid. The heart has two cavities, and
respiration is effected by a surface covered with minute cilia. This
surface is either quite external or is enclosed in a chamber through
which water freely circulates.
The shell is very different from that of a typical head-bearing mollusc,
for it generally consists of two glassy, semitransparent plates,
situated dorsally and ventrally respectively on the body of the animal,
with an opening for the protrusion of the body, and others at the sides
for processes of the mantle; and it terminates behind in one or three
pointed processes. Sometimes, however, its form is conical or spiral,
with or without an operculum. We append illustrations of a few
pteropods, selecting for our purpose species that have been found in the
Atlantic.
It will have been noticed from the above short description that the
pteropod is very unlike the typical Cephalophore as outlined in our
general remarks on the group, especially in the symmetrical form of both
body and shell and in the total or almost total absence of the foot; and
this distinction is so marked that the pteropods are often separated
from all the other _Cephalophora_ into a class by themselves, while all
the remainder are placed in a separate extensive class called the
_Gasteropoda_, because they creep on the ventral surface of the body,
the term signifying stomach-footed.
These gasteropods are divided into four orders: the _Nucleobranchiata_,
in which the respiratory and digestive organs form a nucleus on the
posterior part of the back; the Opisthobranchiata, with gills more or
less exposed towards the rear of the body; the _Pulmonifera_, or
lung-breathing order; and the _Prosobranchiata_, in which the gills are
situated in advance of the heart. The third order includes all the land
snails and slugs, and does not therefore fall within the scope of our
work; but the remaining three consist either exclusively or principally
of marine species, and will be dealt with in the order in which they are
named.
The Nucleobranchs are not really gasteropods in the strictest sense of
the term, for they do not creep along by means of their foot, but all
swim freely in the open ocean, always at the surface, and sometimes
adhere to floating weed by means of a sucker. In fact, the foot of these
creatures is greatly modified in accordance with their habits, one part
being often expanded into a ventral swimming fin, and provided with a
sucking-disc for adhesion, and another produced into a posterior fin for
locomotion.
Like the pteropods, the nucleobranchs are purely pelagic, so that we can
hardly expect to meet with a specimen on or near the shore; and thus we
shall content ourselves with a brief notice of their general characters.
The shell is very variable in size and form, and sometimes even entirely
absent. Large-bodied species often possess but a very small shell, while
some are able to entirely retract themselves and close the mouth of the
shell by an operculum. These animals are generally provided with a large
cylindrical proboscis, and the tongue has recurved teeth. The body is
usually very transparent, often so much so that the blood may be seen
circulating within it, and the nervous system is much more perfectly
developed than in the pteropods. The eyes, too, are perfectly formed.
The presence of special breathing organs may seem to be superfluous in
such delicate and soft-bodied creatures as these, for it may be supposed
that all the oxygen required could be absorbed directly from the water
through their soft structures, as is really the case with many aquatic
creatures; and as a matter of fact some of the nucleobranchs possess no
gills, but others have these organs fully formed.
Passing now to the true gasteropods, we shall first consider the
_Opisthobranchs_, which are commonly known as Sea Slugs and Sea Lemons.
Some of these have no shell at all, and even where one exists it is very
rudimentary, usually very small and thin, and concealed within the
mantle. The gills are either branched and tree-like, or are composed of
tufts or bundles of filaments; and, as the name of the order implies,
are situated towards the posterior part of the body. They are also
retractile, and when the animal is alarmed it will conceal its gills,
thus reducing its body to a shapeless, slimy mass, inviting neither to
sight nor to touch.
The sea slugs are principally animal feeders, subsisting on small
crustaceans, other molluscs, &c.; the food being first reduced by the
rasping action of the teeth, and then masticated in a gizzard which is
provided internally with horny spines or hard, shelly plates.
It will not be necessary to enumerate all the different families of this
order, especially as the species are mostly to be found beyond the
tide-marks, and are therefore obtained only with the aid of the dredge;
but we shall describe a few of the British species with a view of
showing the general characteristics of the animals.
They are usually divided into two sections, those with exposed or naked
gills (_Nudibranchiata_) forming the first, and those in which the gills
are covered either by the shell or the mantle (_Tectibranchiata_)
comprising the second.
In the Nudibranchs the shell exists only during the embryonic stage, and
the external gills are arranged on the back or along the sides. The
tentacles are not employed as organs of touch, but are probably
connected only with the sensation of smell, being provided with
filaments of the olfactory nerve; the eyes are small dark-coloured spots
embedded in the skin behind the tentacles. Various species are to be
found on all rocky coasts, where they range from low-water mark to a
depth of fifty or sixty fathoms, but a few are pelagic, living on the
surface of floating sea weeds.
It is almost impossible to identify the species of nudibranchs from dead
specimens, for the classification of the section is based largely on the
arrangement of the gills, which are almost always retracted in the dead
animals. This is also the case even with living specimens when disturbed
or removed from the water; hence they should always be examined alive in
sea water, while the animals are extended and moving.
[Illustration: FIG. 161.--NUDIBRANCHS
1. _Doto coronata._ 2. _Elysia viridis._ 3. _Proctonotus
mucroniferus._ 4. _Embletonia pulchra_]
It will be understood from the above statements that special methods
will be necessary when it is required to preserve specimens for future
study, the gills being always retracted when the animal is killed for
this purpose by any rapid process. We have found two methods, however,
that are fairly satisfactory in the majority of instances.--Place the
living animals in a suitable vessel of sea water, and leave them quite
undisturbed till they are fully extended, and then either _gradually_
raise the temperature till they are dead, or introduce into the water,
cautiously, a solution of corrosive sublimate. In the latter case a much
larger proportion of the sublimate will be required than when used for a
similar purpose with freshwater molluscs. When the animals are dead it
will be found that their gills are more or less extended, sometimes
fully so, and they may then be transferred to diluted spirit or a two
per cent. solution of formaldehyde.
[Illustration: FIG. 162.--NUDIBRANCHS
1. _Dendronotus arborescens._ 2. _Tritonia plebeia._ 3. _Triopa
claviger._ 4. _Ægirus punctilucens_]
In fig. 162 we represent four species. Two of these--_Triopa claviger_
and _Ægirus punctilucens_--belong to the family _Doridæ_, the members of
which are popularly known as Sea Lemons, and are distinguished by the
presence of plume-like gills situated on the middle of the back. Another
family (_Tritoniadæ_), characterised by the arrangement of the gills
along the sides of the back, and by tentacles that can be retracted into
sheaths, is represented by _Tritonia plebeia_ and _Dendronotus
arborescens_ in the same figure, and by _Doto coronata_ in fig. 161. The
family _Æolidæ_ also have their gills arranged along the sides of the
back, but they differ from the last in that their tentacles are not
retractile. They include the two species numbered 3 and 4 on fig. 161.
The remaining one on fig. 161--_Elysia viridis_--is a member of the
family _Phillirhoidæ_, characterised by a pair of tentacles on the
dorsal side of the head and by the foot being either very narrow or
absent, the latter feature denoting that the animals are not adapted for
creeping on the bottom. In fact, several of the species of this family
swim freely by means of flattened tails.
The Tectibranchs are similar in general structure, but are very
different in appearance, inasmuch as the gills, so prominent in the last
division, are here covered by the mantle, or by the shell, which is
often well developed. The latter is very variable in form, being of a
globular, twisted, spiral, or other shape, but is sometimes absent in
the adult. In fig. 163 we give a few examples of the shells of British
species; and one (_Bulla hydatis_) is shown on Plate V.
[Illustration: FIG. 163.--SHELLS OF TECTIBRANCHS]
We now pass on to the largest and last order of gasteropods--the
_Prosobranchiata_--so called because the gills are situated in front of
the heart. This group is an important one to the sea-side naturalist,
since it contains nearly all the univalve molluscs that are common
between the tide-marks of our shores, as well as some abundant species
that are protected by a shell of several distinct parts. In nearly all
of them the abdomen is well developed, and the shell is sufficiently
large to cover the whole animal when the latter is retracted; and the
gills, which are either pectinated (comb-shaped) or plumed, are lodged
in the chamber formed over the head of the animal by the mantle.
The order is often divided into two sections--the _Holostomata_ or Sea
Snails, in which the margin of the aperture of the shell is entire, and
the _Siphonostomata_, in which the margin of the mantle is prolonged
into a siphon by which water passes into the gill chamber. This division
does not seem to be very satisfactory, as the sections are not separated
by very prominent natural characteristics, but it becomes convenient on
account of the great extent of the order.
In the _Holostomata_ the shell is either spiral, conical, tubular, or
composed of several valves, and the spiral forms are usually closed by
a horny or shelly operculum of the spiral kind. The head is provided
with a proboscis that is generally non-retractile, and the gills usually
extend obliquely across the back, or are attached to the right side
behind the head.
We shall first consider the lower forms, starting with the family
_Chitonidæ_, the animals of which, as the name implies, are covered with
a shell that resembles a coat of mail.
Some of these creatures are very common on our rocky coasts, and yet
their nature is such that they are liable to be overlooked by those who
are not acquainted with their appearance and habits. The shell is oval
or oblong, often so coloured as to closely resemble the rocks and stones
over which they crawl; and the animal is so inactive when left exposed
by the receding tide, and its flat under surface so closely applied to
that on which it rests, that it looks merely like a little convexity of
the rock. But after a few have been discovered the eye becomes
accustomed to their appearance, and large numbers may be obtained in a
short space of time.
The shell will be seen to consist of eight transverse, curved plates,
overlapping each other at their edges, and all enclosed in a leathery
mantle, which also forms a projecting margin all round. The middle six
plates are different from the first and last in that they are grooved in
such a manner that each one displays a dorsal and two lateral areas.
The animal holds on tightly to the rocks by its large creeping disc-like
foot, but may be removed without injury by forcing a knife-blade under
the margin of its shell. When examined it will be found that it has not
a well-formed head like the majority of the gasteropods, and both eyes
and tentacles are wanting. The gills form a series of lamellæ round the
posterior end of the body, between the edge of the foot and the mantle;
and it is interesting to note that the Chitons further justify the low
position assigned to them among the gasteropods by their possession of a
simple, central, tubular heart, similar to that of worms.
Perhaps the commonest of the British species is _Chiton cinereus_. Its
colour is a dull grey, but the ground is variously mottled, often in
such a manner as to give it a protective resemblance to its
surroundings. _C. ruber_ is the largest of our species: its shell is
variously mottled with shades of yellow and brown; _C. fascicularis_ is
bristled. Another rather common species (_C. lævis_) is distinguished by
the glossy appearance of the dorsal portion of the shell.
It will have been observed that the chitons differ from the majority of
gasteropods in that their shells and bodies are both bilaterally
symmetrical, and the same is true of the next family--_Dentaliadæ_,
which derive their name from the tooth-like form of their conical
shells. They are popularly known as the Tooth Shells, and although they
generally live beyond low-water level, they may sometimes be seen alive
on the beach, and the empty shells are often washed up by the waves.
The shells (fig. 165) are curved, and open at both ends, the narrower
extremity being the posterior. The mouth is circular, and the outer
surface is quite smooth or grooved.
[Illustration: FIG. 164.--CHITON SHELLS]
[Illustration: FIG. 165.--SHELLS OF _Dentalium_]
In these animals, too, the head is imperfectly formed, without eyes or
tentacles. The foot is conical and pointed, with two symmetrical side
lobes; and the gills, also two in number, are symmetrically disposed.
The margin of the mouth is fringed, and the animal is attached to the
shell near the posterior end.
The _Dentaliadæ_ are carnivorous, subsisting on minute molluscs,
foraminifera, &c., and generally live on sandy or muddy bottoms, in
which they sometimes bury themselves.
Our next family includes the familiar Limpets, and is designated
_Patellidæ_ on account of the resemblance of the conical shell to a
little dish. In these the apex of the cone is not central, but situated
more or less towards the anterior; and the muscular impression within is
shaped like a horseshoe, with its open end turned to the front.
Unlike the members of the preceding families, the limpets have a
well-formed head furnished with both eyes and tentacles, the former
situated at the bases of the latter. They have a horny upper jaw, and
the tongue, which is very long, is supplied with numerous hooked teeth.
The foot is a very large disc, as large as the shell, and the gills
consist either of one or two branched plumes, or of a series of lamellæ
almost or entirely surrounding the animal between the shell and the
margin of the mantle.
The reader has probably experienced the difficulty of detaching a limpet
from its hold on the rocks. The tenacity of the grip is not due to the
mere adhesive power of the foot itself, but to atmospheric pressure, the
effect of which is complete on account of the total exclusion of air
from under the disc of the foot; and when we remember that this pressure
amounts to fifteen pounds on every square inch of surface, we can
readily understand the force required to raise a large limpet from its
position.
[Illustration: FIG. 166.--_Patellidæ_
1. _Patella vulgata._ 2. _P. pellucida._ 3. _P. athletica._
4. _Acmæa testudinalis_]
The Common Limpet (_Patella vulgata_) is found on all our rocky coasts
between the tide-marks, often at such a level that it is left exposed to
the air for eight or nine hours at a time. The apex of the shell of this
species is nearly central, and the exterior is sometimes nearly smooth,
but more commonly relieved by radiating ribs.
Although the shell itself is not a particularly pretty object, it is
often rendered very beautiful and interesting by the various animal and
vegetable organisms that settle on it. Those shells that are left dry
for hours together are commonly adorned with clusters of small acorn
barnacles, while the limpets that have found a home in a rock pool and
are perpetually covered with water, often resemble little moving gardens
in which grow beautiful tufts of corallines or other weeds, as well as
polyzoa and other animal forms.
It appears that limpets are not great travellers, the appearance of the
rock from which they have been removed being such as to point to a very
long period of rest. Those on hard rocks are generally situated on a
smooth surface just the size of the shell and generally worn slightly
below the surrounding level by the constant friction of the shell; while
others that have settled on very rugged spots have their cones adapted
to the irregular surface. It has been suggested that the animals make
occasional short excursions from their chosen spot, but return again to
it; and whether or not this is the case, it is evident that they
frequently keep to one small spot for a considerable length of time.
Limpets on chalk and other soft rocks are sometimes in circular pits so
deep that even the apex of the shell is below the general level around;
and though it is possible that the abrasion is produced entirely by the
friction of the shell as the animal turns, yet, in the case of chalk,
the action may be partly due to the carbonic acid gas given off by the
animal as a product of respiration, for it is a well-known chemical fact
that this gas, in solution, has the power of dissolving calcareous
material.
The other British Limpets include _P. pellucida_, which lives on the
fronds and stalks of the tangle, the form of the shell varying according
to that of the surface on which it rests; also the Horse Limpet (_P.
athletica_), the bold radiating ribs of which are irregularly notched;
and _Acmæa testudinalis_--the Tortoiseshell Limpet, with reddish-brown
mottlings on the exterior, and a dark-brown patch at the apex within.
The last-named species lives principally on sea weeds, and has a single
pectinated gill in the cavity between foot and mantle, which is
protruded on the right side when the animal is extended. This latter
feature is interesting since it shows a tendency to that one-sided
development already referred to as characteristic of the typical
gasteropod, resulting in the spiral form of the adult.
In the limpets the lingual ribbon is proportionately long, and is easily
removed for examination. In _P. vulgata_ it may exceed an inch in
length, and the teeth are arranged in rows each of which contains four
central, with laterals on either side, while in _Acmæa_ there are only
three laterals on each side of the central line.
Other so-called limpets belong to separate families. Thus we have the
Cup-and-Saucer Limpet and the Bonnet Limpet in the _Calyptræidæ_. Both
these differ from Patella in that the apices of their shells show a
tendency to assume a spiral form, thus denoting a somewhat closer
relationship to the more advanced univalves. They have distinct heads,
with prolonged muzzles, and well-formed antennæ and eyes. The teeth of
the lingual ribbon are single, with dentated laterals on either side.
The Cup-and-saucer Limpet (_Calyptræa sinensis_) is so called on account
of a curved plate that projects from the interior of the shell, at the
apex; and though this plate takes the form of a half-cup rather than of
a cup, the whole shell has suggested the popular name, while the generic
name is derived from _calyptra_, which signifies a cap. This mollusc is
occasionally found among stones at low tide, but usually lives beyond
this line, thus necessitating the use of a dredge. The Bonnet Limpet
(_Pileopsis hungaricus_) is of similar structure and habit, but the
nucleus of the shell is a more decided spiral (see Plate V.). Both these
animals adhere to stones and rocks, and, like the common limpet, seldom
or never move from their selected sites; hence their shells are variable
in form, being adapted to the rock below, and the movements of the shell
often cause a little hollow to be scooped out of the softer materials.
[Illustration: FIG. 167.--_Calyptræa sinensis_]
Yet other limpets belong to the next family _Fissurellidæ_, which is
characterised by a perforation or a notch in the shell. In these, too,
the shell is conical, with a tendency to assume the spiral form, but the
curve of the nucleus, which is always apparent in the young shell,
frequently disappears as the growth proceeds.
[Illustration: FIG. 168.--_Fissurellidæ_
1. _Puncturella noachina._ 2. _Emarginula reticulata._
3. _Fissurella reticulata_]
In the Keyhole Limpet (_Fissurella reticulata_) which is found chiefly
on our southern shores, the perforation is at the summit of the shell;
but as the animal grows the hole increases in size, encroaching on the
curved nucleus until the latter quite disappears. In the genus
_Puncturella_ the perforation is just in front of the recurved apex, and
is surrounded by a rim internally; while in the Notched Limpets (genus
_Emarginula_) it is represented by a fissure on the anterior _margin_ of
the cone. In all, however, the hole or notch serves the same purpose,
for it is the means by which water enters the siphon.
It is doubtful whether we ought to claim the beautiful Ear shell
(_Haliotis tuberculata_) as one of our own, but it is generally included
among the British molluscs on the ground that it is abundant on the
coast of the Channel Islands, where it is called the Omar; and it is
certainly too beautiful an object to be excluded from the British
species without ample cause.
[Illustration: FIG. 169.--_Haliotis_]
It belongs to the family _Haliotidæ_, and our illustration will show
that the shell is less elevated than that of limpets, and that the
spire, though not prominent, is a fairly well-formed spiral. All along
the outer lip of the very large aperture is a series of perforations,
occupying the summit of a prominent, spiral ridge, and becoming
gradually smaller and smaller towards the spire. The whole shell is
pearly in structure, and displays a great variety of rich colouring. It
is used largely for inlaying and other ornamental purposes, and for
making the so-called pearl buttons. The animal is used largely as an
article of food in the Channel Islands, but it is of so tough a nature
that it requires a vigorous beating previously to being cooked.
[Illustration: FIG. 170.--_Ianthina fragilis_]
The same family contains the beautiful violet _Ianthina_, which also is
not a British species, but a free-swimming oceanic snail. It is,
however, occasionally drifted to our shores, though generally in an
imperfect condition. In the Atlantic and the Mediterranean it sometimes
abounds in such multitudes as to distinctly colour the surface of the
sea.
It will be seen that the shell is round, with a well-formed spiral. The
spire is white, but the base is of a deep violet colour. The animal is
very remarkable in some respects. In the first place, though it has
pedicels similar to those on which the eyes of the higher univalves are
placed, yet it has no eyes. Then the foot, which is in itself small,
secretes a float or raft so large that it cannot be retracted into the
shell, with numerous air vesicles to render it light, and the
egg-capsules of the animal are attached to the underside of this. The
animal has no power of sinking, but lives exclusively at the surface;
and, when disturbed, it exudes a violet fluid that colours the
surrounding water. It is apparently the only gasteropod that lives in
the open sea and has a large and well-formed spiral shell.
Passing now to the family _Turbinidæ_ we meet with turbinated or
pyramidal shells that are of a brilliant pearly lustre within, and
frequently without also when the epidermis is removed. The animals
inhabiting them have well-formed heads with a short muzzle, long and
slender tentacles, and eyes mounted on peduncles. The sides are
ornamented with fringed lobes and several tentacle-like filaments, and
the aperture of the shell is closed, when the animal is retracted, by a
spiral operculum. They are all vegetable feeders; and, as is usual with
the plant-eating molluscs, the teeth on the lateral portions of the
lingual ribbon are very numerous.
We have a few common species belonging to this group, mostly members of
the typical genus _Trochus_ and commonly known as Top Shells. In these
the shell is a pyramid formed of numerous flat whorls, with an oblique
and rhomboidal aperture. Of the three species figured (including two on
Plate V.) _T. umbilicatus_ and the Large Top (_T. magnus_) are
umbilicated, the umbilicus being very large in the latter; and the
former is characterised by the zigzag greyish or reddish markings that
run radially across the whorls. The other (_T. zizyphinus_) is usually
of a yellowish or pink colour and has no umbilicus.
The same family contains the pretty little Pheasant Shell (_Phasianella
pullas_), which is richly coloured with red, brown, and yellow on a
light ground; and _Adeorbis subcarinatus_, shown in the same group.
The well-known Periwinkle (_Littorina littorea_) and the species to the
right of it on Plate V., belong to the family _Littorinidæ_, the
members of which are similar in structure and habit to _Trochus_, but
the shell is usually more depressed, and is never pearly. The shell of
the Periwinkle is thick, having but few whorls, and is not umbilicated;
and the lingual ribbon, which is coiled up on the gullet, contains no
less than about five hundred rows of teeth; but only a little more than
twenty of these rows are in action at any one time, the remainder being
a reserve stock to come into active service as the ribbon grows forward.
In the genus _Lacuna_ there is a narrow umbilicus, and the aperture of
the shell is semilunar in form; and the species of _Rissoa_ are very
small, with white or horny shells, much more pointed and having more
whorls than those of the _Littorina_.
Our next illustration shows three shells of the family _Turritellidæ_,
so named from the resemblance of the shells to a tower or spire. The
form indeed is so characteristic that they can hardly be mistaken. It
will be seen that _Turritella communis_ is striated spirally, while the
surface of _Scalaria communis_ (Plate V.) is relieved by strongly marked
transverse ribs. Both these species are very common, and the latter is
peculiar for its power of ejecting a dark purple fluid when molested.
The other representative of the family--_Cæcum trachea_--has a shell
something like that of _Dentalium_ (p. 238), being cylindrical and
tubular, but it differs in being closed at one end.
[Illustration: FIG. 173.--SECTION OF SHELL OF _Turritella_]
[Illustration: FIG. 174.--_Turritella communis_ AND _Cæcum trachea_]
In the succeeding shells, of the family _Cerithiadæ_, the spire is also
considerably produced, so much so that some of the species closely
resemble the Turret shells, but they are distinguished by usually having
an expanded lip, at least in the adult form; and the mouth is channelled
in front, and sometimes also behind. The animals of the group have short
muzzles that are not retractile, the tentacles are wide apart, and the
eyes are mounted on short pedicels. The median teeth are arranged in a
single row, with three laterals on either side of each.
[Illustration: FIG. 175.--_Cerithium reticulatum_ AND _Aporrhais
pes-pelicani_]
_Cerithium reticulatum_ receives its generic name from its appearance to
a small horn, and the specific name refers to the netted appearance of
its surface due to the presence of numerous little tubercles arranged in
rows--a feature that serves to distinguish it from the small Turret
shells. It is a common shell, as is also the other representative of the
family illustrated, but the latter is rendered conspicuous by the
enormously expanded lip that has earned for it the popular name of Spout
Shell. Its scientific name is _Aporrhais pes-pelicani_, and the
application of the specific term will be understood when the shell is
viewed from above, for the expanded lip is drawn out into long
finger-like lobes that suggest the foot of a bird. This is a very solid
shell, sometimes reaching a length of two inches; and the animal
inhabiting it is carnivorous.
[Illustration: FIG. 176.--_Aporrhais pes-pelicani_, SHOWING BOTH SHELL
AND ANIMAL]
We have yet some turreted shells to deal with, belonging to the family
_Pyramidellidæ_, but they need not be confused with the preceding groups
if carefully examined. In the first place, the aperture of the shell is
very small; and the operculum, instead of being spiral, as in the
turreted shells before mentioned, is imbricated or made up of parallel
layers denoting that the growth took place on one side only. Another
distinguishing feature is seen in the nucleus--that small portion of the
spire that was developed within the egg--which is sinistral or
left-handed. In addition to this, the animal has broad, ear-like
tentacles, a retractile proboscis, and a lingual ribbon without teeth.
The British species of this family belong principally to the genera
_Odostomia_, characterised by a tooth-like fold of the columella;
_Eulima_, containing small, white, polished shells with numerous level
whorls; and _Aclis_, with little polished shells not unlike
_Turritella_.
[Illustration: FIG. 177.--1. _Odostomia plicata._2. _Eulima polita._
3. _Aclis supranitida_]
The last family of the _Holostomata_ is the _Naticidæ_, the shells of
which are almost globular, with only a few whorls, and a small, blunt
spire. The mouth is semilunar in form, and the lip sharp. The proboscis
of the animal is long and retractile, and the foot large; but perhaps
the most characteristic feature is the presence of large mantle lobes
which hide some of the shell when the animal is crawling. In _Natica_
(fig. 155), the typical genus, the shells are somewhat thick and smooth,
with a large umbilicus. As the animal crawls a large fold of the mantle
is reflected back over the head, completely covering it, and apparently
obstructing its view; but this is not the case, for the creature has no
eyes. _Natica_ is very abundant on some sandy beaches, where it devours
small bivalves and other animals; and it is frequently washed up alive
by the waves. Its shell is also a favourite one with hermit crabs. Its
eggs, all connected together in a spiral band, may often be seen
stranded on sandy coasts. Several species of Natica are found on our
shores. An allied mollusc--_Velutina lævigata_, so called on account of
the velvety epidermis that clothes the shell, completely surrounds the
shell by its mantle folds when creeping.
The _Siphonostomata_ form a much smaller section than the last, and its
members are distinguished mainly by the presence of a true siphon,
formed by the prolongation of the mantle margin, and serving to convey
water into the gill chamber. In all these the shell is spiral, usually
without an umbilical opening, and the margin of the mouth is prolonged
into a canal or distinctly notched. The operculum is horny, and lamellar
or imbricated. The animal has a retractile proboscis, and the eyes or
eye-pedicels are joined to the tentacles. All the species of this
division are marine.
[Illustration: FIG. 178.--_Cypræa (Trivia) europæa_]
We will first take the family _Cypræidæ_, which contains the familiar
Cowries, these forming the lowest group of the division. An examination
of the shells may at first seem rather puzzling, for the spire is
concealed, and the whole is convoluted in such a manner as to make the
mouth long and narrow, with a channel at either end. The outer lip is
also thickened and bent inward, and there is no operculum.
The animal itself is particularly interesting, for, as it creeps along
on its broad foot, abruptly shortened in the front, the mantle lobes
bend over the top, meeting along the middle line, where they are usually
fringed with little tentacle-like processes; and, as a result, the whole
shell is beautifully enamelled on the outer surface. In all the Cowries
the central teeth are single, and the laterals are arranged either in
twos or threes.
Perhaps the commonest representative of this family is the pretty little
_Cypræa_ (_Trivia_) _europæa_ (Plate V.), the shells of which are
sometimes washed up in large numbers on sandy beaches. The animal lives
mainly below low-water level, but it may often be found in the larger
rock pools, creeping rapidly over the tangles, and may be easily secured
with the aid of a net.
In the same family we have the little _Erato_ (_Marginella_) _lævis_,
the white shell of which is minutely furrowed along the lips; and also
_Ovulum patulum_ (_Calpurna patula_), so called on account of its
fancied resemblance to a poached egg.
We have also several species of Cone shells (family _Conidæ_) on our
coasts, readily recognised by their form, which is a cone, with a long,
narrow aperture, partially closed by a minute operculum. As in the last
family, the foot is abruptly shortened in front. The head is very
prominent, with eyes situated on the tentacles. There are two gills, and
the teeth are arranged in pairs.
[Illustration: FIG. 179.--1. _Ovulum patulum._ 2. _Erato lævis_]
[Illustration: FIG. 180.--_Mangelia septangularis_ AND _Mangelia
turricula_]
The Conidæ are principally inhabitants of tropical seas, where some very
large species exist. Two of the British representatives, both common
shells, are shown in fig. 180.
Our next family (_Buccinidæ_) is so well distributed on our coasts, that
it would be difficult, we imagine, to find a spot quite free from its
familiar forms. It contains all those creatures commonly known as
Whelks, Dog Whelks, and Dog Winkles, ranging from deep water almost to
high-water mark.
In all these the shell is notched in front, or the canal is turned
abruptly upward. The foot of the animal is broad, the eyes are situated
either on the tentacles or at their bases, and there are two gill
plumes.
All the species are carnivorous, and some are said to be very
destructive to mussels and young oysters.
The Common Whelk (_Buccinum undatum_, Plate V.) lives in deep water,
whence it is dredged up largely for the market. Its clusters of egg
cases are washed up in large numbers on the beach, where they form one
of the commonest materials among the refuse at high-water mark. It is
not uncommon, also, especially after storms, to find the unhatched eggs
stranded by the waves, and these are so transparent that the embryos,
several in each capsule, may be seen within. The hole through which the
young escape may also be seen on the inner side.
[Illustration: FIG. 181.--1. _Purpura lapillus._ 2. EGG CASES OF
_Purpura_. 3. _Nassa reticulata_]
The Dog Periwinkle (_Purpura lapillus_) abounds on all our coasts and is
remarkable for the production of a dull crimson or purple fluid that may
be obtained from it by pressing on the operculum. This fluid turns to a
brighter colour on exposure to air, and is said to have been used
largely in former times as a dye. It will be seen from our figure that
the spire of this shell is shorter in proportion than that of
_Buccinum_; but both are alike in that the operculum is made up of
layers with a nucleus on the external edge.
The other species figured is _Nassa reticulata_, popularly known as the
Dog Whelk, and characterised by a tooth-like projection of the inner lip
close to the anterior canal. It is very common near low-water mark,
where it may be seen crawling over the rocks on its broad foot, from
which project two hornlike appendages in front and two narrow tails
behind.
[Illustration: FIG. 182.--_Murex erinaceus_]
From the last family of the gasteropods (the _Muricidæ_) we select two
common species--_Murex erinaceus_ and _Fusus antiquus_ (Plate V.). In
both these the anterior canal of the shell is straight and the posterior
wanting. The eyes are on the tentacles, and there are two plumed gills.
Both are carnivorous species, feeding on other molluscs; and the former
is said to bore through the shells of its prey with the prominent beak
of its shell.
_Murex_ may be readily distinguished by the prominent longitudinal
ridges of the thick shell, its rounded aperture, and by the partly
closed canal running through the beak. It is known to fishermen as the
Sting Winkle; the other species is called the Red Whelk in some parts,
and in Scotland is known as the Buckie. Like the common whelk, it is
dredged largely for the market, and is said to be far more esteemed than
the former, from which it may be distinguished by the fusiform shape of
the shell and the long straight canal.
We now pass to the last and highest class of the mollusca, called the
_Cephalopoda_ because they have a number of arms attached to the head,
round the mouth. Unlike the majority of molluscs they are bilaterally
symmetrical: and are much more highly organised, in some respects even
making an approach to the vertebrates. Thus they generally have an
internal hard structure, either horny or calcareous in structure,
representing the vertebral column, and the circulatory system consists
of arteries and veins, connected by minute capillaries. The corpuscles
of the blood are also similar in form to those of the vertebrates.
Externally they are all naked, with the exception of the nautilus and
argonaut of the warmer seas.
The arms, so characteristic of the class, are eight or ten in number,
long and muscular, and provided with numerous suckers by which the
animal can cling with remarkable tenacity. These suckers are situated on
the inner surface of the arms, and the disc of each one displays a
series of muscular fibres, all converging from the circumference towards
the centre, which is occupied by a softer structure that works inwards
and outwards like the piston of a pump. Thus the suckers form a system
of exhausting air-pumps by which a vacuum can be produced, and the
tenacity of the grip, maintained by atmospheric pressure, is so great
that the arms, strong as they are, may be torn asunder by attempting to
pull them from their hold; and yet the animal can release its grip with
the greatest of ease by simply releasing the pistons of its pumps.
The cephalopods are further distinguished by their very large, glaring
eyes, situated on the sides of the well-formed head, and by powerful
jaws that work in a vertical plane, like those of the vertebrates, but
somewhat resembling the beaks of certain birds. The tongue is also very
large and fleshy, and in part armed with numerous hooked spines or
teeth.
The class is usually divided into two orders, one characterised by the
possession of two gills, and the other of four; but the British species
belong to the former, known technically as the _Dibranchiata_. This
order is subdivided into two sections according to the number of arms;
and the divisions are called the _Octopoda_ and _Decapoda_ respectively.
[Illustration: FIG. 183.--OCTOPUS]
The former section includes the Octopods, of which some species inhabit
our seas. They all have eight arms, of unequal size, with the suckers
arranged in two rows, and their round or oval bodies seldom have any
fins, locomotion being effected by means of the arms, and by the sudden
expulsion of water from the siphon. The shell is rudimentary, being
represented merely by two short ‘styles’ within the mantle. The species
vary considerably in size, some being only about an inch long when fully
grown, while others measure two feet or more, and are looked upon as
formidable creatures by man. Sometimes they are washed up on our
beaches, but the best way to make their acquaintance is to examine the
contents of the fishermen’s drag nets as they are hauled on the beach.
In the same manner we may secure various species of the Decapods or
Ten-footed Cephalopods, which comprise the Calamaries, Squids, and
Cuttlefishes. These, too, properly speaking, have but eight arms, the
other two appendages being really tentacles, which are usually longer
than the arms, and more or less retractile; they are also expanded at
the ends. The decapods are also to be distinguished from the octopods
by their elongated bodies, and a flattened, fin-like appendage on either
side. Their eyes, also, are capable of being rotated within the orbits,
while those of the octopods are fixed; and the shell consists of one or
more horny ‘pens,’ or of a calcareous ‘bone,’ contained in a cavity so
loosely that it drops out of its place when the cavity is opened.
[Illustration: FIG. 184.--_Loligo vulgaris_ AND ITS PEN]
[Illustration: FIG. 185.--_Sepiola atlantica_]
The Common Calamary (_Loligo vulgaris_) may be recognised by the
accompanying illustration, from which it will be observed that the body
tapers behind, bearing two rhomboidal fins in the rear. The suckers are
arranged in two rows on the arms, but in fours on the expanded tips of
the tentacles. The animal is a good swimmer, and sometimes crawls, head
downwards, on the disc surrounding the mouth, pulling itself along by
means of its arms. Its shell is a horny pen, lanceolate in form, but it
divides as the age of the animal advances, so that two or more may be
found in the same specimen.
Belonging to the same family we have the Common Squid (_Sepiola
atlantica_), also a very abundant species. Here the body is shorter and
purse-like, and the fins are dorsal and rounded. It seldom exceeds four
or five inches in length, and, like the Calamary, is used largely as a
bait by fishermen.
Another family--the _Sepiadæ_--contains the Cuttlefish (_Sepia
officinalis_), the ‘bone’ of which is such a common object on the beach.
This latter is a broad, curved plate of carbonate of lime, made up of a
number of regular layers, and having a cavity hollowed out at the
posterior end. It is exceedingly light and porous in structure, and at
one time was used largely as an antacid as well as a dentifrice. It is
also proportionately large, being both as long and as broad as the body
of the animal.
[Illustration: FIG. 186.--_Sepia officinalis_ AND ITS ‘BONE’]
Cuttlefishes live principally in the shallow water close to shore, where
they swim backwards by the sudden propulsion of water from their
siphons; and their eggs, which look like clusters of black grapes, are
frequently thrown up on the beach, generally attached to the stems and
fronds of sea weeds.
As a rule the cephalopods swim slowly by the aid of their fins or by a
rhythmic contraction by which water is expelled from their siphons, but
when in danger the muscular contraction is so violent that they dart
through the water with great speed, and even leap into the air to avoid
their enemies. But they have another and much more remarkable way of
escaping from their foes:--They possess a gland, the duct of which opens
into the base of the funnel or siphon, that prepares an inky fluid; and
when the animal is disturbed it suddenly ejects this fluid, rendering
the surrounding water so cloudy that it is often enabled to retreat
unobserved. The 'ink' of the _Sepia_ was used for writing in former
times, and is still employed in the preparation of the artist’s pigment
that bears the same name. Fishermen are well acquainted with this
peculiar characteristic of the animal, for they are frequently
bespattered with the contents of the ink bag of the _Sepia_ when the
creature is included in the contents of their draw-nets, and have learnt
to handle it cautiously until the objectionable fluid has been all
discharged.
[Illustration: FIG. 187.--EGGS OF _Sepia_]
We will conclude this chapter by giving a tabular summary of the
classification of the molluscs which will probably be useful to the
collector of marine objects.
CLASSIFICATION OF THE MOLLUSCA
Class =LAMELLIBRANCHIATA=--Plate-gilled. Headless, usually enclosed
in bivalve shell.
Section =SIPHONIDA=--Mantle lobes more or less united to form
tubular siphons.
Families--_Pholadidæ_, _Gastrochænidæ_, _Anatinidæ_,
_Myacidæ_, _Solenidæ_, _Tellinidæ_, _Mactridæ_,
_Veneridæ_, _Cyprinidæ_, _Lucinidæ_, _Cardiadæ_, &c.
Section =ASIPHONIDA=--Mantle lobes free or nearly so. No true
siphons.
Families--_Arcadæ_, _Mytilidæ_, _Aviculidæ_, _Ostreidæ_,
&c.
Class =CEPHALOPHORA=--Head-bearing. Usually enclosed in a univalve
shell.
Section =PTEROPODA=--Wing-footed molluscs.
Section =GASTEROPODA=--Stomach-footed molluscs.
Order =Nucleobranchiata=--Viscera form a nucleus on the back.
Order =Opisthobranchiata=--Shell generally absent. Gills more
or less exposed.
Section NUDIBRANCHIATA--Naked gills.
Section TECTIBRANCHIATA--Gills covered by shell or mantle.
Order =Pulmonifera=--Lung-breathers. Terrestrial.
Order =Prosobranchiata=.
Section HOLOSTOMATA--Aperture of shell entire (sea snails).
Families--_Chitonidæ_, _Dentaliadæ_, _Patellidæ_,
_Calyptræidæ_, _Fissurellidæ_, _Haliotidæ_,
_Turbinidæ_, _Littorinidæ_, _Turritellidæ_,
_Cerithiadæ_, _Pyramidellidæ_, _Naticidæ_, &c.
Section SIPHONOSTOMATA--Possess a true siphon. Carnivorous.
Families--_Cypræidæ_, _Conidæ_, _Buccinidæ_, _Muricidæ_,
&c.
Class =CEPHALOPODA=--Sucker-bearing arms round the mouth.
Order =Dibranchiata=--Two gills.
Section OCTOPODA--Eight arms.
Families--_Argonautidæ_, _Octopodidæ_.
Section DECAPODA.
Families--_Teuthidæ_ (Calamaries, Squids), _Sepiadæ_, &c.
Order =Tetrabranchiata=--Four gills (containing _Nautilidæ_).
CHAPTER XIII
_MARINE ARTHROPODS_
The sub-kingdom _Arthropoda_ contains a vast assemblage of animals, all
of which, as the name implies, possess jointed appendages. Their bodies
are covered with a skin that is hardened by a horny substance
(_chitin_), and frequently, also, by the deposit of carbonate of lime.
The body of Arthropods is made up of a chain of segments, all of which
are built up on one common pattern, and each one is surrounded by a ring
of the hardened skin or exo-skeleton that gives attachment to a pair of
appendages. Commonly, however, two or more of the segments become fused
together, being covered by a continuous plate or shield, in which the
boundaries of the rings are almost or completely obliterated; but in
such cases the appendages they bear always remain distinct, so that the
true number of segments is always apparent. The skin between those
segments that are not so fused together remains soft and flexible, thus
allowing the body to be freely bent.
The appendages exhibit a great variety of structure, and are as varied
in their functions. Some are used as feelers, and others as jaws for
seizing or masticating food. Some are developed into powerful seizing
organs for purposes of defence or attack, some into paddles for
swimming, while others are legs adapted for walking.
All these appendages are made up of segments, each of which, like those
of the body itself, is surrounded by a ring of hardened skin, and
connected with its neighbours by a flexible integument that allows
perfect freedom of movement; while within are the muscles, often very
powerful, by which the appendage is moved.
In the arthropods we have a sub-kingdom of highly organised animals,
with distinct, and often very complicated, systems of organs for
digestion, circulation, and respiration; and the nervous system consists
of a well-developed chain of ganglia, connected by nerve cords, and from
which nerve fibres are distributed to the various parts of the body. It
should be noted, however, that some members of the group have
degenerated into parasites, and in these, as with all such degraded
creatures, many of the organs have retrogressed to such an extent that
they are quite functionless, or have even disappeared entirely. These
parasitic forms, when very young, are really highly organised creatures,
not unlike the young of their industrious and more noble relatives; but,
as the natural result of their degraded mode of living, in which they
find no use for their organs of locomotion, digestion, circulation and
respiration, these eventually disappear, with the result that the organs
of reproduction predominate to such an extent that they often fill the
greater part of the cavity of the body.
It should be noted, too, that the sense organs of arthropods are well
developed, most of them being supplied with complex eyes, hearing
organs, and highly sensitive feelers.
This sub-kingdom consists of four classes--the _Crustacea_, including
lobsters, crabs, shrimps, prawns, &c.; _Arachnoidea_, containing
spiders, mites, and scorpions; _Myriopoda_--centipedes and millepedes;
and _Insecta_.
[Illustration: FIG. 188.--THE NERVE-CHAIN OF AN ARTHROPOD (LOBSTER)
_o_, optic nerve; _c_, cerebral ganglion; _i_, large ganglion
behind the œsophagus; _th_, ganglia of the thorax; _ab_, ganglia
of the abdomen]
The first of these classes consists mainly of marine animals, and will
therefore occupy much of our attention, but the members of the other
three are mostly terrestrial and aërial creatures that do not fall
within the scope of this work, except in the case of a few species that
are more or less decidedly marine in their tendencies. The aquatic
members are generally provided with well-formed gills by means of which
they are enabled to extract the dissolved oxygen from the water in which
they live, while those of terrestrial and aërial habits breathe by means
of a system of tracheæ or air-tubes that are open to the air and supply
branches to all parts of the body.
The _Crustaceans_ are mostly gill-breathers, though some of the aquatic
species have no special organs for respiration, but obtain the oxygen
necessary for respiration by absorption through their thin, soft skin,
while the terrestrial species breathe by means of tracheæ, as we have
just observed.
Most of them are covered with a calcified skin, as in the case of crabs
and lobsters; but many are protected with a chitinous or horny covering
such as we observe in shrimps and prawns. In either instance the
hardened integument constitutes what is known as the _exo-skeleton_.
None of the crustaceans have an internal skeleton of any kind, though
some of the inner parts are supported by extensions of the hard skin
that penetrate into the body.
It will be readily understood from the nature of the exo-skeleton of the
crustacean, and especially of the more or less rigid calcareous covering
of the crab and the lobster, that a uniform growth of the body is
absolutely impossible, and, in fact, that an increase in size cannot
take place without an occasional casting of the hard coat of mail. Hence
we find most crustaceans throwing off their coverings at intervals, and
growing by fits and starts during the periods between the ‘moultings’
and the hardening of the newly exposed skin.
When a crab or a lobster is about to undergo the process of moulting, it
retires to a secluded niche in the rock, where it is not so easily found
by its numerous enemies--a necessary precaution, since the creature in
its soft or unarmoured condition is eagerly devoured by fishes and other
marine animals--and there awaits the first stage of the ordeal.
Presently the skin splits; and, after a time, the crustacean succeeds in
extricating itself from its shell, which is cast off in a perfect
condition, every joint being entire, even to the coverings of the
antennæ, the stalked eyes, and other delicate appendages. And not only
this, for the portions of the shell that penetrate inward into the body
are also discarded, as well as the linings of the stomach and the gills;
and these cast-off coats of crabs and lobsters--especially the
former--may often be found in the most perfect condition on the sea
shore, being washed up without injury on the sandy beach, or found in
the very niche in which the creature changed its attire.
If one examines the powerful pincers of a crab or lobster, a thin plate
of considerable size will be seen to extend within from the movable
‘jaw’ to give attachment to the muscles by which it is moved, and it
seems impossible that this can be removed with the cast skin without
considerable injury to the new claw that is already formed, though as
yet in a soft condition, within the old and hard one. But it has been
observed that this plate actually cuts through the new claw, and that
the claw thus divided almost immediately closes up and unites again.
The moulting process being over, the crustacean’s body extends itself
within the new, yielding skin; and, the latter becoming gradually hard
by the deposition of carbonate of lime, the creature is able, after a
period of rest, to roam at large again, without much fear of injury,
until the time for the next moulting has arrived.
Those who have made but a slight acquaintance with the common
crustaceans of our shores must have noted the frequency with which
imperfect specimens occur--specimens with missing appendages, or with a
well-formed limb on one side of the body opposed to a puny and almost
useless fellow on the opposite side. As to the loss of appendages, this
matter will be readily understood by those who have watched crustaceans,
and especially crabs and lobsters, in their native element, so often do
these pugnacious creatures become engaged in furious broils with their
neighbours. And, when we are at work at the collection of various
species on the sea shore, how often do we find that a creature escapes
from our grip by leaving us in possession of a severed limb, while the
owner retreats rapidly among the stones and weeds apparently none the
worse for its trifling loss! This is, in fact, a very common method of
securing its escape from an enemy; and it appears that many crustaceans
have the power of thus rendering a seized limb so brittle that it may be
snapped off with the greatest of ease.
We have spoken of the loss thus sustained as a trifling one; and so it
is, for crustaceans have the faculty of reproducing lost appendages; and
though the loss may be one of considerable inconvenience at first, a new
limb eventually appears in the place of each one so willingly discarded.
When such mutilations occur, it will be observed that the severed limb
invariably breaks away at the end of the first or basal joint--a point
where the bloodvessels are so narrow and contractile that but little
loss of blood takes place when the rupture is made--and it has been said
that the animal would soon bleed to death if the fracture were to take
place at any other point. As it is, the wound soon heals, but no trace
of a new limb is to be seen, at least without dissection, until the time
of the next moult. The part is developing, however, beneath the cover of
the basal joint; and when the moulting period arrives, the new limb,
still very small, is exposed to view. It then rapidly enlarges, though
not to anything like its proper size, and its surrounding skin becomes
hardened by the deposit of the calcareous secretion simultaneously with
that of the rest of the body. Further enlargements of the new appendage
take place at subsequent moults, with the final result that it is but
slightly inferior to its fellow either in size or in power.
The eye of a crustacean is a very complicated structure, commonly
described as a compound eye. It consists of a large number of conical,
radiating, crystalline rods, collected together into a mass that
presents a convex outer surface. This surface is covered with a
transparent layer of chitin which naturally presents a more or less
distinct netted appearance, the bases of the rods being in contact with
its inner surface, and visible through it. Each rod is surrounded by a
layer of pigment that prevents light from passing from one to another,
and the optic nerve passing into the base of the compound structure
sends a sensitive filament into each one.
[Illustration: FIG. 189.--SECTION THROUGH THE COMPOUND EYE OF AN
ARTHROPOD]
In many crustaceans this compound eye is situated on the end of a
movable stalk that generally allows it to be protruded or drawn under
cover as occasion requires, but in others the organ does not project
beyond the general surface of the body. Thus we hear of the animals of
this class being divided into the _stalk-eyed_ and the _sessile-eyed_
groups; the former being represented by crabs, lobsters, shrimps, &c.;
and the latter by sandhoppers and sandborers.
Crustaceans undergo metamorphoses while very young, the body being
altered considerably in form at several successive moults. Some, in
their earliest stage, consist of a little oval body that shows no signs
of a division into segments. It swims about by means of three pairs of
appendages, and has only one eye. Others start life with four pairs of
limbs, attached to the front portion of the body, a segmented abdomen,
as yet perfectly limbless, and a pair of compound eyes. Then as the
successive moultings take place, new segments and new appendages are
developed, until, at last, the form of the adult is assumed. The
accompanying illustration shows four stages in the development of the
Common Shore Crab.
[Illustration: FIG. 190.--FOUR STAGES IN THE DEVELOPMENT OF THE COMMON
SHORE CRAB]
The lowest division of the crustaceans contains the _Cirripedia_ or
Curl-footed crustaceans, which includes the Barnacles that are so
frequently seen attached to the bottom of ships and of floating timber,
and the Acorn Barnacles, the conical shells of which often completely
cover large masses of rock on our shores.
[Illustration: FIG. 191. THE BARNACLE]
For some time naturalists could not agree as to the proper place of
these animals in the scale of life, but the matter was finally settled
when some minute creatures only about a twelfth of an inch in length,
and closely resembling the early stages of certain crustaceans, were
seen to undergo metamorphoses, and finally develop into acorn barnacles.
Their position in the animal kingdom was thus determined by their early
stages; but these, instead of changing into a segmented and highly
organised creature like the typical crustacean, lose some of their
appendages, cease to be free-moving animals, and attach themselves to
floating bodies by which they are carried about. Thus they are enabled
to find the food they can no longer seek without such aid. In their
young state they possess not only the means of freely moving in search
of their food, but have organs of vision to aid them in the capture of
their prey. As they grow, however, the foremost appendages are
transformed into a sucking-disc, and the eyes, no longer necessary,
disappear. It will thus be seen that the degenerated adult--the product
of a _retrograde development_--is attached by what was originally the
front of its body, while the abdomen is undeveloped, and the thorax,
with its appendages, forms the summit of the free extremity.
[Illustration: FIG. 192.--FOUR STAGES IN THE DEVELOPMENT OF THE ACORN
BARNACLE
A, newly hatched larva; B, larva after second moult; C, side view
of same; D, stage immediately preceding loss of activity;
_a_, stomach; _b_, base of future attachment. All magnified]
Some of the Cirripedes attach themselves to the bodies of whales and
other marine animals. The majority of these are
pseudo-parasites--creatures that live on the bodies of other animals,
but do not derive their food at the expense of their hosts; others,
however, are true parasites, subsisting on the nourishing juices they
extract from the animals to which they are attached.
[Illustration: FIG. 193.--A CLUSTER OF ACORN SHELLS]
The Acorn Barnacles, so numerous on our shores, are good types of the
_Cirripedia_, and they are so easily kept alive in the indoor aquarium
that their interesting movements may be well observed. A cluster of
these animals may be obtained by chipping off a piece of the rock on
which they grow; or, instead of this, a few minutes’ searching on a
rocky coast at low tide will certainly provide us with a stone of
suitable size, or the shell of a mollusc, on which the creatures have
found a home.
[Illustration: FIG. 194.--SHELL OF ACORN BARNACLE (_Balanus_)]
Place them in the indoor aquarium, or in any shallow vessel containing
just sufficient sea-water to cover them, and carry out your
observations with the aid of a hand lens. They will soon open the inner
cone of their many-valved shell, and slowly protrude six pairs of
gracefully curved and delicately-feathered appendages which, as
previously stated, are attached to the thoracic portion of the body.
Then, with a much more rapid movement, the appendages will be withdrawn,
and the shell closed. These alternate movements are continued
incessantly, and are the means by which the animals provide themselves
with both food and air. The reader should also obtain some specimens of
the larger species for the examination of the shell, the structure of
which is interesting and, of course, peculiar to this order.
[Illustration: FIG. 195.--THE ACORN BARNACLE (_Balanus porcatus_) WITH
APPENDAGES PROTRUDED]
In general structure and habits Barnacles are very similar to the acorn
barnacles, except that the body is supported on a tough stalk, which, as
we have already stated, is the modified anterior portion of the animal.
These animals also may be easily kept alive and examined in the indoor
aquarium. They are not creatures of the sea shore, but may often be
obtained on masses of timber that have been washed ashore, or from the
bottoms of ships that have been placed in the dry dock for repairs.
Another order of the crustaceans--the _Copepoda_, or oar-footed
group--is so called on account of the bristled feet that are employed
after the manner of oars when the creatures are swimming.
These Copepods are small animals, so small indeed that the compound
microscope is generally necessary merely for the examination of their
external characters. Many species inhabit fresh water, and the study of
the group is more commonly pursued by the investigator of fresh-water
pond life than by the sea-side naturalist. However, marine species are
abundant, and may be captured in the open water or in rock pools by
means of a muslin net. As with the last order, some degenerate from the
comparatively complicated free-swimming and eyed larval state to blind
and limbless parasites that feed on the bodies of fishes and are known
as fish lice.
The body of the typical copepod is distinctly segmented, and the head
and thorax are both enclosed in a hardened buckler. It has two pairs of
antennæ, two pairs of foot jaws by which it captures its prey, and four
or five pairs of bristled feet for swimming. The jointed abdomen has
also a tuft of bristles at its extremity. The annexed illustration
represents some marine species, and will serve to show the general
features of the order.
[Illustration: FIG. 196.--A GROUP OF MARINE COPEPODS, MAGNIFIED]
The sea-side naturalist, intent on the collection of small life, may
possibly meet with representatives of two other orders of
crustaceans--the _Ostracoda_ or shelled crustaceans, the bodies of which
are enclosed in a bivalve, hinged shell; and the _Branchiopoda_, so
called because the branchiæ or gills are attached to the feet.
[Illustration: FIG. 197.--A GROUP OF OSTRACODE SHELLS]
The Ostracodes have two or three pairs of feet which subserve
locomotion, but are not adapted for swimming; and two pairs of antennæ,
one of which assists in locomotion. The mouth is provided with organs of
mastication, the branchiæ are attached to the hind jaws, and the
animals have but one eye. Some of these crustaceans inhabit deep water
only, while others live in sand between the tide-marks; but several
species, belonging chiefly to the genus _Cythere_, abound in rock pools,
where they may be readily obtained by scraping the confervæ and
corallines with a small muslin net.
The branchiopods are free swimmers, and are protected by a buckler-like
envelope. Most of them are inhabitants of fresh water, and are popularly
known as water fleas. We have figured one marine species, belonging to
the genus _Evadne_, which has a colourless body, and a single
conspicuous black eye, and is interesting as being the food of the
herring.
[Illustration: FIG. 198.--_Evadne_]
The four orders of crustaceans that have been briefly described belong
to the division _Entomostraca_, which signifies ‘shelled insects.’ This
term is not a happy one when judged from the standpoint of our present
knowledge of animal life, but it must be remembered that, at the time it
was applied (1785), spiders and crustaceans were all included in the
same class as the insects; and this is hardly surprising when we observe
the close relationship of these animals, as shown in their segmented
bodies and jointed appendages; for, as we have already shown, the lowly
organised parasitic crustaceans which, in the adult state, lose most of
their appendages and cease to be distinctly segmented, are more or less
insect-like in their larval and free-swimming stage.
All the other crustaceans are included under the term _Malacostraca_, or
soft shelled, since, although many of them are protected by an
exo-skeleton that is hardened by the deposit of carbonate of lime, yet,
generally speaking, their coverings are softer than those of the
molluscs; and therefore the term _Malacostraca_ was originally applied
by Aristotle in order to distinguish them from the animals that are
covered by harder and thicker shells.
This division of the crustaceans contains wood lice, sandhoppers,
lobsters, shrimps, crabs, &c., and consists of two main groups--the
Sessile-eyed (_Edriophthalmata_) and the Stalk-eyed (_Podophthalmata_)
crustaceans.
We shall now consider the Sessile-eyed group, dealing first with the
order _Isopoda_ or equal legged, and then the _Amphipoda_, which have
appendages adapted both for walking and swimming.
The general nature of an Isopod may be readily understood by the
examination of the common woodlouse that abounds in gardens and damp
places almost everywhere, and the reader will probably remember having
seen similar creatures crawling over the rocks on the sea shore.
The body is generally depressed or flattened, but convex above, and is
composed of seven segments, each segment bearing a pair of legs which
terminate in a pointed claw, while the posterior appendages are modified
into flat, leaf-like organs of respiration.
[Illustration: FIG. 199.--MARINE ISOPOD
1. _Sphæroma serratum._ 2. _Limnoria lignorum._ 3. _Ligia
oceanica._ 4. _Nesæa bidentata._ 5. _Oniscoda maculosa_]
When engaged in ‘shrimping’ one frequently meets with shrimps or prawns
that are disfigured by a tumourous swelling on the side of the body, and
if the swelling be opened a little parasite will be dislodged. This
parasite is an Isopod (_Bopyrus_), the appendages of which are
imperfectly developed. The female is very much larger than the male,
and, as is usual with parasitic creatures, the greater part of the
body-cavity is occupied by the well-developed organs of reproduction.
There are several other parasitic isopods, some of which live on the
bodies of fishes, and are popularly known as fish-lice, but these are
not so likely to come in the way of the sea-side naturalist as the more
typical forms that crawl about on the rocks and among the weeds of the
coast. A few of the latter are shown in the accompanying illustration,
including the Sea Pill-ball (_Nesæa bidentata_), common on the rocky
coasts of the south-west, and distinguished by the two sharp
projections on the last segment; the Serrated Pill-ball (_Sphæroma
serratum_), very common on most rocky shores, and characterised by the
fine sawlike teeth on the outer edge of the outer plates of the ‘tail’;
the Great Sea-slater (_Ligia oceanica_), also an abundant species; the
Spotted Hog Louse (_Oniscoda maculosa_) that lives among the tufted sea
weeds; and the Boring Pill-ball (_Limnoria lignorum_) that bores into
the woodwork of piers and jetties, often doing considerable damage.
[Illustration: FIG. 200.--MARINE AMPHIPODS
1. The spined sea screw (_Dexamine spinosa_). 2. _Westwoodia
cœcula._ 3. _Tetromatus typicus._ 4. The sandhopper (_Orchestia
littorea_). 5. _Montagua monoculoides._ 6. _Iphimedia obesa._ All
enlarged]
The above and other isopods feed on various animal and vegetable
substances, some species being quite omnivorous in habit. Most of them
are eagerly devoured by birds and fishes.
The Amphipods, six species of which are shown in the above illustration,
include the Sandhoppers or Beach Fleas, so numerous on our coasts that
it is almost impossible to go any distance without making their
acquaintance. They are invaluable as scavengers, as they rapidly devour
decaying sea weeds, and will speedily reduce the body of any animal
washed on the beach to a clean skeleton. Although they are all small
creatures, they make up in numbers for any deficiency in size; and
though devoured in enormous quantities by the various shore birds, they
multiply so prodigiously that they are never lacking wherever there is
decomposing organic matter to be consumed.
The bodies of these animals are usually flattened from side to side,
very distinctly segmented, and have a well-developed abdomen. The head
is furnished with two pairs of antennæ and a pair of sessile eyes,
though some species possess only one pair of antennæ, while others have
four eyes. The limbs of the thorax are used either for walking or for
swimming, and give attachment to the gills. The abdomen has generally
six pairs of appendages, the foremost three pairs of which are usually
small, and employed in swimming, while the others are stronger and
directed backwards, and are often adapted for jumping.
It is very interesting to observe the habits of the Sandhoppers and
other Amphipods both on the sandy beach and in the water, and the
student will find that certain species burrow into the sand with
considerable agility, and live principally at the extreme high-water
mark, where they feed on the organic matter washed in by the breakers at
each high tide, while others dwell almost exclusively in the water,
among weeds and stones, and should be searched for at low water. The
latter may be kept alive for some time in the aquarium providing they
are the only occupants, but a little experience will show that these and
all other Amphipods are readily devoured by many marine creatures, and
consequently they are of real value to the aquarium keeper as food for
other animals.
We now come to the Stalk-eyed Crustaceans (_Podophthalmata_), which
contain those members of the class most generally known, such as crabs,
lobsters, shrimps, and prawns. In these the eyes are mounted on movable
pedicels, the head and thorax are generally covered by a large shield
called the carapace, and the appendages are adapted partly for seizing
and masticating, and partly for locomotion.
The group includes two orders--the _Stomapoda_ or Mouth-footed
crustaceans, so called because some of the limbs are crowded round the
region of the mouth; and the _Decapoda_, or Ten-footed crustaceans.
The Stomapods, though very abundant in tropical seas, are not often met
with on our own shores. However, since a few interesting species are
inhabitants of our seas we will briefly describe the distinguishing
characteristics of the group.
We have just mentioned the fact that the head and thorax of a decapod is
usually covered by a large shield--the carapace. Now, the general
character of this carapace may be seen at once in either the shrimp or
the lobster. In these animals the segments that form the head and the
thorax are all fused together, and are completely covered by the
protective buckler of hardened skin; but in the Stomapoda the carapace
is much smaller in proportion, and a few of the segments of the thorax,
instead of being fused into the general mass of the _cephalo-thorax_,
are quite distinct from it. The abdomen, also, is large and strongly
formed in these animals. Five pairs of the thoracic limbs are directed
forwards, and are adapted both for catching food and for climbing, while
others are used in walking. The limbs of the abdomen generally number
six pairs, of which the first five bear feathery gills.
[Illustration: FIG. 201.--THE MANTIS SHRIMP (_Squilla Mantis_)]
Two species of Mantis Shrimps, one of which is represented in fig. 201,
have been found off the south and south-west coasts, but these are not
likely to be seen on the shore, since they inhabit deep water. Allied to
these, and sometimes included with the Stomapods, are the Opossum
shrimps, so called because the females of some species carry their eggs
in a kind of pouch, thus reminding us of the marsupial quadrupeds of the
same name. They are of very slender build compared with the mantis
shrimps, and differ from them in that the carapace completely covers the
thorax; but though this is the case, the fusion of the thoracic segments
is not complete, since the posterior ones have still a certain amount of
freedom of movement. Some species of opossum shrimps are abundant in the
rock pools of our coasts, particularly in the south-west, but their
bodies being often so transparent as to be almost invisible, they are
consequently easily overlooked. Their general appearance may be
gathered from our illustration of _Mysis chamæleon_, which is probably
the most common species inhabiting our coast.
The highest crustaceans--the Decapods--are divided into two
sub-orders--the _Macrura_, or Great-tailed, including lobsters, shrimps,
&c.; and the _Brachyura_ (Short-tailed), containing the crabs; but the
number of British species is so large that it is impossible to give, in
our limited space, a detailed description of all the commonest even. All
we can do is to note a few of the more interesting features of certain
species, to introduce such illustrations as will enable the young
naturalist to identify a number of the commoner ones, and to give the
general characteristics of the main divisions so that the student may be
able to classify his specimens intelligently.
[Illustration: FIG. 202.--THE OPOSSUM SHRIMP (_Mysis chamæleon_)]
In the _Macrura_, as with other divisions of the crustaceans, we meet
with very interesting modifications of the appendages, adapted to quite
a variety of uses; and if the reader is unacquainted with these
adaptations of structure to habit he cannot do better than secure a
lobster or crayfish for study. It will be observed that the body may be
divided into two main portions--the _cephalothorax_, consisting of head
and thorax combined, and the _abdomen_. The former is composed of
fourteen segments, so thoroughly fused together that they are denoted
only by the fourteen pairs of appendages to which they give attachment,
while the calcified skin forms one continuous shield surrounding the
whole. The abdomen, on the other hand, consists of six distinct
segments, each of which is surrounded by its own ring of the hardened
integument, and is connected with its neighbours by means of a portion
of uncalcified skin that renders the whole very flexible. A groove in
the front portion of the great shield (_carapace_) marks the division
between the head and the thorax, the former composed of six, and the
latter of eight united segments.
[Illustration: FIG. 203.--PARTS OF LOBSTER’S SHELL, SEPARATED, AND
VIEWED FROM ABOVE]
The calcareous covering of each segment consists of an upper portion,
called the _tergum_, and a lower, named the _sternum_, united at the
sides; the sternal portion of the cephalothorax, which gives attachment
to the walking limbs, is a most complicated and beautifully formed
structure.
[Illustration: FIG. 204.--A SEGMENT OF THE ABDOMEN OF A LOBSTER
_t_, tergum; _s_, sternum, bearing a pair of swimmerets; _h_,
bloodvessel; _d_, digestive tube; _n_, nerve chain]
The six pairs of appendages belonging to the head are easily made out
with a little care. The first are the jointed _eye-stalks_ that bear the
compound eyes previously described; and these are followed by two pairs
of _antennæ_, or feelers, the first being shorter and double, while the
second are very long. The former contain the organs of hearing. Then, in
front of the mouth, and completely hiding it, are a pair of strong
_mandibles_ or jaws that move horizontally, and the two pairs of
_maxillæ_ that are also employed in reducing the food.
Following these, but belonging to the thorax, are three pairs of
appendages that are known as foot-jaws; for, although they assist the
preceding organs in breaking up the food, they bear a resemblance in
some respects to the longer limbs behind them. Of the latter there are
five pairs (hence the term _decapoda_), the first being a very powerful
pair of seizers or pincers, and the remaining four, which are well
adapted for walking, terminating in either double or single claws.
All the appendages above mentioned are not only attached to the body by
movable joints, but are themselves made up of jointed parts, sometimes a
considerable number, each of which, like the segments of the body
itself, is surrounded by a ring of hardened skin, and connected with
those above and below it by a portion of soft and flexible skin.
[Illustration: FIG. 205.--APPENDAGES OF A LOBSTER
1. Second maxilla. 2. Third foot-jaw. 3. Third walking leg.
4. Fifth walking leg]
Lastly, beneath the abdomen, are paired limbs called _swimmerets_, which
are used as paddles, and probably assist the animal more or less in its
progress through the water; but the principal organ of locomotion in the
_macrura_ is undoubtedly the powerful muscular abdomen, aided by the
broad and fanlike tail formed by the appendages of the last segment. To
demonstrate this fact, put a live lobster, or even a shrimp, in a still
rock pool, and threaten it from before, when it will rapidly retreat
backwards by a series of powerful jerks, produced by suddenly doubling
its abdomen forwards beneath its body.
In addition to the external characters above mentioned, there are many
interesting features connected with the internal structure of the
lobster that may be studied on making easy dissections. Thus, the gills,
which are attached to the bases of the thoracic limbs, may be exposed by
cutting away the side of the carapace, and at the same time we may
discover the bailing organ by means of which a current of water is kept
flowing forwards through the gill-cavity to keep up the necessary supply
of oxygen for respiration. The removal of the upper portion of the
carapace will expose the heart and some of the principal bloodvessels,
and also the stomach with its powerful and complicated ‘gastric mill,’
formed by the hardening of portions of the wall of the latter organ for
the purpose of crushing and masticating the food. Then, if these organs
be carefully removed from above, together with the others we have not
space to describe, and the powerful muscles that fill up the segments of
the abdomen, the chain of ganglia and their connecting nerve cords that
form the central part of the nervous system may be seen extending along
the central portion of the body.
[Illustration: FIG. 206.--LONGITUDINAL SECTION OF THE LOBSTER
_a_, antenna; _r_, rostrum or beak; _o_, eye; _m_, mouth; _s_,
stomach; _in_, intestine; _l_, liver; _gl_, gills; _h_, heart;
_g_, genital organ; _ar_, artery; _n_, nerve ganglia]
Several species of lobsters inhabit our seas, but they are generally to
be found beyond the tide-marks, and are, therefore, not often caught by
sea-side collectors without the aid of some kind of trap or the
assistance of fishermen. The common lobster (_Homarus vulgaris_),
however, is often left behind by the receding tide on our rocky coasts,
and may be seen and caught if one knows where to look and how to
capture.
On cautiously approaching a deep rock pool one may often see a lobster
rapidly retreat in its usual backward fashion, and snugly house itself
in a narrow chink from which it is impossible to remove it. And, when
once surprised, it is not likely to show itself again as long as the
intruder is in view.
If one remains perfectly still for a time, a pair of waving antennæ may
be seen gradually protruding from the safe retreat; but, as soon as the
stalked eyes have advanced sufficiently to detect the figure of a
stranger, the lobster silently withdraws itself till quite out of sight.
Lobsters, usually of rather small size, may often be seen quite out of
the water at low tide, in the narrow chinks of the rock, or under large
stones, but it is no easy matter, as a rule, to get them out. It is of
little use poking a stick into the entrance of their hiding-places,
though occasionally they will grasp the stick so tenaciously with their
forceps that they may be pulled within reach. You _may_ be able to haul
them out by their long antennæ, but if you can find a second way into
their home such that you can disturb them from behind you are pretty
sure of your victim.
[Illustration: FIG. 207.--THE SPINY LOBSTER (_Palinurus vulgaris_)]
It will be unnecessary to describe other species of lobsters
individually, but we have introduced figures of a few for
identification. The Norway Lobster (_Nephrops norvegicus_) is often
landed in large numbers by the fishermen of the east and south-east
coasts and sold at a shilling or so a dozen under the name of Norway
Prawns. They are pretty and interesting creatures, and may be easily
kept alive in the indoor aquarium, where they may be fed on any kind of
fish.
[Illustration: FIG. 208.--THE NORWAY LOBSTER (_Nephrops norvegicus_)]
Fig. 209 represents the two allied creatures that may sometimes be dug
out of the sandy beach, or from the mud in the estuary of a river. The
one on the left is the mud-borer (_Gebia stellata_), which is of a dull
yellowish colour, marked more or less distinctly by pinkish starlike
spots--a feature that has suggested the specific name. The beak in front
of the carapace is very prominent and spiny, and the long abdomen is
narrower in front than in the middle. This creature hides in the holes
that have been excavated by boring molluscs, and seems also to extend
the cavities it inhabits by its own labours.
The other is very similar in general form, but has no spiny beak and the
abdomen is much broader in the middle than at the base. It is also to be
distinguished by the very unequal size of its front legs, one of which
is much more developed than the other.
It is known as the mud-burrower (_Callianassa subterranea_), and is said
to burrow very deeply into mud-banks, scooping out its retreat
principally by means of the second and third pairs of legs. Although
found at times between the tide-marks, its principal habitat is probably
in the mud that is covered by deep water, for it is not uncommonly to be
found in the stomachs of fishes that habitually feed in such localities.
[Illustration: FIG. 209.--THE MUD-BORER (_Gebia stellata_) (1) AND THE
MUD-BURROWER (_Callianassa subterranea_) (2)]
Lobsters of all kinds, and, indeed, the marine crustaceans generally,
are essentially the scavengers of the sea, for they are carrion-feeders,
greedily devouring flesh in all stages of decomposition. Hence the value
of their work on the sea shore is very considerable.
An examination of shrimps and prawns will at once show their close
relationship with lobsters. The general build of their bodies is
practically the same, and their appendages, though often different in
form from the corresponding limbs of the lobster, will be seen to
resemble them closely in arrangement and structure. The exo-skeletons
of these creatures are, however, generally hardened by a horny substance
(_chitin_) instead of a stony deposit of carbonate of lime.
The shrimps and prawns sold for food in our markets are very similar in
appearance when alive, the leading distinguishing feature being,
perhaps, the presence of a sharp, serrated beak projecting forward from
the front portion of the carapace of the latter.
The reader is probably acquainted with the fact that the shrimps and
prawns used as food have quite a different appearance when alive and in
their native element to that displayed by the corresponding wares in the
fishmonger’s shop--a fact that applies equally well to the edible crabs
and lobsters. Most crustaceans change to a bright red colour when
boiled, and, as stated in a previous chapter, the same result is
produced by the action of strong spirit.
[Illustration: FIG. 210.--THE COMMON SHRIMP (_Crangon vulgaris_)]
The Common Shrimp (_Crangon vulgaris_) is an exception, however, for it
may be distinguished when boiled by its dull greyish brown colour. When
alive this species is of a very pale greenish or greyish tint, lightly
spotted with brown; and its habits are so interesting that it will well
repay one to watch it either in the aquarium or in a rock pool. It
frequents sandy coasts, and can hide itself very quickly by burying its
body in the sand, using for this purpose both its legs and its antennæ.
The Prawn frequents rocky coasts, where it may often be obtained in
large numbers by sweeping with a suitable net under the cover of weeds
and stones. Its body is of an exceedingly pale greenish colour, and so
transparent that it is quite inconspicuous when in the water. Prawns are
turned to a rose-red colour by boiling, and they are captured in large
numbers when young and sold as ‘red shrimps.’
In addition to the common species mentioned there are quite a number of
shrimps and prawns to be found in our seas, but some of them inhabit
deep water and are rarely to be found between the tide-marks. All,
however, are eagerly devoured by fishes, and, on that account, are often
to be obtained in good condition by examining the contents of the
stomachs of freshly caught fishes. In fact, this mode of search for the
smaller species of deep-sea life is not to be despised, for it is a
means by which we can obtain specimens that are not often secured by the
methods coming within the ordinary range of the amateur’s work.
It will be remembered that we spoke of the Decapods as consisting of two
main groups--the Great-tailed (_Macrura_) and the Short-tailed
(_Brachyura_). Frequently, however, we find the order divided into three
sub-orders as follows:--
1. _Macrura_ (Great-tailed), 2. _Anomura_ (Peculiar-tailed),
3. _Brachyura_ (Short-tailed);
the first containing lobsters, shrimps, &c.; the third the typical
crabs, such as the shore crab and the edible crab; while in the second
are placed those species of crabs which have been regarded as
intermediate in character. Thus, in the _Anomura_ we find decapods in
which the abdomen, though not so well developed as in the _Macrura_, is
either permanently extended or is capable of being extended and used for
swimming as occasion requires. The hindmost legs, also, are not well
developed and adapted for walking, but are employed only as organs of
prehension; and, as is the case with the first sub-order, there are
often two pairs of well-developed antennæ.
In this sub-order of ‘queer tails’ we find the Soldier or Hermit Crabs,
and those flat-bodied crabs that live almost exclusively on the surface
of stones, and are hence known as Stone Crabs; but as opinion now seems
inclined against the formation of a special suborder for these
creatures, we shall briefly deal with them as a first section of the
_Brachyura_.
The Stone Crabs are extremely interesting creatures, and the observation
of their habits, both in and out of the water, is particularly
entertaining and instructive. One species--the Broad-Clawed Porcelain
Crab (_Porcellana platycheles_), shown on Plate VI.--is very abundant on
all our rocky coasts, and may be found in immense numbers near low-water
mark.
Turn over some of the large encrusted stones that strew the beach among
the rocks, and you are almost sure to find numbers of these little crabs
clinging to the freshly exposed surface. A few of them may remain
perfectly still, and exhibit no sign of surprise on their untimely
exposure to the light; and these, on account of their small size, the
closeness with which they apply their flattened bodies to the encrusted
stone, and more than all to the protective colouring of their dingy
bodies, which so closely resembles that of the surface to which they
cling, may well be overlooked by the inexperienced collector. But the
majority of them will immediately scamper away in their own peculiar
fashion towards the edge of the stone, and rapidly make their way to
what is now the under side. As they progress with a hasty, sliding
movement they never for one moment loosen their firm hold on the rough
surface of the stone, but keep both body and limbs in close contact with
it, clinging hard by means of their pointed claws as well as by the
numerous hairs and bristles with which their appendages are liberally
fringed.
Attempt to pull one from its hold, or even take other than the gentlest
means to arrest its progress, and you will probably find that it
suddenly parts company with one of its broad claws in its endeavour to
escape; and, unless some special precautions be taken to remove these
crabs, it is possible that quite half the specimens taken will have been
damaged in this way during their struggles to escape. If, however, you
gently thrust the point of a penknife beneath the body, and then apply
the thumb above, you may lift them from a stone without injury. Another
plan is to press a frond of smooth sea weed as closely as possible to
the surface of the stone in the front of the crabs, and then allow them
to crawl on to it, or cause them to do so if necessary. The piece of
weed, with crab or crabs attached, may then be bagged for future
examination.
On turning over the Broad-clawed Crab its under surface will be seen to
be perfectly smooth, with an appearance closely resembling that of white
porcelain. Its foot-jaws, also, are proportionately large, and closely
fringed with hairs; and the last pair of legs, which are very slender in
build, are folded closely beneath the body. Further, the abdomen is
wide, composed of six distinct movable segments, and terminating in a
tail-fin composed of five fringed plates.
Drop the crab into water, and it will immediately extend its abdomen,
which it will flap sharply under its body somewhat after the manner of
lobsters and shrimps, and thus swim backward by a series of jerks as it
sinks to the bottom. On reaching the bottom it instantly grasps the
solid material, applies itself closely to the surface, and glides away
into the nearest chink it can find.
As one observes the nature and movements of these interesting little
crabs one cannot fail to see how beautifully their form and structure
are adapted to their habits. They are peculiarly constructed for abode
in narrow chinks and crannies, and for feeding on the small forms of
life that inhabit such sheltered places. Their legs move in the plane of
their flattened bodies, and as they glide among the confervæ and other
low forms of life that encrust the stones of the beach they feel their
way by, and are possibly also guided by the sense of smell located in,
their long outer antennæ, while the close fringes of their claws and
foot-jaws form admirable sweep-nets by means of which the little animals
that form their food are swept towards the mouth.
We have other species of stone crabs, one or two of which resemble the
last species, and belong to the same genus, but the others are very
different in general appearance. The Northern Stone Crab (_Lithodes_),
found principally on and off the coasts of Scotland and Ireland, has a
spiny covering with a long beak. Another species--_Dromia vulgaris_--is
somewhat similar in habit, though it can hardly be termed a stone crab,
since it inhabits deep water, and apparently lives among the sponges,
sea firs, and weeds that cover the bottom.
[Illustration: FIG. 212.--_Dromia vulgaris_]
[Illustration: FIG. 213.--THE HERMIT CRAB IN A WHELK SHELL]
The remainder of the Peculiar-tailed Decapods belong to the Soldier or
Hermit Crabs, and constitute the genus _Pagurus_.
Every one who has searched a few rock pools will have seen the familiar
Hermits, and will probably have been interested in their varied antics.
First you observe the shell of a mollusc--a Trochus, Periwinkle, or a
Whelk--travelling at an abnormal rate for a member of its class. You
approach closely to make an inquiry into the matter, when the motion
suddenly ceases, and the shell instantly drops into position with its
mouth close to the surface below. If left undisturbed for only a short
time, the rapid and somewhat jerky motion is resumed, only to cease as
suddenly as before as soon as the inhabitant is again threatened.
On examining the shell we find that it is the home of a species of crab,
and that the animal within it is completely hidden with the exception of
its head, stalked eyes and long, slender antennæ, one very large claw,
and a few walking legs.
To remove the creature from its home is no easy matter as a rule. To
pull it out by means of its legs or its antennæ would probably be to
sever some portion of its body; but if you thrust the creature, shell
and all, among the spreading tentacles of a large anemone, it will at
once grasp the peril of the situation; and, if the shell has already
been secured by the clinging petals of this dangerous marine flower, the
hermit will speedily quit its home and endeavour to rush from the many
snares in order to secure its freedom. Or, it not infrequently happens
that the occupied shell is one that has withstood many a storm, but not
without the loss of the apex of its cone. In this case the insertion of
a very flexible fibre into the opening thus made will cause the hermit
to leave its home in the possession of the enemy.
Having, by some means or other, managed to drive the crab from its
shell, we place it in a shallow rock pool, or in a vessel of sea water,
and observe the chief features of its structure.
The first thing that strikes one is the absence of a calcified skin on
the extended abdomen, which is so soft that, remembering with what
eagerness fishes will attack and devour crabs of all kinds, we can at
once understand the necessity of such a home as the creature selects.
Again, we observe the presence of appendages at the tip of the abdomen
by means of which the crab is enabled to hold itself securely in the
shell. Also, when we note the general form of the armoured portion of
the body, and the position of the soft-skinned abdomen, we can see how
well adapted the whole is to fit snugly into the spiral shell of a whelk
or winkle.
We also observe that one of the pincers is much larger than the other,
and the value of such an arrangement may be estimated when we see the
animal at home. The smaller claw, together with the other appendages
used for walking or prehension, can be retracted within the shell, but
the large claw, which constitutes a formidable weapon of attack and
defence, is not only in such a position as to be ready for immediate
use; but, lying as it does in front of the body, with other portions
hidden more or less behind it, it serves the purpose of a shield when
the animal retires.
If we place a homeless hermit crab in a rock pool, the behaviour of the
creature immediately suggests a feeling of uneasiness--a sense of
danger--for it moves about in a very erratic fashion that is quite
different from the straightforward and deliberate action of the same
animal when properly protected; and very amusing results may be obtained
by making it the subject of a few harmless experiments. For instance,
drop down before it an empty whelk-shell that is much too large to
properly accommodate its body. It will immediately approach the
untenanted house, search and probe it well with its antennæ and other
appendages, and then, finding it uninhabited, and having no apartment of
more suitable size at hand, will abruptly gives its body a turn and
hastily thrust itself backwards into it.
If at the time of this experiment the advancing tide disturbs the water
of the pool, the result is somewhat ludicrous, for the shell, too
cumbersome to be controlled by the creature within, is, regardless of
its attempts to maintain a normal position, turned over and over as each
wave advances and retreats.
Again, supposing the shell supplied to be too small for the intended
occupant, it will, after the usual examination of the interior, thrust
its soft abdomen as far in as possible, and make the best of the
unsatisfactory circumstances until a more suitable home can be found.
And if, at this distressing period, we drop before it a shell of just
the right size--the one from which the creature was originally expelled
for instance, it is astonishing how quickly the change of houses will be
accomplished. After a brief examination of the shell with the object of
determining whether all is right within, during which the crab continues
to avail itself of the imperfect accommodation afforded by the previous
shell, it rapidly extracts its body from the one and thrusts itself
backwards into the other. Its normal habits are at once resumed, all its
movements being now suggestive of confidence and contentment.
We have already referred (p. 153) to the fact that a large anemone
(_Sagartia parasitica_) is commonly found attached to a whelk shell,
which at the same time forms the home of the hermit crab, and (p. 44)
that a marine worm (_Nereis_) is also a common associate of the hermit,
taking up its abode in the interior of the same shell; and we also
briefly discussed the mutual advantage of such an arrangement to the
parties concerned. These triple combinations are not so frequently met
with on the shore between the tide-marks, but are dredged in
considerable numbers by the trawler; and the reader will find it repay
him to secure one in order that he may be able to watch the interesting
habits of the associates. The movements of the hermit crab are always
pleasing, particularly the manner in which it seizes and manipulates its
food; and still more so is the occasional appearance of the head of the
worm, always in exactly the same place, for the purpose of deliberately
stealing the food from the very jaws of the crab.
Hermit crabs are easily kept in captivity, and may be fed on any kind of
animal food, but care should be taken not to allow an excess of food to
remain in the water and render it putrid by decomposition. As long as
the crabs are active and remain within their shells you may assume that
the conditions are favourable; but when they become sluggish in their
movements, and leave their homes, the sanitary condition of the
aquarium should be regarded with suspicion; for hermit crabs, like many
of the marine tube worms, generally quit their homes when the conditions
are unfavourable, as if they preferred to die outside.
The Common Hermit Crab (_Pagurus Bernhardus_), also known as the Soldier
Crab, on account of its very pugnacious habits, is common almost
everywhere on our coasts, and may be distinguished by the numerous
little tubercles on the claws and on the upper edge of the front legs;
and there are several other species, belonging to the same genus,
distributed more or less locally on the various shores. All are similar
in general structure and habits, the various species being identified
principally by means of their colour, the variations in the form of the
appendages, and the general character--smooth, tubercular, spiny,
&c.--of the exo-skeleton. One species, found in the sandy bays of
Cornwall, burrows rapidly in the sand.
Coming now to the true crabs--the _Brachyura_, or Short-tailed
crustaceans, as sometimes distinguished from the _Anomura_--we find
quite a variety of interesting creatures, many species of which are
always within the reach of the collector at work between the tide-marks.
In all these the abdomen is only slightly developed, and is never used
in swimming, being permanently folded beneath the thorax. This portion
of the body, however, is usually very distinctly segmented, and if it be
lifted from its position it will be found that some of the segments bear
appendages corresponding with the swimmerets of the lobster. It is also
wider in the female than in the male, and crabs of the former sex may
often be found during the summer with the abdomen more or less
depressed, and the space beneath it quite filled with eggs.
The upper surface of the carapace of crabs is often very distinctly
grooved, and it is interesting to note that these features of the
exo-skeleton are not merely of external significance, for they usually
correspond in position with various internal structures, some of them
denoting the areas of the insertions of important muscles, and others
enclosing the regions of certain of the internal organs.
It will be noticed, too, that the carapace, which in lobsters is often
less than half the length of the body, covers the entire body of the
crab, except, perhaps, a very small linear portion between the bases of
the last pair of legs, where the first part of the segmented abdomen is
visible from above.
The true crabs of our seas may be divided into four groups, as follow:
1. _Oxystomata_, or Pointed-mouthed Crabs;
2. _Oxyrhyncha_, or Pointed-beaked Crabs;
3. _Catometopa_, with forehead turned downwards; and
4. _Cyclometopa_, or Round-headed Crabs;
and we shall briefly observe some of the more conspicuous and
interesting species in the order of the tribes as just given.
The first division is not well represented in our seas, the principal
species being the Nut Crabs and the Long-armed Crab, all of which may be
distinguished by the peculiar arrangement of the foot-jaws, which, when
closed, form a triangle with an acute angle turned towards the front.
The Nut Crabs are mostly small; and, since they generally inhabit deep
water, are not commonly seen on the shore; but perfect specimens may
sometimes be found among the contents of fishes’ stomachs. They derive
their name from the nature of the carapace, which is of a rounded form
and very hard and strong.
Pennant’s Long-armed Crab (_Corystes Cassivelaunus_) may commonly be
seen entangled among fishermen’s nets, but is not often seen on the
shore at low tide. Its carapace is very convex above, with three sharp
spines on each side, and the grooves are so arranged as to suggest the
appearance of a face. Our illustration represents the female, but the
‘arms’ of the male are very much longer than those of this sex.
The Sharp-beaked Crabs (_Oxyrhyncha_) include all those long-legged
creatures that are known collectively as the Spider Crabs; and here,
again, we have to do with species that almost exclusively inhabit deep
water. Although this is the case, but little difficulty is experienced,
as a rule, in obtaining specimens. If you are unable to take a trip in a
trawler for the purpose of examining the ‘rubbish’ that is dredged from
deep water, simply obtain permission to search the nets and the boats as
they arrive in port. In the latter case you are almost certain to find
the crabs you require, though it is probable that some of the species
will have been damaged by the hauling and shaking of the nets.
[Illustration: FIG. 214.--THE LONG-ARMED CRAB (_Corystes
Cassivelaunus_)]
These interesting crabs have been spoken of as the monkeys of the sea,
and the comparison will certainly be tolerated by anyone who has watched
the creatures as they climb among the corallines and sea firs in an
aquarium. Among such growths they are quite at home; and although their
movements do not often suggest the extreme agility of the monkey tribe,
yet the ease with which they seize the branches of the submarine forest
with their long ‘arms’ and pull their bodies from one tree-like
structure to another is decidedly monkey-like. Their comparison with the
long-legged spiders is also a happy one as far as their general form and
movements are concerned, but it must be remembered that they have not
the same reputation for cruel, predaceous habits, for they are more
truly the scavengers of the deep, subsisting mainly on the decomposing
bodies of their dead associates. The movements of most spider crabs are
so slow and deliberate that one can hardly imagine them capable of
anything of the nature of violent action; yet, when occasion requires
it, they will sometimes strike at the object of their wrath with a most
vigorous snap of their claws.
[Illustration: FIG. 215.--SPIDER CRABS AT HOME]
In these crabs, too, we find most interesting instances of protective
resemblance to their surroundings. Some of the small, slender-legged
species are not to be recognised without a careful search when they are
at rest among clusters of sea firs, their thin appendages and small
bodies being hardly discernible in the midst of the slender, encrusted
branches, and their peculiar forms are still more concealed by their
colouring, which generally closely resembles that of the growths among
which they live. Further, the carapace of spider crabs is in itself a
garden on which thrive low forms of both animal and vegetable life.
Minute _Algæ_, and occasionally some of moderate size, are rooted to the
shell, often securely held by the aid of the rough hairs and tubercles
that are so characteristic of the exo-skeletons of these creatures; and
patches and tufts of animal colonies that have found a convenient
settlement on the moving bed still further serve to obscure the nature
of the living mass below--a mass that is always in danger of becoming
the prey of the fishes which inhabit deep water. It is probable,
therefore, that this association is one that is beneficial to both
sides as far as the animal life is concerned, the lower species serving
to disguise the true nature of the crab, thus protecting it from its
numerous enemies, while they in return are conveyed, carriage paid, to
the feeding-grounds, where they can freely partake of the fragments that
become diffused in the surrounding water.
Our illustration on p. 288 shows three species of spider crabs, all of
which are common on parts of our shores. The Scorpion Spider Crab
(_Inachus dorsetensis_) derives its specific name from the fact that it
was first found off the coast of Dorset; but it is abundant off many of
our shores, both in the south and north, and may frequently be seen
entangled among the fishermen’s nets. It may be distinguished from other
and similar species by the four spines arranged in a line across the
front portion of the carapace, and the five large, pointed tubercles
behind them. This species is undoubtedly a favourite food of the cod,
for several specimens may often be taken from the stomach of a single
fish.
The next species--The Slender-beaked Spider Crab (_Stenorhynchus
tenuirostris_)--is seldom missing from the dredgings hauled in off the
south-west coast, and is fairly common in other parts. Its legs are
extremely slender, and bear spines on the inner side, and its body,
where free from the incrustations so often covering the carapace of
spider crabs, is of a fresh pink colour.
The other one shown in the same illustration is _Arctopsis lanata_,
sometimes known as Gibb’s Crab, the carapace of which is pointed behind,
bears a large pointed tubercle on each side, and is completely covered
with a thick clothing of stiff hairs. It is also common on many parts of
our coasts, more especially the coasts of Devon and Cornwall.
Closely allied to the last-named, and belonging to the same family, is
the well-known Thornback Crab (_Maia Squinado_), also a very common
crab, of which we give a separate illustration.
The tribe _Catametopa_ does not contain many British species, the
principal being the Pea Crabs; the Floating Crab, which is occasionally
washed on the south-west coast; and the beautiful Angular Crab. In these
the front of the carapace is turned downwards--a feature that has
suggested the name of the tribe.
The pea crabs are all small, and they are parasites, living within the
shells of bivalve molluscs. One species--the Common Pea Crab
(_Pinnotheres pisum_) is frequently found in the Edible Mussel; the
female, which is much larger than the male, being much more commonly
found. Another species--the Pinna Pea Crab (_P. veterum_), infests the
Pinna and Modiolus.
[Illustration: FIG. 216.--THE THORNBACK CRAB (_Maia Squinado_)]
[Illustration: FIG. 217.--THE PEA CRAB (_Pinnotheres pisum_)]
On Plate VI. is a drawing of the Angular Crab (_Gonoplax angulata_)
mentioned above, the striking form and delicate colouring of which can
never be mistaken. We would, however, call particular attention to the
broad and square front of the cephalothorax, with its two sharp spines,
and to the length of the eye-stalks. Unfortunately for the amateur, this
pretty crab is only to be found in deep water, off the coasts of Devon
and Cornwall, so that here, again, the aid of the fisherman is valuable;
but, as observed in the case of other deep-sea dwellers, may also be
looked for in the stomachs of cod and other bottom fishes. The sex
figured is the male, in which, when fully grown, the front legs are much
longer than in the female.
[Illustration: PLATE VI.
CRUSTACEA
1. Gonoplax angulata
2. Xantho florida
3. Portunus puber
4. Polybius Henslowii
5. Porcellana platycheles]
The remaining division of the crabs--the _Cyclometopa_ or Round-fronted
Crabs, contains the larger number of species that may truly be described
as common objects of the shore, for while some of them are well adapted
for swimming, and live in the open water, the majority inhabit the
shore, either between or just beyond the tide-marks, roaming about more
or less freely when in the water, but usually hiding under stones or
weeds, or burrowing into the sand, when left behind by the receding
tide.
[Illustration: FIG. 218.--THE COMMON SHORE CRAB (_Carcinus mænas_)]
The members of this tribe may be known at sight by the form of the
carapace, which is wide and rounded in front, and narrowed behind.
The accompanying illustration represents the commonest of the group--the
Common Shore Crab (_Carcinus mænas_), which is found plentifully on all
our coasts, and even in brackish water far up the estuaries of rivers.
It is a very voracious and pugnacious creature, probably the most active
of all our crabs, and its movements, whether connected with its feeding,
its sports, or its warfare, are always very interesting when observed
through clear water. This crab varies considerably in colour, but is
usually of the greenish tinge shown in the frontispiece.
Another abundant and well-known species is the Edible Crab (_Cancer
pagurus_), which is as familiar an object in town as on the sea coast.
Unlike the common lobster, its natural colour is not considerably
changed by boiling, being only turned from a dull to a brighter red.
The finest specimens of this crab are to be caught beyond low-water
mark, the usual snare being the basket or pot, baited with fish refuse,
but large numbers live among the stones and rocks left exposed at low
tide, and sometimes include specimens of considerable size. They should
be looked for under large stones that are loosely piled together, or in
the narrow chinks of rocks.
It is very interesting to compare the habits of the two common crabs
just mentioned. The former, when molested, will run off in great haste,
but always retreat with its front to the enemy, and its sharp and
powerful pincers far apart and wide open, ready for immediate use in its
own defence if necessary. The latter species, on the other hand, though
strongly built and provided with formidable claws, seldom runs far, and
hardly ever attacks one in the act of pulling it out of its
hiding-place; but, on the contrary, doubles all its ten legs under its
body as if endeavouring to approach, as nearly as possible, the form of
a ball, and will allow itself to be rolled about without showing any
signs of life.
The genus _Xantho_ contains two or three species that are common on the
Cornish and Devon coasts, and which may be known by their depressed and
deeply-grooved carapace and the presence of three or four prominent
tubercles on the latero-anterior margins. The abdomen of the female has
seven joints, while that of the male has only five. One of these
(_Xantho florida_), shown on Plate VI., is a powerfully built crab, as
may be seen when, after being disturbed, it pushes its way among the
loose stones of the beach, often lifting masses many times its own
weight.
On the same plate is also a figure of the pretty Velvet Crab (_Portunus
puber_), also known as the Lady Crab and the Violet Fiddler. The first
of these popular names has its origin in the dense covering of close
hairs that clothe the carapace, and the last refers to the beautiful
violet colouring of parts of the front legs, and, to a lesser extent, of
the remaining legs. This is, perhaps, the most ferocious of all our
shore crabs, and its attacks, when disturbed, are of such a determined
nature that the catching of the larger specimens is quite a lively
sport. Though it can hardly be described as an abundant species, yet it
sometimes occurs locally in such numbers that it may be found under
nearly every stone of any size. In fact, we have searched two or three
localities on the south-west coast where this crab is not only
extremely numerous, but is at the same time almost the only species to
be found; and it seems not unlikely that the pugnacious Lady has been
the means of driving the less formidable species from its favourite
haunts.
When you disturb a Velvet Crab it will immediately raise itself in a
menacing attitude, stretching its brightly coloured pincers as wide
apart as possible, and then it will either retreat backwards, or even
make a firm stand, ready to strike as soon as it is threatened with an
attempted touch. Try to grasp it, and its two powerful weapons of
defence are brought together with lightning-like rapidity giving one a
decidedly smart blow, possibly followed by a grip of great tenacity for
a creature of its size; but, should it miss its aim, its pincers strike
together with a sharp click, only, however, to extend at once in
preparation for the next attempt.
It will be observed that the walking legs of this crab are all
flattened, and that while the first three pairs terminate in sharp,
lance-like claws, the last pair are broad and fringed with hairs, thus
showing their close relationship to the swimming crabs. In fact, the
same genus contains British species which are popularly known as
Swimming Crabs.
One of the swimmers is represented in fig. 4 of Plate VI. It is
generally known as Henslow’s Swimming Crab or the Nipper, the scientific
name being _Polybius Henslowii_. The carapace of this species is quite
smooth, thus enabling the crab to move through the water with less
resistance, and the walking legs, particularly the last pair, are
flattened and fringed for use as paddles. It is said that this crab can
raise itself from the bottom to the surface of moderately deep water by
means of the swimming feet, and that it preys on fishes which it pursues
with some vigour.
Other crabs than those briefly described will reveal themselves to the
sea-side collector, but we have not the space to introduce them here.
Sufficient information has been given, however, to enable the reader to
broadly classify his specimens--a matter of more importance to the young
naturalist than the mere naming of species.
Leaving the crustaceans now, and passing for a moment to the
_Arachnoidea_--the second great division of the arthropods--we shall
briefly describe the Shore Spider (_Pycnogonum littorale_), which is the
only representative of the class likely to be met with by the sea-shore
collector.
It will be seen by our illustration that this creature by no means
resembles a typical spider. The powerful jaws, really modified antennæ,
that are such formidable weapons in the latter, together with other
appendages of the head, are undeveloped in the shore spider, and the
head is prolonged forward to form a rigid beak with the mouth at the
summit, and the head and thorax together form a cephalothorax of four
distinct segments, each of which bears a pair of legs. Further, the
cephalothorax forms almost the whole of the body, for the abdomen,
usually so large in spiders, is here represented by a mere tubercle. The
shore spider is unable to swim, but crawls about among the weeds and
stones of the bottom, clinging firmly by means of the curved claws of
its eight thick legs, and is protected by its dull grey colour which
closely resembles that of the encrusted stones among which it spends the
greater portion of its existence. It may sometimes be found hiding under
stones near low-water mark, but is far more commonly seen among the
‘rubbish’ hauled in by the trawl.
[Illustration: FIG. 219.--THE SHORE SPIDER]
We shall conclude our brief survey of the marine arthropods by a short
account of the insect life of the sea shore, referring to a few of the
more prominent forms and observing some of their habits; but since it is
probable that some of our readers are not well acquainted with the
general characters of this interesting class of animal life, it will be
advisable to precede our remarks by a short summary of their principal
distinguishing features, more particularly those in which they differ
from the other arthropods.
Insects, then, may be defined as those arthropods in which the body is
divided into three distinct parts--the _head_, composed of from four to
six fused segments, and bearing as many pairs of appendages; the
_thorax_, formed of three segments, each of which gives attachment to a
pair of legs; and the _abdomen_, composed of eight segments that bear no
appendages.
The head of an insect is furnished with a pair of compound eyes, very
similar in structure to those of a crustacean, and often, in addition, a
cluster of simple eyes; also a pair of antennæ, usually composed of many
joints. These antennæ are important organs of touch, and are employed,
at least by many forms, as a means of communication between one insect
and another. In them are also located the organs of hearing, and,
possibly, those of other senses.
The mouth varies very considerably in different insects, but is often
supplied with a pair of mandibles or biting jaws, and, below them, a
pair of maxillæ or chewing jaws, both pairs being jointed to the head in
such a manner as to be capable only of horizontal movements. Above and
below these jaws are, respectively, the upper lip or labrum, and the
lower lip or labium, the latter having appended to it a pair of jointed
feelers called the labial palpi, and an additional pair of palpi are
also frequently attached to the maxillæ, and therefore called the
maxillary palpi.
These organs of the mouth of an insect are modified in various ways
according to the functions they are called upon to perform. Thus, in
bees, the upper lip, as well as the mandibles, are adapted for chewing,
while the maxillæ and the labium are grooved in such a manner that when
brought together they form a tube through which fluids may be sucked
into the mouth. Also, in the butterfly and the moth, the maxillæ are not
constructed for chewing, but consist of two channelled rods which, when
approximated, form a long tube or proboscis employed for suction; and in
these insects the labial palps are large for the protection of the
proboscis, which is retracted and closely coiled between them when not
in use. Further, in the bugs, the labium is long and tubular, while the
mandibles and maxillæ are often modified into sharp, stiff bristles that
work within the tube, the whole thus forming a combined piercing and
sucking arrangement.
[Illustration: FIG. 220.--THE LEG OF AN INSECT]
The leg of an insect is built up much in the same manner as that of the
typical crustacean. It consists of a basal hip joint or coxa, a ring
segment or _trochanter_, a thigh (_femur_), a shin (_tibia_), and the
tarsus or foot of several joints which terminates in a claw or claws,
and is often provided with sucking-pads. The wings, when present, are
attached to the second and third segments of the thorax, if two pairs,
but if, as in the case of the house fly, the insect has only one pair of
wings, these are always appended to the second segment.
Insects are developed from eggs, but in their young state they are
segmented larvæ, with strong jaws, antennæ, simple eyes, and usually
three pairs of legs attached to the first three segments next to the
head.
As regards internal structure, we need only mention here that the body
is traversed by numerous branching tubes (_tracheæ_) that open at the
exterior and constitute the respiratory apparatus; that the insect is
provided with a contractile, tubular heart by means of which the blood
is propelled through a system of blood-vessels; that the nervous system
consists of a chain of ganglia, connected by a nerve cord, sending nerve
filaments to all parts of the body; and that the digestive tube is often
a complicated structure, especially in the case of those insects that
feed on herbivorous matter.
[Illustration: FIG. 221.--TRACHEA OF AN INSECT, MAGNIFIED]
The above outline will be sufficient to show that insects are not very
unlike the crustaceans in their general characteristics; and, indeed,
when we examine certain forms, noting the distinct segmentation of the
body, the hardened exo-skeleton of chitinous material, and the
unhardened skin between the segments to admit of freedom of movement, we
see a striking resemblance in external appearance to some of the typical
crustaceans.
Insects are divided into several orders, and some of these are fairly
well represented on the sea coasts, though it must be understood that
but few species are strictly aquatic and marine in their habits.
Fresh-water pools and streams teem with insect life, and quite a large
number of the insects that live in these situations are peculiarly
adapted for a life of submersion, their general form being often such as
to allow of rapid progress through the water, their appendages modified
into admirable swimming organs, and, in many cases, their breathing
apparatus adapted for the direct absorption of oxygen dissolved in the
water.
However, one would hardly expect to find similar forms of life abundant
in the water that washes our shores, the disturbing action of the waves,
even in calm weather, being more than such fragile creatures could
withstand. And this is really the case, for there are but few insects
that may be described as marine in the strictest sense of the word; and
of these the species that have been observed are mostly inhabitants of
warmer seas.
It is noteworthy that all the insects which exhibit marine tendencies
are small, and they seldom, if ever, live permanently below the surface.
But few of them can swim. A few run on the surface of the water,
supporting themselves on the surface film after the manner of
water-gnats, whirligig beetles, &c., without ever being wetted; and
these are said to feed on different kinds of floating matter, and
occasionally to dive below the surface.
A rambler on the sea shore in the summer time will always meet with
plenty of insect life, but the number of species observed may not be
large: and omitting all those which show no decided preference for the
coast, but are found in inland districts as well, we find that by far
the larger proportion live at or near the high-water mark, where they
feed on the refuse washed up by the waves. Some species, however, live
among the stones, or burrow into the sand, between the tide-marks; and
these, as a rule, are not driven inland by each advancing tide, but
allow the sea to wash over them, having at first protected themselves
from disturbance by burrowing or seeking other suitable shelter.
These latter, like many of the insects that inhabit fresh water, are
well adapted to withstand prolonged immersion. Their bodies are not
capable of being wetted, a covering of short hairs effectually
preventing the water from coming into actual contact with the body. The
openings of the breathing tubes (spiracles) are also guarded by closely
set hairs which prevent the water from entering; and, in some cases, the
creatures are provided with special air-sacs in which a supply of air is
stored for use while the insect is shut off from the external
atmosphere.
The lowest order of insects includes the so-called Bugs (_Rhynchota_),
which are parasitic on plants or animals. Quite a number of these are to
be found inhabiting fresh water, but only one is truly marine in its
tendencies. This one is a small insect, only about an eighth of an inch
in length, and named _Æpophilus_ (fig. 222). It has never been seen
except between the tide-marks, and occurs so near low-water level that
it is submerged during the greater part of its existence. But little is
known of this peculiar creature. Even its food has not been ascertained.
As with the other Rhynchota, but little change of form takes place
during growth, the young being very much like the adult in appearance.
It has been observed that the larvæ live crowded together under the
protection of stones.
The reader is probably acquainted with those fresh-water bugs that are
popularly known as ‘boatmen’ on account of the oar-like action of their
long, fringed hind legs; and although none of these may be described as
marine, yet certain species may often be seen in salt and brackish
water, living in company with creatures that are decidedly inhabitants
of the sea.
We frequently meet with a pretty, slender-bodied insect, measuring about
half an inch in length without appendages, creeping over the rocks in
the sunshine, generally very near the crevices in which they hide, and
leaping from place to place when disturbed. These are the Bristle-tails
(_Machilis_), belonging to the order _Thysanura_, the members of which,
like the bugs, scarcely undergo any metamorphoses. This insect (fig.
222) has long antennæ, and also a long, stiff, and elastic bristle
extending backwards from the tip of the abdomen; and this bristle is the
means by which the creature leaps. Occasionally the machilis may be
found resting on the surface of the still water of a rock pool, in which
case its body is not wetted, its weight not being sufficient to break
the surface film of the water; and, in fact, the film is even
sufficiently firm to enable the insect to leap on the surface just as it
would on a solid body.
Allied to the bristle-tails, and usually grouped with them in the same
order, are the little Spring-tails, some species of which may often be
seen huddled together on the surface of the water of a rock pool. They
are so small that, unless closely examined, they may be mistaken for
particles of floating inorganic matter which have been blown into a
sheltered corner of the pool, and this idea may be strengthened by the
fact that these minute creatures _are_ driven by the wind into such
sheltered spots. But when we disturb them their true nature immediately
becomes apparent, for they may then be seen to move about on the surface
of the water, sometimes creeping on the surface film, and clambering on
the adjacent rock or weed, or leaping more or less vigorously, in which
latter case their bodies do not become wetted, the surface film
remaining unbroken by their exertions. And even when the rising tide
drives the spring-tails into crevices where they remain submerged,
perhaps for hours together, their bodies still remain dry, the water
being kept off by numerous short bristles and prominences with which
they are furnished.
When we examine a spring-tail by means of a lens we observe that it has
no traces of wings, but that each of the three segments representing the
thorax bears a pair of short legs, and that the abdomen consists of only
five or six segments. The head is furnished with a pair of jaws, and the
antennæ, which are short and thick, are composed of but few
joints--never more than six in number.
Some spring-tails live among the refuse washed up on the beach, where
they may be seen jumping about in company with the sandhoppers when the
material is disturbed. Such is the case with _Isotoma maritima_, the
illustration of which shows the forked tail that enables the little
animal to jump about so vigorously. But some of the marine spring-tails
are not so true to their name, since they are not provided with this
characteristic jumping organ, and have to content themselves by creeping
about slowly with the aid of their short legs. One of these springless
spring-tails (_Anurida maritima_) is one of the commonest of the group,
and is distributed over almost every part of our coast.
Passing over several orders of insects which do not seem to have any
marine representatives, we come to the _Diptera_ or two-winged insects,
of which the familiar house-fly is a type, and here we have to deal with
those troublesome creatures that literally swarm in the neighbourhood of
the matter washed up to the highest level of the tide during the whole
of the summer months. But although these insects are so very numerous,
we do not find among them a particularly large number of species, their
abundance being due more to the extreme prolificacy of those that
occur.
In this order, which includes all gnat-like creatures, as well as those
insects that are generally known as flies, the first pair of wings are
well developed, while the second pair are rudimentary, and represented
merely by a pair of scales, or by two little pin-like bodies called the
balancers or _halteres_. Some are provided with piercing organs by means
of which they can inflict a small wound and then extract the juices of
their victim, as does the female gnat, but the majority have a proboscis
adapted for suction only. The larvæ of the _Diptera_ are generally
limbless maggots, gifted with a pair of jaws, and they are usually very
voracious feeders, devouring decomposing animal or vegetable matter in
enormous quantities.
If we turn over a fermenting mass of the miscellaneous matter thrown up
on the beach quite beyond the reach of the tides, we may observe a
multitude of little maggots which feed on the moist, odorous portion
that was protected from the direct rays of the sun, together with a
number of dark-coloured pupæ that lie at the very bottom of the heap or
buried in the sand below. These are two stages of the black fly
(_Cœlopa frigida_) that is so attentive to us when we rest on the dry
sand above high-water mark. This fly is very like the common house-fly
in general appearance, though its body is rather smaller. Other species
of the same genus often accompany them, all being very similar in
general appearance and habits, and none of the larvæ seem adapted to a
life in the water. They are always found beyond the reach of the tide,
and are drowned if submerged for any length of time.
Another species belonging to the genus _Actora_ will often be seen in
the same company, and this is readily distinguished by their lighter
greyish colour and its superior size. Also, along the water-line, we
often meet with species of the family _Dolichopodidæ_, so called on
account of the length of their legs, and noted for the beautiful
metallic colours which adorn their bodies. These flies are carnivorous
in habit, deriving their food from living as well as from freshly killed
animals, and their short, fleshy proboscis contains a piercing bristle
by which they can puncture the skins of the animals that provide them
with food. Most of the flies of this group live on trees, walls, fences,
&c., where they pursue and attack their prey, but certain species follow
the line of breakers on the sea shore, as before indicated, and obtain
their food from the various marine animals that are stranded on the
beach. A peculiar feature of the family is the nature of the abdomen of
the males, which is bent under the body and furnished with a number of
appendages.
Another marine dipterous insect is a gnat-like fly closely allied to
_Chironomus_, which we have described in a former work[A] of this series
dealing with fresh-water life; and it will be sufficient to mention here
that _Chironomus_ is commonly known as the window-gnat on account of the
frequency with which it may be seen flying on the windows of our
dwellings; also that the larva, known popularly as the bloodworm, is
truly aquatic in habit, being able to swim by rapidly looping its body
in opposite directions, and being provided with a breathing apparatus
adapted for the absorption of the oxygen gas contained in solution in
water. The larva of the marine species referred to above may sometimes
be seen in rock pools, where it shelters itself among the sediment at
the bottom. It is much like the bloodworm in appearance and structure,
but its body is greenish instead of red.
The last order of insects calling for notice here is the _Coleoptera_ or
sheath-winged insects, popularly known as beetles, and characterised by
the hard and horny nature of the front pair of wings (elytra), which are
modified into sheaths and serve to protect the second pair; the latter
are thin and membranous, usually adapted for flight, and lie folded
beneath the former when not in use.
One large section of beetles is known as the _Geodephaga_ or Ground
Beetles--a group of very predaceous insects that burrow into the soil
and attack almost every living thing that comes in their way, and well
represented by numerous species that may be found in our gardens, and,
in fact, almost everywhere.
A considerable number of these insects show a decided preference for
salt marshes and the sea shore, where they hide under stones, or burrow
into the sand or mud in search of their prey. They are not marine in the
strictest sense of the word, for they are not adapted for a life of
submersion in water, either in the larval or in the perfect condition;
yet they are often found below high-water level, and some species burrow
into the sand of the beach as the tide advances, allowing the water to
cover them for hours together.
One interesting family of the ground beetles (the _Bembidiidæ_) includes
several small species, all of which frequent salt and wet places, such
as salt marshes, the mouths of rivers, and the sea shore. We give
enlarged illustrations of a few of these, the actual size being denoted
at the side of each.
[Footnote A: _Life in Ponds and Streams._]
[Illustration: FIG. 223.--MARINE BEETLES OF THE GENUS _Bembidium_
1. _B. biguttatum._ 2. _B. pallidipenne._ 3. _B. fumigatum._
4. _B. quadriguttatum_]
_Bembidium biguttatum_ may be identified by its brilliant bronze-green
colour, and the two distinct impressions on the elytra which have
suggested the specific name. _B. pallidipenne_ is, as its name implies,
a pale-winged species, the elytra being of a light yellowish colour. _B.
fumigatum_ is so called on account of the smoky tint of the elytra; and
the last species of the same genus figured (_B. quadriguttatum_) may be
known by the four conspicuous spots on the deep violet-coloured outer
wings.
The same family contains an interesting little beetle--_Cillenium
laterale_--only about one-sixth of an inch in length, that lives among
the refuse washed on the beach, where it feeds on the sandhoppers; and
although the latter are so much superior in size, the beetle has no
difficulty in holding and killing its prey, always seizing it on the
ventral side of the body, which is less protected by the hardened skin.
This species, which is of a copper colour, does not confine its ravages
to that portion of the beach which is above high-water mark, but often
allows itself to be covered by the advancing tide, remaining submerged
for a considerable time. Another species--_Aëpus (Æpys) marinus_--is
even more aquatic in its habits, for it searches out its prey among
stones, chiefly at the mouths of rivers, below high-water level, and is
often submerged for hours together. It is even provided with air-sacs to
enable it to withstand such prolonged submersions.
[Illustration: FIG. 224.--MARINE BEETLES
1. _Æpys marinus._ 2. _Micralymma brevipenne_]
There is another section of beetles which has elytra so short that they
cover only a small portion of the abdomen; but although so short, these
elytra completely cover the long membranous wings, which are folded up
beneath them in a wonderfully compact manner. The section referred to is
termed _Brachelytra_, from the feature just mentioned, and includes a
few species that are more or less marine in their habits. One of
them--_Micralymma brevipenne_--lives under stones below high-water
level, and apparently passes through all its stages within reach of the
waves. Another of the _Brachelytra_ (_Bledius_) burrows into the sand or
mud near high-water mark, throwing up the débris as it proceeds. Both
these beetles are carnivorous, and the latter is in turn preyed upon by
a ground beetle of the genus _Dyschirius_, which hunts and devours it
within its own home.
The reader will have observed that the sub-kingdom _Arthropoda_ is not
only a very extensive one in the sense that it contains a vast number of
animal forms, but also that its members exhibit a very great variety of
form and structure; and the beginner will probably find no little
difficulty in locating his specimens in their correct position in the
scale of life. The following table, however, will serve to show the
general classification of the group at a glance, and thus form a basis
for a more detailed study at any future time:--
SUB-KINGDOM ARTHROPODA
CLASSIFICATION
Class =CRUSTACEA=.
Sub-class =ENTOMOSTRACA=.
Order =Astracoda=--Free. Body enclosed in a bivalve shell.
Order =Copepoda=--Free. Five pairs of feet adapted for swimming.
Order =Cirripedia=--Sessile. Enclosed in a shell of many valves.
Order =Branchiopoda=--Free. Gills attached to feet.
Sub-class =MALACOSTRACA=.
Division =EDRIOPHTHALMATA=, or Sessile-eyed Crustaceans.
Order =Isopoda=--Body flattened. Seven pairs of legs--equal.
Order =Amphipoda=--Body flattened laterally. Legs adapted for
both walking and swimming.
Division =PODOPHTHALMATA=, or Stalk-eyed Crustaceans.
Order =Stomapoda=--Anterior appendages directed towards the
mouth.
Order =Schizopoda=--Cleft-footed Crustaceans.
Order =Decapoda=--Ten-footed Crustaceans.
Sub-order =Macrura=--Great-tailed. Lobsters, &c.
Sub-order =Brachyura=--Short-tailed. Crabs.
Class =ARACHNOIDEA=.
Order =Scorpionidæ=--Scorpions.
Order =Araneidæ=--Spiders.
Order =Acarina=--Mites.
Class =MYRIOPODA=.
Order =Chilopoda=--Centipedes.
Order =Chilognatha=--Millepedes.
Class =INSECTA=.
Order =Rhynchota=--Imperfect metamorphoses, suctorial mouth.
Bugs.
Order =Thysanura=--Imperfect metamorphoses. No wings.
Divided tail. Spring-tails.
Order =Euplexoptera=--Abdomen with terminal forceps. Earwigs.
Order =Thysanoptera=--Four equal membranous wings. Thrips.
Order =Orthoptera=--Anterior wings usually shorter and firmer.
Grasshoppers, &c.
Order =Neuroptera=--Two pairs of glassy wings--equal.
Order =Trichoptera=--Wings unequal, clad with hairs or scales.
Caddis flies.
Order =Aphaniptera=--No wings, no compound eyes. Fleas.
Order =Diptera=--Two membranous wings. Flies.
Order =Lepidoptera=--Wings clad with scales. Butterflies and
Moths.
Order =Coleoptera=--Fore wings hard and horny. Beetles.
Order =Hymenoptera=--Four membranous wings. Larvæ, footless
grubs. Ants, Bees, &c.
CHAPTER XIV
_MARINE VERTEBRATES_
The vertebrates form the highest sub-kingdom of animal life--the
sub-kingdom to which we ourselves belong, the chief distinguishing
characteristic of the group being the presence of an internal skeleton,
the principal part of which consists of a rod or column of cartilaginous
or bony material running along the dorsal side of the body, known as the
_vertebral column_.
[Illustration: FIG. 225.--TRANSVERSE SECTION THROUGH THE BONY
FRAMEWORK OF A TYPICAL VERTEBRATE ANIMAL
1. Spinous process of the vertebra. 2. Neural arch. 3. Transverse
process. 5. Body of the vertebra. 6. Breast-bone. 7. Rib. The space
between 2 and 5 is the neural cavity; and that between 5 and 6 is
the visceral cavity]
This column is usually composed of a number of elements called vertebræ,
each of which gives off two processes that unite and form an arch on its
dorsal side, while all the arches form a tube through which passes the
central portion of the nervous system.
Below, or on the ventral side of the column, is the body-cavity
containing the organs of digestion and circulation; so that if we make a
transverse section of a vertebrate animal we find that there are two
distinct tubes or cavities--a _neural_ or _cerebro-spinal cavity_ on
the dorsal side of the vertebral column, formed by extensions from the
substance of the latter, and enclosing the chief portion of the nervous
system; and a _body-cavity_ on the ventral side containing the viscera
or internal organs.
The above features are highly important, and will always prove quite
sufficient to enable us to decide whether any particular animal is a
vertebrate or an invertebrate, for it will be remembered that the body
of the latter has only one cavity, containing the nervous system as well
as the viscera, and that the nervous system is commonly placed along the
ventral side, but never along the dorsal. In addition to this the
vertebrates never have more than two pairs of limbs, and these are
always directed _from_ the nervous system; and the jaws, which are
appendages that move in the horizontal plane in invertebrates, are, in
the higher animals, portions of the framework of the head and move
vertically. In vertebrates, too, there is always a complete blood
system, consisting of a heart with two, three, or four cavities, a
system of arteries to convey the blood to the different parts of the
body, veins to return the blood to the heart, and networks of fine
capillaries connecting the former with the latter.
All vertebrates, at an early stage of their existence, have a
cartilaginous rod running through the dorsal portion of the body, called
the _notocord_. In some of the lowest animals of the division this rod
persists without any important alterations in structure, while in the
higher forms it gives place to the series of cartilaginous or bony
elements above referred to as the vertebræ; and the arrangement of the
vertebrates into their relative positions in the scale of life is based
largely on the degree of development of the vertebral column from the
notocord. Another interesting feature in the development of a vertebrate
is the formation of five or more transverse, archlike thickenings on
each side of the digestive tube, just behind the head; and, in the
spaces between them, of a series of slits forming a communication
between the pharynx and the exterior. These arches and clefts have but a
brief existence in many vertebrates, while in others they persist
throughout life; and, like other points referred to, they assist us in
recognising the relations of the vertebrates to one another.
The vertebrates are divided into the following classes:--
1. _Cyclostomata_--Lampreys.
2. _Pisces_--Fishes.
3. _Amphibia_--Frogs, Toads, Newts, &c.
4. _Reptilia_--Snakes, Lizards, Tortoises, &c.
5. _Aves_--Birds.
6. _Mammalia_--Mammals.
The first of these includes only a few species, one of which is found in
our seas, and will receive a short notice here. The fishes will, of
course, demand a fair share of our attention. Amphibians and reptiles
have no British marine representatives, and are therefore quite excluded
from this work. As to the birds, although there are so many that live
entirely on the sea and in its immediate neighbourhood, these have been
so ably dealt with by Mr. Hudson in one of the books of this series that
it would be superfluous to mention them. The mammals include a
considerable number of marine species, but as only one of these--the
Porpoise--is really commonly observed round our coasts, it alone will be
selected for description.
Lampreys and their few allies were formerly classified with fishes, but
are now made to form a small class by themselves; and there is abundant
reason for the separation. It will be remembered that vertebrates, in
the early stages of their development, are characterised by a
cartilaginous rod running through the dorsal region of the body, below
the central cord of the nervous system, and that they possess a series
of slits opening into the sides of the pharynx. Now, while these
characteristics are usually only transitory in the vertebrates, the
Lampreys and their relatives are the only animals in which they persist
throughout life, and it is for this reason that they are exalted to the
dignity of a class under the title _Cyclostomata_.
This name signifies ‘round-mouthed,’ while the Lampreys themselves form
the still smaller division _Marsipobranchii_, which means
‘pouch-gilled,’ these two being among the most evident characters of the
creatures concerned. They have no true jaws, the circular mouth being
supported by a ring of cartilage, and provided with a rasp-like tongue
that enables them to divide their food. They have no true bone in their
bodies, the simple skeleton, without limbs and ribs, being entirely
cartilaginous, and the rudimentary skull is not movable on the dorsal
cartilage. Their bodies are elongated and eel-like, with a single medial
fin, supported by fine cartilaginous rays, and with seven little slits
on each side of the neck, communicating with as many gills in the form
of little pouches. The mouth is suctorial, presenting, when open, a
circular adhesive disc, by which the animals can attach themselves to
any solid object, but assumes the form of a mere slit when closed. The
young differ from the adult in a few points of structure. Thus they have
no eyes, and the long fin, divided in the adult, is continuous. With the
above characteristics in mind, there will be no danger of confusing the
lampreys with the eels and other similar fishes.
There are three or four British lampreys, two or three of which inhabit
fresh water. Their habits do not seem to be well understood, but it
appears certain that the Sea Lamprey (_Petromyzum marinus_), which
reaches a length of from one to two feet, ascends rivers to spawn, while
the smaller River Lamprey (_P. fluviatilis_) has been caught in the sea;
and it is probable that the migrations of both, together with the
sojourn of the young of the former for a longer or shorter period in
fresh waters, have been the cause of the widespread confusion between
species.
Lampreys are carnivorous creatures, and attach themselves to fishes by
their suctorial mouths, and rasp away the flesh. They have also been
known to attack bathers.
[Illustration: FIG. 226.--THE SEA LAMPREY]
Passing now to the true fishes, we must first study the general features
of the group by which they are to be distinguished from other animals.
Since there are so many creatures outside this class that are more or
less fishlike in some respects, it becomes no easy matter to give a
concise definition of a fish, and the shortest satisfactory description
must necessarily include several points of structure. Thus, we may
define a fish as a cold-blooded vertebrate that does not undergo
metamorphoses, with limbs modified into fins, possessing also median
fins on the dorsal and ventral surfaces, having distinct jaws, a heart
with two chambers, and breathing by gills. To this we may add that the
young are generally produced from eggs, and that the skin is covered
with scales or bony plates, or is naked.
But let us now look more closely into the structure of fishes, so that
we may be enabled to see how marvellously they are adapted to their
aquatic life, and in order that we may become acquainted with the few
technical terms which will, as a matter of convenience, be used in the
descriptions of species.
Taking first the external features, we note that the body is generally
covered with scales, sometimes very large and distinct, but often so
small and closely set that they are not visible without careful
examination; indeed they are often so small, and so thoroughly embedded
in the slimy skin as not to be discovered without the aid of a
microscope. When the scales have unbroken edges and overlap one another
they are said to be _cycloid_, but when the projecting edges are toothed
or serrated, giving a roughness to the touch, they are described as
_ctenoid_. Sometimes the scales are modified into bony plates or little
isolated bony granules, and in either case they are practically
identical in structure with teeth, consisting as they do of dentine,
capped with a little harder substance resembling enamel.
[Illustration: FIG. 227.--THE PILCHARD
1. Dorsal fin. 2. Pectoral fin. 3. Pelvic fin. 4. Ventral or anal
fin. 5. Caudal fin.]
We often observe a row of scales, of a different nature from those
covering the body generally, running along each side of a fish from near
the eye to the end of the tail; and these constitute what is called the
_lateral line_. If we examine these scales closely, we observe that each
one is pierced by a hole that communicates with a little sac beneath
containing a gelatinous material, and in which a nerve tendril
terminates. The presence of the nerve filament evidently denotes that
the scales in question, with the little sacs beneath them, are organs
connected with sensation, and it is also believed that they have
something to do with the secretion of the slimy mucus that covers the
scales of the body.
The mouth of a fish is generally situated on the extreme front of the
head, but occasionally, as in the sharks and rays, quite on the under
side. If it contains a tongue at all, this organ is of small size and
simple structure; thus it is highly probable that the sense of taste is
very feeble in these animals, and this is just what one might expect
when one remembers that fishes never retain their food in the mouth for
any length of time, but simply bolt it without any attempt at
mastication.
The arrangement and nature of the teeth are very variable. Often they
are developed on the membrane of the mouth only, in which case they are
generally renewed as fast as they are worn down, but sometimes they are
persistent structures more or less embedded in the bone of the jaws. In
some cases teeth are altogether wanting, but in others they are situated
not only on the jaws, but also on the tongue, the roof of the mouth, and
even on the bony arches that support the gills.
A glance at the fins of a typical fish will suffice to show that they
may be divided into two groups--the paired fins, representing the two
pairs of limbs in most of the higher animals, and the median fins
occupying the middle line of the body. The former comprise the two
_pectoral fins_ that correspond with our arms, and are attached to the
bones of the pectoral or shoulder girdle; and the _pelvic fins_,
corresponding with the lower extremities. The pectorals, too, are
present in nearly all fishes, while the pelvic pair are rather more
frequently absent than the pectorals.
The medial fins comprise the _dorsal_, the _ventral_, and the _caudal_
or tail-fin, and are not to be regarded as limbs, but rather mere
outgrowths of the skin. They are not directly connected with any part of
the main bony framework of the body, though they are generally jointed
with a series of bones (interspinal bones) that run between processes of
the vertebral column. The dorsal and ventral fins are often divided into
two or more parts, and the tail fin is commonly distinctly forked.
Although the seven fins above mentioned differ considerably in general
form, some being fanlike, while others form fringe-like expansions, yet
they generally agree in that they consist of bony or cartilaginous rays,
between which is a soft membrane. The rays, however, vary much in
character, being sometimes developed into very hard and sharp spines,
and sometimes quite soft and flexible. The fins also differ in function,
as will be seen when we observe the movements of a fish as it swims. It
will then be noticed that the caudal fin, which is spread in the
vertical plane and moved sharply from side to side by the powerful
muscles of the tail, is the chief propelling organ, while the others are
concerned principally in maintaining the balance of the body. This
latter point becomes much more evident when we observe the movements of
a fish in which one or more of the fins have been injured or lost, as we
shall see presently.
It is true that the pectoral fins are sometimes used to propel, but
forward movement is brought about almost entirely by the caudal fin,
which acts much in the same way as the blade of the propelling ‘screw’
of a steam-vessel, the pectorals being used at the same time for
steering. Occasionally, too, the latter are both spread out at right
angles to the body when the fish desires to stop suddenly, and are even
employed at times in swimming backwards.
When a fish wants to turn to one side, it will be seen to give the tail
a sharp motion to the opposite side. The pectoral of the latter side is
also brought into play, while the other is kept close against the body.
If the pectoral or pelvic fin of one side is injured, the body of the
fish will incline to the opposite side; and if all the paired fins are
functionless the fish swims with its head inclined downwards.
Observations of fishes in which the dorsal or ventral fins are injured
will also show that these organs are necessary to maintain a steady
motion in the water.
In addition to the above facts, it may be mentioned here that the paired
fins are often modified into long finger-like processes that serve as
organs of touch, and even as means by which the fish can creep along the
bottom. This is notably the case with gurnards and a few of the other
fishes that spend their time almost exclusively on the bed of the sea.
Fishes are essentially gill-breathers, the gills being generally
fringe-like organs, supported on bony arches (the gill arches),
numbering four on each side, the cavity containing them being covered by
a gill-cover (_operculum_) that opens behind. Water is taken in at the
mouth, whence it passes into the gill-chamber; and after passing between
and around the gills, it escapes under the opercula. The gills
themselves are richly supplied with bloodvessels that are distributed
close to the surface, and an exchange of gases takes place through their
exceedingly thin walls, carbonic acid gas passing from the blood to the
surrounding water, and oxygen, held in solution in the water, passing
from the water to the blood.
When fishes are in foul water, containing but little oxygen in solution,
they rise to the surface in order to make up the deficiency by taking
oxygen direct from the air. This, however, is an unnatural proceeding
with the majority of fishes; but there are some that are provided with
accessory breathing organs specially adapted to the extraction of oxygen
direct from the air, and these are so dependent on the supply from this
source that they are suffocated if prevented from reaching the surface.
In other fishes, such as the sharks and rays, the gills are of an
entirely different character from those described above, for they are
pouch-like and five in number on each side, each pouch communicating
with the pharynx as well as with the exterior by a slit-like opening.
Before leaving the external characters of fishes we must say a word or
two about their forms and colours. As regards the former, it is well
known that fishes are well adapted for rapid progression through water,
but there are many exceptions to this rule. These exceptions, however,
apply principally to those species that have no need to swim rapidly,
and a study of their habits will show that their form is just as
perfectly adapted to their mode of life. They are often species that
live on the bottom, or hide in the crevices and holes of rocks, and
examples will be given in our future descriptions.
Variations in colour are even more interesting, especially as they are
so commonly connected with the nature of the surroundings and the
protection of the animals. In nearly all cases the colour is darker on
the upper surface than on the lower, thus making it appear that the
influence of light has something to do with the formation of the
pigments of the skin, and experiment proves that this is, at least to a
certain extent, the case; for when fishes have been kept for some time
in an aquarium into which light is admitted through the bottom only,
pigment spots have formed in the skin on the lower surface.
Fishes that swim at the surface are generally tinted on the dorsal side
with some shade that closely resembles the colour of the water as viewed
from above, and are white and silvery below. Such colouring is of course
highly protective, for they are not readily distinguished by the sea
birds and other enemies that would pounce on them from above, and are
almost invisible against the sky to eyes below. This form of protective
resemblance is beautifully illustrated in the mackerel, which is barred
on the back with black and green, closely imitating the ripples on the
surface of the deep green sea, while the under side is of a silvery
whiteness that is hardly visible from below with the bright sky as a
background.
The flat fish afford other interesting examples, for these live on the
bottom, and are coloured above so as to resemble the bed on which they
live; the tints being those of mud, sand, or gravel.
But what are we to say of the gaudy colours of the gurnards, rock
fishes, &c.? These are certainly not protective in all cases, for we
sometimes find brightly coloured species conspicuous among duller
surroundings. Such instances, however, are comparatively rare, the gaudy
species living principally among the variously coloured rocks, weeds,
and corals; and when they do occur it is probable that they serve
principally as a means by which the brightly coloured sex--usually the
male--attracts its mate. We say ‘usually the male,’ but why so? Because
the female requires the protection of a more sombre colour in order that
she may with safety deposit her spawn for the perpetuation of her
species. Again, the male referred to needs the assistance of his gaudy
coat only during the breeding season, hence we find that he assumes the
bright colours as a wedding garment, to be cast off when the breeding
season is over.
This leads us to the subject of changeability of colours in the same
individual. That such changes do occur is well known, and it is still
more remarkable that they are produced in rapid succession, apparently
at the will of the fish concerned; for its tints will vary as it moves
from place to place so as to always harmonise with the surroundings, and
also in response to other conditions. The mechanism by which such
variations are produced has also been studied and explained:--The
colouring matter is held in little vesicles beneath the skin, and these
vesicles are capable of being compressed by muscles quite under the
control of the fish. When they are globular in form the contained
pigment appears dark, but when they are flattened by muscular
compression, the pigment is spread over a much larger area, and thus
greatly reduced in depth of tint.
As with all vertebrates, the central axis of the internal skeleton of a
fish consists of the backbone and the skull. The structure of the latter
is so complicated, and its description so full of technicalities, that
we deem it advisable to pass it over in a work like this where the scope
is so large in proportion to the space available; and this we do with
reluctance, because the detailed study of the skull is of real
importance to those who would thoroughly understand the principles of
classification.
The backbone consists of a variable number of cylindrical vertebræ,
united end to end to form a continuous column, both the anterior and
posterior faces of each being concave. On the dorsal surface of each
vertebra there is a V-shaped arch, surmounted by a spine, the former
serving to protect the spinal cord, and the latter giving attachment to
the muscles of the back. Some of the vertebræ are also provided with
processes for the attachment of the ribs, and those of the tail possess
an arch and a spine on the ventral as well as on the dorsal side.
It has already been shown that the pectoral fins are jointed to a
girdle. This girdle corresponds with the shoulder-blade of higher
animals, and gives direct attachment to the rays of the fin, which may
be regarded as the equivalent of the fingers, and thus there is no part
of the limb corresponding with the arm. The pelvic fins also are
frequently jointed to a pelvic girdle or hip, but this is a very
rudimental structure, or is even entirely absent in some species.
The rays of the caudal fin articulate with the extremity of the
backbone, but this portion of the fish’s anatomy undergoes such
remarkable changes that we must devote a few words to it. It is probably
well known to our readers that the tails of fishes exhibit three
distinct forms. The first of these is a simple fringe formed by the
union of unaltered dorsal and ventral fins; the second is the
unsymmetrical or unequally lobed tail so characteristic of sharks,
dogfishes, and rays; and the third is the broad symmetrical tail fin,
often distinctly forked or bi-lobed, such as we meet with in the
majority of our bony fishes. These three kinds are known respectively as
the _diphycercal_, _heterocercal_, and the _homocercal_ tails.
[Illustration: FIG. 228.--THE SKELETON OF A FISH (PERCH)
_d_, dorsal fin; _p_, pectoral fin; _v_, pelvic fin; _t_, tail fin;
_a_, anal fin]
Now, it is an interesting fact that the most ancient fishes of our globe
possessed tails of the first type; and that these gradually gave place
to the heterocercal form; while the higher fishes of the present day
nearly all possess the homocercal tail. Thus as time advanced the
heterocercal tail was gradually evolved from the diphycercal, and the
homocercal from the heterocercal.
Further, if we watch the development of one of the highest fishes of the
present day from its embryo, we find that similar changes take place in
the individual. At first its tail is a simple fringe round the extremity
of the backbone, the latter being straight, or nearly so, to the end, so
that the embryo fish, as yet still in the egg, reflects a characteristic
of its very early ancestors. Then the end of the vertebral column turns
upward, and strong fin-rays are developed on its ventral side, so that
the tail becomes a heterocercal one like that of the less remote
ancestors of a later geological period. Next, the upward-bending portion
of the vertebral column is slowly absorbed, till nothing of it remains
except a small upturned bony spine, while, at the same time, the ventral
lobe expands on the upper side until the tail fin is once more of a
symmetrical form.
[Illustration: FIG. 229.--THE INTERNAL ORGANS OF THE HERRING
_a_, œsophagus; _bc_, stomach; _e_, intestine; _l_, duct of
swimming bladder; _k_, air-bladder; _h_, ovary]
Following these interesting changes, it becomes evident that the
symmetry of the tail fin of the bony fishes is really a false one, the
whole of it having been formed from the ventral lobe of a heterocercal
tail; and although the backbone seems to terminate abruptly exactly
opposite the middle of the fin, it still contains the remnant of the
raised extremity of the backbone that ran to the tip of the dorsal lobe
when the tail was of the heterocercal type.
The flesh or muscle of fishes is usually white, but it often assumes a
pink colour in the case of those fishes that feed largely on
crustaceans. This is due to the presence of a substance in the horny or
calcareous skins of the crustaceans that is turned red by the action of
the digestive fluids--the same substance that is turned red when the
crustaceans are boiled. This is notably the case with the salmon; but
the red pigment thus derived originally from the crustaceans frequently
shows itself more in the skin of the fish than in the flesh, as
observed in the common red gurnard.
Most fishes possess a membranous bag containing air, situated just below
the backbone, and known as the air-bladder; but this organ does not
exist in sharks and rays and in some of the heavier bony fishes that
live on the bottom. The air-bladder is capable of being compressed by
the action of certain muscles, and its principal use seems to be the
adjustment of the specific gravity of the fish to that of the
surrounding water; but it is interesting to note that the development of
this air-bladder is precisely the same as that of the lungs of
air-breathing animals, and that in some fishes which live in foul muddy
waters it is really a functional lung by means of which the fishes can
breathe direct from the atmosphere.
We can find space to refer only to one other internal structure of the
fish, namely, the roe of the female. This usually consists of a very
large number of eggs of small size, sometimes numbering many thousands,
and even millions, in a single individual. So numerous, indeed, are the
eggs, that were it not for the multitudes of carnivorous animals that
devour both eggs and fry, the sea and fresh-water lakes and rivers would
soon become so thickly populated that the fish would die in millions for
lack of food and air.
In some cases, however, the eggs are much larger and fewer in number,
but these are generally protected from the ravages of predaceous species
by a hard covering, as we shall observe in the sharks and rays.
Finally, a word or two must be said about the distribution of fishes. We
have already referred briefly to species that live principally at the
surface, and others that make the bottom their home: but some of the
former go to the bottom for food or to deposit their spawn, while some
of the latter occasionally rise to the surface and swim in shoals. We
have noticed, too, that the paired fins of bottom fishes are sometimes
modified into feelers, or into fingerlike processes adapted for
creeping. Similar organs, employed undoubtedly as organs of touch, and
called barbels or barbules, are often developed on the chins or jaws of
these fishes.
Although we have to deal principally with the species that belong more
or less to the shore--the _littoral_ fishes--we should like to refer
briefly to one or two interesting features of those that live at great
depths. It will be readily understood that much light is lost as the
rays penetrate into deep water, so that the bottoms of deep seas must
be more or less darkened. To allow for this loss, we find that the
species living at moderate depths are provided with larger eyes to
enable them to see their prey and their mates; but at still greater
depths, where the sun’s light cannot penetrate, the fishes are either
blind, or are possessed of luminous organs which enable them to see
their way. Again, as the sea is so thinly populated at such great
depths, the carnivorous species do not find abundant food always at
hand, hence they are often provided with such mouths and stomachs as
will allow them to make the best of favourable opportunities, some being
capable of swallowing a fish quite as large as themselves.
We often find fishes roughly classified into fresh-water and salt-water
species, and although such a division is at times convenient, it must be
remembered that some of the former migrate into brackish and even into
salt water, while some of the latter ascend estuaries and rivers either
for the purpose of obtaining suitable food, or for the deposition of
their eggs.
The fishes that frequent our coasts may be classified into two main
groups, those with cartilaginous skeletons (_Elasmobranchii_), and the
bony fishes (_Teleostomi_). Both these are divided into family groups,
and we shall deal more or less briefly with all the important families
that include common British marine fishes, but giving more attention to
those species that are truly littoral in habit--species that may be
found in the rock pools or under stones at low tide, and which may be
obtained by the amateur angler working from rocks, piers, &c.
The cartilaginous fishes include the Sharks, Dogfishes, and Rays. They
have pouchlike gills, five or more on each side, each one opening to the
exterior by a separate slit. The skin generally contains bony elements
that are toothlike in structure and often in form; the mouth is usually
on the under side of the head, and the tail is nearly always of the
heterocercal kind. They are all carnivorous creatures, and often
exceedingly voracious; and are represented in our seas by the Rays and
Dogfishes.
Rays or Skates (family _Raiidæ_), of which there are six or seven
British species, are readily known by their broad flattened rhomboidal
bodies, with the mouth on the under side of the head, a longitudinal
fold on each side of the tail, and pectoral fins extending quite or
nearly to the front point of the head.
Two of these fishes are very common in our markets, one being the
Thornback Skate (_Raia clavata_), distinguished by the clawlike spines
down the middle of the back as well as on other parts of the body; and
the Common Skate (_R. vulgaris_), a very voracious species, from two to
four feet long, with a very sharp muzzle.
All the members of this family are bottom fish, without air-bladders;
and their eggs, which are large and detached, are enclosed in horn
capsules which are so commonly washed up on the beach that they are well
known to frequenters of the sea-side, who call them Skates’ Barrows or
Shepherds’ Purses. These cases are oblong in form, with a process at
each corner, and the material of which they are composed looks very much
like that of some of the coarser sea weeds after they have been dried in
the sun. As a rule only the empty cases are cast ashore by the waves,
open at the end where the little skate made its escape; but occasionally
we meet with the complete egg, and the case, while still wet, is
sometimes sufficiently transparent to show the form of the embryo
within.
[Illustration: FIG. 230.--THE EGG-CASE OF DOGFISH]
Dogfishes are also fairly well known to sea-side ramblers, for not only
are some species used as food in many places, but they are also
frequently to be seen cast aside with the refuse from the fishermen’s
nets. The common Spiny Dogfish (_Acanthias vulgaris_), belonging to the
family _Spinacidæ_, frequents all parts of our coasts. It reaches a
length of three or four feet, and is of a slate-blue colour above and
very pale yellow below. The pectoral fins are very large, the ventral
fin absent, and there is a very sharp spine in front of each dorsal. The
creature is ovo-viviparous; that is, the eggs are hatched while still
within the body of the parent.
Another family (_Scylliidæ_) contains two British species without
spines, and is also characterised by having the first dorsal fin far
behind. They are the Larger Spotted Dogfish (_Scyllium canicula_) also
known as the Nurse Dog and the Bull Huss; and the Lesser Spotted
Dogfish (_S. catulus_), called also the Huss and the Rough Hound. The
egg capsules of both these are occasionally washed on the beach, and
those of the latter species may be known by the yellowish colour and the
long tendrils by which they are anchored to sea weeds.
In addition to these we may briefly refer to two of the Blue Sharks
(family _Carchariidæ_) that frequent our shores, distinguished by their
long and prominent muzzle, and the crescent-shaped mouth. They may be
regarded as higher in the scale of fish life, as compared with the
sharks and rays previously named, because the vertebræ are more or less
hardened by the deposit of calcareous matter, and, therefore, make a
nearer approach to the character of true bone. The species referred to
are the Common Blue Shark (_Carcharius glaucus_), and the Smooth Hound
(_Mustelus lævis_). The former often exceeds twelve feet in length, and
is commonly seen off our south and west coasts during the summer months.
It is a nocturnal marauder, and is said to sleep at the surface by day
with its tail exposed above the water. The Smooth Hound is a bottom
feeder, subsisting on molluscs and crustaceans, the shells of which are
easily crushed by its flat and blunt teeth. It is a small shark,
measuring only three or four feet in length, and brings forth its young
alive.
[Illustration: FIG. 231.--THE SMOOTH HOUND]
The next division (_Teleostomi_) contains all the bony fishes, which may
be distinguished generally from the cartilaginous group by the following
features:--The skeleton is more or less hardened by the deposit of
calcareous matter, and the tail is generally not of the heterocercal
type. The paired fins are fan-like, and the pectoral girdle is attached
to the hinder part of the skull. These fishes generally have an
air-bladder, and the gills lie close together in a cavity covered by an
operculum. The eggs, too, are generally very small and numerous, and
massed together.
Of these we will take first the family _Salmonidæ_, of which the Salmon
(_Salmo salar_), and the Smelt (_Osmerus eperlanus_) are well-known
examples. Several species of the family are remarkable for their
periodical migrations from fresh to salt water or _vice versa_, and we
cannot do better than briefly relate the interesting life-history of the
salmon as a striking instance of these peculiar wanderings. This fish
quits the sea at the close of the summer, and ascends the rivers for the
purpose of depositing its spawn, the colder water of the rivers being
necessary for the development of the young. Its upward journey is beset
with many difficulties, for it has to shoot the various rapids and leap
the cascades, the latter often demanding the most prodigious efforts on
the part of the fish, which frequently leaps several feet out of the
water, and even then has sometimes to renew its attempts over and over
again before it finally succeeds. Indeed, the difficulties to be
overcome are so numerous that the fish often reaches the goal in such an
exhausted condition that it would hardly be recognised as the salmon by
those who have only seen it in the prime condition in which it is
captured during its return to the sea in the following spring or summer.
The male, at this period called the _kipper_, is of a dull red colour,
irregularly blotched with yellow and light brown, and its skin is
covered with a slimy secretion. Its body is lean, and the head, now
large and out of all proportion, is rendered still more unsightly by the
protrusion of the lower jaw, which at this season, when the males are
particularly pugnacious, becomes a formidable weapon of offence. The
condition of the female, now called the _baggit_, is equally poor, and
the skin has changed its bright silvery colour for dark and dingy
shades.
The female digs a nest in the form of a deep trench by wriggling her
body in the gravel of the bed of the stream, and there deposits her
eggs, many thousands in number, small quantities at a time. As each
batch is deposited the eggs are fecundated by the kipper, and then
covered over lightly with gravel by the baggit; and this work having
been accomplished, both male and female rest and feed, with the result
that their condition is rapidly improved.
After about eighteen weeks the eggs begin to hatch, and the fry wriggle
out of the nest and seek shelter under stones in the immediate
neighbourhood. They are now peculiar little creatures, as much like
tadpoles as fishes, with big heads and narrow bodies, and a bag of
albuminous yolk-matter attached to the ventral side. The young subsist
on this store of food for from twelve to twenty days, during the whole
of which time they remain under shelter, having, of course, no need to
expose themselves to the numerous enemies with which they are
surrounded, and they then leave their hiding-place in search of food,
being now about an inch in length. They feed on aquatic and other
insects, which are now becoming plentiful on the approach of the warm
weather; and, growing rapidly, reach a length of four inches in a month
or two. They are now called _parr_, and are distinguished by the dark
bars that cross their bodies transversely--a feature that persists for a
year or more from this time.
Towards the end of May the parr migrate seawards, accompanied by the
adult salmon, but as their enemies include the voracious fishes, wading
birds, and even the adults of their own species, it is probable that
only a small proportion of the original number ever enter salt water.
In the sea they feed on crustaceans, molluscs, and small fishes, the
young still growing rapidly, and attaining a weight of about five pounds
in the following autumn, when both young (now called _grilse_) and old
again ascend the rivers to spend the colder half of the year; the former
will have reached a weight of ten pounds or more on their return to the
sea in the following year.
The Smelt may be seen in thousands in our estuaries during the spring,
for at that time they come up to spawn in the brackish water. In the
summer they swim about in shoals along the coast, and are caught largely
in nets for the market. In some parts they are taken in large shallow
circular nets suspended on a line. This is lowered into the water, and
hauled up when the fish are seen swimming above it. Many amateurs secure
numbers of smelt by means of rod and line, fishing from piers, jetties,
&c. They bite freely at almost any kind of bait, and will snap at an
almost bare hook, with the tiniest fragment of the bait at its point.
The Herring family (_Clupeidæ_) contains some well-known food-fishes to
which we need only casually refer. They are mostly littoral species,
none inhabiting deep water, and none straying into the open ocean. Their
bodies are covered with silvery scales, and are laterally compressed, so
much so on the ventral side that there is a moderately sharp ridge along
the middle line. The principal fishes of the family are the Herring
(_Clupea harengus_), the Sprat (_C. sprattus_), and the Pilchard (_C.
pilchardus_).
These fishes are particularly interesting on account of their gregarious
habits and the enormous size of the shoals they form, a single shoal
often containing millions of individuals; and they are often captured in
such quantities that large numbers are sold to farmers as manure to
enrich the soil. The shoals are followed closely by many larger
carnivorous species that devour them in great numbers, as well as by
flocks of sea birds that prey on them, and yet their numbers are not
appreciably reduced by such ravages. They spawn in shallow waters near
the coast, and feed principally on the crustaceans and worms of the
littoral zone.
Sprats were once considered to be the young of the Herring, but it is
now universally acknowledged that they are a distinct species, and quite
a number of characteristics have been given as a means of distinguishing
between the two. The young of the herring are, however, used largely as
food, for that miscellaneous mixture of fry and small species known as
Whitebait consists largely of these and the young of the sprat.
[Illustration: FIG. 232.--THE COMMON EEL]
Herrings are captured principally off the north and east coasts, but the
pilchards, which are often confused with them, and even at times sold
under the same name, are caught chiefly off the coast of Cornwall.
Although the Eels (_Anguillidæ_) are so readily distinguished by their
general form and appearance, yet it may be advisable to call attention
to one or two of the leading characters that would possibly be
overlooked by an ordinary observer, and in doing this we ask the reader
to note that our remarks apply to the true eels only, and not to the
sand eels and other fish that may be confused with them.
The elongated bodies of the _Anguillidæ_ are covered with a slimy skin
that is apparently scaleless, but an examination with the microscope
will show that there are small scales embedded in it. The dorsal and
ventral fins extend to the tail, and the pelvics are absent; the
gill-slits, which are very narrow, are at the base of the pectorals.
It might well be expected that eels would be possessed of some form of
accessory breathing apparatus, seeing that they can live so long out of
water, but this is not the case. They have, however, a pouch-like
gill-cavity which can be inflated and filled with water by the fish,
thus keeping the gills moist and functional. In most other fishes the
gill-chamber is not capable of holding water, and thus the gills soon
become dry and sticky, so that they adhere together and fail to absorb
the necessary oxygen when the fish is out of water.
Thus the Eel (_Anguilla vulgaris_), in the remarkable migrations for
which it is noted, is capable of travelling over dry land for
considerable distances in search of suitable homes.
If an eel be taken out of the water, these gill-pouches will be seen to
swell out almost immediately, and remain filled with water as long as
the fish is kept on land; but when it is returned to its natural
element, it will at once discharge the water that kept its gills moist,
and which has become foul with the products of respiration, and, with a
few vigorous gulps, renew the supply.
Eels spend their breeding season, which extends from July to September,
in salt or brackish waters; and early in the following summer, the
young, which are now called _elvers_, and measure from three to five
inches in length, ascend the rivers, travelling enormous distances and
overcoming obstacles that we might well expect to be insurmountable.
Thus they perform two migrations annually, though it is thought by some
observers that the adult never returns to the sea, but dies soon after
it has deposited its spawn.
The family of Flat-fishes (_Pleuronectidæ_) present many interesting
points of structure and habit in which they stand alone, the variations
in structure as compared with other fishes being due, of course, to the
habits which they have acquired.
One of the first features that strike the observer on looking at a
flat-fish is the unsymmetrical form of the body. It is very much
compressed, and the fish having acquired the habit of lying on the bed
of the sea, sometimes on the left and sometimes on the right side, the
lower surface has become flattened more, and is of an almost pure white
colour, while the upper convex side is more or less coloured with
pigment produced by exposure to light. The dorsal and ventral fins are
both very long; and, as is usual with bottom fishes, the swimming or air
bladder is absent.
Young flat-fish are at first perfectly symmetrical in form, with one eye
on each side of the head, and they swim freely in the water with their
bodies in a vertical plane; but they very soon acquire the habit of
swimming on one side, and the eye of that side slowly passes round to
the other side of the skull, rotating in its orbit as it moves, till at
last both are on the uppermost surface. This, of course, is accompanied
by a considerable distortion of the bones of the skull, which is very
evident in the skeleton of the adult. The young fish then takes to the
bottom, with the result that its under-surface is flattened, while the
upper becomes strongly pigmented.
These fish spend almost the whole of their time on the bottom, only
occasionally rising for short intervals, when they swim by undulatory
movements of their bodies and fins; their food consists of crustaceans,
worms, and other small marine animals.
They furnish very interesting illustrations of protective colouring, the
upper surface always closely resembling the ground on which they rest
and feed; and thus they are not only protected from their own enemies,
but are enabled to lie unseen by the animals that form their prey. Those
which live on sandy shores are finely spotted with colours that closely
imitate the sand, while those that lie on mud are of dark and dingy
hues. Others, again, are irregularly marked with spots of various sizes
and colours that resemble a gravelly bottom; and most species are still
further protected by their habit of throwing sand or mud on the top of
their bodies by means of their dorsal and ventral fins.
Small flat-fishes, especially young Plaice and Flounders, live so close
to the shore that they are often left behind in rock pools and sandy
hollows by the receding tide, and it is very interesting to observe the
habits of these in their natural conditions. It will generally be
noticed that it is most difficult to detect them while they are at rest;
and when disturbed, they usually swim but a short distance, settling
down very abruptly, and immediately throwing a little sand over their
bodies by a few vibrations of their fins.
Another peculiarity of some of the flat-fishes is their indifference to
the nature of the water in which they live. Flounders may not only be
caught in the estuaries of our rivers, but they even ascend to, and
apparently live perpetually in, perfectly fresh water. In many
instances they may be seen miles from the sea, and even flourishing in
little fresh-water streams only a few feet in width. Thus they may be
found in numbers in the upper waters of the small rivers of the Isle of
Wight and of many streams of the mainland.
The principal British flat-fishes are the Plaice (_Pleuronectes
platessa_) and Flounder (_P. flexus_) above mentioned, and also the Sole
(_Solea vulgaris_), the Lemon Sole (_S. aurantiaca_), the Turbot
(_Rhombus maximus_), and the Halibut (_Hippoglossus vulgaris_); and as
all these are well-known food-fishes it is hardly necessary to describe
them.
[Illustration: FIG. 233.--THE LESSER SAND EEL]
Sand Eels (family _Ophidiidæ_) resemble the true eels in the general
form of their elongated bodies, but may be readily distinguished by
their bright silvery colour, the large gill-openings, and the more
strongly developed dorsal and ventral fins, the former of which extends
almost along the whole length of the back. The lower jaw is also longer
than the upper.
Two species are to be found on our shores--the Lesser Sand Eel
(_Ammodytes tobianus_), and the Greater Sand Eel (_A. lanceolatus_), the
former attaining a length of six or seven inches, and the latter nearly
three times this size. They may be seen off the south coast, swimming in
shoals over sandy bottoms, and when disturbed they descend and burrow
into the sand with remarkable agility. They approach the shore so
closely that they are often washed up by the waves, but immediately
disappear into the sand; and large numbers commonly remain behind as
the tide recedes, burying themselves to the depth of a few inches, and
are dug out by fishermen for bait.
The smaller species is by far the more common, and is taken in large
numbers by means of the draw net to be sold as food. It is particularly
abundant at Teignmouth, where it is known as the Sand Sprat, and forms
an important article of diet.
Quite a number of our important food-fishes belong to the Cod family
(_Gadiadæ_), and although some of these are caught almost entirely in
deep water some distance from shore, others give employment to the
angler fishing from rocks, piers, and jetties.
In all, the gill-openings are very wide, and the body is covered with
small overlapping scales. The caudal fin is quite free, the dorsal is
generally divided into three distinct parts which extend over the
greater part of the back, and the ventral fin is also frequently
divided.
[Illustration: FIG. 234.--THE THREE-BEARDED ROCKLING]
The typical species--the Cod (_Gadus morrhua_)--is too well known to
need a description, and although it is a large fish, often measuring
four feet and more, it approaches so close to the shore that it may be
caught with a hand line thrown out from rocks or piers. The barbel
projecting from the chin denotes that it is a bottom feeder.
On the rocky coast of the south the Pollack or Pollock (_G. pollachius_)
is very abundant, and may be taken with rod and line from the shore. It
also enters estuaries in large numbers, and may be caught close to quays
and jetties. This species is a very free biter, and will take almost any
of the baits used for sea fishing. It has no barbel.
The same genus includes the Whiting (_G. merlangus_), distinguished by a
black spot at the base of the pectoral fin and the absence of barbels;
the Whiting Pout (_G. luscus_), with a similar black spot at the base of
the pectorals, also dark, transverse bands, and a barbel; and the
Haddock (_G. æglefinus_), with a black patch on either side above the
pectorals, and a dark lateral line. The family also includes the Ling
(_Molva vulgaris_) and the Hake (_Merluccius vulgaris_), both of which
are caught in deep water; and the Rocklings (genus _Motella_), three
species of which frequent our rocky shores.
[Illustration: FIG. 235.--THE SNAKE PIPE-FISH]
The last mentioned are interesting little fishes that may be found on
stony beaches at low tide, for they often remain under cover between the
tide-marks, and may be seen on turning over stones and weeds. Perhaps
the commonest of them is the Five-bearded Rockling (_M. mustela_), which
has four barbels on the upper lip and one on the lower. It is of a
dark-brown colour above, and light below, and makes nests of corallines
in rock cavities. The Three-bearded Rockling (_M. tricirrhata_), known
also as the Sea Loach and the Whistle-fish, is a larger species,
sometimes reaching a length of a foot or more. Its colour is light
brown, marked with darker spots, and, like the other species, it lives
in the shallow water of rocky and weedy places. Another species--the
Four-bearded Rockling (_M. cimbria_), known by the three barbels on the
upper lip and one on the lower, is about eight inches long when full
grown, and is found principally on the northern shores.
Our next family (_Syngnathidæ_) contains some peculiar creatures called
Pipe-fishes because their jaws are united into a tube. They have long
and slender bodies that are covered with bony plates which form a kind
of coat of mail and give them an angular form. They have very small
gill-openings, a single dorsal fin, and no pelvics.
Pipe-fishes are very sluggish in habit, swimming but little, and living
in the shelter of weeds and stones on rocky coasts. In fact, they are
not adapted for swimming, and their attempts at this mode of locomotion
are awkward in the extreme, for their bodies are rigid and the tail very
small. When removed from their hiding-places they move but little, and
look as much like pieces of brown or greenish wood as fishes; and their
rigid bodies are so completely encased in the bony plates that they
alter but little in appearance when dried, and consequently the dried
specimens are often seen in museum collections.
All the British species, four in number, are small fishes, inhabiting
the shallow water of rocky shores, and are often found hiding under
stones near low-water mark. The largest is the great Pipe-fish or
Needle-fish (_Syngnathus acus_), which grows to a length of about
fifteen inches; and the smallest is the Worm Pipe-fish (_S.
lumbriciformis_), which is of an olive-green colour, and has a short,
upturned snout. The Lesser Pipe-fish (_S. typhle_), also known as the
Deep-nosed Pipe-fish, is very abundant on nearly all rocky coasts, and
may be distinguished from the others by having the ridge on the tail
continuous with the lateral line and not with the dorsal angle. The
other species is the Slender-nosed Pipe-fish or Snake Pipe-fish
(_Nerophis ophidium_), the body of which is extremely slender, and the
tail long and narrow. The male is provided with a series of small,
cup-like cells, in each of which he carries an egg.
In all the bony fishes previously mentioned the fin rays are soft and
flexible, and in this respect they differ from those that are to follow,
for the remaining families are all characterised by the presence of one
or more sharp rigid spines on the dorsal fin, and often by similar
spines on other fins. They constitute the group of Spiny-finned fishes.
Of these we shall first take the prettily coloured Wrasses (family
_Labridæ_), which live in the holes of rocks and under the cover of
weeds on rugged coasts. These fishes are very voracious in habit, and
the sea angler will find that they are ready to seize almost any bait
that may be offered them, and even to attack almost everything that
moves within sight; but they are likely to give much trouble since they
will rush into the crevices of rocks or among large weeds when hooked,
and thus frequently lead to the breaking of the line.
Wrasses feed principally on molluscs and crustaceans, and are provided
with extensile telescopic lips that enable them to pull the former from
the rocks on which they creep, and the latter from their hiding-places
among the rocks. They have also strong teeth in the gullet, by which
they can crush the shells of their prey.
There are several British species of Wrasses, one of which is shown in
the accompanying illustration. The commoner ones are known to fishermen
and juvenile anglers by quite a variety of local names.
[Illustration: FIG. 236.--THE RAINBOW WRASS (_Labrus julis_)]
The family _Gobioesocidæ_ contains some small and very prettily coloured
fishes of very peculiar habits, known popularly as Sucker-fishes. They
have one or two adhesive suckers between the pelvic fins by which they
attach themselves to rocks, stones, and shells. Some are littoral
species, and may be searched for at low tide; but others inhabit deeper
water, and are seldom obtained without a dredge.
[Illustration: FIG. 237.--THE CORNISH SUCKER]
One of the former is the Cornish Sucker (_Lepadogaster cornubiensis_),
which may sometimes be taken in a hand net by scraping the rocks and
weeds at low tide on the south-west coast. It has two suckers, each
circular in form, surrounded by a firm margin, within which is a soft
retractile centre. This central portion is attached to muscles by which
it can be withdrawn; and a vacuum is thus produced, so that the sucker
adheres by atmospheric pressure. The structure of the sucking organs can
be seen to perfection when the fish attaches itself to the side of a
glass aquarium, and if it be taken in the hand it will cling quite
firmly to the skin.
This peculiar little fish is only about three inches long, and its broad
head is marked with two conspicuous purple spots, with a blue dot in the
centre, and surrounded by a yellowish ring.
The allied species include the very small Two-spotted Sucker (_L.
bimaculatus_), which is of a bright red colour, and adheres to stones
and shells in deep water; the Sea Snail (_Cyclopterus liparis_), about
four or five inches long, with a soft and slimy semi-transparent body;
and Montagu’s sucker (_C. Montagui_), which is usually under three
inches in length, and may be distinguished by its peculiar habit of
curling the body laterally when at rest.
Equally interesting are the little Sticklebacks (family _Gastrosteidæ_),
the fresh-water representatives of which are known to almost everyone.
Their pugnacious habits, the bright colours assumed during the breeding
season, and the wonderful nests which they build for the protection of
their eggs and young, have all served to make them popular with those
who take interest in the forms and ways of animals. They are, moreover,
such hardy creatures that they may be kept alive for a considerable time
in any well-managed aquarium.
[Illustration: FIG. 238.--THE FIFTEEN-SPINED STICKLEBACK AND NEST]
In this family the hindmost portion of the dorsal fin is soft-rayed, but
the front portion is represented by a row of strong, sharp, erectile
spines, which constitute a formidable weapon of offence and defence.
Most of the species live in fresh water, but all the members of the
family seem to be able to live almost equally well in both salt and
fresh water.
We have one marine species--the Sea Stickleback or Fifteen-spined
Stickleback (_Gastrosteus spinachia_), which may be caught on rocky and
weedy coasts. It derives one of its popular names from the presence of
fifteen spines along the middle of the back. Its tail is long and
narrow, and its snout elongated, with the under jaw projecting beyond
the upper.
The nest of this species is a pear-shaped mass of soft sea weeds and
corallines, all bound together by a silky secretion, and suspended to
the rock in a sheltered spot. Within this the female deposits her eggs
in little clusters, all of which are bound together and to the nest
itself by the silk. If the nest is damaged while occupied, it is
immediately repaired, the male, it is said, taking upon himself the
responsibility of this task.
Sand Smelts (family _Atherinidæ_) resemble the true smelts previously
described, but may be readily distinguished by the anterior dorsal fin,
which is small and spinous. We have two species of this family, of which
_Atherina presbyter_ is by far the more common. It is a very pretty
fish, about five inches long, with a broad silvery stripe along each
side. It is very common on the sandy coasts of the south, where it also
enters the brackish waters of estuaries. Young anglers catch them in
considerable numbers by means of rod and line; but the professional
fisherman, taking advantage of the fact that sand smelts swim in shoals,
captures them in large, round, shallow nets. The net is baited with
bread, crushed mussels, or offal of almost any kind, and is then lowered
several feet below the surface by means of a long pole, to the end of
which it is suspended. It is raised to the surface at short intervals,
and will often enclose dozens of fish in a single haul.
The shallow waters of our southern coasts, including the estuaries and
harbours, are also frequented by the Grey Mullet (_Mugil capito_), of
the family _Mugilidæ_. This fish may be distinguished from other similar
species by the four stiff spines of the front dorsal fin, and by the
absence of a lateral line. The mouth is small, and without teeth, and
the mode of feeding is somewhat peculiar. The food consists of worms,
molluscs, and various organic matter contained in the sand or mud of the
bottom. It is sucked into the mouth, together with more or less of the
mud and sand, and the former is strained through a special straining
apparatus situated in the pharynx.
The Grey Mullet may be taken with rod and line, and bites freely when
the rag-worm is employed as bait. It is often taken in the fisherman’s
drag net; but, being a splendid jumper, it frequently makes its escape
as the net is drawn on the beach.
Few of our littoral fishes are so well known as the Little Blennies
(family _Blenniidæ_), which are to be found hiding amongst the weeds in
almost every rock pool, and under stones as they await the return of
the tide. Their bodies are generally cylindrical, and are either naked
or covered with very minute scales. The dorsal fin runs along the whole
length of the back, and each pelvic has one spine and two soft rays.
When taken out of the water the gill-cavities widen considerably, and
the eyeballs will be seen to move independently of each other, like
those of the chamæleon.
Most of the blennies are very active and voracious fishes, often giving
considerable trouble to the angler when fishing with a rod among the
rocks. They will bite at almost anything that moves, and, completely
swallowing the angler’s hook, will immediately rush into a crevice from
which it is often difficult to remove them.
Most of them have tentacles on the head by which they assist their
movements among the rocks and stones; and some actually creep up the
rugged surfaces of rocks by means of their ventral fins. They can all
live for a long time out of the water, being able to retain a supply of
water in their expanded gill-chambers to keep the gills moist.
[Illustration: FIG. 239.--THE SMOOTH BLENNY]
The Smooth Blenny or Shanny (_Blennius pholis_) is one of the commonest
species. It reaches a length of four or five inches, and has no
tentacles on the head. The Eyed Blenny or Butterfly Blenny (_B.
ocellatus_) may be distinguished by the conspicuous spot on the spinous
portion of the dorsal fin. The Large Blenny (_B. gattorugine_) inhabits
deeper water, chiefly off the south-west coast, and reaches a length of
a foot or more. The Crested Blenny (_B. cristatus_) is named from the
small crest on the head which can be raised and depressed; and the
Viviparous Blenny (_Zoarces viviparus_), as its name implies, brings
forth its young alive. The last species often exceeds a foot in length,
and is found principally on the north and east coasts. The newly-born
young are so transparent that the circulation of the blood within the
body may be seen under the microscope quite as easily as in the web of
the frog’s foot and in the tail of the tadpole.
One very common species of the _Blenniidæ_ differs considerably in
general form from the others, its body being elongated and eel-like, but
much compressed laterally. We refer to the Butterfish or Butter Gunnel
(_Blennius gunellus_), which is often mistaken for a small eel by young
sea-side naturalists. It is exceedingly common under stones at low tide,
and may be recognised at once by the light rectangular spots along the
flattened sides of the body. It is quite as slippery and as difficult to
hold as the eel itself.
It will be interesting to note that the ugly Sea Cat or Wolf-fish
(_Anarrhichas lupus_), which is sometimes sold for food in our large
towns, is also a member of the blenny family. It is a powerful,
rapacious fish--a veritable wolf of the sea, always ready to attack
anything. It feeds on molluscs and crustaceans, the shells of which are
easily reduced between the powerful crushing teeth that line the jaws
behind the formidable canines.
[Illustration: FIG. 240.--THE BUTTERFISH]
The Gobies (_Gobiidæ_) form another interesting family of small littoral
fishes, easily distinguished by the fact that the ventral fins are
united in such a manner that they enclose a conical cavity. The first
portion of the dorsal fin has also six flexible spines. The Spotted Goby
(_Gobius minutus_) is commonly to be found on sand-banks, where it is
well protected by the colouring of its upper surface, which closely
resembles that of the sand on which it rests. It is said to make a nest
by cementing fragments together round some little natural hollow, or to
utilise an empty shell for a similar purpose, fixing the shell to the
surrounding bed, and constructing a tunnel by which it can enter or
leave. The eggs are deposited in this nest, and the male keeps guard
over the home. The Black or Rock Goby (_G. niger_) inhabits rocky
coasts, clinging to the rocks by means of a sucker formed of the
modified pelvic fins.
A brightly coloured fish known as the Dragonet (_Callionymus lyra_) is
sometimes classed with the Gobies, though its pelvic fins are not
united. It is not a well-known species, and is seldom obtained except
with the dredge, as it inhabits deep water.
[Illustration: FIG. 241.--THE BLACK GOBY]
A peculiar little fish called the Pogge or Hook-nose (_Agonus
cataphractus_), also known as the Armed Bull-head, is commonly taken in
shrimpers’ nets on the south and east coasts. Its head and body are very
angular, and are covered with an armour of keeled scales. It seldom
exceeds six inches in length, and is classed with the Flying Gurnards in
the family _Dactylopteridæ_.
[Illustration: FIG. 242.--THE FATHER LASHER]
The true Gurnards and the Sea Bullheads form the family _Cottidæ_.
Several species of the former are included among our food-fishes, and
are therefore more or less familiar to our readers. They are
characterised by their large, square, bony heads, and by the finger-like
rays of the pectoral fins which are used as organs of touch and for
creeping along the bottom of the sea. The Bullheads are represented by
the peculiar Father Lasher or Sting Fish (_Cottus bubalis_), which is
very common on our rocky coasts and is frequently captured in shrimp
nets. Its head and cheeks are armed with sharp spines which constitute
formidable weapons of offence. When taken out of the water it distends
its gills enormously; and, unless very cautiously handled, its sharp
spines may be thrust deeply into the flesh. Young specimens, with
imperfectly developed spines, may be seen in almost every rock pool, and
the full-grown fish is easily taken with rod and line by fishing in the
deep gulleys between the rocks.
The remarkable Angler Fish (_Lophius piscatorius_), known also as the
Fishing Frog and the Sea Devil (family _Lophiidæ_) is sometimes taken
off the coasts of Devon and Cornwall; and although it cannot be truly
described as a littoral species, its structure and habits are so
peculiar that it deserves a passing notice. It is an ugly fish, with an
enormous head, a short naked body, and a comparatively slender tail. The
mouth is very capacious, sometimes measuring over a foot from angle to
angle, and is directed upwards. The scaleless body is furnished with
numerous slender filaments that resemble certain filamentous sea weeds,
and these together with the dull colouring of the body generally enable
the fish to rest unobserved on the bottom. The front portion of the
dorsal fin is on the head and fore part of the body, and consists of a
series of six tentacles, three long ones on the top of the head and
three shorter just behind them; and the foremost of these, which is the
longest, terminates in a little expansion which is kept in constant
movement by the fish. The mouth is armed with rasplike teeth which can
be raised or depressed at will, and when raised they are always directed
backward; the eyes are directed upward, and the gill-openings are very
small.
This strange creature habitually rests on the bottom of the sea,
disguised by its filamentous appendages and adaptive colouring, dangling
the expanded extremity of its first dorsal filament just over its
upturned cavernous mouth. It does not swim much, indeed it is at the
best but a bad swimmer; and when it moves it simply shuffles its heavy
body along the bottom, gliding between the stones and rocks, where it
may remain unobserved, its movements being produced by the action of the
tail, and of the paired fins, which are better adapted for walking than
for swimming. Unwary fishes, attracted by the dangling of the angler’s
bait, approach the watchful monster, and while speculating on the nature
of the bait, are suddenly engulfed in the capacious mouth, from which
there is no escape on account of the backward direction of the teeth.
The family _Trachinidæ_ contains the fishes known popularly as the
Stargazers and the Weavers. These are small, carnivorous species, with
rather elongated bodies, terminating in tail fins that are not forked.
The first dorsal fin is distinct and spinous, and the spines, as well as
others that are developed on the gill-covers, are grooved for the
passage of a poisonous fluid that is secreted at their bases.
Our littoral species include two well-known fishes (the Greater and
Lesser Weavers) that are dreaded by fishermen on account of the very
painful wounds they are capable of inflicting, and the smaller of the
two is also a considerable annoyance to bathers on certain sandy coasts.
[Illustration: FIG. 243.--THE LESSER WEAVER]
The Greater Weaver (_Trachinus draco_) lives at the bottom of deep
water, and is often dredged up in the trawl. Some fishermen call it the
Sting Bull, and always take the precaution of cutting off the poisonous
spines before disposing of the fish. It lives on the bottom with its
mouth and eyes directed upward, always in readiness to seize its unwary
prey, and the sharp spines of the dorsal fins are kept erect for the
purpose of promptly attacking approaching foes. Its mouth and palate are
armed with sharp teeth which render the escape of its prey almost
impossible. The smaller species (_T. vipera_) seldom exceeds six inches
in length. It lives in shallow water on sandy coasts, with dorsal spines
erect; and the wounds it produces on the unprotected feet of bathers are
often exceedingly painful on account of the injected poison, which also
causes the part to swell and turn to a dark purple colour.
The remaining important families, although they contain well-known
British food-fishes, do not include littoral species, and for this
reason we shall pass them over with but brief notice.
The Mackerel (_Scomber vernalis_) belongs to the family _Scomberidæ_,
and is so well known that no description need be given for the purposes
of identification. We have already referred to it as a beautiful
illustration of protective colouring, its upper surface resembling the
ripples of a deep green sea and the lower the brightness of the sky.
Mackerel swim in shoals in the open sea, pursuing and devouring the fry
of herrings and other fish; and in order that they may be enabled to
cover enormous distances their muscles are richly supplied with blood.
This not only gives a pinkish colour to the flesh, but results in a
greater amount of oxidation and the maintenance thereby of a body
temperature several degrees higher than that of the surrounding water.
We would also call attention to the five or six small fins behind the
dorsal and anal fins as characteristic of the _Scomberidæ_.
Our next family (the _Cyttidæ_) contains the John Dory (_Zeus-faber_),
concerning which some superstitions are still prevalent in parts. It is
brightly coloured, but not graceful in form, and is often caught in
large numbers off the coasts of Devon and Cornwall. Some fishermen call
it the Cock, on account of the crest on the back; while others know it
as St. Peter’s Fish, and will point out the impression of the Apostle’s
finger on each side--a black spot surrounded by a light ring.
The Horse Mackerel (_Caranx trachurus_) is found principally in the same
parts, where it devours the fry of other fishes. It is not a very close
relative of the common mackerel, but belongs to a distinct family
(_Carangidæ_), of which it is the only British representative. It is a
carnivorous fish, easily distinguished from _Scomber_ by its conical
teeth, as well as by the bony plates of the lateral line, the posterior
of which are keeled or spined.
While the last-mentioned families contain only fishes of truly pelagic
habits, the next (_Sparidæ_), formed by the Sea Breams, generally keep
near the coast, and often enter fresh waters. In these the body is much
compressed laterally, and is covered with large scales; the first half
of the dorsal fin is also spinous. The Common Sea Bream (_Sparus
auratus_), characterised by its red colour with brilliant golden
reflections, and by a dark spot on the shoulder, may often be angled
from rocks and piers. The young, in which the dark spots have not yet
appeared, are known as Chads, and are often regarded as a distinct
species. The Black Bream (_Cantharus lineatus_) is an omnivorous feeder,
and will take both animal and vegetable baits.
The Red Mullets (family _Mullidæ_) may be distinguished from the grey
mullets previously described by the two long erectile barbules on the
lower jaw. The scales are large and thin, with serrated edges, and the
front portion of the dorsal fin has weak spines. The common British
species (_Mullus barbatus_) frequents our south and east coasts, being
specially abundant round Devon and Cornwall, where they often occur in
vast shoals, and the young are often to be caught in estuaries and
harbours.
Our last example is the Common Bass or Sea Perch (_Morone abrax_), of
the family _Serranidæ_. It is also known locally as the White Salmon
and the Salmon Dace. This fish may be taken with rod and line on rocky
coasts and at the mouths of rivers. The sand-eel, or an artificial
imitation of it, is commonly used as bait, but the Cornish fishermen
more frequently employ a piece of herring or pilchard for the purpose.
The first dorsal fin of this fish has very strong spines which may
inflict severe wounds when the live creature is carelessly handled.
* * * * *
Omitting all mention of sea birds, for the reason previously given, we
now pass to the highest division of vertebrates--the Mammals--of which
we shall describe but one species--the Common Porpoise, this being the
only marine mammal that can be regarded as a frequent visitor to the
British coasts in general.
It may be well at the outset to understand exactly why the porpoise is
classed with the mammals and not with the fishes--to see how its
structure and functions correspond with those of our own bodies rather
than with those of the animals dealt with in the preceding portion of
the present chapter.
First, then, while the young of fishes are almost invariably produced
from eggs and are not nourished by the parents, the young of the
porpoise are produced alive, and are nourished with milk secreted by the
mammary glands of the mother. This is an all-important feature, and is
the one implied in the term _mammal_. The porpoise also differs from
nearly all fishes in that it breathes by lungs instead of gills,
obtaining its air direct from the atmosphere, and not from the water.
Hence we find it coming to the surface at frequent intervals to
discharge its vitiated air and to inhale a fresh supply. The body-cavity
of a mammal is divided into two parts by a muscular diaphragm, the
foremost division, called the thorax, containing the heart and lungs,
and the other (the abdomen) the remainder of the internal organs, while
the diaphragm itself plays an important part in the respiratory movement
by which air is drawn into the lungs. The body of the porpoise is so
divided, but no such division ever occurs in any of the fishes. Lastly,
the heart of the porpoise, in common with the rest of the mammals, is
divided into four cavities, and the blood is warm, while the heart of a
fish has generally only two divisions, and the blood propelled by it is
of about the same temperature as that of the surrounding medium. Several
other important differences between the porpoise and the fish might be
given, but the above will be quite sufficient to show why they are
placed in different classes.
Mammals are divided into several classes, and one of these (_Cetacea_)
includes the fish-like Whales, Porpoises, and Dolphins, all of which are
peculiarly adapted to a purely aquatic life. Like most of the fishes,
their upper surfaces are of a dark colour, and the lower very light.
Their fore limbs are constructed on the same plan as those of the higher
mammals, the bones of the arm being attached to a large shoulder-blade,
and the hand formed of four or five well-developed fingers which are
enclosed in skin, so that they constitute a paddle or flipper well
adapted for propulsion through water. There is no collar-bone, however,
and the fingers have no nails or claws. There are no hind limbs visible
externally, but a rudimentary pelvic girdle forms a part of the internal
skeleton. A dorsal fin exists, but this is merely an extension of the
skin of the back, and is not supported by either bones or rays. The skin
itself has no scales, like that of most fishes, but is smooth and naked;
and below it lies a large amount of fat, which, being a very bad
conductor of heat, serves to prevent the escape of heat from the body.
The tails of cetaceans are also mere folds of the skin, supported in the
centre by the extremity of the vertebral column; but unlike the tail
fins of fishes, they are expanded horizontally instead of in the
vertical plane. This latter is an important adaptive feature of the
cetaceans, since the vertical movement of a tail so disposed is exactly
what is required to assist the animals as they alternately rise to the
surface for air and again descend into the sea in search of their food.
Among the other external characters of the cetacean we may note the
nostrils, which are always situated on the highest point of the head,
and are thus the first part exposed when the creature rises to renew its
supply of air; also the ears, which are two small apertures behind the
eye, without any form of external appendages.
The skeleton of the cetacean is formed of light spongy bones, saturated
with oily matter; and although the animal has no true neck, visible as
such externally, it is interesting to note that, in common with all
other mammals, even with the long-necked giraffe, it possesses its seven
cervical or neck vertebræ.
Porpoises and Dolphins together form the family _Delphinidæ_,
characterised by having the blow-hole in the form of a crescent with its
convexity turned towards the front, and of these the Porpoises
constitute the genus _Phocæna_.
The Common Porpoise (_P. communis_) is the species that is so often
seen close to our shores and in the harbours and estuaries, swimming in
shoals with a graceful undulatory movement. Porpoises move forward
entirely by the vertical action of their powerful horizontal tails, and
extend their flippers only to change their course or to arrest their
progress. At short intervals they rise to the surface, exposing their
slate-coloured backs and dorsal fins for a moment, and then immediately
dive downwards in such a manner as to appear to turn a series of
somersaults. Occasionally they will leap quite out of the water,
exhibiting their white under surfaces, which shine with a sudden flash
when illuminated by the rays of a bright sun. The blow-hole is the first
part exposed, and if one is sufficiently near the shoal a fountain of
spray may be seen to shoot into the air, and the outrush of the expired
air may be heard as each one makes its appearance.
[Illustration: FIG. 244.--THE COMMON PORPOISE]
The true nature of the spouting of a cetacean seems to be very generally
misunderstood, the fountain of spray produced at each exhalation giving
the idea that the animal is expelling a quantity of water from its
nostrils. This, of course, is not the case; for the cetacean, being an
air-breather, has no need to take in a supply of water, as the
gill-breathing fishes have. Air only is expelled through the nostrils;
but as the expiration sometimes commences before these apertures are
brought quite to the surface, a certain amount of water is shot upwards
with the expired air; and even if the expiration commences after the
nostrils are exposed, the small quantity of water they contain is blown
into a jet of spray; and in a cool atmosphere, the density of this is
increased by the condensation of vapour contained in the warm and
saturated air from the lungs of the animal. It will be noticed, too,
that the creature does not check its course in the least for the purpose
of respiration, the foul air being expelled and a fresh supply taken in
exchange during the short time that the blow-hole remains above the
surface of the water.
The Common Porpoise measures five or six feet in length, and subsists on
pilchards, herrings, mackerel, and other fish, the shoals or ‘schools’
of which it pursues so closely that it is often taken in the fishermen’s
nets. Its flesh was formerly eaten in our own country, but it is now
seldom hunted except for its oil and its hide. About three or four
gallons of the former may be obtained from each animal; and the latter
is highly valued on account of its durability, though it should be known
that much of the so-called porpoise-hide manufactured is really the
product of the White Whale.
CHAPTER XV
_SEA WEEDS_
We now pass from the animal to the vegetable kingdom, our object being
to give a general outline of the nature and distribution of the
principal marine algæ or sea weeds that grow on our shores; and to
supply a brief account of those flowering plants that either exhibit a
partiality for the neighbourhood of the sea, or that grow exclusively on
the rocks and cliffs of the coast. The present chapter will be devoted
to the sea weeds themselves, but we consider it advisable to precede our
account of these beautiful and interesting plants by a brief outline of
the general classification of plant-life, in order that the reader may
be able to understand the true position of both these and the flowering
plants in the scale of vegetable life.
Plants are divided into two great groups, the _Cryptogams_ or Flowerless
Plants and the _Phanerogams_ or Flowering Plants. In the former the
reproductive organs are not true seeds containing an embryo of the
future plant, but mere cells or _spores_, which give rise directly to a
thread or mass of threads, to a cellular membrane, or to a cellular body
of more or less complexity of form from which the flowerless plant is
afterwards developed; while in the latter the reproductive organs are
flowers that give rise to true seeds, each of which contains the embryo
plant.
The _Cryptogams_ are subdivided into four groups--the _Thallophytes_,
the _Charales_, the _Muscineæ_, and the _Vascular Cryptogams_.
The first of these includes all the very low forms of vegetable life,
the simplest of which (_Protophyta_) are minute plants, each consisting
of a single microscopic cell that multiplies by a process of budding, no
sexual organs of any kind being produced. Some of these minute
unicellular organisms contain chlorophyll--the green colouring matter of
plants, by the action of which, under the influence of light, the plant
is enabled to decompose the carbonic acid gas of the atmosphere, using
the carbon for the purpose of building up its own substance, and setting
free the oxygen into the air again. Others contain no chlorophyll; and
these, having no power of feeding on carbonic acid gas, are more or less
dependent on organic matter for their supplies of carbon.
Only very slightly removed from these minute plants are the _Algæ_ of
fresh and salt water, varying in size from microscopic dimensions to
enormous plants, the lengths of which may reach many yards and the
weight several stone. They contain chlorophyll, and can therefore avail
themselves of inorganic food material; and although some multiply only
by repeated subdivision of their cells, others develop sexual organs by
the union of which fertilised spores are formed. The nature of these
Algæ will be more fully described presently; and we will go no further
now than to justify the location of such large and conspicuous plants
(as many are) so low in the scale of vegetable life by stating that they
are entirely cellular in structure, never producing true vessels such as
we see in higher plants; and that though some of them develop parts
which more or less resemble the leaves and roots of higher forms, the
former are far more simple in structure and function than true leaves
and the latter are never engaged in the absorption of food from the soil
to which they are fixed.
Another important group of the _Thallophytes_ is formed by the _Fungi_,
which include the familiar mushrooms, toadstools, and the sap-balls so
commonly seen on decaying trees; also the smaller forms known as moulds,
mildew, and smut. These, also, are entirely cellular in structure; and,
since they develop no chlorophyll, are compelled to live as parasites on
living beings or to derive their food from decaying organic matter. Thus
they are the creatures of corruption, their presence always denoting the
breaking down of living matter or of matter that has previously lived.
Now leaving the _Thallophytes_, and passing over the small group of
aquatic plants known as the _Charales_, we come to the _Muscineæ_, which
contains the Liverworts (_Hepaticæ_) and the Mosses (_Musci_).
The plants of both these groups require much moisture, and are found
principally in damp, shady situations. Like the preceding groups they
are cellular in structure, never producing true vascular bundles such as
the higher plants possess; and their life histories are rendered
interesting by the ‘alternation of generations’ which they exhibit. The
first generation is a sexual one produced from the spores, and consists
either of a mass of delicate threads from which a plant with a leafy
axis is developed by a process of budding, or of a little green frond
(the _thallus_). These bear the male and female elements, called
respectively the _antheridia_ and the _archegonia_; and when the central
cells of the latter are fertilised by the former, they give rise to a
case, with or without a stalk, containing a number of spores. When the
case is ripe, it opens horizontally by means of a lid, thus liberating
the spores.
Following these in the ascending scale are the _Vascular Cryptogams_, in
which some of the cells become modified into true vessels. Here, too,
the plants exhibit a distinct alternation of generations, the spore
first giving rise to a small, leafless body, the _prothallium_, which
bears the sexual organs; and then the female elements, after
fertilisation, produce the spore-bearing plant.
This group contains quite a variety of beautiful and interesting plants,
including the Ferns (_Filicales_), Horsetails (_Equisetales_),
Club-mosses (_Lycopodiales_), Water Ferns (_Rhizocarpeæ_), and
_Selaginellales_.
Ferns usually produce their little green prothallia above ground, and
the perfect plant generally has a creeping rhizome or underground stem.
Some, however, have strong, erect, woody stems, such as we see in the
tree ferns of tropical and sub-tropical countries. The horsetails and
the club-mosses are also produced from prothallia that are formed above
ground. The perfect plants of the former have branching underground
stems which give off numerous roots, and send up annually green,
jointed, aërial stems that bear whorls of fine leaves, each whorl
forming a toothed, ring-like sheath. The fertile shoots terminate in
cones, on the modified leaves of which the sporangia are produced. The
stems of the club-mosses are clothed with small overlapping leaves, in
the axes of which the sporangia are produced; and the spores, which are
formed in abundance, constitute the lycopodium powder with which
druggists often coat their pills.
Water ferns either float on the surface of water or creep along the
bottom, and produce their fruit either at the bases of the leaves or
between the fibres of submerged leaves. The Selaginellas are
characterised by a procumbent stem that branches in one plane only,
producing small, sessile leaves, with a single central vein. A number of
roots grow downward from the under side of the stem, and the fruit is
developed in the axils of the leaves that form the terminal cones of the
fertile branches.
The above are all the principal divisions of the flowerless plants, and
we have now to note the general characteristics of the _Phanerogams_.
The chief of these is, of course, the possession of flowers as
reproductive organs; and although it is not convenient to give a full
description of the flower at the present time, it will be necessary to
say a little concerning it in order that we may be able to grasp the
broad principles of classification.
A flower, in its most complex form, consists of parts arranged in four
whorls arranged concentrically. The first and second whorls, commencing
from the outside, usually consist of leaf-like bodies, united or
distinct, and are called respectively the _calyx_ and the _corolla_. The
third whorl consists of _stamens_, which are the male reproductive
organs of the plant, and each stamen consists essentially of a case--the
_anther_--in which are formed a number of little _pollen cells_. When
the anther is ripe it opens, thus liberating the pollen, so that it may
be dispersed by insects, by the wind, or by other mechanical means. The
remaining whorl constitutes the _pistil_, which is generally made up of
parts (_carpels_) arranged round a common centre, and each surmounted by
a _stigma_ adapted for the reception of the pollen cells. This portion
of the flower contains the _ovules_, enclosed in a case called the
_ovary_, and is, therefore, the female organ of the plant. When the
ovules have been fertilised by the pollen, they develop into seeds, each
one of which contains an embryo plant; and the ovary itself, ripening at
the same time, develops into the _fruit_.
Such is the general description of a flower in its most complex form,
but it must be remembered that one or more of the whorls named above may
often be absent. Thus, calyx or corolla, or both, may not exist; and the
male and female organs may be developed on separate flowers of the same
plant, or even, as is frequently the case, on different plants of the
same species. In the latter instance the flowers are spoken of as
unisexual, those bearing the stamens being the staminate or male
flowers, and those bearing the pistil the pistillate or female flowers.
The _Phanerogams_ are divided into two main groups, the _Gymnosperms_
and the _Angiosperms_. In the former the ovules are naked, no ovary or
seed-case being developed. The pollen, carried by the wind, falls
directly on the ovule, and then develops a tube which penetrates to the
nucleus of the ovule, thus fertilising it. In the Angiosperms the
ovules are always enclosed in an ovary, and the pollen grains, alighting
on the stigma, are held by a gummy secretion. The tubes they produce
then penetrate through the underlying tissues, and thus come into
contact with the ovules.
The _Gymnosperms_ include a group of small palm-like trees and shrubs
(the _Cycadeæ_), of which the so-called Sago Palm is a representative;
and the _Coniferæ_ or cone-bearing shrubs and trees, which may be spoken
of collectively as the Pines. In the latter the leaves are either stiff,
linear, and needle-like, or short and scale-like, or are divided into
narrow lobes; and the plants are noted for their resinous secretions.
The flowers are always unisexual, and are generally arranged in
cylindrical or short catkins, where they are protected by closely packed
scales; but the female flowers may be solitary. There is no calyx or
corolla, but the naked ovules and seeds are sometimes more or less
enclosed in the scales (_bracts_) or in a fleshy disc.
The _Angiosperms_ form the highest division of the flowering plants; and
are subdivided into two extensive groups--the _Monocotyledons_ and the
_Dicotyledons_. The chief distinguishing feature of these is that
implied in the above names, the embryo of the former containing but one
rudimentary leaf (_cotyledon_), while that of the latter contains two.
The Monocotyledons are also characterised by having the bundles of
vessels (_vascular bundles_) of the stems dispersed; the veins of the
leaves are also usually parallel, and the parts of the flower are
arranged in whorls of three or six. In the Dicotyledons the vascular
bundles of the stem are united into a ring which surrounds a central
pith; the veins of the leaves form a network, and the parts of the
flower are arranged in whorls of four or five.
We are now enabled to understand the relative positions of the principal
groups of plants in the scale of vegetable life, and to locate
approximately the forms with which we have to deal; and to aid the
reader in this portion of his work we present a brief summary of the
classification of plants in the form of a table for reference:--
THE CLASSIFICATION OF PLANTS
I. =CRYPTOGAMIA=--Flowerless plants.
(_a_) =THALLOPHYTES=--Leafless, cellular plants.
1. =Protophyta=--Unicellular plants.
2. =Algæ=--Sea weeds, &c.
3. =Fungi=--Mushrooms, &c.
(_b_) =CHARALES.=
(_c_) =MUSCINEÆ.=
1. =Hepaticæ=--Liverworts.
2. =Musci=--Mosses.
(_d_) =VASCULAR CRYPTOGAMS.=
1. =Filicales=--Ferns.
2. =Equisetales=--Horsetails.
3. =Lycopodiales=--Club-mosses.
4. =Rhizocarpeæ=--Water ferns.
5. =Selaginellales.=
II. =PHANEROGAMIA.=
(_a_) =GYMNOSPERMIA.=
1. =Cycadeæ=--Cycads.
2. =Coniferæ=--Cone-bearing trees.
(_b_) =ANGIOSPERMS.=
1. =Monocotyledons.=
2. =Dicotyledons.=
We have now to deal more particularly with those marine _Algæ_ that are
commonly known as Sea Weeds, and which add so much to the beauty of our
rocky coasts. These exhibit such a variety of graceful forms, and such
charming colours, that they are admired and treasured by thousands of
sea-side ramblers, who are attracted by them merely on account of their
pleasing general appearance; but the naturalist has all this and a great
deal more to interest and instruct him, for the sea weeds possess quite
a number of peculiar and characteristic features that render them well
worthy of a detailed study, especially when they are compared and
contrasted with the better-known flowering plants of our fields, woods,
and hedgerows.
It has already been observed that sea weeds differ from the majority of
flowering plants in that they have no true roots or leaves, though they
are often attached to rocks and other substances by a root-like disc,
and sometimes have leaf-like expansions that are supported by stem-like
rods. The root-like structures, however, serve simply for the attachment
of the plant, and are never concerned in the absorption of nourishment
like the true roots of higher plants; and the leaf-like expansions,
though they are sometimes symmetrical in form, never exhibit the spiral
arrangement that obtains in the leaves of higher plants, from which they
also differ in function.
The plant-body of a sea weed is called a _thallus_, and differs
considerably in the various species. Sometimes it has no expanded
portion whatever, but is more or less cylindrical in all parts, and may
be either branched or simple; and in some species it forms a simple
crust or a soft jelly-like covering on a rock.
All portions of a sea weed are made up of cells, and these are never
modified into vessels such as we see in the stems, leaves, and roots of
higher forms of vegetable life; and one who is commencing the study of
the algæ will find much interesting work in the examination of their
microscopic structure. Thin sections of various parts of the larger
weeds, cut with a sharp knife or a razor, and examined in a drop of
water under a cover-glass, will show the cellular structure perfectly;
while minute fragments of the small and slender species are sufficiently
thin and transparent to display the form and arrangement of their cells
without any previous preparation.
One of the principal charms of the marine algæ lies in the great variety
of colour that they display. They all contain chlorophyll--that
remarkable green colouring matter which enables a plant, under the
influence of light, to feed on the carbonic acid gas existing in the
atmosphere, or held in solution in water; and with its aid the sea weeds
can utilise this product of decay and animal respiration that would
otherwise accumulate in the water of the sea. But, in addition to this
bright green chlorophyll, many of the sea weeds contain a second
colouring substance, and in these the great variety of tint is dependent
on the nature of the latter and on the proportion in which it is present
as compared with the chlorophyll itself.
The different means by which the algæ reproduce their kind forms a most
engrossing subject, and to the botanist a most important one, for it has
much to do with the classification of the species. The affinities of
plants may be better determined by the nature of their reproductive
processes than by any other features, but unfortunately this is not so
well understood with regard to the algæ generally as compared with many
other divisions of the vegetable kingdom; and, as a consequence, there
is still a considerable difference of opinion, not only as to the extent
of the whole group, but also as to its divisions and subdivisions. The
reason for this is clear; for while it is quite an easy matter to trace
a flowering plant through its complete cycle from seed to seed, it
requires a much more careful examination, combined with much microscopic
work, to trace a lowly organised plant from spore to spore.
Some of the algæ may be reproduced without the agency of any sexual
elements; that is, without the aid of parts that correspond with the
ovules and the fertilising pollen of a flowering plant. Some of these
are reproduced by a repeated subdivision, or by the separation of a
portion of the plant that is capable of independent growth; while others
produce spores that do not result from the fusion of two different
cells. In most, however, sexual differences are to be observed, some
cells being modified into female organs, containing one or two more
minute bodies that are capable of developing into new plants after they
have been fertilised, and other cells produce the male elements by means
of which the fertilisation is accomplished. The fertilised cells are
spores, but are named differently according to the nature of their
development. They all differ from true seeds in that they never contain
an embryo plant, but germinate by the elongation of some particular
part, which subsequently grows by a continuous process of cell-division;
or the cell-division may originate directly in the spore without any
previous elongation or expansion.
The sea weeds are usually classified according to the colour of their
spores; but, since this colour generally corresponds with that of the
plant itself, we may almost say that they are grouped according to their
general tints. There are three main divisions:--
The _Chlorospermeæ_, or Green-spored;
The _Rhodospermeæ_, or Red-spored; and
The _Melanospermeæ_, or Brown-spored.
The _Chlorospermeæ_ contain no colouring matter other than the
chlorophyll. They are mostly small weeds, of a delicate green colour;
and, although they are not particularly conspicuous on our shores, they
contribute very considerably to the beauty of the rock pools, where
their delicate green fronds contrast richly with the olive
_Melanosperms_ and the pink and white corallines. The thallus or
plant-body is very varied in form, sometimes consisting of a broad
membrane, but more commonly of tufts of slender green filaments or of
narrow, flattened fronds.
These weeds are most beautiful objects for the microscope, and they are
generally so thin and transparent that no section-cutting is necessary,
nothing being required except to mount very small portions in a drop of
water. In this simple manner we may study the beautiful arrangement and
the various forms of the cells of which they are composed. The more
delicate species will be found to consist of a single layer of cells
only, while in the larger forms--the _Ulvaceæ_, for example--the thallus
may be formed of two or three distinct layers, and some of the cells may
be elongated into tubes.
A remarkable feature of the green-spored weeds is the large size of the
chlorophyll granules as compared with those of the other groups, and
also the great variety of forms which these granules assume. They may be
easily seen under a low power, and the examination of the weeds will
show that the thalli are not uniformly green, but that the colour of the
plants is due entirely to the chlorophyll granules, the remainder of the
plant substance being quite colourless.
If a green sea weed be placed in alcohol for a short time, it will be
found that the liquid assumes a green colour, while the plant itself
becomes colourless. The explanation is, of course, that chlorophyll is
soluble in alcohol. The presence of starch also in the weed may be
proved in a very simple manner, as follows:--Mount a small piece in
water, and then put a drop of iodine solution by the edge of the
cover-glass. The solution will gradually diffuse itself around the
object, turning the starch-grains to a deep blue colour, and so
rendering them very conspicuous under a moderately high power.
The manner in which the green weeds are reproduced is very interesting
also. In some cases the fragments of a thallus that have been detached
by storms or other mechanical means possess the power of independent
growth, and develop into plants; and this mode of reproduction may often
be watched in the indoor aquarium. Another method is by the agency of
little spores (_zoospores_) that are produced at the edges or
extremities of the thallus. Certain of the cells become modified into
what are called _zoosporangia_, and the minute zoospores are formed
within them. The walls of the cells either gradually degenerate, or are
fractured, and the zoospores are thus set free. The latter are provided
with little vibratile cilia, by which they move about freely in the
water. Some eventually settle down and germinate without any further
aid, but others are unable to develop until they have been fertilised by
fusion with another cell. The former is therefore an _asexual_
development, while the latter is _sexual_.
Some of the delicate, filamentous green algæ are reproduced by another
process termed _conjugation_. In this case two adjacent threads that lie
close together become lightly united by a covering of gelatinous
substance, and a cell of each throws out a process. The processes are
directed towards each other, and unite to form a tube in which the
contents of the two cells become fused together, with the result that
zoospores are produced.
Among the lowest of the green sea weeds are the plants known
collectively as the _Confervaceæ_, which consist of delicate green
filaments, usually attached to rocks in dense masses, but often found
floating freely in the rock pools. The filaments are composed of cells
joined together at their ends, and are always unbranched.
Confervæ are found principally in the tide pools, especially near
high-water mark, and often abound in hollows in the rock even above
high-water mark, where the spray of the waves is mingled with rain-water
or the drainage from the land. They exist in both fresh and salt water,
and some species seem capable of thriving in brackish water of any
degree of salinity.
Allied to the confervæ is a group of marine algæ called _Cladophora_,
very similar to the former in general appearance, and found in similar
situations, but readily distinguished by the branching of their jointed
filaments. The various species of this group are very beautiful weeds,
their delicate filaments looking very pretty as they float and sway in
the water of the pools. They are also exquisite objects for the
microscope; but, unfortunately, often lose their natural colour when
preserved dry. They vary in colour, some few being of a dull green tint,
while others are bright green, sometimes with a beautiful silky gloss.
One species (_C. pellucida_) is more rigid than most of the others; its
fronds stand out erect and firm, and are repeatedly forked near the
tips. It is a moderately common weed, found in the lower rock pools, and
may be readily recognised by the long one-celled joints, from the tops
of which the branches proceed. Another species (_C. diffusa_) is also
very firm in structure, so much so that its bristly tufts retain their
form when removed from the water, instead of becoming matted together in
a shapeless mass. Its branches are rather long, and bear a few simple
branchlets towards their extremities. It is found in rock pools between
the tide-marks. _C. lanosa_ is a very pretty little weed, growing in
dense globular woolly tufts, an inch or more in diameter, on the olive
tangles between the tide-marks. It is of a pale yellowish-green colour,
which becomes much paler, or is even altogether lost, when the plant is
preserved in a dry state, and, at the same time its fine glossy
appearance is lost. Its fronds have straight branches, all making very
acute angles, and they have also small root-like filaments. It much
resembles another species (_C. arcta_), which grows in dense tufts on
rocks, but the latter is larger, not so slender, and more freely
branched. The cells, too, of _C. arcta_ are longer, being about ten
times the length of the diameter, and the fronds are silvery at the
tips.
Nearly thirty species of _Cladophora_ have been described, but it is
impossible to give here a detailed description of all. We add, however,
a brief summary of the distinguishing features of a few other species
that are common on our coasts.
_C. rupestris_ is common everywhere, and easily recognised by its rigid,
branching, tufted fronds, of a dark greyish-green colour; its branches,
which are opposite, bear awl-shaped branchlets. It is found in rock
pools from half-tide downwards, and in deep water beyond the tide-marks,
the plants growing in the latter situations being generally of a fine
dark-green colour.
_C. lætevirens_ is also very common on rocks between the tide-marks. Its
fronds are tufted and freely branched, of a pale-green colour and soft
flexible texture, and about six inches long. The branchlets are usually
slightly curved.
_C. gracilis_ is a beautiful plant that grows on large weeds, especially
the Sea Grass (_Zostera_) in deep water; and although not very common,
it is sometimes found on the beach after storms. It is characterised by
its slender silky fronds, from a few inches to a foot in length, of a
yellowish-green colour. It may always be known by the comb-like
branchlets growing only on one side of each branch.
_C. refracta_ grows in dense tufts, two or three inches long, in rock
pools near low-water mark. Its fronds consist of rigid stems in
rope-like bundles that are very freely branched, the whole tuft being of
a yellow-green colour and silky texture. _C. albida_ closely resembles
it in structure and habit, but may be distinguished by its paler colour,
which disappears when the weed is dried, and by its longer and more
delicate branches.
In another order of the green-spored algæ (the _Siphoneæ_ or
_Siphonaceæ_) the frond is formed of single branching cells, and many of
these are often interwoven into a spongy mass, and sometimes coated with
a deposit of calcareous matter.
In the genus _Codium_ the fronds are of a sponge-like texture, composed
of interwoven branching fibres, and are of a globular, cylindrical, or
flattened form. The commonest species is _C. tomentosum_ (Plate VII.),
which consists of sponge-like, dark-green cylindrical fronds, which are
forked and covered with short hairs that give it a woolly appearance
when in the water. Each frond is composed of slender interwoven fibres
with club-shaped filaments passing vertically to the surface. It grows
on rocks in the pools between the tide-marks, and is abundant on nearly
all our coasts.
The Purse Codium (_C. bursa_) has spongy hollow fronds of a globular
form, varying from a quarter of an inch to five or six inches in
diameter. It is a rare species, being found only at a few places on the
south coast. Another species (_C. adhærens_) adheres to rocks, over
which the fronds spread in irregular soft patches, the club-shaped
vertical filaments of its interwoven fibres giving it the appearance of
rich green velvet.
An allied weed (_Bryopsis_), named from its moss-like appearance, grows
in erect tufts, each frond consisting of a branched one-celled filament.
There are two species of the genus, one (_B. plumosa_) characterised by
the light feathery nature of its fronds, the stems of which are branched
only near the top. It is found in rock pools on most of our coasts. The
other (_B. hypnoides_) is more freely branched, and the branches are
long, and issue from all sides of the stem. Like the last species, it
has branches on the outer part of the stem only, but it is of a softer
texture.
The best known of the green-spored weeds are certainly those belonging
to the _Ulvaceæ_, characterised by their flat or tubular fronds,
sometimes of a purplish colour, the cells of which multiply both
horizontally and vertically as the plants grow. In the typical genus,
_Ulva_, the frond is sometimes in two distinct layers, and becomes more
or less inflated by the accumulation of either water or oxygen between
them. The commonest species are _U. lactuca_ and _U. latissima_, both of
which are eaten by the dwellers on some of our coasts. The former,
commonly known as the Lettuce Ulva, has a frond of a single layer of
cells, and grows on rocks and weeds between the tide-marks. It is common
on many oyster beds, and is employed by the fishermen to cover the
oysters when sent to market; they call it ‘oyster green.’ This species
is shown on Plate VIII. _U. latissima_ or the Broad Ulva sometimes
reaches a length of two feet, and a breadth of nearly a foot. The fronds
are composed of two layers of cells, are of an irregular shape, with a
very wavy, broken margin, and of a bluish-green colour, It is known
as the Green Laver, and is used as food in districts where the true
laver (_Porphyra_) is not to be obtained. A third species--the Narrow
Ulva (_U. Linza_)--has smaller and narrower fronds, of a more regular
shape and of a bright-green colour. The fronds are composed of two
layers of cells.
[Illustration: Plate VII.
SEA-WEEDS
1. Fucus nodosus
2. Nitophyllum laceratum
3. Codium tomentosum
4. Padina pavonia
5. Porphyra laciniata]
The _Ulvæ_ retain their colour perfectly when dried, and, with the
exception of _U. latissima_, are of a mucilaginous nature, and adhere
well to paper, but, unfortunately, the graceful wavy outline of the
fronds is lost in pressed specimens.
The ‘true laver’ mentioned above, which is also popularly known as
Sloke, is closely allied to _Ulva_, but may be distinguished from it by
the colour of its membranous fronds, which vary from a light rose to a
deep purple or violet, occasionally inclining to olive, but never green.
Its scientific name is _Porphyra laciniata_ (Plate VII.), and it differs
from the majority of the _chlorospermeæ_ in having dark-purple spores,
which are arranged in groups of four in all parts of the frond. The
fronds are very variable in form and size, being sometimes ribbon-like,
and sometimes spreading into an irregular sheet of deeply-divided
segments; and the remarkable variety of form and colour has led to a
division into several species. These, however, merge into one another so
gradually that the separation seems to be hardly necessary.
The same remark concerning the multiplicity of species applies to
another allied genus called _Enteromorpha_, in which the fronds are
green and tubular, and often more or less branched. In these the colour
varies from a pale to a dark green, and the cells are arranged in such a
manner as to give a reticulated appearance. The commonest and
best-defined species are _E. intestinalis_, the tubular fronds of which
are constricted at intervals in such a manner as to resemble the
intestines of an animal, and _E. compressa_, with branched fronds of
variable form and size. The former is common on all our coasts, and may
even be found in rivers and ditches some distance from the sea. It
thrives equally well in fresh and salt water, and appears to grow most
luxuriantly in the brackish waters of tidal rivers. The latter species
also thrives best in similar situations.
Coming now to the red-spored sea weeds (_Rhodospermeæ_), we have to deal
with some of the most charming of the marine algæ that invariably
attract the sea-side rambler, and provide many of the most delightful
objects in the album of the young collector. Their brilliant colours,
varying from a light red to dark purple and violet, are sufficient in
themselves to render them popular with the collector, but in addition to
this striking feature they are characterised by extreme elegance of form
and delicacy of texture. They are to be found in most rock pools, from
near high-water mark downwards, the smaller and more delicate forms
adding much to the beauty of these miniature seas; but the largest and
many of the prettiest species exist only at or beyond the lowest ebb of
the tide, and hence the algologist, in quest of these beautiful plants,
will find it necessary to work at the very lowest spring tides, with the
occasional aid of a small boat drifted into the narrow channels among
outlying rocks, and a long hook with which to haul up submerged
specimens; and it will also be advisable to search the line of débris at
high-water mark after stormy weather for rare weeds that may have been
detached and washed ashore by the angry waves.
While engaged in the former of these employments--the searching of
outlying rocks with the boat--and also when examining the outer rock
pools which are disturbed by the waves that wash over their banks, the
simple instrument known as the water-telescope will prove invaluable.
Everyone must have noticed how difficult it is to observe objects in
water, the surface of which is disturbed by the wind or some other
cause; but the simple appliance named, consisting only of a long tube of
metal, a few inches in diameter, and painted a dead black inside, will
enable the observer to see all submerged objects with the greatest of
ease when the water is itself clear. The principle of the
water-telescope is as simple as its construction; for the tube,
protecting the surface of the water within it from the disturbances
outside, prevents the light from being refracted successively in
different directions, while the dead-black surface of the interior
prevents those internal reflections that would otherwise cause the
vision to be indistinct.
A few hours spent with the rhodosperms at the sea-side will be
sufficient to show not only the great variety of their form and
colouring, but also that the same species may vary according to the
position in which it grows. Most of the smaller forms are delicate and
filamentous, but others have expanded fronds which are very leaf-like.
The brightest colours are usually to be found at or beyond low-water
mark, where the weeds are covered with a considerable height of water
for hours together, and also in shady situations at higher levels, while
some of the species that grow in the upper rock pools are often of such
a deep colour, with so much admixture of brown, that they may be easily
mistaken for the olive melanospores to be presently described.
Most of the rhodosperms are attached directly to the rocks, and the
larger species have often a root-like disc by which they are very firmly
held; but some of the smaller species grow attached to larger weeds,
into the substance of which they frequently penetrate; and it is
possible that these derive some amount of nourishment from the sap of
their supporters. Some are of a recumbent nature, being attached to the
rock throughout their whole length, while others are so incrusted with
carbonate of lime which has been extracted from the water that they
resemble corals rather than forms of vegetable life. Nearly all of them
contain a bright-red colouring matter in addition to the chlorophyll by
which they are enabled to feed on carbonic acid gas.
None of the rhodosperms are of really microscopic dimensions, and they
all grow by the repeated division of the cells of the apex, while the
branches are derived by the similar division of new cells at the sides.
All plants are particularly interesting during the period of fruiting,
and this is remarkably the case with many of our red-spored sea weeds,
which are brighter and prettier while laden with their spore-producing
cells; and the collector of marine algæ should always endeavour to
obtain as many species as possible in fruit, not only on account of the
brighter appearance that may characterise them at this time, but mainly
because the opportunity of studying the mode of reproduction should not
be missed.
In the rhodosperms the reproduction may be either asexual or sexual. In
the former case fertile spores are produced without the necessity for
any outside fertilising element, and four are usually produced in each
one of the sporangia, hence they are generally known as _tetraspores_.
Where the reproduction is of the sexual type, the male cells are
produced singly in the terminal cells of the fronds, and since they are
usually crowded together in considerable numbers, and contain none of
the red colouring matter that exists in the other parts of the plant,
their presence is easily observed.
The female cells (_carpogonia_) are also produced on the tips of the
branches, and when the male elements escape from their cells, they are
conveyed passively by the movements of the water, for they have no
vibratile cilia by which they are propelled, and on coming into contact
with the female cell they adhere closely. An opening is then formed in
the latter, and the male element enters the carpogonium, which
germinates, deriving its nourishment from the parent plant, and the
spores are thus formed. Lastly, it is interesting to note that the
asexual spores, the male cells, and the female cells are generally
produced on different plants of the same species.
We will now proceed to examine some of the best known and most
interesting of the rhodosperms, beginning with the order _Ceramiaceæ_,
which contains a number of red or reddish-brown weeds with jointed,
thread-like fronds that enclose a single tube, and which are generally
surrounded by a cuticle of polygonal cells. The spores are contained in
transparent berry-like sacs which are naked; and the four-parted spores
(_tetraspores_) are formed in the cells of the cuticle or at the tips of
the fronds.
Over twenty British species belong to the genus _Callithamnion_, and
nearly all of them are pretty red or rose-coloured, feathery plants that
are conspicuous for their beauty. Nearly all are of small size, the
largest measuring only seven or eight inches, while some are so small
that they would scarcely be noticed except by those who search
diligently for them. The principal features of the genus are, in
addition to those mentioned above as common to the order, that the
spores are angular, and clustered within a transparent sac, and the
tetraspores are naked and distributed on the branches.
In some species the fronds have no stem, and these are very small,
generally only about a quarter of an inch in height or less, and they
grow on rocks or weeds, sometimes clothing the surfaces with a
velvet-like covering. _C. floridulum_ forms a kind of reddish down on
the rocks, sometimes in little rounded patches, but sometimes completely
covering the surface. It occurs on several parts of the English coast,
but is so abundant on the west coast of Ireland that the beach is strewn
with it after stormy weather. Other allied species grow in minute tufts
on rocks, or are parasitic on other weeds, and are so inconspicuous that
they are but little known.
Another section of the genus is characterised by pinnate fronds with
opposite segments, and the species are very pretty plants with fronds
generally a few inches in length. One of the commonest of these is the
Feathered Callithamnion (_C. plumula_), a great favourite with
collectors of sea weeds, and a most interesting object for the
microscope. Its soft and flexible fronds grow in tufts from two to five
inches long. The branches are regularly arranged, and the comb-like
branchlets bear the tetraspores on the tips of the plumules. This
beautiful weed grows near low-water mark, and in deep water, and is
often very abundant on the beach after storms. _C. Turneri_ is another
common species, easily known by its creeping fibres, attached by little
discs to some larger weed, and from which the tufts of branched fronds
stand out erect. On the west and south-west coasts of Britain we may
often meet with the allied Crossed Callithamnion (_C. cruciatum_), which
grows on rocks, close to low-water mark, that are covered with a muddy
deposit. It grows in tufts, somewhat resembling those of _C. plumula_,
but its plumules are arranged two, three, or four at a level, and are
very crowded at the tips of the branches.
[Illustration: FIG. 245.--_Callithamnion roseum_]
[Illustration: FIG. 246.--_Callithamnion tetricum_]
Still another section of this large genus contains weeds of a more
shrubby growth, with veined stem and branches jointed obscurely. Of
these the Rosy Callithamnion (_C. roseum_) is not uncommonly found on
muddy shores, and especially in and near the estuaries of rivers. It
grows in dense dark-coloured tufts, two or three inches long, with
alternate branches much divided. The tetraspores occur singly, one at
the top of each of the lower joints of the pinnules of the plumes. _C.
byssoideum_ grows on larger weeds in the rock pools, and especially on
_Codium tomentosum_ (p. 353), in dense tufts of exceedingly fine
filaments, jointed, and branched irregularly. The upper branches are
plumed, and their tips bear very fine colourless filaments. The
spore-clusters are arranged in pairs, and the tetraspores are thinly
scattered on the pinnules of the plumes. This species is so very
delicate in structure that a lens is absolutely necessary to make out
its structure. It is, in fact, impossible to distinguish between the
various species of Callithamnion without such aid; and many of them,
particularly the species last described, require the low power of a
compound microscope.
Among the other common species, belonging to the same section, we may
mention _C. corymbosum_, distinguished by its very slender, rosy,
jointed fronds, with the ultimate divisions of the branches disposed in
a level-topped (_corymbose_) manner, growing on rocks and weeds near
low-water mark; _C. polyspermum_, growing in globular tufts on _Fucus
serratus_ and _F. vesiculosus_, with short awl-shaped pinnules, and
closely-packed clusters of spores; _C. Hookeri_, with opaque stem and
branches, and spreading branchlets that are themselves branched, and
bear spreading plumules at their tips; and _C. arbuscula_, found on the
west coasts, with a stout stem, naked below, and having a very bushy
habit.
It is often by no means an easy matter to distinguish between the
different species in such a large genus as _Callithamnion_, and we
strongly recommend the beginner to first study the characteristics on
which the classification of the _Algæ_ is based, and to arrange his
specimens according to the orders and genera to which they belong; and
then, after mastering the principles of classification, he should refer
to one of those larger works in which all known British species are
described, and make himself acquainted with the features of each
individual species in his collection.
Before leaving the present genus we ought also to mention the fact that
many of the species lose their natural colour rapidly when placed in
fresh water; hence when they are being cleansed for mounting salt water
should be employed. Further, even after they have been satisfactorily
mounted, they are liable to be spoiled if left exposed to moist air. The
salt water used need not be the natural sea water; a solution of common
table salt, made up to approximately the same strength as sea water,
will answer the purpose just as well.
The genus _Griffithsia_ includes some very beautiful weeds of delicate
threadlike structure and of a fine rose colour. The frond contains a
single tube, and is jointed and forked, the joints being usually
transparent. The spore clusters are enclosed in a gelatinous sac
surrounded by a whorl of little branchlets, the spores themselves being
minute and angular. The tetraspores are attached to the inner side of
whorled branchlets.
The commonest species is _G. setacea_, which is of a bright-red colour
and slightly branched. It is also of a somewhat firm structure, but soon
loses both firmness and colour when removed from salt water; and, like
_Callithamnion_, rapidly fades if put into fresh water, which is
readily absorbed through its membranes, causing them to burst and
discharge their colouring matter. It receives its specific name from its
bristle-like forked fronds. _G. secundiflora_ is somewhat like
_Setacea_, but is larger, and the tips of its branches are obtuse. Its
fronds grow in fan-shaped tufts five or six inches long. It is not a
common weed, but may often be met with on the coast of Devon and
Cornwall.
[Illustration: FIG. 247.--_Griffithsia corallina_]
_G. barbata_, or the Bearded Griffithsia, receives its name from its
very delicate fibres, which bear spherical, pink tetraspores. It seems
to occur only on the south and south-west coasts, where it grows on
stones or attached to other weeds. Our last example of the genus is _G.
corallina_, which is of a deep-crimson colour, and is so jointed as to
have the appearance of a coralline. Its fronds are from three to eight
inches long, regularly forked, and of a gelatinous nature. The joints
are somewhat pear-shaped, and the spore clusters are attached to their
upper ends. It soon fades, and even if its colour is satisfactorily
preserved, the pressure of the drying press destroys the beautiful
rounded form of its bead-like joints. It forms a lovely permanent
specimen, however, when preserved in a bottle of salt water, with the
addition of a single grain of corrosive sublimate.
[Illustration: FIG. 248.--_Halurus equisetifolius_]
[Illustration: FIG. 249.--_Pilota plumosa_]
Our next genus (_Halurus_) contains a common weed of the south coast
which was once included in _Griffithsia_. It is the Equisetum-leaved
Halurus (_H. equisetifolius_), so called because its branches are
regularly whorled round the nodes of the jointed branches, thus
resembling the semi-aquatic Mare’s Tail. Its frond is tubular, and the
spore-clusters are situated on the tips of the branches, surrounded by a
whorl of small branchlets.
The genus _Pilota_ has a slightly flattened cartilaginous frond, divided
pinnately, and the axis surrounded by a cuticle of two layers of cells.
The spore-clusters, at the tips of the branches, are surrounded by a
whorl of branchlets. It contains only two British species, one of which
(_P. plumosa_) is a very feathery species, with comb-like branchlets,
growing on the stems and fronds of other weeds found on our northern
shores. The other (_P. elegans_), with narrower fronds, in long flaccid
tufts, is found all round our coasts.
Our last genus of the _Ceramiaceæ_ is the large and typical one
_Ceramium_, which contains about a dozen British species in which the
frond is threadlike, jointed, branched or forked repeatedly, with the
tips of the branchlets usually curled. The spore-clusters are enclosed
in transparent sessile sacs, surrounded by a whorl of very short
branchlets; and the tetraspores are embedded in the cortex, but
distinctly visible. As a rule the fronds are very symmetrical, and the
branches radiate in a regular fan-like manner.
In one species of the genus the frond is completely covered with cortex
cells, and at each node of the frond there is a single spine which,
although so small as to be invisible without a lens, so effectually
locks the threads together that they form an entangled mass that is not
easily arranged to the satisfaction of the collector. The species
referred to is _C. flabelligerum_--the Fan-bearing Ceramium--and is very
rare except in the Channel Islands.
Other species are armed with one or more spines at the nodes, but the
nodes only are covered with cortex cells, which render them opaque,
while the internodes or joints are transparent. In this group we have
_C. ciliatum_--the Hairy Ceramium, with reddish-purple segments, and a
regular whorl of hairs, directed upwards, round each node; each hair or
spine consists of three segments. This plant is common during the summer
and autumn, and may be found in the tide pools at all levels, either
attached to the rocks or parasitic on other weeds. The same section
contains _C. echinotum_, with rigid, forked fronds, and
irregularly-scattered one-jointed spines; it is common on the south
coast, where it may be found on the rocks and weeds of the upper tide
pools; and _C. acanthonotum_, also common in the rock pools, with a
single strong three-jointed spine on the outer side of each filament.
The last-named weed is found principally on the northern shores,
especially on rocks covered with the fry of the common mussel.
Other species are characterised by transparent internodes as above
described, but have no spines at the joints, and may thus be easily
floated on to a sheet of paper without the troublesome matting of their
fronds. These include the Straight Ceramium (_C. strictum_), with erect
and straight branches growing in dense tufts, and conspicuous
tetraspores arranged round the nodes of the upper branchlets, _C.
gracillimum_, of the lower rock pools, with very slender gelatinous
fronds, swollen nodes and small fan-shaped branchlets; _C. tenuissimum_,
closely resembling _C. strictum_ in general appearance, but
distinguished by having its tetraspores only on the outer side of the
nodes; and the Transparent Ceramium (_C. diaphanum_), which may be found
throughout the year on rocks and weeds in the rock pools. The last
species is the largest and most beautiful of the genus, and may be
readily recognised by its light-coloured, transparent stem with swollen
purple nodes, and its conspicuous spore-clusters near the tips of the
filaments.
[Illustration: FIG. 250.--_Ceramium diaphanum_]
Our last example of the genus is the Common Red Ceramium (_C. rubrum_),
which may be found in the rock pools at all levels. It is very variable
in form, but may be known by its contracted nodes, in which the red
tetraspores are lodged, and its spore-clusters surrounded by three or
four short branchlets. It differs from most of the other species in
having both nodes and internodes covered with cortex-cells, and hence
the latter are not transparent.
The order _Spyridiaceæ_ has a single British representative which may be
found in various localities on the south coast. It is _Spyridia
filamentosa_, a dull-red weed with thread-like, tubular, jointed fronds,
from four inches to a foot in length. The main stem is forked, and
densely clothed with short and slender branchlets. The frond is covered
with a cortex of small cells. The spore-clusters are grouped together,
several being enclosed in a membranous cell in conceptacles, or external
sacs, at the ends of the branchlets; and the tetraspores are arranged
singly along the jointed branchlets.
The next family (_Cryptonemiaceæ_) is an extensive one, containing
nearly twenty British genera of red or purple weeds, with unjointed,
cartilaginous, gelatinous, and sometimes membranous fronds. The spores
are irregularly distributed, and are contained either in sunken cells or
in conceptacles. The tetraspores are either in cells at the edges of the
frond or collected together in compact groups.
Of the genus _Dumontia_ we have only one species (_D. filiformis_), the
frond of which is a simple or branched tube, from an inch to more than a
foot in length, containing a loose network of filaments when young, and
only a gelatinous fluid when the plant is mature. The spores exist in
rounded clusters among the cells of the tube, and the tetraspores are
similarly situated. A variety with wide wavy fronds is sometimes found
in the brackish water near the mouths of rivers.
_Gloiosiphonia capillaris_ is a very delicate and beautiful weed found
in the lowest tide pools of the south coast. Its frond is a very slender
branched tube, filled with a gelatinous fluid, and composed of delicate
filaments embedded in transparent gelatine. It is a beautiful object for
the microscope.
_Schizymenia_ (_Iridæa_) _edulis_ has flat, oval, dark-red fronds that
grow in clusters; and, being eaten by various marine animals, is often
found imperfect and full of holes. The fronds are sometimes a foot or
more in length, and five or six inches wide. They are thick and
leathery, and each is supported on a short, cylindrical stem.
In the lower tide pools we commonly meet with _Furcellaria fastigiata_,
with brownish-red, cylindrical fronds, solid, forked, and densely
tufted. The branches are all of the same height, with sharp tips; and
the spore-clusters are contained in terminal lanceolate pods. This weed
is very much like _Polyides_, of another order, but may be distinguished
by its fibrous, creeping root, while that of _Polyides_ is a disc.
The genus _Chylocladia_ is characterised by a tubular rounded frond
composed of two layers, the inner consisting of branching filaments, and
the outer cellular. The spores are contained in external cones with a
pore at the apex, and the tetraspores are among the superficial cells of
the branches. There are two common British species of the genus, one of
them--_C. articulata_--with long, tubular fronds, constricted at
intervals, the lower branches forked and the upper whorled and tufted;
and _C. clavellosa_, with freely branched fronds bearing short
spindle-shaped branchlets.
One of the best-known algæ of the present family is the Irish Moss or
Carrageen (_Chondrus crispus_), which will be at once recognised by its
representation on Plate VIII. Its fronds are cartilaginous, forked and
fan-shaped; and, when growing in deep, sheltered pools, its branches are
often broad and much curled. This weed is an important article of
commerce, being still used as a food for invalids. When boiled it
yields a colourless gelatine.
In the genus _Gigartina_ the frond is cartilaginous, flat, or
threadlike, irregularly branched, and of a purplish-red colour. The
spores are contained in external tubercles, and the tetraspores are
arranged in masses beneath the surface. The only common species is _G.
mamillosa_, which has a linear, furrowed stem, with fan-shaped,
deeply-cleft fronds. The spores are contained in mamilliform tubercles
scattered over the surface of the frond.
_Callophyllis_ (_Rhodymenia_) _laciniata_ is found on most rocky coasts.
It has bright-red, fleshy fronds that are deeply cleft into wedge-shaped
segments, the fertile specimens with waved edges and small marginal
leaflets. It is found on rocks and Laminaria stems beyond the
tide-marks, but is commonly washed up on the beach during storms. It is
a beautiful weed, and retains its colour well when dried.
_Cystoclonium_ (_Hypnæa_) _purpurascens_ is a very common weed, growing
on other algæ between the tide-marks, and sometimes reaching a length of
two feet. Its cartilaginous, purple fronds are much branched, and become
almost black when dried. The spores are embedded in the smallest
branches, and the tetraspores are arranged among the superficial cells.
The genus _Phyllophora_ contains a few British weeds with a stiff,
membranous frond, bearing leaf-like appendages, and supported on a
stalk. The tetraspores are contained in external wart-like swellings.
The commonest species is _P. membranifolia_, the fronds of which are
divided into wedge-shaped segments, and grow in tufts from an expanding
root. The spores are contained in stalked sporangia, and the tetraspores
are near the centres of the segments. Another species--_P. rubens_--has
a shorter stem, and grows in deep and shady rock pools. Its fronds are
densely tufted; and, as the plant grows, new series of segments are
formed at the tips of the older ones. A third species (_P.
palmettoides_) has a very bright-red frond and an expanded root.
The order _Rhodymeniaceæ_ includes a number of red or purple sea weeds
with flat or thread-like unjointed, cellular fronds, the surface cells
forming a continuous coating. The spores are lodged in external
conceptacles, and are at first arranged in beaded threads. The
tetraspores are either distributed among the surface cells, collected in
clusters, or situated in special leaflets.
The typical genus (_Rhodymenia_) contains two red, membranous weeds,
the commoner of which is _R. palmata_ (Plate VIII.), so common on the
Scottish and Irish coasts, where it forms an important article of diet,
and is known as the Dulse or Dillisk. It is also widely distributed over
the English coasts. Its broad, fleshy fronds are divided into
finger-like lobes, and are either sessile or supported on a stalk that
proceeds from a small discoid root. The frond is very variable in form,
being sometimes divided into very narrow segments, and sometimes quite
undivided. One variety has a number of small stalked leaflets on its
margin (see Plate VIII.); and another is very narrow, with wedge-shaped
irregular lobes. _R. palmetta_ is a smaller and less common species that
grows on rocks and large weeds in deep water. The tetraspores form
crimson patches on the tips of the lobes.
_Maugeria_ (_Delesseria_) _sanguinea_ (Plate VIII.) is a large and
beautiful weed, of a blood-red colour, that grows in the lower rock
pools or beyond low-water mark, under the shade of high rocks or hidden
by the olive tangles. Its frond is thin and membranous, with a
well-defined midrib. The spores are contained in globular stalked
conceptacles, usually on one side of the midrib; and the tetraspores may
be seen in pod-like leaflets attached to the bare midrib during the
winter.
Passing over some of the rarer membranaceous _Rhodymeniaceæ_, we come to
the beautiful _Plocamium_, distinguished by its linear compressed
crimson fronds, which are pinnate, with comb-like teeth, the branchlets
being alternately arranged on either side in threes and fours. The
spores are on radiating threads, in globular conceptacles; and the
tetraspores are in the outer divisions of the frond. We have only one
species of this beautiful genus, and that is _P. coccineum_, which is of
such a brilliant colour that it is always a favourite with collectors.
[Illustration: FIG 251..--_Plocamium_]
Our last example of the order is _Cordylecladia_ (_Gracilaria_)
_erecta_, with threadlike, cartilaginous frond, irregularly branched and
cellular in structure. The fronds arise from a disc-like root; and bear
spores in thickly-clustered spherical conceptacles, and tetraspores in
lanceolate pods at the tips of the branches, both in the winter. It is a
small weed, and grows principally on sand-covered rocks near low-water
mark.
The order _Sphærococcoideæ_ contains red or purple sea weeds with
unjointed cartilaginous or membranaceous fronds, composed of many-sided,
elongated cells, with spores in necklace-like strings, lodged in
external conceptacles. The typical genus (_Sphærococcus_) contains the
Buck’s-horn sea weed which grows at and beyond low-water mark on the
south and west coasts, where it is sometimes washed up on the beach
during storms. Its fronds are flattened and two-edged, freely branched,
and the upper branches are repeatedly forked, and terminate in
fan-shaped, cleft branchlets. Both branches and branchlets are fringed
with slender cilia, in which the spores are embedded. It is a handsome
weed, of a bright-red colour and a somewhat coral-like form.
Allied to this is _Gelidium corneum_, with flattened, horny fronds,
repeatedly pinnate, with the smallest branchlets obtuse and narrower at
the base. The spores are contained in conceptacles near the extremities
of the branchlets, and the tetraspores are imbedded in club-shaped
branchlets. There are a large number of varieties of this species,
differing in form, size, and the mode of branching of the fronds. The
size varies from one to five or six inches, and the colour is red or
reddish green.
In the genus _Gracilaria_ the frond is thick and horny, and the surface
cells are very small, while the central ones are large. The spores,
formed on necklace-like threads, are enclosed in sessile conceptacles
along the branches, and the tetraspores are imbedded among the surface
cells of the fronds. The only common species is _G. confervoides_, with
cylindrical cartilaginous fronds bearing long thread-like branches,
sometimes reaching a length of two feet. The spore conceptacles are
situated on the slender branches, giving them a knotted or beaded
appearance. The colour is a dark purple, which rapidly fades when the
weed is placed in fresh water or left exposed to the air. Two other
species--_G. multipartita_ and _G. compressa_--are rare.
_Calliblepharis ciliata_, perhaps more commonly known as _Rhodymenia
ciliata_, has a branching root, short round stem, and a broad, crisp
frond that is generally ciliated. Sometimes the frond is simple and
lanceolate, with small leaf-like appendages on its edge; and sometimes
it is deeply cleft. The spores are arranged in beaded threads in sessile
conceptacles on the marginal leaflets. Another species of the same genus
(_C. jubata_) is very similar in structure, but is of a duller-red
colour, gradually changing to olive green at the tips; and it has its
tetraspores in the cilia only, while in _C. ciliata_ they are collected
in patches in all parts of the frond. Both species grow in deep water,
and are frequently washed up during storms.
The large genus _Nitophyllum_ contains some beautiful rose-red sea
weeds, with irregularly cleft membranaceous fronds, either veinless, or
with a few indistinctly visible veins only at the base. The spores are
in rounded sessile conceptacles scattered on the surface of the frond;
and the tetraspores occur in clusters similarly scattered.
One of the species--_N. laceratum_--so called from the torn and jagged
appearance of the frond, is represented on Plate VII. The fronds are
attached to a disc-like root, and are very variable in form, being
sometimes so narrow as to appear almost threadlike. The plant grows on
rocks and large weeds in the lower rock pools and in deep water. In the
same genus we have _N. punctatum_, with broad pink fronds, dotted all
over with spore-conceptacles and dark-red clusters of tetraspores; also
a few other less common species that are seldom seen except after
storms, as they grow almost exclusively in deep water.
The genus _Delesseria_ contains some beautiful rose-coloured and
reddish-brown weeds with delicate, leaf-like, symmetrical fronds, each
of which has a darker midrib from which issue transverse veins. The
spores are arranged like minute necklaces, and are contained in sessile
conceptacles either on the midrib of the frond or on leaflets that grow
from the midrib. The tetraspores are in clusters which are scattered
over the frond or on its leaflets. The algæ of this genus are seldom
found growing between the tide-marks, as they generally thrive in deep
water, but splendid specimens are often washed up on the beach during
storms, especially on the south and south-west coasts.
[Illustration: FIG. 252.--_Delesseria alata_]
[Illustration: FIG. 253.--_Delesseria hypoglossum_]
Among these we may specially mention _D. alata_, known popularly as the
Winged Delesseria, with a dark-red, forked frond, consisting of a
strong midrib, bordered by a wing-like lamina of very variable width,
supported by opposite veins. In this species the clusters of tetraspores
are arranged on each side of the midrib or special leaflets near the
tips of the frond. _D. sinuosa_ is a less common weed, with a disc-like
root and an oblong, cleft and toothed frond, and tetraspores in leaflets
growing from its margin. Another species--_D. hypoglossum_--is
characterised by the leaflets of the midrib bearing still smaller
leaflets in the same manner.
We have already referred (p. 366) to a sea weed commonly known as the
Dock-leaved Delesseria, the scientific name of which is _Maugeria_
(_Delesseria_) _sanguinea_. This plant was once included in the present
order, but has been removed on account of the different structure of its
fruit.
Our next order is the interesting one containing the coral-like weeds,
some of which are so common and so conspicuous in the rock pools. The
order is known as the _Corallinaceæ_, and all its species secrete
carbonate of lime, which hides their vegetable structure and gives them
more the appearance of stony corals.
The typical genus (_Corallina_) includes two weeds with jointed pinnate
fronds, and spore-conceptacles at the tips of the branches with a
terminal pore.
These and the allied sea weeds are very unlike plants in their general
nature, their stony covering of carbonate of lime hiding all traces of
the delicate cellular structure so characteristic of the various forms
of vegetable life, and especially those of aquatic or marine habit. If,
however, the weed is put into dilute hydrochloric (muriatic) acid the
calcareous matter will be completely dissolved in a minute or two, with
evolution of bubbles of carbonic acid gas; and if a portion of the frond
be then examined in a drop of water under the microscope, the cellular
structure referred to will be seen as well as in any other weed. Another
characteristic of the plant, or rather of the carbonate of lime which it
secretes, is its property of becoming intensely luminous when held in a
very hot flame. Thus if a tuft of coralline be held in the flame of a
Bunsen burner, it will glow so brilliantly as to remind us of the lime
light. Further, if we examine the plant in its natural state, we find
that the carbonate of lime is not secreted uniformly in all parts, but
that the nodes of the jointed frond are free from the stony deposit, and
are therefore flexible.
Our commonest species--_C. officinalis_--may be found in almost every
rock pool between the tide-marks, growing on rocks, shells, and other
weeds. The joints of the stem and branches are cylindrical or somewhat
wedge-shaped, while those of the branchlets are linear; and the colour
varies from a dark purple to white, the former prevailing in the deep
and shady pools and the depth of tint decreasing according to the amount
of exposure to the bleaching action of the sun.
A second species (_C. squamata_) is very similar in growth and habit,
but is much less common, and is confined to the neighbourhood of
low-water mark. It may be distinguished from the last by the form of the
segments, which are short and globose in the lower portions of the stem,
and become broader and more flattened towards the tips of the branches.
Another genus--_Jania_--contains a few coralline weeds that are somewhat
like _Corallina_, but are of a more slender habit and smaller, and have
a moss-like appearance. They may be distinguished by the _forked_
branching of the slender frond, and by the position of the conceptacles
in the axils of the branches, and not at the tips. _J. rubens_ is a very
common red species that grows in tufts on other weeds. It has
cylindrical segments, longer towards the tips of the branches; while
another and less common one (_J. corniculata_), found principally on the
south coasts, has flattened segments except in the branchlets.
A third genus of the order--_Melobesia_--contains a very peculiar group
of algæ that would certainly never be regarded as plants by those who
did not know them. They are apparently mere solid incrustations of
calcareous matter, without any jointed structure, and often of very
irregular form, covering the surfaces of rocks, shells, or weeds. They
are of varying colours, some prevailing tints being dark purple, lilac,
rose, and yellow; and they are equally variable in form, some being
decidedly lichen-like, some resembling fungoid masses, and others
consisting of superimposed leaf-like layers. They are not weeds to be
pressed for the collector's album, but require storing in boxes or trays
like sea shells. As in the case of the branched corallines, the hidden
vegetable structure may be revealed by dissolving away the carbonate of
lime; and the spore-conceptacles, with terminal pores, may be seen
scattered irregularly over the surface.
The order _Laurenciaceæ_ contains some beautiful pink, red, and purple
weeds with round or flattened branching fronds. They may be known by the
disposition of the tetraspores, which are irregularly scattered over the
branches; and by the pear-shaped spores in rounded capsules. The
typical genus (_Laurencia_) includes an abundant weed (_L. pinnatifida_)
which was formerly eaten in parts of Scotland, where it is known as the
Pepper Dulse on account of its peppery taste. It is found in the tide
pools on many parts of the coast, and varies much in size, form, and
colour according to the situation in which it grows. The plants which
are exposed to the air at low tide are usually small, and of a pale
brown colour, while those found in the permanent rock pools at or near
low-water mark are larger and dark brown or purple. The fronds are flat
and cartilaginous, with stout branches bearing alternate divided
branchlets, which are blunt at the tips. The stem itself is unbranched.
The spores are pear-shaped, in oval cells; and the tetraspores are
irregularly distributed near the tips of the branches.
Another common species, known as the Tufted Laurencia (_L. cæspitosa_),
is very similar to the last mentioned, and is not easily distinguished
from it. It is, however, of a bushy habit, while _L. pinnatifida_ is
flat, and its fronds are less firm. This species grows on rocks and
stones between the tide-marks, and is variegated in colour from a pale
green to a purple.
[Illustration: FIG. 254.--_Laurencia pinnatifida_]
[Illustration: FIG. 255.--_Laurencia obtusa_]
A third species--the Obtuse Laurencia (_L. obtusa_)--is widely
distributed on our coasts, and may be known by its thread-like bipinnate
fronds with short blunt branchlets, cup-shaped at the tips. It is
parasitic on various other weeds.
The genus _Lomentaria_ includes a few weeds with tubular fronds that are
constricted at intervals, and divided internally by transverse
membranous septa. The spores are pear-shaped and lodged in spherical
cells; and the tetraspores are scattered on the surface of the branches.
One species called the salt-wort (_L. kaliformis_) is widely
distributed. Its colour is pink, sometimes yellowish, and it grows on
rocks or stones, and sometimes on other weeds. It may always be known by
its spherical fruit, without any visible opening, containing crimson
pear-shaped spores. Another species (_L. ovalis_), found on the coasts
of Devon and Cornwall, may be recognised by its _solid_ branched frond
and little oval leaf-like branchlets, which are hollow, jointed, and
divided by partitions internally.
The one remaining order of the red-spored sea weeds is the
_Rhodomelaceæ_, which has either a jointed or a many-tubed axis, and the
surface divided up into little definite areas. The fronds are either
leafy or thread-like, and the prevailing colours are red, reddish brown,
and purple. The spores are pear-shaped, and occupy the terminal cells of
tufted threads in external, globular, or rounded conceptacles; and the
tetraspores are lodged in special receptacles, or in special modified
branchlets. The order contains some of our most beautiful weeds, while
some of its members are of a very dark colour and unattractive form.
The typical genus--_Rhodomela_--contains two British species with
dark-red, cartilaginous fronds, cylindrical, unjointed, and irregularly
branched; and the tetraspores imbedded in the tips of the slender
branchlets. The name of the genus signifies ‘red-black,’ and is applied
on account of the tendency of the dark-red fronds to turn black when
dried.
_R. subfusca_ is very common on all our coasts. It has rigid fronds,
irregularly branched; and is in its best condition during the summer.
The other species--_R. lycopodioides_--has long undivided branches with
thickly-set and freely-divided branchlets.
When turning over the fronds of different species of the larger olive
weeds we commonly find them more or less clothed with tufts of
filamentous plants, sometimes small and delicate, and sometimes larger
and of more robust growth, varying in colour from a purplish brown to a
dark violet, and the articulated filaments more or less distinctly
striated with parallel lines. These weeds belong to the genus
_Polysiphonia_, and derive their generic name from the fact that the
threadlike fronds are composed of several parallel tubes. The surface
cells are also arranged in regular _transverse_ rows, and it is this
which gives rise to the striated appearance above referred to.
Over twenty species of _Polysiphonia_ are to be found on our shores,
where they exist at all levels between the tide-marks. They are
distinguished from one another partly by their general form and mode of
growth, and also by the number of tubes in their threadlike fronds.
Although they would not always be considered as lovely weeds and are
often anything but beautiful when dried and mounted, yet in their fresh
condition they are generally pretty objects, and their microscopic
structure is particularly interesting on account of the beautiful and
symmetrical arrangement of their siphons and tubes.
If the reader is the fortunate possessor of a compound microscope, it
will amply repay him to make transverse sections of the fronds for
examination. A short length of the frond should be inserted into a slit
cut in a piece of carrot or elder pith; and, while thus supported, very
thin transverse sections may be easily cut with a sharp razor, care
being taken to keep both razor and object very wet during the process.
Allow the sections to fall into a vessel of water as they are cut, and
then select the thinnest for examination, mounting them in a drop of
water in the usual way.
Specimens in fruit should always be obtained when possible, so that the
nature of the fructification may be observed. Two kinds of spores may be
seen in each species, but, as is usually the case with the red sea
weeds, on different plants. Some are small pear-shaped bodies, enclosed
in oval cells at the tips of the fronds; and the others are arranged in
clusters of four in swollen parts of the threads.
The commonest species is _P. fastigiata_, which may be found in
abundance as bushy brownish tufts on the fronds of _Fucus nodosus_ (p.
386). A transverse section of this weed is a very beautiful microscopic
object. It resembles a wheel, with a dark centre to the nave, and
several spokes enclosing about sixteen regularly arranged tubes. The
swollen tips of fronds should also be examined for the urn-shaped cells
containing the spores; and if a gentle pressure be applied to the
cover-glass with a needle, the little pear-shaped spores may be
expelled. The other kind of spores may be found near the bases of the
branches on different plants.
[Illustration: FIG. 256.--_Polysiphonia fastigiata_]
Among other species we may briefly mention--_P. parasitica_, sometimes
found near low-water mark, growing in little feathery tufts of a
bright-red colour, on the lichen-like _Melobesia_ or on corallines. It
has seven or eight parallel siphons in its fronds, all regularly
arranged round a small central space.
_P. Brodiæi_ is moderately common on our coasts. This is a large brown
species, with seven siphons surrounded by a thick cellular layer which
conceals the articulations and is too opaque to allow the siphons to be
seen without dissection. Its branches, which are alternate, bear short
tufts of delicate branchlets.
[Illustration: FIG. 257.--_Polysiphonia parasitica_]
[Illustration: FIG. 258.--_Polysiphonia Brodiæi_]
_P. byssoides_, so called on account of the pink filaments that fringe
the fronds, has also seven siphons. It is a large and beautiful weed,
moderately common on our coasts, of a bright-red colour, with
conspicuous fructification. The branches are alternate, and the
branchlets are clothed with the byssoid filaments above referred to.
_P. violacea_ is of a reddish-brown colour, with long silky alternate
branches, and four siphons. It receives its specific name from the fact
that it turns to a violet colour when dried.
_P. nigrescens_ has, as the specific name implies, blackish fronds, and
these are freely branched. The tubes, about twenty in number, are flat,
and are arranged round a large central space.
[Illustration: FIG. 259.--_Polysiphonia nigrescens_]
Our last example--_P. atro-rubescens_--is of a dark reddish-brown
colour, with rigid and densely-tufted fronds. It has twelve tubes,
arranged _spirally_ round a central cavity. It is common in the lower
rock pools of some coasts.
In the same order we have the genus _Chondria_, so called on account of
the cartilaginous nature of its thread-like fronds. These are pinnately
branched, and the club-shaped branchlets taper below. The main stem is
jointed and contains many siphons. The genus includes a common species
(_C. dasyphylla_), with thick fronds, that is found in shallow sandy
pools, where it grows on pebbles, shells, or on other weeds, the colour
varying from pink to a dark purple. _C. tenuissima_ is a very similar
weed, but may be distinguished by its more slender growth, and by its
long, rod-like simple branches, clothed with slender, bristle-like
branchlets that taper from the middle towards both ends.
On the northern coasts of Britain we may meet with _Odonthalia dentata_,
the blood-red fronds of which are tufted, and arise from a hard,
disc-like root. Each frond projects from the axil of a tooth-like
projection of the main stem, and is deeply pinnatifid, with a distinct
midrib in the lower part, and thin and membranaceous towards the tip.
The pinna are dentate, and the spores are in stalked, oval conceptacles
in the axils of the pinnæ. The tetraspores are similarly situated in
stalked, lanceolate leaflets.
The weeds of the genus _Rytiphlæa_ are very similar to some of the
_Polysiphonia_, the axis of the frond being jointed and transversely
striped, but the nodes are less distinct and are not constricted. They
are shrub-like weeds, with tufted spores in oval, sessile conceptacles;
and tetraspores in spindle-shaped branchlets or in little pod-like
leaflets. The principal British species are:--
_R. pinastroides_, a much-branched and shrub-like weed, of a dull-red
colour, which turns black when the plant is dried. The branches have
rigid, hooked branchlets arranged in such a manner as to give a combed
appearance. This species occurs on the south coast, and is in its prime
in very early spring. It is often rendered peculiarly interesting by the
colonies of zoophytes and the patches of _Melobesia_ with which it is
more or less covered.
_R. fruticulosa_ is another shrubby species, with irregularly branched,
interlacing stems. It is to be found in the rock pools of the south and
west coasts, and is of a deep-purple colour in the deeper shady pools,
but varying to a yellowish tint where exposed to the full light of the
sun. The whole of the frond is covered with hooked branchlets, and the
weed is peculiar for the fact that, when removed from the rock pool,
little glistening beads of water remain attached to the tips of the
terminal branches. The tetraspores are situated in distorted branchlets.
_R. thuyoides_ has creeping, fibrous roots, from which arise the erect
stems of purple-brown, branched fronds with short spine-like branchlets.
It occurs in the shallower rock pools, where it grows attached to rocks
or to other weeds. It is in its best condition during the summer, when
we may see its oval spore-conceptacles and the tetraspores in distorted
branchlets.
The last genus of the _Rhodomelaceæ_ is _Dasya_, which contains some
very graceful and brightly-coloured weeds that are found principally on
our south and west coasts. In these the fronds are thread-like or
flattened, branched, and without visible joints. The main stem contains
many tubes, but the tubular structure is hidden by the outer layer of
cells; and the branchlets, which are slender, one-tubed, and jointed,
bear little lanceolate pods that contain the tetraspores.
_D. ocellata_ has small tufted fronds, about two or three inches long,
attached to a small discoid root. The main stems are densely covered
with slender, forked branchlets, those at the tips being clustered in
such a manner as to recall the eye-like marks of the peacock’s tail. It
grows principally on the mud-covered rocks beyond low-water mark, and is
not by any means a common weed. Another species--_D. arbuscula_--is
somewhat plentiful on parts of the Scottish and Irish coasts, but
comparatively rare in South Britain. It has a small disc-like root, and
stems thickly clothed with short branchlets. The spore-conceptacles are
tapering, on short stalks, and the tetraspores are contained in pointed
pods on the branchlets. The scarlet Dasya (_D. coccinea_) may be
commonly seen at and beyond low-water mark during late summer, at which
time splendid specimens may also be found on the beach after storms. Its
stem is thick, proceeding from a discoid root, and is clothed with
hair-like filaments; and the branches bear short, slender branchlets
that give them a feathery appearance. The tetraspores are contained in
elongated, pointed, and stalked pods. There are three other species on
the British list, but they are not common weeds.
The last of the three great groups into which the sea weeds are divided
is the _Melanospermeæ_, or olive-spored algæ, the different species of
which are generally very readily distinguished by their olive-green or
olive-brown colour, for the whole plant, as well as the spores, contains
a dark olive colouring matter, in addition to the chlorophyll which is
always present.
These weeds are often very large, frequently attaining a length of
twenty feet or more in our seas, and from eighty to a hundred feet in
warmer parts; and, being also extremely abundant almost everywhere, they
form a most conspicuous feature of the shore. They usually grow on rocks
and stones, from high-water mark to moderately deep water, but some of
the smaller species are pseudo-parasitic on other algæ.
Their form is most varied. Some are minute filamentous plants,
consisting only of slender jointed threads, and others are mere
shapeless masses; but many of the larger species exhibit a great
differentiation of form, having root-like and stem-like structures, and
expansions that resemble leaves. The latter, too, often have large
vesicles that contain air, sometimes arranged singly along the median
line of the frond, or in lateral pairs, or a single vesicle at the base
of each segment of the thallus.
The air vesicles, of course, serve to buoy up the plant when it is
submerged, thus enabling the light to penetrate between its fronds to
lower portions; and when the plants have been wrenched from their
moorings by the force of the waves, they immediately rise to the surface
and are drifted on to the shore or accumulate in the eddies of the
surface currents. In this way immense masses of floating weeds are
formed, the most remarkable being that of the Sargasso Sea in the North
Atlantic.
Like other algæ, the melanospores grow by a continued process of
cell-division, and when portions of the thallus are worn away during
stormy weather, they are renewed by the same process.
The cell-walls of many species are very mucilaginous, the gelatinous
covering being either the result of the degeneration of the cell-walls
themselves, or the secretion of special glands.
As with the last division, the reproduction of the melanospores may be
asexual or sexual. The asexual spores, which are not motile, are formed
in some of the surface cells of the thallus. The male and female sexual
organs, called respectively the _antheridia_ and the _oogonia_, are
produced in cavities on special portions of the thallus, both kinds
being often formed in the same cavity or depression. The latter contains
from one to eight little bodies called _oospheres_. These escape and
float passively away when the wall of the oogonia ruptures. The
antheridia are also discharged whole, but the minute fertilising
elements (_antherozoids_), which are eventually set free from them,
swarm round the oospheres, being attracted by the latter. Soon one of
the antherozoids enters the oosphere, and from that moment all
attraction ceases, the remainder of the antherozoids floating passively
away; and the oosphere, previously naked and barren, now develops a
cell-wall, and becomes the fertile progenitor of a new plant.
Starting with the lowest of the melanospores, we first deal with the
order _Ectocarpaceæ_, which is characterised by olive, thread-like,
jointed fronds, with spores on the branchlets or embedded in their
substance; two kinds of spores often existing in the same plant.
The typical genus (_Ectocarpus_) contains many British species, though
several of them are rare. They are soft and flexible weeds, generally of
a dull olive colour, with slimy, tubular fronds, and grow in tufts on
other weeds or on mud-covered rocks. Spores of various shapes are
scattered over the fronds, and are also contained in pod-like bodies
formed of the branchlets. This latter feature is, perhaps, the best
distinguishing characteristic of the genus, but it is not an easy matter
to identify the several species it contains.
_E. tomentosus_ is very commonly found on _Fucus_ and other weeds, where
it forms matted tufts of slender threads of a yellowish-brown colour.
The threads are clothed with transparent cilia, and together form a
dense, spongy mass. The spores are contained in narrow pods supported on
short stalks. _E. littoralis_ is another common species, of a very
unattractive appearance. It grows in matted tufts on other weeds, on
rocks, mud, or any submerged object, and its spores are contained in
linear swellings of the branches. This species thrives well in brackish
water, and may be seen far up certain tidal rivers.
[Illustration: FIG. 260.--_Ectocarpus granulosus_]
[Illustration: FIG. 261.--_Ectocarpus siliculosus_]
[Illustration: FIG. 262.--_Ectocarpus Mertensii_]
Among the other species we may briefly mention _E. granulosus_, an
abundant and beautiful weed that grows in feathery tufts on rocks and
weeds, with elliptical, stalkless pods, quite visible to the naked eye,
freely distributed over the opposite branchlets; _E. siliculosus_, a
pale olive, parasitic species with lanceolate stalked pods, pointed and
striped; _E. sphærophorus_, a small, soft, brownish-yellow species, with
dense matted branches and spherical pods arranged either opposite to one
another or to a branchlet; and _E. Mertensii_, a pretty species that
grows on muddy rocks, freely branched but not matted, and having pods
enclosed by the branchlets. The last species is rare, but may be found
in Cawsand Bay and a few other localities about Plymouth Sound. The
genus includes several other species, but all these are more or less
rare.
In the genus _Myriotrichia_ we have two parasitic species with fragile,
hair-like, jointed fronds bearing simple straight branches that are
covered with transparent fibres. In these the spore-cases are rounded
and transparent, and arranged along the main threads; and the dark olive
spores are readily visible within. In _M. filiformis_ the branchlets are
short, and clustered at intervals, thus giving a somewhat knotted
appearance to the threads, and both branches and branchlets are covered
with long fibres. The other species--_M. clavæformis_--is very similar,
but may be distinguished by the arrangement of the branchlets, which are
not clustered at intervals, but are distributed regularly, and are
longer towards the tip of the frond, giving the appearance of minute
fox-brushes.
[Illustration: FIG. 263.--_Sphacelaria cirrhosa_]
[Illustration: FIG. 264.--_Sphacelaria plumosa_]
The genus _Sphacelaria_ contains several British weeds with rigid
branched and jointed fronds, most easily distinguished by the tips of
the branches, which are flattened, contain a granular mass, and have a
withered appearance. _S. cirrhosa_ forms hair-like tufts of slender
fibres with closely-set branches on small weeds, the tufts varying from
a quarter of an inch to over an inch in length. The fronds are naked at
the base, and the spore-cases, which are globular, are arranged on the
branches. _S. filicina_ is, as its name implies, of a fern-like
appearance, but is very variable in form. Its fronds vary from one to
three inches in length, and the spores are arranged singly in the axils
of the branchlets. Excluding some rarer species we mention one other
example--the broom-like _S. scoparia_, the frond of which is coarse and
very rigid, of a dark-brown colour, two or three inches long, with the
lower portion clothed by woolly fibres. Its spores are arranged in
clusters in the axils of the branchlets.
[Illustration: FIG. 265.--_Sphacelaria radicans_]
The last genus of the _Ectocarpaceæ_ is _Cladostephus_, which grows in
dark-green tufts, usually five or six inches long, in the deeper tide
pools. The fronds are cylindrical, branched, inarticulate, and rigid;
and the branchlets, which are short and jointed, are arranged in whorls.
The spores are situated in short accessory branchlets, or in masses at
the tips of the ordinary branchlets. _C. verticillatus_ is a very common
species, the whorled branchlets of which are deciduous in winter, when
the accessory branchlets that bear spores begin to develop. _C.
spongiosus_ is densely clothed with branchlets, and is of a bushy habit,
with a very spongy feeling. It is by some regarded as a variety of _C.
verticillatus_.
[Illustration: FIG. 266.--_Cladostephus spongiosus_]
[Illustration: FIG. 267.--_Chordaria flagelliformis_]
The order _Chordariaceæ_ is characterised by a compound gelatinous or
cartilaginous frond, consisting of interlacing horizontal and vertical
threads. The spores are not external as in the _Ectocarpaceæ_, but
contained in cells in the substance of the frond. In the typical genus
the frond has a cylindrical, branched, cartilaginous axis, surrounded by
whorls of club-shaped threads and slender gelatinous fibres. We have
only one common species--_Chordaria flagelliformis,_ the fronds of which
are from four to twenty inches long, of uniform thickness throughout,
with long, glistening, soft and slimy branches among which the spores
are disposed. It may be found in rock pools at almost all levels.
In the genus _Elachista_ there are some very small and peculiar weeds
that are almost sure to be overlooked by inexperienced collectors. They
are parasitic, and are composed of two kinds of jointed threads, the
inner of which are forked and combined into a tubercle, while the outer
are simple and radiate from the tubercle. The spores are attached to the
inner threads. The largest species (_E. fucicola_) is parasitic on
_Fucus_, growing in brush-like tufts about an inch long. Some of the
smaller ones are mere star-like tufts of no attractive appearance, and
would be disregarded as troublesome parasites by most young collectors,
but all of them are very interesting objects for the microscope.
The members of the genus _Myrionema_ are similarly liable to be
neglected, for they are minute parasites appearing only as decaying
spots on larger weeds, but nevertheless form interesting studies for the
microscope. Like the last group, they have two sets of jointed fibres,
the inner being branched, and spread over the surface of the plant on
which it grows, while the outer are simple and stand out at right
angles, but all are united into a rounded mass by a gelatinous
substance. Perhaps the best known is _M. strangulans_, which infests
_Ulva_ and _Enteromorpha_, producing the appearance of small decaying
spots.
In the genus _Leathesia_ we have other unattractive weeds, the jointed
and forked threads of which are all united together into tuber-like
fronds that are common on rocks and weeds between the tide-marks. There
are three or four species, all similar in general appearance, with the
spores distributed among the outer threads. These weeds cannot be
satisfactorily pressed and dried in the usual way, and should be
preserved in formaldehyde or dilute spirit, when they will always be
available for microscopic examination.
The last genus of the _Chordariaceæ_ is _Mesogloia_, so called because
the central axis of loosely-packed, interlacing threads is covered with
gelatinous substance. Around this axis there are radiating, forked
threads which are tipped with clubbed and beaded fibres among which the
spores are distributed. One species (_M. vermicularis_), common in most
rock pools, is of a wormlike form, of a dirty olive or yellow colour,
with soft, elastic fronds growing in tufts from one to two feet long.
_M. virescens_, also a common species, is of a pale greenish or olive
colour, and very soft and slimy. Its stem is round and slender, freely
branched, with short, simple branchlets.
The order _Dictyotaceæ_ contains the olive weeds with inarticulate
fronds, and superficial spores disposed in definite lines or spots. In
the typical genus (_Dictyota_) the frond is flat and forked, somewhat
ulva-like and ribless, and the spores are produced in little superficial
discs just beneath the cuticle. There is only one British species--_D.
dichotoma_--but that is a very common one, and it assumes a great
variety of forms as regards the shape and division of its fronds
according to the situation in which it grows, the fronds being broadest
and strongest in the deepest water. The root is covered with woolly
fibres, and the frond is regularly forked.
One of the most interesting algæ of this order is the Turkey-feather
Laver (_Padina pavonia_), which is the only British representative of
its genus (see Plate VII.). Its very pretty fan-shaped fronds are of a
leathery nature, curved, fringed along the upper margin, and marked with
concentric lines. They often bear small leaflets, and are partially
covered with a powdery substance which renders them beautifully
iridescent when in the water. The root has woolly fibres, and the spores
are arranged in lines along the upper margin. This weed seems to be
confined to the south coast, where it may often be seen in the deeper
tide pools; though in some of the sandy bays of the Isle of Wight it may
be seen in shallow pools, and even in places left exposed to the air at
low tide.
The genus _Zonaria_ contains a British species (_Z. parvula_) that
covers the rocks in round patches; and though moderately common is not
very frequently seen by collectors on account of the fact that it grows
in the deep crevices of rocks at or near low-water mark. Its frond is
flat and membranaceous, more or less divided into lobes, without veins,
and rather obscurely divided into concentric zones. It is attached to
the rock by fibres that proceed from the under surface of the frond, and
the spores are arranged in clusters beneath the superficial cells.
_Cutleria multifida_, though not very abundant, is to be found on most
of our coasts; but since it grows almost exclusively beyond low-water
mark, it should be looked for on the beach after storms, or in the
fishermen’s nets. The frond is olive-green, fan-shaped, rather thick,
and irregularly divided into forked branches; and it has a beautifully
netted surface. The spore-cases may be seen scattered over the surface
of the frond as so many black dots, and the antheridia are elongated,
cylindrical bodies attached to tufted filaments on all parts of the
frond.
In the genus _Stilophora_ the root is discoid; the frond cylindrical,
hollow, and branched; and the spores arranged in clusters over the
surface. One species (_S. rhizodes_) is occasionally to be seen on the
south coast. It is of a yellowish colour, from six to twenty inches
long, and may be known by its long thread-like branches, with scattered,
forked branchlets, and by the wart-like projections of the stem which
contain the spores. This weed is often the source of some disappointment
to the collector, for it soon turns to a jelly-like mass when removed
from the water, and should therefore be mounted as soon as possible
after it has been collected.
The fennel-like _Dictyosiphon fœniculaceus_ is abundant in tide pools,
where it may be seen in its best condition during spring and early
summer. Its root is a small disc, the frond is tubular, thread-like and
branched, and the branches bear hooked branchlets. The spores are naked,
and distributed either singly or in clusters over the surface of the
frond.
Our next genus--_Punctaria_--contains a few British species with a
shield-shaped root, and a flat, membranous, undivided frond, without a
midrib, and having the spores disposed as minute dots over the surface.
A plantain-like species (_P. plantaginea_) has broad, leathery,
lanceolate fronds, of a dark olive-brown colour, usually from six inches
to a foot in length. Two other weeds--the broad-leaved _P. latifolia_ of
the tide pools, and the slender, tufted _P. tenuissima_, which is
parasitic on _Zostera_ and soe algæ, are sometimes regarded as mere
varieties of _P. plantaginea_.
In the genus _Asperococcus_ the root is shield-shaped, and the frond is
a membranous tubular sac of two distinct layers. The colour is pale
green, and the general appearance very similar to that of _Ulva_. The
spores are arranged in small oblong clusters which appear as dark dots
on the surface of the frond. _A. compressus_ has slightly swollen flat
fronds of a linear lanceolate form, tapering below. It grows in deep
water, but is often washed up during storms. A second species--_A.
Turneri_--has large, puffy, green fronds, contracted at intervals, and
grows in tufts on rocks between the tide-marks, being specially partial
to muddy shores. The genus also includes the prickly _A. echinatus_, the
long, thin fronds of which grow in dense tufts in deep water.
The last genus of the order is _Litosiphon_, a parasitic group
characterised by a cylindrical, cartilaginous, unbranched frond, with
scattered, naked spores. A very small species (_L. pusillus_) with
tufted green fronds grows parasitic on the fronds of _Chorda_ and the
stems of _Laminaria_. It is only two or three inches long, has a
reticulated surface, and is covered with minute jointed fibres. A still
smaller species (_L. laminariæ_), seldom exceeding half an inch in
length, forms brown tufts on _Alaria_, and the rounded apex of its frond
is covered with minute fibres.
The order _Laminariaceæ_ contains olive, inarticulate algæ, mostly of
large size, and generally growing in deep water beyond the tide-marks.
Their spores are superficial, either covering the whole surface of the
frond or collected into indefinite cloudy patches.
[Illustration: FIG. 268.--_Laminaria bulbosa_]
[Illustration: FIG. 269.--_Laminaria saccharina_]
The typical genus (_Laminaria_) is characterised by flat leathery,
ribless fronds, either simple or cleft, and supported on a stem which is
often very thick and strong. The old laminæ fall off every year, and are
replaced by new fronds. The well-known Tangle or Sea Girdle (_L.
digitata_), is a very common species on the rocks just beyond low-water
mark. It has a very thick, solid, cylindrical stem, and an oblong
leathery frond which is entire when young but deeply cleft later. Small
specimens may be found just above low-water mark, but fine large ones
are commonly washed up on the beach. Although this weed may not be
regarded as an acquisition from the collector’s point of view, it will
generally repay a careful examination, as it frequently bears rare
parasitic species. The other common species are the Furbelows (_L.
bulbosa_), known by its flat stem with waved margin, oblong frond cleft
into narrow strips, and the hollow bulb or tuber just above the root;
and the Sugared Laminaria (_L. saccharina_) characterised by a round
solid stem, and a lanceolate, entire, membranous frond. The last species
is the one most commonly used by the sea-side cottager as a weather
indicator.
[Illustration: PLATE VIII.
SEA-WEEDS
1. Chorda filum
2. Fucus vesiculosus
3. Fucus canaliculatus
4. Delesseria (Maugeria) sanguinea
5. Rhodymenia palmata
6. Chondrus crispus
7. Ulva lactuca]
[Illustration: FIG. 270.--_Alaria esculenta_]
_Alaria esculenta_ is an edible species known as the Badderlocks in
Scotland, and also locally as the Henware, Honeyware, and the Murlins.
It has a fibrous root, and a stalked, lanceolate, entire frond with a
distinct midrib throughout. The stem is winged with finger-like
leaflets, in which the spores are arranged in oblong clusters.
In the genus _Chorda_ the frond is a simple, cylindrical tube, divided
internally by numerous transverse membranes, and the spores are
distributed over the surface. The commonest species is _C. filum_ (see
Plate VIII.), the frond of which is very slimy, and often from ten to
twenty feet in length. In its young state it is covered with gelatinous
hairs, but these are worn off as the plant develops. A smaller species
(_C. lomentaria_) is sometimes found on our shores. Its fronds are
constricted at intervals, taper at the tip, and grow in tufts. It is
seldom more than a foot long, and is not of a slimy nature.
[Illustration: FIG. 271.--_Sporochnus pedunculatus_]
The _Sporochnaceæ_ have inarticulate, thread-like fronds, and the spores
are contained in oblong, stalked receptacles, each of which is crowned
with a tuft of slender jointed filaments. The typical genus contains
only one British species--_Sporochnus pedunculatus_--and even that is by
no means common. It is, however, a very pretty weed of a delicate
texture and pale olive-green colour. Its stem is long and slender,
pinnately branched, and the branches bear numerous small thread-like
tufts.
The same order contains the genus _Desmarestia_, in which the frond is
long and narrow, thread-like or flattened, with a tubular jointed
thread running through it. Young specimens have marginal tufts of
branching filaments. The species decay very rapidly after removal from
the water, and should therefore be dried and mounted as quickly as
possible. _D. ligulata_, so named from the flat, strap-like frond, is
common on all our coasts. It is pinnately branched, and all the branches
and branchlets taper towards both ends. _D. viridis_ has a cylindrical,
thread-like and freely-divided frond, with opposite branches and
branchlets. It occurs more commonly on the northern shores.
[Illustration: FIG. 272.--_Desmarestia ligulata_]
The last order of olive-spored weeds is the _Fucaceæ_, some species of
which are so abundant between the tide-marks, from high-water to
low-water levels, that they form a very important characteristic of our
shores. They are mostly large, tough, and leathery weeds, without
joints, and the spores are contained in spherical receptacles embedded
in the substance of the frond.
In the typical genus--_Fucus_--the root is a conical disc, and the frond
flat or compressed and forked. Most of the species are furnished with
one-celled air-vessels in the substance of the frond, and these serve to
buoy up the plants and keep them more or less erect when submerged. The
spore-receptacles are usually embedded near the tips of the branches,
but are sometimes borne on special branches or shoots. They are filled
with a slimy mucus and contain a network of jointed filaments. The weeds
are very hardy, capable of withstanding long exposures to air and sun,
and are sometimes to be found _above_ high-water mark, where they are
watered only by the spray of the waves for a brief period at intervals
of about twelve hours. Although they are not usually looked upon as
ornaments in the collector's herbarium, they will repay examination for
the tufts of smaller and more beautiful weeds to which they often give
attachment and shelter.
Four species are common on our coasts, and these may be readily
distinguished by the most cursory examination. The Serrated Wrack (_F.
serratus_) has a flat, forked frond with toothed edges and a strong
midrib, ranging from one to four feet long, and no air-vessels. The
Knotted Wrack (_F. nodosus_--Plate VII.) may be known by its flattened,
thick and narrow frond, without a distinct rib, from one to five feet
long. The branches are narrow at the base, pointed at the tip, and are
jointed to short projections on the main stem; and both these and the
main stem have very large oval air-vessels. The spore-receptacles are
mounted on slender stalks which arise from projections on the branches,
and are of a bright yellow colour when mature. This species does not
grow so near to high-water mark as do the others. Another species, the
Twin-Bladder Wrack (_F. vesiculosus_--Plate VIII.)--is abundant
everywhere along the coast, and is largely used by agriculturists both
as manure and as fodder for cattle. The frond is flat, with a distinct
midrib, and a non-serrated edge. Air-vessels are not always present, but
when they are they usually occur in pairs, one on each side of the
midrib, and are globular in form. The spore-receptacles are situated at
the tips of the branches, are full of mucus, and are frequently forked.
The last of the common species is the Channelled Wrack (_F.
canaliculatus_--Plate VIII.), distinguished by a narrow frond, rounded
on one side and channelled on the other. It has no midrib or
air-vessels, and the fruit is contained in forked receptacles at the
tips of the branches. This is the smallest of the genus, and may be
found at all levels between the tide-marks. Stunted specimens may also
be seen in situations where they are never submerged, but watered only
by the spray of the highest tides.
[Illustration: FIG. 273.--_Himanthalia lorea_]
The genus _Himanthalia_ provides us with a single species (_H. lorea_)
which is very peculiar on account of the small size of the frond as
compared with the enormous dimensions of the spore-receptacles. The
young frond is a pear-shaped sac which soon becomes flattened into a
hollow disc. This disc then becomes solid, and concave above, and from
its centre there arises a bi-forked, strap-like receptacle that often
reaches a length of three or four feet, and may be mistaken for the
frond of the weed by those who do not take the trouble to examine it.
This weed is commonly known as the Sea Thong.
Belonging to the genus _Cystoseira_ we have a few well-known weeds with
conical disc-roots, and shrubby fronds with woody stem and alternate
branches. The air-cells are in the substance of the frond, and the
spore-receptacles at the tips of the branches. One of the species (_C.
ericoides_) is of a heath-like habit, with a short, woody stem, and
slender branches bearing hooked, leaf-like branchlets. Its air-cells are
small, and are arranged singly near the tips of the branches; and the
spore-receptacles are cylindrical, with hooked points. This weed is
common on the south and west coasts, and may be readily distinguished by
the beautiful iridescence it displays when in the water. _C. fibrosa_ is
very similar in general form, but is larger, and the air-vesicles are
more conspicuous. It is not iridescent when in the water. A third
species is named _C. granulata_ from the rough and knobby appearance of
the stem, due to numerous oval projections, from some of which spring
the slender, much-divided branches. The air-vesicles are arranged in
groups of two or three, and the spore-receptacles are at the ends of the
branchlets. Our last example is _C. fœniculacea_, found on the south
coast only, and readily distinguished by the numerous blunt spines that
cover its long branches. The air-vesicles are narrow and pointed, and
situated just below the forkings of the branchlets.
[Illustration: FIG. 274.--_Cystoseira ericoides_]
We conclude our _résumé_ of the British sea weeds with a short
description of the Podded Sea Oak (_Halidrys siliquosa_), which grows in
the tide pools from high-water to low-water mark, the specimens
inhabiting the shallow pools being only a few inches long, while those
that grow in deep water often reach a length of three or four feet. It
is an olive, shrub-like weed, with a conical, disc-like root that
adheres very firmly to the rock, and a pinnately-branched frond with
leaf-like branchlets. The air-vesicles are cylindrical and pod-like,
divided internally into about ten cells, and the spores are contained in
globular receptacles at the tips of the branchlets.
The young algologist will probably meet with many difficulties in his
attempts to classify his sea weeds and name the various species in his
collection. In dealing with an unknown weed we strongly recommend him to
first determine the order to which it belongs. The genus should next be
settled; and then, if possible, the species. It must be remembered,
however, that he who has made himself acquainted with the principles of
classification has done good work, and that it is far better to be able
to arrange the weeds into properly-classified groups than to merely
learn the names of the different species without regard to the relations
which they bear to one another. The following table will probably assist
the reader in the determination of the orders, but it must be remembered
that a microscope will often be necessary for the examination of the
spores and the minute structure of fronds.
CLASSIFICATION OF SEA WEEDS
=A.= =Chlorospermeæ=--Green-spored weeds. Fronds usually
grass-green, and filamentous or membranous.
1. _Confervaceæ_--Frond thread-like, composed of cylindrical
cells placed end to end. Spores very minute, formed
within the cells.
2. _Ulvaceæ_--Frond grass-green or purple, flat or tubular.
Spores minute, ciliated, formed in the cells of the
frond.
3. _Siphonaceæ_--Frond a single, thread-like, branching cell,
or a spongy mass of many such cells.
=B.= =Rhodospermeæ=--Red-spored weeds. Spores in globular
conceptacles. Tetraspores (four-clustered spores) in
globular or cylindrical cells. Frond red, reddish
brown, or purple.
4. _Ceramiaceæ_--Frond thread-like, jointed, one-siphoned, and
more or less covered with a layer of cortical cells.
Spores grouped in transparent, membranous sacs,
sometimes surrounded by a whorl of short branchlets.
5. _Spyridiaceæ_--Frond thread-like, jointed, one-siphoned,
more or less covered with small cells. Spores formed in
the upper cells of branched, jointed, radiating
threads, enclosed in a cellular membrane in external
conceptacles.
6. _Cryptonemiaceæ_--Frond more or less cartilaginous, composed
of numerous jointed threads compacted by gelatine.
Spores grouped without order in internal cells or in
external conceptacles.
7. _Rhodymeniaceæ_--Frond inarticulate, membranaceous, composed
of polygonal cells, the surface cells forming a
continuous layer. Spores in beaded threads in external
conceptacles.
8. _Wrangeliaceæ_--Frond inarticulate, thread-like, traversed
by a jointed tubular axis. Spores formed in the
terminal cells of clustered, branching, naked threads.
9. _Helminthocladiæ_--Frond cylindrical, gelatinous, composed
of filaments imbedded in gelatine. Spores formed on
branching, radiating threads that are enclosed in the
frond without conceptacles.
10. _Squamariæ_--Frond lichen-like, rooted by under surface,
composed of _vertical_ filaments imbedded in firm
gelatine. Spores in beaded threads in wart-like
projections.
11. _Spongiocarpeæ_--Frond cylindrical, branching,
cartilaginous, composed of netted filaments imbedded in
firm gelatine. Spores large, in radiating clusters in
wart-like excrescences.
12. _Gelidiaceæ_--Frond cartilaginous, inarticulate, composed
of hair-like filaments. Spores attached to slender
threads in internal conceptacles.
13. _Sphærococcoideæ_--Frond leaf-like or thread-like,
inarticulate, cellular. Spores formed in beaded threads
in external conceptacles.
14. _Hapalidiaceæ_--Frond minute, calcareous, composed of a
single layer of cells.
15. _Corallinaceæ_--Frond calcareous. Spores in tufted threads
at the bases of the conceptacles.
16. _Laurenciaceæ_--Frond rounded or flattened, branching,
inarticulate, cellular. Spores in external oval or
globular conceptacles. Tetraspores irregularly
scattered over the branches.
17. _Rhodomelaceæ_--Frond leafy, thread-like, or jointed,
composed of polygonal cells. Spores in external
conceptacles. Tetraspores in distorted branchlets or in
receptacles.
=C.= =Melanospermeæ=--Olive-spored weeds. Frond tough, leathery.
Spores in globular cavities in substance of frond.
18. _Ectocarpaceæ_--Frond jointed, thread-like. Spores attached to
or imbedded in branchlets.
19. _Chordariaceæ_--Frond gelatinous or cartilaginous, composed of
interlacing vertical and horizontal filaments. Spores
internal, attached to the filaments.
20. _Dictyotaceæ_--Frond inarticulate. Spores superficial, arranged
in definite spots or lines.
21. _Laminariaceæ_--Frond inarticulate. Spores covering the whole
frond or in cloud-like patches.
22. _Sporochnaceæ_--Frond inarticulate. Spores attached to jointed
filaments which are either free or compacted.
23. _Fucaceæ_--Frond inarticulate, large and tough. Spores in
globular cavities.
CHAPTER XVI
_THE FLOWERING PLANTS OF THE SEA-SIDE_
A considerable number of our flowering plants exhibit a decided
partiality for the neighbourhood of the sea, and many are to be found
only on the sea cliffs or in salt marshes not far from the shore. The
principal of these will be now briefly described, dealing first with the
monocotyledons, and then with the more highly organised dicotyledons.
The chief distinguishing features of these two groups have already been
referred to, but it will be advisable here to give them in somewhat
fuller detail.
[Illustration: FIG. 275.--TRANSVERSE SECTION OF THE STEM OF A
MONOCOTYLEDON]
The _monocotyledonous plants_, then, are those in which the stem is more
or less woody and cylindrical, without either true bark or pith; and the
woody tissue is not arranged in concentric rings, but in isolated
bundles, which first bend inwards, as they rise, towards the centre of
the stem, and then curve outwards towards the surface, which is hardened
by the formation of a layer of hard woody matter. As a rule the stem is
unbranched, and its growth takes place by a single bud at the summit. In
nearly all of them the leaves are long and narrow, with veins running
parallel throughout their length; and the parts of the flower are
arranged in whorls of three or six. The outer whorl of the flower is
often a conspicuous white or coloured _perianth_ (that portion of the
flower which lies outside the anthers), but in some the perianth is
absent, the flower being protected by scaly bracts. The seeds are
produced in a case called the ovary, and are fertilised by pollen grains
which are developed in the anthers. When the pollen grains are set free
they alight on the adhesive stigma, and grow, sending their tubes down
into the ovary. The term monocotyledon is applied to these plants
because the embryo has only one cotyledon or seed-leaf.
[Illustration: FIG. 276.--LEAF OF A MONOCOTYLEDON]
The principal divisions of this group are the _Glumaceous
Monocotyledons_, in which the flower has no perianth, but is enclosed in
scaly bracts or husks called glumes; and the _Petaloid Monocotyledons_,
distinguished generally by the presence of a more or less conspicuous
white or coloured perianth. The first of these includes the rushes,
sedges, and grasses; and the other contains the lilies and orchids, with
their allies, together with certain aquatic and semi-aquatic plants.
Among the Grasses there are several species that show a preference for
the immediate neighbourhood of the sea, some growing luxuriantly at the
bases of the cliffs where the beach is sandy, and others thriving best
in salt marshes; but before dealing with these individually we shall
note the general characteristics of the order (_Gramineæ_) to which they
belong.
Grasses are distinguished by their jointed stems, which are usually
hollow, with a split sheath, and bearing alternately arranged narrow
leaves. The flowers, which are disposed either in spikes (sessile
flowers arranged along a common axis) or in panicles (flowers stalked
and arranged as in fig. 281), consist of scale-like bracts enclosing the
stamens and the pistil. The bracts are in two series, the outer usually
consisting of two _glumes_, and the inner of two _pales_; the upper
pale, however, has two ribs running through it, and is therefore usually
looked upon as a combination of two. In some species both glumes and
pales are absent; but the former, when present, enclose one or more
flowers, among which may be some that are abortive. The stamens are
generally three in number, attached to the base of the flower; and the
ovary is superior or free, that is, it grows above the other parts of
the flower, and contains but one seed.
It will be convenient at this stage to refer briefly to the two
principal methods by which the pollen of flowers is transferred to the
stigmas for the purposes of fertilisation, and to see how various
species are structurally adapted to the means by which the transfer is
brought about.
Speaking generally, we may classify flowers into those which are
fertilised by the wind (anemophilous flowers) and those in which the
pollen is transferred by insects (entomophilous flowers). The former
offer no attractions to allure the various forms of insect life. They
are, generally speaking, very inconspicuous, being of small size and
having no bright corollas. None of them are scented, nor do they produce
the sweet nectar that forms the principal food of so many insects. Their
anthers are borne on long filaments, so that they are exposed freely to
the wind; and they produce abundance of pollen to compensate for the
very wasteful method of wind-dispersion. The pollen, too, is not very
adherent, so that it may be readily carried away by the breeze; and the
plants concerned often produce their flowers early in the spring, before
the leaves have appeared, thus giving the wind very free play.
[Illustration: FIG. 277.--EXPANDED SPIKELET OF THE OAT
G. glumes; P.e, outer pale; P.i, inner pale; A, awn; F.S, a sterile
flower. The stamens and the feathery stigmas of the fertile flower
are also shown]
Insect-fertilised flowers, on the other hand, are usually of attractive
appearance; and, though often small and inconspicuous individually, they
are in such cases grouped together in more or less showy clusters. They
are also usually scented, and supply nectar and pollen to the insects
which they allure. Some are fertilised by insects that fly by day, and
these often close their petals on the approach of night, thus protecting
their pollen during the period in which their fertilisers sleep. Others,
fertilised by nocturnal insects, always spread their petals during the
night, and generally protect their pollen from waste by sleeping
throughout the day. As a rule, too, these night-bloomers have large and
pale-coloured petals that are more easily seen by night; they also evolve
a powerful scent to aid the insects in searching them out.
It will be seen that the economic relationship existing between flowers
and insects is a mutual one, the latter visiting the former in order to
obtain food, while the former derive in return the advantage of a direct
transfer of pollen from flower to flower.
It is a well-known fact that the self-fertilisation of a flower often
results in the development of very weak seedlings as compared with those
that are produced by crossing; and it often happens that the pollen of a
flower is incapable of producing the least effect when deposited on the
stigma of the same bloom. In some cases the contact of the pollen of a
flower with its own stigma will even act as a poison, causing the whole
to shrivel and die; and truly wonderful are the varied means by which
flowers contrive to secure a cross-fertilisation. It is here that the
work of the wind and insects proves so valuable to flowers; but, in
addition to this, a very large number of flowers are absolutely
incapable of self-fertilisation, for the anthers and the stigma are not
mature at the same time, or they exist in separate flowers, either on
the same plant or on distinct plants of the same species. It is most
interesting and instructive to study the many contrivances by which
flowers compel certain insects to convey the pollen exactly in the way
that best serves their purpose, sometimes even entrapping them after
they have been allured, and not allowing them to escape until they are
thoroughly dusted with the pollen which they are required to convey; but
it is hardly our province to enter more fully into this matter in these
pages.
An examination of the grasses will show at once that they are adapted
for fertilisation by the wind. The flowers produce no nectar; and,
consistently, develop no bright petals and evolve no odours to attract
insects. On the other hand, their anthers produce abundance of
lightly-adhering pollen, and are mounted on long filaments which hold
them well exposed to the wind; and the stigmas are well adapted for
catching the scattered grains, being long and protruding, and often
covered with sticky hairy or feathery appendages.
Although the flowers of grasses are generally wanting in attractive
colours, the clusters of blossoms are often very graceful and pretty,
especially when the large anthers, covered with bright-yellow pollen,
dangle in the breeze.
We will now briefly describe the principal British grasses that grow
chiefly or exclusively in the immediate neighbourhood of the sea.
The Sea Hard Grass (_Lepturus filiformis_) is a perennial species,
usually about six inches in height, very common on some sandy coasts,
and found in flower during the hottest months of the summer. The flowers
are arranged in simple spikes, on slender erect stems; and the glumes,
which are united at their bases, enclose a single bloom.
In similar situations we may find the Sea Lyme Grass (_Elymus
arenarius_), a tall species, often reaching a height of four feet, with
glaucous rigid leaves. The flowers are arranged in a simple spike, but
the spikelets are clustered two or three together. This species flowers
in August.
Of the well-known Barley Grasses there is one species (_Hordeum
maritimum_) that has its habitat along the coast. Like the others of its
genus, the spikelets are arranged in threes, each bearing a single
flower, and the pales have long slender processes (_awns_) which
constitute the so-called beard. It also resembles the common Meadow
Barley Grass in having the middle flower of each three perfect, while
the two laterals are abortive, but may be distinguished by its rough and
bristly glumes, and the semi-oval form of the pales of the lateral
flowers. It is a somewhat stunted species, sometimes only five or six
inches in height, and may be found in flower about Midsummer.
The Brome Grasses have also a representative of a sea-loving nature,
which is to be found in fields near the cliffs. It is the Field Brome
Grass (_Bromus arvensis_), an annual grass that grows to a height of two
or three feet. Brome grasses generally are known by their loose panicles
of flowers, lanceolate and compressed spikelets, and awned florets
enclosed in unequal glumes; and _B. arvensis_ may be distinguished by
its hairy leaves and stem-sheath, and the drooping panicle with the
lower peduncle branched.
[Illustration: FIG. 278.--THE SEA LYME GRASS]
Among the Meadow Grasses we have three or four coast species. In these
the florets are in panicles and are not awned. The outer glumes are
keeled and traversed by several veins; and the lower pales are also
keeled, with five or more nerves. The Sea Meadow Grass (_Poa maritima_)
grows in salt marshes near the sea, its erect rigid panicles reaching a
height of about eight or ten inches. It has a creeping root, and its
leaves are curved inward at the margins. The Procumbent Meadow Grass
(_P. procumbens_) and a variety of the Reflexed Meadow Grass (_P.
distans_) are also plentiful in salt marshes. The former may be known by
the short rigid branches of its panicle and the five ribs of the lower
pales; and the latter is much like _P. maritima_, but grows taller, and
its spikelets are crowded. The Wheat Meadow Grass (_P. loliacea_) grows
on sandy shores. Its spikelets are arranged singly and alternately along
the central axis, and the upper glume reaches to the base of the fourth
floret. This species flowers in June, but the other three of the same
genus bloom from July to September.
The reader is probably acquainted with the Fescue Grass, with its awned
flowers arranged in one-sided panicles. There are no less than seven
species, one of which--the Single-husked Fescue (_Festuca
uniglumis_)--grows on sandy shores, flowering in June and July, and
reaching a height of from nine to twelve inches. The panicles are
upright and unbranched, and the species may be readily known by the
flowers, which are compressed, with long awns, and with the lower glumes
wanting.
_Knappia agrostidea_ is a dwarf species, rarely exceeding four inches in
height, that is found on certain sandy shores, but is very local. Its
flowers are arranged in a simple spike, the spikelets being solitary and
unilateral, with only a single flower, and the pales are shaggy. The
plant has several stems which bear short, rough leaves.
The Mat Grass or Sea Reed (_Ammophila arundinacea_) is common on many
sandy coasts, where it grows to a height of three or four feet, and
flowers in July. The white flowers are clustered in dense cylindrical,
pointed spikes; and the leaves are of a glaucous green colour, rigid,
and curved inward at the edges.
Dog’s-tooth Grass (_Cynodon dactylon_). This species has a creeping
root, and the leaves are downy on the under side. The flowers are
arranged in a compound spreading spike, of three to five parts, and the
spikelets are of a purplish colour, ovate in form, and arranged in
pairs. The glumes are equal in size. It is found on sandy shores, grows
to a height of about six inches, and flowers in July.
A species of Canary Grass (_Phalaris arundinacea_) is also to be seen on
sandy coasts. Unlike the other species of the same genus, its flowers
form an erect spreading panicle, and the glumes are not keeled. It is
also taller than the common canary grass of waste places, often reaching
a height of three feet, and is commonly known as the Reed Canary Grass.
[Illustration: FIG. 279.--_Knappia agrostidea_]
[Illustration: FIG. 280.--THE DOG'S-TOOTH GRASS]
[Illustration: FIG. 281.--THE REED CANARY GRASS]
The Sea Cat's-tail Grass (_Phleum arenarium_) is common on many coasts.
It is much smaller than the common species of Cat's-tail, being
generally less than a foot high. The spike is of an elongated oval form,
blunt at the tip and narrow at the base; and the glumes are narrow,
pointed at both ends, and fringed. Each spikelet has but one flower.
In salt marshes we occasionally meet with the Perennial Beard Grass
(_Polypogon littoralis_), but it is somewhat rare. It has a creeping
root, and the flowers form a somewhat dense spike-like panicle. The
glumes have a slender awn. It grows to a height of one to two feet, and
flowers in July.
The Tuberous Fox-tail Grass (_Alopecurus bulbosus_) is another rare
grass of the salt marshes, where it grows to the height of twelve to
sixteen inches, flowering in May and June. The genus to which it belongs
is very closely allied to _Phleum_, but may be distinguished by having
only one pale to each flower, and this species has a long awn attached
to the back portion. The panicle, too, is cylindrical and slender, the
glumes quite free and abruptly pointed, and the awns longer than the
pales.
The last of the sea-side grasses are two rare species of Cord Grass
(_Spartina_), both of which are found in salt marshes. In these the
inflorescence is a compound spike, with one-sided spikelets inserted in
a double row. The glumes are keeled and pointed; the pales cleft,
pointed and without awns; and the styles two in number, very long. The
only British species of the genus are the two (_S. stricta_ and _S.
alternifolia_) referred to above. They both grow to a height of about
eighteen inches, and flower in late summer. In the former the spikes
number two or three, and are longer than the leaves; and the outer glume
is hairy, with a single nerve. The latter, which is the rarer of the
two, bears several spikes, shorter than the leaves; and the outer glume
has five nerves.
Certain of the sedges (order _Cyperaceæ_) are also more or less familiar
to the sea-side naturalist, and must therefore receive a small share of
our attention. In general terms these are grasslike, monocotyledonous
plants, the stems of which are solid, jointed, and frequently angular.
The leaves are very similar to those of grasses, except that the
sheaths, which surround the stem, are not split. The flowers are
generally arranged in a spike, overlapping each other, and each one
supported on a scale-like bract. In some sedges the flowers are perfect,
each one possessing both stamens and pistil; but in some species the
flowers are unisexual, some bearing stamens and no pistil, and others
pistil only. The stamens are generally three in number, the ovary is
superior, and the stigmas either two or three.
Sedges abound in moist places, some being peculiar to salt marshes,
while others grows on sandy shores; and a few of the British species of
the latter habitat are often so abundant that their creeping roots bind
the sand together, effectually holding it in place while the surrounding
portions of the beach are mercilessly driven by the wind.
A few of the sea-side sedges belong to the genus _Carex_, in which the
flowers are imperfect, and the fruit is enclosed in the outer parts of
the flower. _C. extensa_ thrives in salt marshes, growing to a height of
a foot or more, and flowering about midsummer. Its fertile flowers form
oblong erect spikelets, while the barren spikelets are solitary. The
bracts are long and leafy, with short sheaths surrounding the stem. The
leaves are curved in at the edges, and the fruit is oval and ribbed,
with a short straight beak.
On sandy shores the Sea Sedge (_C. arenaria_) is often common, and its
underground stems are used for sarsaparilla. It is a perennial species,
growing to a height of about nine inches, and flowering in June and
July. The flowers grow in an oblong interrupted spike, the upper
spikelets being barren, and the intermediate ones barren at the tip.
The fruit is oval, veined, and winged.
Another species of this genus--the Curved Sedge (_C. incurva_)--is
sometimes to be seen on sandy shores, but it is rare, and is also a very
small sedge, growing only to a height of about three inches. It derives
its specific name from its curved stem, and may be further distinguished
by its channelled leaves and the globular mass of spikelets which are
barren on the top.
[Illustration: FIG. 282.--MALE AND FEMALE FLOWERS OF _Carex_,
MAGNIFIED]
Some of the so-called rushes belong to the same order as the sedges, and
a few of these are more or less restricted to the neighbourhood of the
sea. The Salt-marsh Club Rush (_Scirpus maritimus_), as its name
implies, is to be found in marshes near the sea. It is very variable in
height, ranging from one to three feet, and displays its dense terminal
cluster of spikelets in July and August. In this genus all the flowers
are perfect, the glumes imbricated and bristled; and the present species
may be distinguished by the glumes being divided into two sharply
pointed lobes. A variety of _S. lacustris_ may also be found on the sea
shore, but it is somewhat rare. It has a leafless glaucous stem, and
flowers arranged in compound spikes. The glumes are rough, and contain a
compressed fruit.
A very small species of the Spike Rush (_Eleocharis parvula_), growing
only one or two inches high, is sometimes found on the muddy shores of
Ireland. It has perfect flowers, in a single terminal spikelet. The
leaves are very narrow, growing from the base of the plant; and the
round stem is enclosed in a single leafless sheath.
The true rushes belong to the order _Juncaceæ_. These have fibrous roots
and narrow leaves, and bear clusters of brown flowers. The perianth
consists of six parts, and the stamens are usually six in number. The
ovary is generally three-celled, developing into a three-valved capsule.
The Lesser Sea Rush (_Juncus maritimus_) is common in salt marshes,
growing to a height of two or three feet, and flowering in July. It has
a rigid leafless stem, bearing lateral clusters of flowers. The segments
of the perianth are very narrow and sharp, and the seeds are enclosed in
a loose testa. Closely allied to this species is the Great Sea Rush (_J.
acutus_), which grows three or four feet high on sandy shores. In
general characteristics it resembles_ J. maritimus_, but the segments of
the perianth are oval and have thin transparent margins; and it is a
much rarer species.
[Illustration: FIG. 283.--THE SEA SEDGE]
[Illustration: FIG. 284.--THE CURVED SEDGE]
[Illustration: FIG. 285.--THE GREAT SEA RUSH]
We now pass to the peculiar Sea Grasses or Grass Wracks (_Zostera_)
which grow in salt water. They belong to the order _Naiadaceæ_, and are
characterised by cellular leaves with parallel veins, and inconspicuous
unisexual or bisexual flowers. The perianth, when present at all,
consists of two or four scale-like parts, and the stamens correspond in
number with these. The ovary is free, and the carpels, one or more in
number, contain each a single ovule. In _Zostera_ the flowers are
imperfect, and seem to grow in the slit of the leaf. There are two
species, both of which grow in shallow water close to the shore, often
in such dense masses that they impede the progress of boats. They have
long creeping stems that lie buried in the sand, giving off numerous
root-fibres, and send up to the surface slender branches that bear
grass-like leaves. The flowers are unisexual, and are arranged in two
rows on the same side of a flattened stalk that is enclosed in a sheath
formed by short leaves. They have no perianth, the male flowers being
composed of a single anther, and the female of a one-celled ovary
containing a single ovule, and surmounted by a style with two long
stigmas.
There are two species--the Broad-leaved Grass Wrack (_Z. marina_) with
leaves one to three feet long and traversed by three or more parallel
veins, and the Dwarf Grass Wrack (_Z. nana_), the leaves of which are
less than a foot long, with veins numbering one to three. There is a
variety of the former, however, named _Angustifolia_, in which the
leaves are much narrower than usual, and the veins fewer in number.
[Illustration: FIG. 286.--THE BROAD-LEAVED GRASS WHACK]
[Illustration: FIG. 287.--THE SEA-SIDE ARROW GRASS]
[Illustration: FIG. 288.--THE COMMON ASPARAGUS]
The order _Alismaceæ_, which contains the water plantains, arrow-heads,
and other semi-aquatic plants, has a representative of marine tendencies
in the Sea-side Arrow Grass (_Triglochin maritimum_). The flowers of
this order are bisexual, with six stamens and a six-parted perianth. The
fruit consists of many carpels; and, although the plants are
monocotyledons, their leaves have netted veins; and altogether they
somewhat resemble the ranunculaceous exogens. The Sea-side Arrow Grass
is abundant in some salt marshes, growing to a height of about a foot,
and produces loose simple spikes of green flowers all through the
summer. The leaves are radical, narrow and fleshy; and the ovary
consists of six carpels.
Of the interesting order _Liliaceæ_ we have only one plant of the coast,
and even that--the _Asparagus_--is not by any means generally common. It
is the same plant that is so largely cultivated as an article of diet,
and which is so highly valued on account of its diuretic properties. It
is moderately common on parts of the south coast, particularly in the
Isle of Portland and in West Cornwall, and its general appearance is so
graceful that it is largely employed as an ornamental garden plant. The
stem is erect and freely branched, bearing feathery bunches of bristled
leaves and pale-yellow axillary flowers. As is the case with the
_Liliaceæ_ generally, the flowers are bisexual, with a six-parted
perianth, six stamens, and a three-celled superior ovary; and the last
named, in the Asparagus, forms a bright-red berry in the autumn.
We have now to leave the monocotyledonous plants and pass on to the
_dicotyledons_, which form the most highly developed of the primary
divisions of the vegetable kingdom. A few of the general characteristics
of this group have already been given, but we must now look rather more
closely into the nature of the plants included.
The class receives its name from the presence of two cotyledons or
seed-leaves in the embryo plant, and is also known as the _Exogenæ_
because the stems increase in thickness by the addition of zones of
woody tissue at the exterior. When the young dicotyledonous plant first
appears above the ground, the two cotyledons, which formerly served to
shelter the immature bud, usually appear as tiny fleshy leaves; but
these soon wither away, while the bud produces the more permanent leaves
that are of a very different structure. A section of the stem will
reveal distinct pith, wood, and bark, the wood being more or less
distinctly divided into wedge-shaped masses by rays from the pith; and,
in the case of perennial stems, the wood is arranged in concentric
rings, the number of which correspond approximately with the years of
growth. The leaves of exogens have their veins in the form of a network,
and the parts of the flower are generally arranged in whorls of two or
five or of some multiple of these numbers.
The flowers always have stamens and pistil, but in some these organs
exist in separate flowers, either on the same plant, or on different
plants of the same species, and the ovules are nearly always contained
in a case called the ovary.
Dicotyledons are divided into three main groups, the division being
based on the structure of the flowers. They are the _Apetalæ_ in which
the petals are absent, but the perianth is frequently petaloid, though
it is occasionally also absent; the _Gamopetalæ_, in which the petals
are united; and the _Polypetalæ_, in which the petals are always
distinct.
Dealing with these divisions in the above order we come first to the
Spurges, three species of which occur on sandy shores. They belong to
the order _Euphorbiaceæ_, which includes, in addition to the spurges, a
number of herbs, trees, and shrubs with entire leaves often a milky
juice, and small flowers, sometimes enclosed in calyx-like bracts. The
flowers may have one or several stamens, and the perianth, if present,
consists of three or four parts; but perhaps the best distinguishing
feature of the order is the nature of the fruit, which separates
elastically into three carpels.
[Illustration: FIG. 289.--THE SEA SPURGE]
The Sea Spurge (_Euphorbia Paralias_) is commonly seen on sandy shores,
where its yellow flowers bloom in late summer and in autumn. It may be
distinguished among the numerous species of the genus by its narrow
oblong imbricated leaves, of a tough leathery nature, the broad
heart-shaped bracts, and the wrinkled capsules containing smooth seeds.
The Portland Spurge (_E. portlandica_) is a similar plant, found in
similar situations, and flowering from May to September. Its leaves are
oval and narrow, obtuse, and of a glaucous colour, and the bracts are
more triangular than those of the last species. The capsules are
slightly rough, as are also the seeds. There is yet another sea-side
spurge--the Purple Spurge (_E. peplis_)--a somewhat rare plant, found on
some of the sandy shores of the south of England. It grows to about
eight or nine inches in length, and blooms in late summer, the flowers,
like those of most of the spurges, being yellow. The stem is of a
glaucous colour, and trails along the ground; the leaves are opposite
and somewhat heart-shaped, and the flowers solitary. This species may be
distinguished from other spurges by its stipuled leaves.
On sandy cliffs we sometimes meet with the Sea Buckthorn (_Hippophaë
rhamnoides_)--a spiny shrub, ranging from about two to seven feet in
height, the bark of which is covered with a silvery scaly scurf that
forms a beautiful object for the microscope. It is the British
representative of the Oleasters (order _Eleagnaceæ_). The leaves are
alternate, lanceolate, with a silvery surface; and the flowers are
small, green and unisexual. The male flowers grow in catkins, each
arising from a scaly bract, and have a green perianth. The female
flowers have a tubular perianth, and a free one-celled ovary. The latter
forms a hard nut-like fruit, which is surrounded by a succulent mass
formed by the former. This shrub flowers in the spring, while the leaves
are still very small.
[Illustration: FIG. 290.--THE PURPLE SPURGE]
[Illustration: FIG. 291.--THE SEA BUCKTHORN]
Of the order _Polygonaceæ_, which includes the docks, knot grasses,
buckwheats, and sorrels, we have two sea-side representatives, both
belonging to the typical genus _Polygonum_. These are the sea-side Knot
Grass (_P. maritimum_) and Ray’s Knot Grass (_P. Raii_). The plants of
this order are herbs, characterised by their alternate leaves with
sheathing stipules; and small flowers, usually bisexual, often with a
coloured perianth. Most of the species are remarkable for their
astringent and acid properties. In the genus _Polygonum_ the flowers are
usually in spikes or racemes; the perianth funnel-shaped, regular, and
five-cleft. The stamens vary from five to eight in number, and the
styles number two or three. The fruit is a small angular nut, usually
enclosed in the perianth.
The sea-side Knot Grass is very common on some parts of the shore, where
it grows from one to three feet long, and flowers in August. The stem is
recumbent, tough and woody, bearing fleshy glaucous leaves with curled
edges. It may be further distinguished from the other knot grasses by
its long stipules, with freely-branching veins, and by the length of the
fruit exceeding that of the perianth. As in the other knot grasses, the
flowers arise from the axils of the leaves.
Ray’s Knot Grass is very much like the common knot grass so abundant in
all waste places, the leaves being flat; and the stipules, shorter than
in the last species, having but few veins; but while in the latter the
fruit is shorter than the calyx, in _P. Raii_ it is longer. This species
is found on many sandy shores, and flowers in July and August.
The order _Chenopodiaceæ_ is particularly rich in sea-side plants, more
than a dozen of the British species growing almost exclusively near the
shore. They are mostly inconspicuous plants, with small flowers which
are sometimes unisexual. The perianth is deeply divided, and the stamens
are inserted in its base, opposite the divisions. The ovary is free,
containing a single ovule.
The typical genus (_Chenopodium_) contains the weeds designated by the
name of Goosefoot, all characterised by their straggling stems and small
flat leaves. One species (_C. botryoides_) is common on some sandy
shores. It is a small weed, its prostrate stem measuring only a few
inches in length. The leaves are triangular and fleshy, and the flowers
are arranged in dense leafy clusters. A variety of the Red Goosefoot
(_C. rubrum_) is also found on the coast. It is of a reddish colour,
with rhomboid leaves and short crowded spikes of flowers.
[Illustration: FIG. 292.--_Chenopodium botryoides_]
On muddy shores we meet with the Common Beet (_Beta maritima_), the
leaves of which are often cooked and eaten where the plant is abundant;
and it is this species from which the different varieties of garden beet
and mangold wurzel have been produced by cultivation. There are two
distinct varieties of the wild plant. In one the root and leaves are of
a purple colour, while in the other they are of a yellowish green. The
former has been cultivated for its root, while the latter is sometimes
grown for the leaves. In the wild state it has many stems, the lower
parts being more or less procumbent, and the leaves are fleshy,
gradually narrowing down into the stalk. The flowers, which are arranged
in long, simple, leafy spikes, are bisexual, with a five-parted
perianth, five stamens inserted opposite each segment, in a fleshy ring
and a flattened one-celled ovary which develops into a one-seeded
utricle.
In similar situations we meet with two species of Sea Purslane
(_Obione_), in which the flowers are unisexual, both male and female
flowers being on the same plant. They are also distinguished from most
other Chenopods by the perianth adhering to the wall of the ovary. The
Shrubby Sea Purslane (_O. portulacoides_) is, as its name implies, a
shrubby plant. It grows to a height of eighteen inches or two feet,
bearing silvery oval lanceolate leaves and sessile fruit. The other
species referred to--the Stalked Sea Purslane (_O. pedunculata_)--is
herbaceous, with oval, mealy leaves, and stalked fruit.
[Illustration: FIG. 293.--THE FROSTED SEA ORACHE]
[Illustration: FIG. 294.--THE PRICKLY SALT WORT]
The Oraches (genus _Atriplex_) resemble the Purslanes in the granular
mealiness of the foliage, and the two are so closely allied that they
are often placed in the same genus. Oraches are most readily
distinguished among the Chenopods by the two bracts which enclose the
fruit and enlarge after flowering; and, like the Purslanes, they have
unisexual flowers, both male and female being on the same plant. Three
of our five British species are sea-side plants. The Frosted Sea Orache
(_A. arenaria_) grows on sandy shores, about six or eight inches in
height, and flowers during late summer and autumn. It may be known by
its buff-coloured stem, with triangular or rhomboidal, jagged, silvery
leaves, and clusters of sessile flowers in the axils of the leaves.
Another species (_A. Babingtonii_) may be seen on both rocky and sandy
shores, usually from one to two feet in height, and flowering from July
to September. Its stem is procumbent, green with reddish stripes; leaves
oval-triangular, lanceolate towards the top, three-lobed at the base of
the stem, light green, with a mealy surface; flowers in terminal
clusters as well as in the axils of the leaves. A third species--the
Grass-leaved Orache (_A. littoralis_) grows in salt marshes. All its
leaves are grass-like and entire, and the stem is generally marked with
reddish stripes as in _A. Babingtonii_. The flowers, too, are in sessile
axillary clusters only. This plant reaches a height of from one to two
feet, and flowers in the late summer.
The Prickly Salt Wort (_Salsola kali_) is a very common sea-side plant
on some of our coasts, and may be recognised at a glance by its general
form and habit. The stem is very much branched and prostrate, forming a
very bushy plant about a foot in height. It is also very brittle and
succulent, furrowed and bristly, and of a bluish-green colour. The
leaves are fleshy, awl-shaped, nearly cylindrical, with a spiny point,
and little prickles at the base. The flowers are axillary and solitary.
This plant and its exotic allies are very rich in alkaline salts,
particularly carbonate of soda, and were formerly the principal source
from which this compound was obtained.
[Illustration: FIG. 295.--THE CREEPING GLASS WORT]
Our last example of the sea-side chenopods is the Glass Wort
(_Salicornia_), which thrives in salt marshes. In this genus the stem is
jointed and the flowers bisexual. The Jointed Glass Wort (_S. herbacea_)
is common in most salt marshes, where its erect, herbaceous, leafless
stem may be seen growing to a height of a foot or more. The joints are
thickened upwards, and shrink to such an extent when dry that the upper
part of each segment of the stem forms a membranous socket into which
fits the base of the next segment above. The flowers are arranged in
dense tapering spikes, also jointed, with a cluster of three flowers on
the two opposite sides of the base of each segment. Each flower is
composed of a perianth, closed with the exception of a small aperture
through which the stigma and, later, the stamens protrude. The Creeping
Glass Wort (_S. radicans_) has a woody procumbent stem, with the joints
only slightly thickened, and the spikes do not taper so much as in _S.
herbacea_. Both these plants yield considerable quantities of soda, and
they are named ‘Glass Wort’ because they formerly constituted one of the
sources from which soda was obtained for the manufacture of glass.
We now come to those flowers in which both calyx and corolla exist, and
shall deal first with the division _Gamopetalæ_ or _Monopetalæ_, in
which the petals are united.
Our first example of this division is the Seaside Plantain (_Plantago
maritima_), of the order _Plantaginaceæ_. This is a stem-less
herbaceous plant, with ribbed leaves and small green flowers, common on
many parts of the coast, and also found on the mountains of Scotland,
flowering throughout the summer. It may be distinguished from the other
plantains by its narrow fleshy leaves. As in the other species, the
flowers form a cylindrical spike.
[Illustration: FIG. 296.--THE SEA-SIDE PLANTAIN]
[Illustration: FIG. 297.--THE SEA LAVENDER]
The order _Plumbaginaceæ_ contains several sea-side plants, including
the Sea Pink or Thrift (_Armeria maritima_) and the various species of
Sea Lavender (genus _Statice_). They are characterised by a tubular
membranous calyx, persistent and often coloured, a regular corolla of
five petals united at their bases, five stamens opposite the petals and
attached at the base of the ovary, and a free one-celled and one-seeded
ovary. The well-known Sea Pink, with its compact head of rose-coloured
flowers, in bloom throughout the spring and summer, and linear
one-veined leaves, may be seen on most of our coasts, as well as on high
ground in inland districts. The Sea Lavender, of which there are four
British species, have their flowers arranged in spikes. The commonest
species (_Statice limonium_) may be found principally on muddy shores.
Its leaves are narrow and one-ribbed, and the bluish-purple flowers
arranged in short dense spikes, the flower stalk being branched only
above the middle. One variety of it has its flowers in a loose pyramidal
cluster, while another bears its spikes in a compact level-topped corymb
with short firm branches. Another species (_S. bahusiensis_) is
characterised by long spikes of distant flowers, the stalk being
branched from near the base. The Upright Sea Lavender (_S. binervosa_)
of rocky shores has the stalk branched from the middle, with, usually,
nearly all the branches flowering, though there are varieties in which
the flowers are differently arranged. The Matted Sea Lavender (_S.
caspia_) grows in salt marshes on the east coast of England. Its flower
stalk is branched from the base, but the lower branches are barren and
tangled, while the upper bear small crowded lilac flowers. The leaves of
the last two species are spatulate in form.
The Bittersweet or Woody Nightshade (_Solanum Dulcamara_) of the order
_Solanaceæ_ is common in hedgerows and waste places almost everywhere,
but a variety of it (_marinum_) has its habitat along the coast. It may
be distinguished from the normal form by its prostrate branched and
non-climbing stem, and by its fleshy leaves. The latter are all cordate,
while in the normal the upper leaves are auricular. The order to which
_Solanum_ belongs is characterised by a regular five-cleft calyx and
corolla, four or five stamens attached to the corolla, and a superior
two-celled ovary. The flowers are in axillary cymes, and the fruit is a
berry.
_Convolvulaceæ_ is represented on sandy shores by the Sea-side Bindweed
(_Convolvulus Soldanella_), a small species, with pinkish purple
flowers, the prostrate stem of which rarely measures more than a foot in
length. The plants of this order are generally climbing plants with
alternate leaves and regular showy flowers. The calyx is composed of
five sepals, the corolla of four or five lobes, and the stamens are
attached to the corolla. The ovary is superior, two- or four-celled, and
the fruit a capsule. The above species may be recognised by its reniform
leaves (sagittate in the others), which are also fleshy.
To the order _Gentianaceæ_ belong the Centaury (_Erythræa_), three out
of the four British species of which grow on sandy shores. In the
flowers of this order the calyx has from four to ten lobes; the stamens
also number four to ten, and are alternate with the lobes of the
corolla. The ovary is one- or two-celled, and the fruit is a berry with
many seeds. The leaves are usually opposite and entire, and the flowers
are generally showy, regular, and solitary. _Erythræa_ has a
funnel-shaped corolla, five stamens, and two stigmas, on a deciduous
style; and in all our species the flower is rose-coloured. The Dwarf
Centaury (_E. pulchella_), which is common on some sandy shores, is much
smaller than the species that thrives in pastures, being only two or
three inches in height. Its stem is also more freely branched, and its
flowers are axillary and terminal. The Tufted Centaury (_E. littoralis_)
and the Broad-leaved Centaury (_E. latifolia_) occur in similar
situations, but are comparatively rare. They are both small species, the
former with an unbranched stem, narrow leaves, and corymbose
inflorescence; and the latter with branched stem, broad elliptical
leaves, and flowers in dense forked tufts.
[Illustration: FIG. 298.--THE DWARF CENTAURY]
The extensive order _Compositæ_ contains comparatively few sea-side
plants, and, in dealing with these, we pass to another division of the
monopetalous flowers, in which the ovary is inferior and the stamens are
on the corolla. The order includes those herbaceous plants in which
sessile flowers are collected together into compound heads (_capitula_)
surrounded by a whorl of bracts. The corolla is either tubular or
strap-shaped (_ligulate_), the stamens four or five in number, and the
fruit one-seeded, usually crowned with the limb of the calyx in the form
of a scaly feathery or hairy pappus.
The Little Lettuce (_Lactuca saligna_) is found in chalky pastures near
the east and south-east coasts, growing to a height of about a foot, and
bearing heads of yellow flowers in July and August. All the flowers are
ligulate and perfect, the pappus is composed of silvery hairs, and the
fruit is compressed and beaked, the beak being twice as long as the
fruit. The leaves are smooth, linear, and sagittate, terminating in a
sharp point. The Sea-side Cotton Weed (_Diotis maritima_) is
occasionally met with on sandy shores, and may be recognised by its
dense coating of downy hair, its sessile obtuse leaves, and heads of
yellow flowers forming a corymb. The heads are discoid, and the fruit
has no pappus. The Sea Wormwood (_Artemisia maritima_) is a common
sea-shore composite, bearing drooping heads of reddish-white flowers in
August. This is another of the downy species, its pinnatifid leaves
having quite a woolly appearance. The capitulum contains but few
flowers, all of which are perfect; and the fruit has no pappus. A
variety of this plant is sometimes seen, with dense erect capitula. The
Sea Aster or Michaelmas Daisy (_Aster tripolium_) of salt marshes may be
known by the yellow discs and purple rays of its flower heads, which are
arranged in a corymb. The florets of the ray form a single row, and the
fruit has a hairy pappus. The leaves of this plant are spatulate and
fleshy. A variety occurs in which the purple florets of the ray are
absent. The Golden Samphire (_Inula crithmoides_) is a very local
sea-side plant, being found principally on the south-west coast. Its
leafy stems grow to a height of a foot or more, and bear yellow heads of
flowers that radiate in all directions. The leaves are linear, acute,
and fleshy, and the bracts are linear and imbricated. Our last example
of the sea-side composites is the Sea-side Corn Feverfew or Scentless
Mayweed, which is a variety of _Matricaria inodora_ of waste places. The
leaves are sessile and pinnatifid, with very narrow segments, and the
white flowers grow in solitary heads. The maritime variety differs from
the normal form in having fleshy leaves.
We next deal with another very extensive order (the _Umbelliferæ_),
which, however, has only three or four representatives on the shore, and
these introduce us to the last great division of the flowering plants,
namely, the _Polypetalous Dicotyledons_, in which the petals are not
united. Of these we shall first deal with that subdivision in which the
stamens are attached at the side of or upon the ovary.
The most obvious characteristic of the _Umbelliferæ_ is that implied in
the name--the arrangement of the flowers in that form of inflorescence,
called the umbel, in which the pedicels all branch from one point in the
main stalk, and are such that the flowers are all approximately on a
level. The flowers are mostly small and white, with five sepals (when
present), five petals, and five stamens. The inferior ovary is
two-celled, bearing two styles; and the fruit separates into two dry
one-seeded carpels that are ribbed longitudinally.
Our first example of this group is the Sea Carrot, a variety of the Wild
Carrot (_Daucus carota_). In the ordinary form, which is so common in
fields, the leaflets are pinnatifid, with acute segments; and the
central flowers of each umbel are purple, while the outer ones are
white. The umbel, when in fruit, is concave above. The maritime variety
differs from this in having fleshy leaves, and the umbel convex above
when in fruit. The Sea Samphire (_Crithmum maritimum_) grows on the
rocks close to the sea, and thrives well where there is hardly a
vestige of soil. It usually grows to a height of seven or eight inches,
bearing greenish-white flowers surrounded by a whorl of very narrow
leaves. The other leaves are glaucous and bi-ternate, the leaflets being
narrow, fleshy, and tapering towards both ends. On cliffs near the sea,
especially in chalky districts, we meet with the Fennel, with its
finely-divided leaves, split up into numerous capillary leaflets, and
its small yellow flowers without bracts. It may be distinguished from
other closely-allied plants by the form of the fruit, which is flattened
at the sides. It is grown in some parts for use as a potherb, and an
aromatic oil is also obtained from the seeds. The plant grows to a
height of four or five feet, but there is a smaller variety known as the
Sweet Fennel, and distinguished by the stem being compressed at the
base. Our next example of the _Umbelliferæ_ is the Sea Holly (_Eryngium
maritimum_), easily distinguished from the other umbellifers by its
spiny glaucous leaves, and the thistle-like heads of blue flowers
surrounded by a whorl of spiny bracts. Its fleshy creeping roots were
formerly gathered largely for the purpose of converting them into the
once-prized ‘candied eryngo root,’ which is still prepared in a few of
the fishing villages of our coast. The lower leaves of this plant are
spinous and very glaucous, and the upper ones palmate. The venation is
particularly strong and durable, so that the leaves and flowers are used
largely by the sea-side cottagers in the construction of skeleton
bouquets and wreaths. Another plant of the same genus--The Field Eryngo
(_E. campestre_)--is occasionally seen on sandy shores. It differs from
the last in having ternate radical leaves with pinnatifid lobes, and the
upper leaves, bi-pinnatifid. Our last example of the sea-side
umbellifers is the Wild Celery (_Apium graveolens_) of salt marshes and
ditches. This is the plant from which our highly-valued garden celery
has been produced, and it is remarkable that this sweet crisp and
wholesome vegetable has been derived from a wild plant of coarse taste
and odour, the acrid sap of which is highly irritating if not dangerous.
The plant may be known by its furrowed stem, and ternate leaves, the
leaflets of the lower leaves being round and lobed, while those of the
upper ones are notched. The umbels are sessile or nearly so, the flowers
have no calyx, and the fruit has five prominent ridges.
[Illustration: FIG. 299.--THE SEA SAMPHIRE]
On the sandy shores of the south-western counties we may meet with the
very local Four-leaved Allseed (_Polycarpon tetraphyllum_) of the order
_Illecebraceæ_. It is a small plant, only four or five inches in height,
with the lower leaves in whorls of four and the upper ones in opposite
pairs. The flowers are minute, and are disposed in small dense clusters.
Another rare species is the shrub known as the English Tamarisk
(_Tamarix anglica_), which is our only representative of the order
_Tamariscaceæ_. There is some doubt, however, whether even this is
indigenous to Britain, though it occurs in a wild state on the coast. It
is a very twiggy shrub growing from six to ten feet in height, with
minute scale-like, acute leaves, and slender spikes of small
pinkish-white flowers.
We now pass to the large order of Leguminous plants, characterised by
their stipuled leaves, and irregular papilionaceous flowers. The latter
usually have five united sepals, five petals forming an irregular,
butterfly-like corolla, ten stamens, and a superior ovary that develops
into a pod.
Of these the Starry-headed Trefoil (_Trifolium stellatum_) is very
partial to the sea shore, though it is sometimes found some distance
inland. The genus to which it belongs is so called on account of its
trifoliate leaves which are characteristic of the clovers, trefoils, and
vetches, and which have stipules adhering to the petioles. The species
under notice receives its name from the star-like arrangement of the
long teeth of the hairy calyx. The stem of the plant is procumbent,
usually about six or eight inches long, with cylindrical and terminal
heads of yellowish-grey flowers.
The Rough-podded Yellow Vetch (_Vicia lutea_) is somewhat rare, and
occurs principally on very rocky coasts. In common with the other
vetches it has pinnate, tendrilled leaves, without a terminal leaflet,
one stamen free and the rest united into a bundle, and a long, slender,
hairy style. Its stem is tufted and prostrate, averaging about a foot in
length, the leaflets long and narrow, and the yellow flowers sessile and
solitary. The teeth of the calyx are unequal, and the pods hairy and
curved.
[Illustration: FIG. 300.--THE SEA-SIDE EVERLASTING PEA]
The Sea-Side Everlasting Pea (_Lathyrus maritimus_) is a much commoner
plant of the coast, and may be readily recognised by its general
resemblance to the garden sweet-pea. The genus to which it belongs is
closely allied to the vetches, but may be distinguished by the style,
which is flattened below the stigma, hairy on the inner or upper side,
but quite smooth on the outer side. The sea-side species has an angled
(but not winged) stem, from one to three feet long, compound tendrilled
leaves with many oval leaflets, and large oval or cordate stipules. Its
purple flowers are in bloom during July and August. A variety of this
plant (_acutifolius_), with a slender straggling stem and narrow acute
leaflets, occurs on some parts of the Scottish coast.
[Illustration: FIG. 301.--THE SEA STORK’S-BILL]
The _Geraniaceæ_ is represented at the sea-side by the Sea Stork’s-bill
(_Erodium maritimum_), which, however, is by no means a very common
flower. Its relationship to the other stork’s-bills and the
crane’s-bills may be readily proved by the five persistent sepals, five
distinct clawed petals, the five to ten stamens attached _under_ the
ovary (for we have now reached that division of the polypetalous exogens
distinguished by this mode of insertion of the stamens), and the five
carpels surrounding a long beak resembling that of the stork and the
crane. The plant may sometimes be seen on sandy shores, averaging a foot
in height, though very variable in this respect, and displaying its
pretty pink flowers during the whole of the summer. The principal
features by which it is to be distinguished from the two other British
plants of the same species are its ovate or cordate leaves with very
short petioles, and the presence of only one or two flowers on each
peduncle.
Passing now to the Sea Mallow (_Lavatera arborea_), we are dealing with
another rather rare plant, of the order _Malvaceæ_, sometimes met with
on rocky coasts, chiefly, it appears, on the north coast of Cornwall and
Devon. This is a very shrubby plant, as its specific name implies, and
it is sometimes popularly known as the Tree Mallow on that account. It
has a very woody stem, growing to a height of four or five feet, and
bearing seven-pointed, downy leaves, and solitary, axillary, purple
flowers. As in the other mallows, the flowers have five petals, which
are curiously twisted when in the bud, five sepals, a large number of
stamens united into a tube, and an ovary of many cells, but it may be
distinguished from the other species of the order by its three-lobed
bracts. The plant is found principally in wild, uncultivated spots, but
is commonly grown as a garden plant by the cottagers of villages in the
south-west, and under cultivation it frequently grows to a height of
nine or ten feet, with a tree-like stem three or four inches in
thickness; and it produces such a quantity of fibre that its cultivation
for manufacturing purposes has been suggested.
We now come to another of the very extensive orders, at least as far as
British plants are concerned, although it contains only a few sea-side
species. We refer to the _Caryophyllaceæ_, containing the pinks,
campions, catchflies, chickweeds, &c. The chief features of the order
are jointed, herbaceous stems, opposite leaves, and regular white or red
flowers with four or five sepals and petals, eight or ten stamens, and a
capsular fruit opening at the top with teeth.
One of the commonest species we have to consider is the Sea Campion
(_Silene maritima_), common on nearly all coasts, and often growing in
small crevices of the bare rocks quite within the reach of the spray of
storm-waves. In common with the other members of its genus it is
characterised by a tubular calyx of united sepals, ten stamens, and a
three-celled capsule opening at the top with six teeth; but it may be
known at once by its small size, being only a few inches in height, and
its solitary flowers with calyx much inflated and the corolla only
shortly cleft.
The Sea Sand Wort (_Spergularia marina_) is another common plant of the
coast, recognised by its slender, creeping stems; linear, stipuled,
fleshy leaves, convex below and blunt at the apex; and its pinkish-white
flowers. The Sea Purslane (_Honckenya peploides_), belonging to the same
order, is also a creeping plant, with ovate, acute fleshy leaves,
flowering from May to August. It is the only British plant of its genus,
and may be distinguished from others by the absence of stipules,
distinct sepals, petals entire, ten stamens, and from three to five
styles. The flowers are white, solitary, and sessile. The one remaining
species of the sea-side _Caryophyllaceæ_ is the Sea Pearl Wort (_Sagina
maritima_). This plant is closely allied to the last, being a creeper
with exstipulate leaves and distinct sepals, but its flowers are reddish
white, on erect peduncles, with very small petals. The leaves, too, are
linear, fleshy, and obtuse. There are three distinct varieties of this
plant, two of which have erect stems with short internodes, while the
third is procumbent with long internodes; and in all three the capsules
are shorter than the sepals.
[Illustration: FIG. 302.--THE SEA CAMPION]
A variety of the Common Milk Wort (_Polygala vulgaris_)--order
_Polygalaceæ_--is moderately common on sandy shores. The ordinary form
of the species, which is so common on heaths, is a small plant with a
woody stem, small ovate leaves crowded below, and opposite lanceolate
leaves above. The flowers are irregular with five persistent sepals, two
larger than the others; three to five petals, the lowest keeled, and all
united to the tube formed by the eight stamens, which are divided above
into two bundles; and the fruit is a flat capsule with two one-seeded
cells. The flowers are very variable in colour, being white, pink,
lilac, or blue; and the seeds are downy. The sea-side variety
(_oxyptera_) has smaller flowers than the normal form, and the wings of
the calyx are narrower.
One species of Pansy (_Viola Curtisii_) is occasionally to be met with
on sandy shores, and may be at once recognised as one of the _Violaceæ_
by its irregular spurred corolla, its five persistent sepals, and the
three-parted, one-celled ovary. The flowers are variable in colour and
size, the prevailing tints being blue and yellow, and the diameter of
the corolla occasionally reaching to one inch. It has a creeping woody
rootstock, and a rough angular stem; and the petals are generally but
little longer than the sepals.
[Illustration: FIG. 303.--THE SEA PEARL WORT]
[Illustration: FIG. 304.--THE SHRUBBY MIGNONETTE]
The Shrubby Mignonette (_Reseda suffruticulosa_), of the order
_Resedaceæ_, is a common sea-side plant that grows to a height of one or
two feet on sandy shores, bearing spikes of white flowers in July and
August. The order is characterised by alternate exstipulate leaves,
persistent calyx with four or five sepals, corolla of from four to seven
petals, many stamens, and a three-lobed, one-celled ovary. The sea-side
species is very much like the wild mignonette so common in chalky
districts, but differs in having all its leaves pinnate, waved, and
glaucous, with linear segments; and in having five _equal_ sepals and
petals. In a variety of the species, however, the sepals and petals are
six in number.
The Crucifers are fairly well represented by coast plants, there being
several maritime species of the order. The _Cruciferæ_ are named from
the nature of the corolla, the limbs of the four petals of which are
arranged so as to resemble the Maltese cross. The flowers have also four
sepals, six stamens, two of which are shorter than the other four, and
the fruit takes the form of a two-celled pod or pouch which opens by the
separation of its two valves from the central partition.
[Illustration: FIG. 305.--THE WILD CABBAGE]
[Illustration: FIG. 306.--THE ISLE OF MAN CABBAGE]
Our first example is the Wild Cabbage (_Brassica oleracea_), which,
although so unlike the cabbage of our gardens, is really the parent of
all the cultivated varieties, including the cauliflower, broccoli,
Brussels sprouts, &c. It is a biennial plant, with fleshy lobed wavy
leaves that are covered with bluish bloom, and a fleshy cylindrical
root. It grows erect to a height of one or two feet, bearing yellow
flowers during the summer months. An allied species (_B. monensis_),
with a prostrate stem and deeply-divided leaves, occurs locally on the
sandy shores of the Isle of Man.
Two species of Stock (_Matthiola_) are to be found on the coast, both
being characterised by purple flowers. The Great Sea Stock (_M.
sinuata_) is a rare plant growing on the shores of Wales and Cornwall,
and may be known by its herbaceous stem and narrow downy leaves; and the
other species--the Hoary Shrubby Stock (_M. incana_)--is also a rare
plant, found principally on the cliffs of the Isle of Wight, and is the
parent of the Brompton Stocks of our gardens. The latter has a branched
woody stem and narrow leaves. Both species grow to a height of about
eighteen inches, and the latter flowers in May and June, while the
former is in bloom during the hottest summer months.
The Hare’s-ear Treacle Mustard (_Erysimum orientale_) is a rare
crucifer, frequenting the cliffs of the southern and eastern counties.
It grows to a height of one to two feet, and bears its white flowers
about midsummer. It has glaucous leaves, and the fruit-pods are
quadrangular in form.
[Illustration: FIG. 307.--THE GREAT SEA STOCK]
[Illustration: FIG. 308.--THE HOARY SHRUBBY STOCK]
The Common Scurvy Grass (_Cochlearia officinalis_) is abundant on many
shores, and its fleshy leaves, once highly valued as an antiscorbutic,
are still used for salad by the cottagers near the sea. It generally
grows to a height of six or seven inches, and displays its white flowers
during late spring and early summer. The root-leaves are cordate in
form, and the upper ones are sessile and angled, half embracing the
stem. The fruit is a rounded pouch. A variety (_danica_) with stalked,
deltoid leaves and an oval veiny pod, is _plentiful_ in some places.
[Illustration: FIG. 309.--THE SCURVY GRASS]
[Illustration: FIG. 310.--THE SEA RADISH]
On some coasts we find the Sweet Alyssum (_Koniga maritima_)--a
naturalised plant with procumbent stem, narrow lanceolate, acute
leaves, and white flowers. It may be recognised by its compressed,
pointed pouch with one-seeded cells. This species flowers towards the
end of the summer.
The Sea Radish (_Raphanus maritimus_) is a much larger plant, growing
three or four feet in height. In common with the Wild Radish of our
corn-fields, it has a tapering pod divided into one-seeded joints, but
it may be distinguished from the latter by its superior height and the
deeply-divided radical leaves. Its flowers are always yellow, while in
the field species they may be either yellow or white; and the style is
also shorter, being about the same length as the last joint of the pod.
On sandy shores the Sea Rocket (_Cakile maritima_) is commonly seen, and
is readily distinguished by its zigzag branches, deeply-lobed, smooth,
fleshy leaves of a glaucous colour, and its succulent pod, which is
divided into two one-seeded cells by a horizontal partition. It grows
from one to two feet high, and bears pretty lilac flowers about
midsummer.
[Illustration: FIG. 311.--THE SEA ROCKET]
Our last example of the crucifers is the Sea Kale (_Crambe maritima_), a
hardy perennial, commonly seen growing among the sand and shingle of the
shore, which is the parent of the sea kale now so commonly cultivated in
our market gardens. It may be readily recognised by the fine glaucous
bloom of its stem, and its broad wavy toothed leaves of a glaucous grey
colour. It grows to a height of about eighteen inches, and bears white
flowers in June. The fruit is a two-jointed pouch, the upper being
rounded and one-seeded, while the lower is stalk-like and barren. This
plant is particularly common in the south-west of England, where the
leaves are sometimes blanched for food by burying them in the sand.
One of the most striking plants of the coast is the Yellow Horned Poppy
(_Glaucium luteum_) of the order _Papaveraceæ_, which contains the
well-known poppies of corn-fields. The general characteristics of the
order are two deciduous sepals, four petals, many stamens inserted below
the ovary, and the ovary one-celled with membranous divisions. The
plants of this species usually contain a milky juice, have alternate
leaves without stipules, and the flowers, which are regular, generally
nod when in bud. The Horned Poppy is a very conspicuous plant, usually
growing quite alone on some inaccessible portion of the cliff, or among
the pebbles or shingle not far from high-water mark. Its stem is
glaucous and branched, and the large waved and deeply-cut leaves, which
clasp the stem, are also of a glaucous hue. The flowers are rendered
conspicuous by their large yellow petals, which, however, last only for
a day, and are succeeded by the hornlike seed-pods that sometimes reach
a foot in length.
[Illustration: FIG. 312.--THE SEA KALE]
We will conclude our list of sea-side flowers by a brief mention of the
Lesser Meadow Rue (_Thalictrum minus_), a variety of which (_maritimum_)
grows on sandy shores. The Meadow Rue belongs to the _Ranunculaceæ_, as
may be seen from the fruit of several distinct carpels, each containing
a single seed, the corolla of distinct petals, and the numerous stamens
inserted below the carpels. The normal form of the Lesser Meadow Rue,
which grows freely in some chalky pastures and thickets, has leaves
three or four times pinnate, and lax panicles of drooping flowers
without any petals. The sea-side variety differs from this in having the
stem leafless at the base, and the panicles leafless and broad. The
flowers are greenish white, and bloom in July and August.
[Illustration: FIG. 313.--THE HORNED POPPY]
To assist the reader in the identification of sea-side flowers we append
a list of the orders to which they belong, together with the principal
distinguishing characteristics of each.
SYNOPSIS OF THE NATURAL ORDERS
WHICH CONTAIN OUR PRINCIPAL
SEA-SIDE FLOWERING PLANTS
I. MONOCOTYLEDONS
A. GLUMIFERÆ
FLOWERS WITHOUT A PERIANTH, ENCLOSED IN GLUMES
=1. Gramineæ=--Grassy plants with hollow stems enclosed in split
sheaths. Flowers generally bisexual with (usually) three
stamens.
=2. Cyperaceæ=--Grassy plants with solid stems and entire sheaths.
Flowers arranged in spikelets, unisexual or bisexual, with
from one to three stamens.
B. PETALOIDÆ
PERIANTH PETALOID
=3. Juncaceæ=--Rushes, with narrow leaves and small brown flowers.
Perianth 6-partite, with scarious segments. Stamens
usually 6; ovary superior; fruit a 3-valved capsule.
=4. Naiadaceæ=--Aquatic herbs with inconspicuous, unisexual or
bisexual flowers. Perianth absent or scale-like. Stamens
as many as the segments of the perianth. Fruit of from one
to four carpels--superior.
=5. Alismaceæ=--Aquatic plants with radical net-veined leaves, and
(generally) conspicuous, white, bisexual flowers. Perianth
6-partite. Stamens 6. Fruit of many carpels--superior.
=6. Liliaceæ=--Herbs with narrow leaves and showy, bisexual
flowers. Perianth 6-partite. Stamens 6. Ovary superior,
3-celled. Fruit a berry or capsule.
II. DICOTYLEDONS
A. CALYX, OR COROLLA, OR BOTH ABSENT
=7. Euphorbiaceæ=--Herbs with entire leaves and (generally) a milky
juice. Flowers small, unisexual, diœcious (male and
female flowers on separate plants), sometimes enclosed in
calyx-like bracts. Perianth 3- or 4-partite or absent.
Stamens one or more. Ovary inferior. Fruit separating
into carpels elastically.
=8. Eleagnaceæ=--Shrub with silvery scales, alternate, entire
leaves, and small, unisexual flowers--the staminate
flowers in catkins. Sepals of male flowers 3 or 4. Stamens
4 to 8. Ovary superior. Fruit indehiscent (not splitting).
=9. Polygonaceæ=--Herbs with sheathing stipules, alternate leaves,
and small (generally) bisexual flowers. Stamens 5 to 8.
Ovary superior. Fruit indehiscent.
=10. Chenopodiaceæ=--Herbs with jointed stems and small unisexual or
bisexual flowers. Stamens usually 5, sometimes 1 or 2,
opposite the sepals. Ovary superior. Fruit indehiscent.
B. PLANTS WITH BOTH CALYX AND COROLLA
_a._ COROLLA MONOPETALOUS
1. _Ovary Superior and Stamens generally on the Corolla_
=11. Plantaginaceæ=--Herbs with radical entire leaves, and spikes
of small, green flowers. Calyx 4-cleft. Corolla 4-lobed,
scarious. Stamens 4. Ovary 2- to 4-celled. Fruit
many-seeded.
=12. Plumbaginaceæ=--Herbs with radical or alternate leaves, and
(generally) regular, blue flowers. Calyx tubular,
scarious. Corolla of 5 petals, united below. Stamens 5,
opposite the petals, attached below the ovary. Ovary
1-celled and 1-seeded.
=13. Primulaceæ=--Herbs with (generally) radical leaves and
conspicuous, regular flowers. Calyx 4- to 7-cleft. Corolla
4- to 7-cleft. Stamens 4 to 7, generally opposite the
petals. Ovary 1-celled. Fruit a capsule with many seeds.
=14. Solanaceæ=--Herbs with alternate leaves and axillary clusters
of regular flowers. Calyx 5-cleft. Corolla 5-cleft.
Stamens 4 or 5. Ovary 2-celled. Fruit a berry.
=15. Convolvulaceæ=--Climbing herbs with alternate leaves and showy,
regular flowers. Sepals 5. Corolla 4- or 5-lobed. Stamens
4 or 5. Ovary 2- to 4-celled. Fruit a capsule.
=16. Gentianaceæ=--Herbs with opposite entire leaves and solitary
regular flowers. Calyx 4- to 10-lobed. Corolla 4- to
10-lobed. Stamens 4 to 10, alternate with the lobes of the
corolla. Ovary 1- or 2-celled. Fruit a capsule.
2. _Ovary Inferior and Stamens on the Corolla_
=17. Compositæ=--Herbs with flowers (generally yellow or white)
collected into compact heads. Calyx absent or represented
by a pappus. Corolla tubular or ligulate. Stamens 4 or 5.
_b._ COROLLA POLYPETALOUS
1. _Stamens Perigynous_ (_around the Ovary_), _or Epigynous_
(_upon the Ovary_)
=18. Umbelliferæ=--Herbs with (generally) compound leaves, and
small, white, umbelled flowers. Sepals (if present) 5.
Petals 5. Stamens 5. Ovary inferior. Fruit of two
adhering carpels.
=19. Illecebraceæ=--Small herbs with sessile, entire leaves, and
small flowers. Sepals 4 or 5. Petals 4 or 5 or absent.
Stamens 1 to 5. Ovary superior.
=20. Tamariscaceæ=--Shrub with small, scale-like leaves, and lateral
spikes of small regular flowers. Sepals 4 or 5. Petals 4
or 5. Stamens 4 or more.
=21. Leguminosæ=--Herbs or shrubs with alternate, stipuled, pinnate
or ternate leaves, sometimes tendrilled, and irregular
flowers. Sepals 4 or 5. Corolla of 5 petals,
papilionaceous (butterfly-like). Stamens usually 10. Ovary
superior. Fruit a pod.
2. _Stamens Hypogynous_ (_attached below the Ovary_)
=22. Geraniaceæ=--Herbs with stipuled, lobed leaves, and showy
regular flowers. Sepals 5. Petals 5. Stamens 5 or 10.
Fruit of 5 carpels surrounding a long beak.
=23. Malvaceæ=--Herbs with alternate, stipuled leaves, and axillary,
red, or purple flowers. Sepals 5. Petals 5, twisted in the
bud. Stamens numerous, united into a tube. Ovary of many
cells.
=24. Caryophyllaceæ=--Herbs with (generally) jointed stems, opposite
leaves, and regular white or red flowers. Sepals 4 or 5.
Petals 4 or 5. Stamens 8 or 10. Fruit a 1-celled capsule
opening at the top with teeth.
=25. Polygalaceæ=--Herbs with alternate, simple leaves (without
stipules), and irregular flowers. Sepals 5, the inner
petal-like. Petals 3 to 5, unequal. Stamens 8, in two
clusters. Fruit a 2-celled capsule.
=26. Violaceæ=--Herbs with alternate, stipuled leaves and irregular
flowers. Sepals 5. Petals 5, unequal, the lower one
spurred. Stamens 5. Ovary 3-partite, but 1-celled.
=27. Resedaceæ=--Herbs or shrubs with alternate, exstipulate leaves,
and spikes of irregular, green flowers. Sepals 4 or 5.
Petals 4 to 7, unequal. Stamens more than 10. Ovary
3-lobed, and 1-celled.
=28. Cruciferæ=--Herbs with alternate, exstipulate leaves, and
regular flowers. Sepals 4. Petals 4, cruciate. Stamens
6--4 longer and 2 shorter. Ovary 1- or 2-celled. Fruit a
siliqua or a silicula.
=29. Papaveraceæ=--Herbs with alternate, exstipulate leaves, a milky
juice, and regular, showy flowers. Sepals 2, deciduous.
Petals 4. Stamens numerous. Ovary 1-celled with membranous
partitions.
=30. Ranunculaceæ=--Herbs with (generally) alternate leaves and
regular flowers. Sepals generally 5, distinct. Petals 5 or
more. Stamens numerous. Fruit of many, distinct carpels.
INDEX
Acalephæ, 134
Acanthias, 319
Acarina, 304
Aclis, 246
Acmæa, 240
Acorn Barnacles, 263
Actinia, 142
Actinoloba, 143
Actora, 300
Adamsia, 154
Adeorbis, 243
Ægirus, 235
Æolidæ, 235
Æpophilus, 297
Aëpus, 303
Agonus, 335
Aiptasia, 144
Alaria, 385
Alcyonium, 155
Algæ, 344, 347
-- reproduction, 351
Alismaceæ, 401, 423
Allseed, 413
Alopecurus, 397
Ambulacrum, 163
Ammodytes, 326
Ammophila, 396
Amœba, 102
Amphibia, 307
Amphipoda, 267, 304
Anarrhichas, 334
Anatinidæ, 204, 255
Anemones, 127, 138
Angiosperms, 346, 348
Angler Fish, 336
Angling, 34
Anguilla, 324
Anguillidæ, 323
Angular Crab, 289
Annelida, 177
Anomia, 222
Anomura, 279
Antedon, 160
Anthea, 149
Anurida, 299
Apetalæ, 402
Aphaniptera, 305
Aphrodita, 179
Apium, 412
Aporrhais, 245
Aquarium, 51
-- aeration of, 61, 63
-- cement for, 54, 57
-- construction of, 53
-- fountain, 64
-- temporary, 52
-- weeds for, 61
Arachnoidea, 257, 293, 304
Araneidæ, 304
Arca, 216
Arcadæ, 216, 255
Arctopsis, 289
Arenicola, 178
Armeria, 408
Artemisia, 410
Arthropoda, 255
-- classification, 304
Asiphonida, 198, 216, 255
Asparagus, 402
Asperococcus, 383
Astarte, 212
Aster, 410
Asteroidea, 171
Atherina, 332
Atherinidæ, 332
Atriplex, 406
Aurelia, 135
Aviculidæ, 219, 255
Badderlocks, 385
Baits, 39
Balanophyllia, 152
Balanus, 6, 263
Banded Cockle, 216
Barley Grasses, 395
Barnacles, 261
Bass, 338
Beach Fleas, 263
Beadlet, 142
Beard Grass, 397
Beet, 405
Bembidiidæ, 301
Bembidium, 302
Beroe, 137
Bittersweet, 409
Bledius, 304
Blennies, 332
Blenniidæ, 332
Blennius, 334
Blue Shark, 320
Bonnet Limpet, 240
Bopyrus, 267
Boring Pill-ball, 268
Boring Sponge, 124
Bottle-brush, 132
Brachelytra, 303
Brachiopods, 224
Brachyura, 271, 279, 285, 304
Branchiopoda, 265, 304
Brassica, 418
Bread-crumb Sponge, 123
Bristle-tails, 298
Brittle Starfish, 157, 159, 161
Broad-clawed Crab, 280
Brome Grasses, 395
Bromus, 395
Bryopsis, 354
Bryozoa, 188
Buccinidæ, 248, 255
Buccinum, 248
Bugs, 297
Bulla, 236
Bull-heads, 335
Bull Huss, 320
Bunodes, 150
Butter Gunnel, 334
Byssus, 43, 195
Cabinets, 89
Cæcum, 245
Cakile, 420
Calamary, 252
Calcarea, 119
Calcareous Sponges, 119
Callianassa, 277
Calliblepharis, 367
Callionymus, 335
Callithamnion, 61, 358
Callophyllis, 365
Calpurna, 248
Calyptræa, 241
Calyptræidæ, 240, 255
Canary Grass, 396
Cancer, 292
Carangidæ, 338
Caranx, 338
Carapace, 272
Carchariidæ, 320
Carcharius, 320
Carcinus, 291
Cardiadæ, 214, 255
Cardium, 214
Carex, 398
Carrageen Moss, 61, 364
Caryophyllaceæ, 415, 425
Caryophyllia, 151
Catometopa, 286, 289
Cave-dweller, 147
Cell for live objects, 95
Cement for aquarium, 57
Centaury, 409
Centipedes, 305
Cephalophora, 191, 225, 255
Cephalopoda, 191, 250, 255
Ceramiaceæ, 358, 389
Ceramium, 61, 362
Cerati-solen, 207
Cerithiadæ, 245, 255
Cerithium, 245
Cetacea, 340
Chætopoda, 177
Chalina, 122
Chalk, 109
Chambered Mussel, 219
Channelled Wrack, 387
Charales, 343, 348
Chenopodiaceæ, 405, 424
Chenopodium, 405
Chilognatha, 305
Chilopoda, 305
Chironomus, 301
Chiton, 237
Chitonidæ, 237, 255
Chlorophyll, 74
Chlorospermeæ, 350, 389
Chondria, 374
Chondrus, 61, 364
Chorda, 385
Chordaria, 381
Chordariaceæ, 380, 390
Chrysaora, 136
Chylocladia, 364
Cillenium, 303
Circe, 212
Cirripedia, 261, 304
Cladophora, 352
Cladostephus, 380
Cliffs, 2
Cliona, 124
Cloak Anemone, 154
Club-mosses, 345
Club Rush, 399
Clupea, 322
Clupeidæ, 322
Coast--general characters of, 1
Cochlearia, 419
Cockles, 214
Cod, 327
Codium, 353
Cœlenterates, 127
Cœlopa, 300
Coleoptera, 301, 305
Columella, 226
Common sponges, 119
Compositæ, 410, 425
Cone Shells, 248
Conidæ, 248, 255
Coniferæ, 347, 348
Confervaceæ, 352, 389
Convolvulaceæ, 409, 425
Convolvulus, 409
Copepoda, 264, 304
Corallina, 61, 369
Corallinaceæ, 369, 390
Corallines--preserving 87
Corals, 151
Corbula, 206
Cord Grass, 398
Cordylecladia, 366
Cornish Sucker, 330
Corrosive sublimate, 75
Corystes, 286
Cottidæ, 335
Cottus, 335
Cowries, 247
Crab-pots, 26
Crabs--as bait, 44
-- preserving, 81
Crambe, 420
Crangon, 278
Crenella, 219
Crinoidea, 171
Crithmum, 411
Cruciferæ, 417, 426
Crustacea, 257, 304
Crustaceans--preserving, 80
Cryptogams, 343, 347
Cryptonemiaceæ, 363, 389
Ctenophora, 137
Cup Coral, 151
Cup-and-saucer Limpet, 240
Cutleria, 382
Cuttlefishes, 191, 251, 253
Cycadeæ, 347, 348
Cyclometopa, 286, 291
Cyclostomata, 307, 308
Cydippe, 137
Cynodon, 396
Cyperaceæ, 398, 423
Cypræa, 248
Cypræidæ, 247, 255
Cyprina, 212
Cyprinidæ, 212, 255
Cystoclonium, 365
Cystoseira, 387
Cythere, 266
Cytheria, 211
Cyttidæ 338
Dactylopteridæ, 335
Dahlia Wartlet, 143
Daisy Anemone, 146
Danica, 419
Dasya, 376
Daucus, 411
Dead Men's Fingers, 155
Decapoda (Decapods), 251, 255, 269, 271, 279, 304
Delesseria, 366, 368
Delphinidæ, 340
Demospongia, 119
Dendronotus, 235
Dentaliadæ, 238, 255
Desmarestia, 385
Devon Cup-coral, 151
Dibranchiata, 251, 255
Dicotyledons, 347, 403, 424
Dictyosiphon, 383
Dictyotaceæ, 382, 390
Dillisk, 365
Diotis, 410
Diptera, 299, 305
Dissecting microscope, 91
Dissecting trough, 98
Dissection, 91
Dog-fishes, 318
Dog Whelks, 248
Dog Winkles, 248
Dog's-tooth Grass, 396
Dolichopodidæ, 300
Dolphin, 340
Donax, 208
Doridæ, 235
Doto, 235
Dragonet, 335
Dredge, 26
Dreissina, 219
Dromia, 282
Dulse, 61, 365
Dumontia, 363
Dyschirius, 304
Ear-shell, 242
Echinocyamus, 168
Echinoderms, 157
Echinoidea, 171
Echinus, 168
Ectocarpaceæ, 378, 390
Ectocarpus, 378
Edible Cockle, 214
Edible Crab, 292
Edible Mussel, 217
Edriophthalmata, 266, 304
Eel, 323
Elachista, 381
Elasmobranchii, 318
Eleagnaceæ, 403, 424
Eleocharis, 399
Elymus, 395
Elysia, 235
Emarginula, 242
Enteromorpha, 61, 355
Entomostraca, 266, 304
Equisetales, 345, 348
Erato, 248
Erodium, 414
Eryngium, 412
Eryngo, 412
Erysimum, 418
Erythræa, 409
Establishment of port, 17
Eulima, 246
Euphorbia, 403
Euphorbiaceæ, 403, 424
Euplexoptera, 305
Exogenæ, 402
Father Lasher, 335
Feather Starfish, 159, 160
Ferns, 345
Fescue Grass, 396
Festuca, 396
Filicales, 345, 348
Fishes, 307
-- classification, 318
-- colour of, 313
-- distribution, 317
-- fins of, 311
-- gills, 312
-- preserving, 85
-- scales of, 309
-- skeleton, 314
-- tails, 315
Fishing, 34
Fishing Frog, 336
Fissurella, 241
Fissurellidæ, 241, 255
Five-fingered Starfish, 157
Flat-fishes, 324
Floating Crab, 289
Flounders, 325
Flowering Plants--classification, 423
Flowers--fertilisation, 393
-- preserving, 86
-- structure, 346
Flustra, 188
Flying Gurnards, 335
Foraminifera, 106
Formaldehyde, 73
Fox-tail Grass, 398
Fragacea, 142
Fucaceæ, 386, 390
Fucus, 386
Fungi, 344, 347
Furbelows, 384
Furcellaria, 364
Fusus, 249
Gadiadæ, 327
Gadus, 327
Galeomma, 214
Gamopetalæ, 403
Gaper shell, 205
Gasteropoda, 232, 255
Gastrochæna, 203
Gastrochænidæ, 203, 255
Gastrosteidæ, 331
Gastrosteus, 331
Gebia, 276
Gelidiaceæ, 390
Gelidium, 367
Gem Pimplet, 150
Gentianaceæ, 409, 425
Geodephaga, 301
Gephyrea, 176
Geraniaceæ, 414, 425
Gibb's Crab, 289
Gigartina, 364
Glass-wort, 407
Glaucium, 420
Globigerina, 109
Globular Beroe, 137
Gloisiphonia, 364
Glumiferæ, 423
Glycerine, 73
Goadby's fluid, 73
Gobies, 334
Gobiidæ, 334
Gobioesocidæ, 330
Gobius, 334
Golden Samphire, 411
Gonoplax, 290
Goosefoot, 405
Gracilaria, 366
Gramineæ, 392, 423
Grantia, 120
Grass-wracks, 400
Green Laver, 61
Green Pea-urchin, 168
Grey Mullet, 332
Griffithsia, 61, 360
Ground bait, 49
Gurnards, 335
Gymnosperms, 346, 348
Haddock, 327
Hake, 328
Halecium, 131
Halibut, 326
Halichondria, 123
Halidrys, 388
Haliotidæ, 242, 255
Haliotis, 242
Halurus, 361
Hapalidiaceæ, 390
Hare's Ear, 418
Heart Cockle, 212
Heart Urchin, 168
Helminthocladiæ, 389
Henslow's Crab, 293
Henware, 385
Hepaticæ, 344, 348
Hermit Crab, 44, 154, 280, 232
Herring, 322
Herring-bone Polype, 131
Hexactinellida, 119
Himanthalia, 387
Hippoglossus, 326
Hippophaë, 403
Hog-louse, 268
Holostomata, 236, 255
Holothuroidea, 169
Homarus, 274
Honckenya, 416
Honeyware, 385
Hook-nose, 335
Hooks--fishing, 37
Hordeum, 395
Horned Poppy, 420
Horse Limpet, 240
Horse Mackerel, 338
Horse Mussels, 218
Horsetails, 345
Hydrozoa, 130
Hymenoptera, 305
Hypnæa, 365
Ianthina, 242
Illecebraceæ, 412, 425
Inachus, 289
Infusoria, 104, 112
Insecta (Insects), 257, 294, 305
Inula, 411
Iridæa, 364
Irish Moss, 61, 364
Isocardia, 212
Isopoda, 267, 304
Isotoma, 299
Jania, 370
Jelly-fishes, 127, 134
John Dory, 338
Juncaceæ, 400, 423
Juncus, 400
Keyhole Limpet, 241
Knappia, 397
Knot-grasses, 404
Knotted Wrack, 386
Koniga, 419
Labial palpi, 197
Labridæ, 329
Lactuca, 410
Lacuna, 244
Lady Crab, 292
Lamellibranchiata (Lamellibranchs), 191, 192, 255
Laminaria, 384
Laminariaceæ, 384, 390
Lampreys, 308
Lathyrus, 413
Laurencia, 370
Laurenciaceæ, 370, 390
Lavatera, 415
Laver, 61, 354
Leathesia, 381
Leda, 217
Leguminosæ, 413, 425
Lemon Sole, 326
Lenses, 91
Lepadogaster, 330
Lepidoptera, 305
Lepturus, 395
Lesser Rue, 422
Leucosolenia, 121
Ligia, 268
Liliaceæ, 402, 423
Limnoria, 268
Limpets, 43, 238
Ling, 328
Lithodes, 282
Litosiphon, 383
Little Lettuce, 410
Littorina, 243
Littorinidæ, 244, 255
Liverworts, 344
Lobster pots, 26
Lobsters, 274
preserving, 81
Loligo, 252
Lomentaria, 371
Long-armed Crab, 286
Lophius, 336
Lucinidæ, 213, 255
Lugworm, 39, 178
Lutraria, 209
Lycopodiales, 345, 348
Machilis, 298
Mackerel, 337
Macrura, 271, 279, 304
Mactra, 209
Mactridæ, 209, 255
Maia, 289
Malacostraca, 266, 304
Malvaceæ, 415, 425
Mammals, 307, 339
Mantis Shrimps, 270
Marginella, 248
Marine aquarium, 51
Marsipobranchii, 308
Mat-grass, 396
Matricaria, 411
Matthiola, 418
Maugeria, 366
Meadow Grasses, 395
Meadow Rue, 421
Medusæ, 134
Medusoids, 133
Melanospermeæ, 350, 376, 290
Melobesia, 370
Merluccius, 328
Mesembryanthemum, 142
Mesenteries, 139
Mesogloia, 381
Methylated spirit, 72
Michaelmas Daisy, 410
Micralymma, 303
Milkwort, 416
Millepedes, 305
Modiola, 218
Molluscs, 190
-- bivalve, 192
-- classification, 255
Molva, 328
Monera, 110
Monocotyledons, 347, 391, 423
Montagu's Sucker, 331
Morone, 338
Moss Polyps, 188
Mosses, 344
Motella, 328
Mud-burrower, 277
Mugil, 332
Mugilidæ, 332
Mullidæ, 338
Mullus, 338
Murex, 249
Muricidæ, 249, 255
Murlins, 385
Musci, 344, 348
Muscineæ, 343, 344, 348
Museum, 88
Mussels, 42, 217
Mustelus, 320
Mya, 205
Myacidæ, 205, 255
Myrionema, 381
Myriopoda, 257, 305
Myriotrichia, 379
Mytilidæ, 217, 255
Mytilus, 217
Naiadaceæ, 400, 423
Nassa, 249
Natica, 246
Naticidæ, 246, 255
Nautilidæ, 255
Needle-fish, 329
Nephrops, 275
Nereis, 284
Nerophis, 329
Nesæa, 268
Nets, Collecting, 23
Neuroptera, 305
Nitophyllum, 367
Noctiluca, 114
Norway Lobster, 275
Notched Limpets, 242
Nucleobranchiata, 232, 255
Nucula, 217
Nudibranchiata, 233, 255
Nummulites, 108
Nummulitic limestone, 110
Nurse Dog, 320
Nut Crabs, 286
Obione, 405
Octopoda, 251, 255
Octopus, 251
Odonthalia, 375
Odostomia, 246
Oleasters, 403
Oligochæta, 177
Omar, 242
Oniscoda, 268
Opelet, 149
Operculum, 83, 227
Ophidiidæ, 326
Ophiuroidea, 171
Opisthobranchiata, 232, 255
Opossum Shrimps, 270
Oraches, 406
Orange-disked Anemone, 148
Orthoptera, 305
Osmerus, 321
Ostracoda, 265, 304
Ostrea, 221
Ostreidæ, 221, 255
Outdoor work, 21
Ovulum, 248
Oxyptera, 416
Oxyrhyncha, 286
Oxystomata, 286
Oysters, 221
Padina, 382
Pagurus, 282, 285
Pallial line, 193
Pansy, 417
Papaveraceæ, 420, 426
Parasitic Anemone, 153
Patella, 239
Patellidæ, 255
Paternoster, 48
Pea Crabs, 289
Pea Urchin, 168
Peachia, 145
Pearl Oysters, 219
Pecten, 222
Pectunculus, 216
Pennant's Crab, 286
Pepper Dulse, 370
Pericardium, 196
Peristome, 226
Periwinkle, 62, 243
Petaloidæ, 423
Phalaris, 396
Phanerogams, 343, 346, 348
Phasianella, 243
Pheasant Shell, 243
Phleum, 397
Phocæna, 340
Pholadidæ, 199, 255
Pholadidea, 201
Pholas, 200
Phosphorescence, 18, 111
Phyllirhoidæ, 286
Phyllophora, 365
Piddocks, 200
Pilchard, 322
Pileopsis, 241
Pilota, 361
Pimplet, 150
Pinna, 221
Pinna Pea-crab, 290
Pinnotheres, 290
Pipe-fishes, 328
Plaice, 325
Plantaginaceæ, 408, 424
Plantago, 408
Plants, classification, 343, 347
Plate-gilled Molluscs, 191
Pleuronectes, 326
Pleuronectidæ, 324
Plocamium, 61, 366
Plumbaginaceæ, 408, 424
Poa, 396
Podded Sea-oak, 388
Podophthalmata, 266, 269, 304
Pogge, 335
Pollack, 327
Polybius, 293
Polycarpon, 413
Polychæta, 177
Polygala, 416
Polygalaceæ, 416, 426
Polygonaceæ, 404, 424
Polygonum, 404
Polypetalæ, 403
Polypogon, 397
Polysiphonia, 372
Polystomata, 115
Polyzoa, 188
Porcelain Crab, 280
Porcellana, 280
Porifera, 115
Porphyra, 355
Porpoise, 339
Portland Spurge, 403
Portunus, 292
Prawn, 44, 278
Preservation of marine objects, 71
Preservatives, 72
Prickly Cockle, 215
Prickly Salt-wort, 407
Primulaceæ, 424
Prosobranchiata, 232, 236
Protophyta, 343, 347
Protoplasm, 102
Protoplasta, 104, 110
Protozoa, 102
-- classification, 104
Psammobia, 208
Pteropoda, 230, 255
Pulmonifera, 255
Punctaria, 383
Puncturella, 241
Purple Spurge, 403
Purple-tipped Urchin, 168
Purpura, 249
Pycnogonum, 293
Pyramidellidæ, 246, 255
Radiata, 140
Radiolaria, 104, 110
Ragworm, 40, 179
Raiidæ, 318
Ranunculaceæ, 422, 426
Raphanus, 420
Rays, 318
Red Mullets, 338
Red-specked Pimplet, 150
Reptilia, 307
Reseda, 417
Resedaceæ, 417, 426
Rhizocarpeæ, 345, 348
Rhizopods, 104
Rhizostoma, 136
Rhodomela, 372
Rhodomelaceæ, 372, 390
Rhodophyllis, 61
Rhodospermeæ, 350, 355, 389
Rhodymenia, 61, 365, 367
Rhodymeniaceæ, 365, 389
Rhombus, 326
Rhynchota, 297, 305
Rissoa, 244
Rock-fishes, 46
Rocklings, 328
Rock-pools, 6, 31
Rosy Anemone, 149
Rosy Feather Star, 160
Rotifers, 189
Rushes, 400
Rytiphlæa, 375
Sabella, 184
Saddle Oyster, 222
Sagartia, 146
Sagina, 416
Salicornia, 407
Salmo, 321
Salmon, 321
Salmon Dace, 339
Salmonidæ, 321
Salsola, 407
Salt-wort, 407
Sand Eels, 326
Sandhoppers, 268
-- preserving, 81
Sand Smelts, 332
Sandworm, 178
Saxicava, 203
Scalaria, 244
Scallops, 222
Scentless Mayweed, 411
Schizopoda, 304
Schizymenia, 61, 364
Scirpus, 399
Scomber, 337
Scomberidæ, 337
Scorpionidæ, 304
Scorpion Spider-crab, 289
Scurvy Grass, 419
Scylliidæ, 319
Scyllium, 319
Sea angling, 34
-- Aster, 410
-- Buckthorn, 403
-- Bullheads, 335
-- Bream, 338
-- Campion, 415
-- Carrot, 411
-- Cat, 334
-- Cat's-tail Grass, 397
-- Cucumbers, 169
-- Devil, 336
-- Eggs, 165
-- -- preserving, 79
-- Girdles, 384
-- Grass, 61, 353, 400
-- Hard-grass, 395
-- Holly, 412
-- Kale, 420
-- Lavender, 409
-- Lemons, 233
-- Lettuce, 61
-- Loach, 328
-- Lyme-grass, 395
-- Mallow, 415
-- Mat, 188
-- Meadow Grass, 396
-- Mouse, 179
-- Pearl-wort, 416
-- Perch, 338
-- Pill-ball, 268
-- Pink, 408
-- Purslane, 406, 416
-- Radish, 420
-- Reed, 396
-- Rocket, 420
-- Rushes, 400
-- Salt, 17, 59
-- Saltness of, 17
-- Samphire, 411
-- Sand-wort, 415
-- Sedge, 398
-- Slater, 268
-- Slugs, 233
-- Snails, 331
-- Spurge, 403
-- Squirts, 188
-- Stock, 418
-- Stork's-bill, 414
-- Urchins, 157, 165
-- -- preserving, 79
-- -- shell of, 166
-- teeth, 167
-- water, artificial, 59
-- composition, 59
-- weeds, 343
-- -- classification, 389
-- -- preserving, 86
-- Wormwood, 410
Seaside Arrow Grass, 401
-- Bindweed, 409
-- Cottonweed, 410
-- Feverfew, 411
-- Grasses, 392
-- Knot Grass, 404
-- Plantain, 408
-- plants, 391
-- classification, 423
Section cutting, 96
Sedges, 398
Selaginellales, 345, 348
Sepia, 253
Sepiadæ, 253, 255
Sepiola, 252
Serpula, 185
Serranidæ, 338
Serrated Pill-ball, 268
Serrated Wrack, 386
Sertularia, 128
Sessile-eyed crustaceans, 266
Shanny, 333
Sharks, 318
Shells, preserving, 83
Shore Crab, 261, 291
-- Spider, 293
Shrimps, 278
-- preserving, 81
Shrubby Mignonette, 417
Silene, 415
Silicia, 122
Siphonaceæ, 358, 389
Siphonida, 198, 255
Siphonostomata, 236, 247, 255
Six-rayed Sponges, 119
Skates, 318
Slender-beaked Crab, 289
Sloke, 61, 355
Smelt, 321
Smooth Hound, 320
Snoods, 37
Solanaceæ, 409, 424
Solanum, 409
Soldier Crab, 280
Sole, 326
Solea, 326
Solecurtus, 207
Solenidæ, 255
Sparidæ, 338
Spartina, 397
Sparus, 338
Spergularia, 415
Sphacelaria, 279
Sphærococcoideæ, 366, 390
Sphærococcus, 366
Sphæroma, 268
Spicules, 118
Spider Crabs, 288
Spike Rush, 399
Spiny-finned fishes, 329
Spirorbis, 187
Sponges, 115
Spongiocarpeæ, 390
Spoon Worms, 176
Sporochnaceæ, 385, 390
Sporochnus, 385
Spotted Dogfish, 320
Spotted Hog-louse, 268
Spout Shell, 245
Sprats, 323
Spring-tails, 299
Spurges, 403
Spyridia, 363
Spyridiaceæ, 368, 389
Squamariæ, 390
Squid, 252
Squirt Worms, 176
Stalk-eyed crustaceans, 266, 269
Starfishes, 157
-- preserving, 79
Stargazers, 336
Statice, 408
Stenorhynchus, 289
Sticklebacks, 331
Stilophora, 383
Sting Bull, 337
Sting Fish, 335
Stock, 418
Stomopoda, 269, 304
Stone Crab, 280
Strawberry Beadlet, 142
Sucker Fishes, 330
Sweet Alyssum, 419
Swimming Crab, 293
Sycon, 121
Syngnathidæ, 328
Syngnathus, 329
Tamariscaceæ, 413, 425
Tamarisk, 413
Tangles, 384
Tapes, 211
Tealia, 143
Tectibranchiata, 238, 255
Tectibranchs, 236
Teleostomi, 318, 320
Tellina, 208
Tellinidæ, 207, 255
Terebella, 181
Terebratulina, 225
Teredo, 201
Tetrabranchiata, 255
Thalictrum, 421
Thallophytes, 343, 344, 347
Trichoptera, 305
Thornback Crab, 289
Thracia, 204
Thrift, 408
Thuiaria, 132
Thysanoptera, 298, 305
Tides, 9
Tooth shells, 238
Top shells, 243
Trachinidæ, 336
Trachinus, 337
Treacle Mustard, 418
Tree Mallow, 415
Trefoil, 413
Trifolium, 413
Triglochin, 401
Triopa, 235
Tritonia, 235
Tritoniadæ, 235
Trivia, 248
Trochus, 243
Trumpet Anemone, 141
Tubularia, 132
Tunicates, 188
Turbellaria, 175
Turbinidæ, 243, 255
Turbot, 326
Turkey-feather Laver, 382
Turret shells, 245
Turritella, 244
Turritellidæ, 244, 255
Twin-bladder Wrack, 387
Two-spotted Sucker, 331
Ulva, 61, 354
Ulvaceæ, 389, 354
Umbelliferæ, 411, 425
Umbilicus, 226
Umbo, 193
Vascular cryptogams, 345
Velutina, 247
Velvet Crab, 292
Veneridæ, 210, 255
Venus, 210
Vermes, 172
Vertebrates, 306
Vetch, 413
Vicia, 413
Viola, 417
Violaceæ, 417, 426
Violet Fiddler, 292
Water Ferns, 345
Weavers, 336
Wedge shells, 208
Whales, 340
Wheel animals, 189
Whelks, 248
Whirl Worms, 175
Whistle Fish, 328
Whitebait, 323
White Salmon, 339
Whiting, 327
Wild Cabbage, 418
Wild Celery, 412
Wing shells, 219
Wolf Fish, 334
Woody Nightshade, 409
Worms, 172
-- parasitic, 174
Worm Pipe-fish, 329
Wrangeliaceæ, 389
Wrasses, 329
Xantho, 292
Xylophaga, 201
Yellow Poppy, 420
Zeus, 338
Zoantharia, 138
Zoarces, 333
Zonaria, 382
Zostera, 353, 400
_Printed in England at_ THE BALLANTYNE PRESS
SPOTTISWOODE, BALLANTYNE & CO. LTD.
_Colchester, London & Eton_
Transcriber's Note
Minor inconsistencies in the punctuation of tables or captions are
silently corrected.
Hyphenation is variable. Those compound words which are hyphenated only
on line breaks are rendered using modern usage.
The word 'movable' appears only once as 'moveable' (165), which is
retained.
The index entry for 'Œpophilus' is considered to be an error. All
instances of the word appear in the text as 'Æpophilus'. This has been
corrected and moved to the appropriate alphabetic position.
The following corrections were made to obvious printer's errors,
devel[e/o]ped (336); co[n/m]posed (364);
The following list contains punctuation corrections made:
p. 65 one of them[.] Added.
p. 255 [Class] =LAMELLIBRANCHIATA= Added to match other
entries.
p. 257 their tendencies[,/.] Corrected.
p. 292 low-water[-]mark Unhyphenated elsewhere.
p. 340 [(]_Cetacea_) Added.
p. 390 in firm gelatine[,/.] Corrected.
p. 403 by its stipuled leaves[.] Added.
p. 434 Rhodospermeæ, 350, 355, 38[9] Added.
*** End of this LibraryBlog Digital Book "The Sea Shore" ***
Copyright 2023 LibraryBlog. All rights reserved.
FIG. 94.--THE TRUMPET ANEMONE (_Aiptasia Couchii_),
CORNWALL; DEEP WATER
FIG. 172.--_Rissoa labiosa_ AND _Lacuna pallidula_
FIG. 211.--THE PRAWN (_Palæmon serratus_)
FIG. 222.--SEA SHORE INSECTS
1. _Æpophilus._ 2. _Machilis maritima._ 3. _Isotoma maritima._ 4.
_Cœlopa_