The Crayfish: An Introduction to the Study of Zoology.

by Thomas Henry Huxley

LIST OF WOODCUTS.

• [Frontispiece.] THE COMMON CRAYFISH, Astacus fluviatilis, (MALE)
• [1]. Astacus fluviatilis. SIDE VIEW OF THE MALE • 6
• [2]. — — DORSAL VIEWS OF MALE AND FEMALE • 18
• [3]. — — VENTRAL VIEWS OF MALE AND FEMALE • 21
• [4]. — — THE GILLS • 26
• [5]. — — DISSECTION FROM THE DORSAL SIDE (male) • 28
• [6]. — — LONGITUDINAL VERTICAL SECTION OF THE ALIMENTARY CANAL • 29
• [7]. — — A GASTROLITH OR “crab’s EYE” • 30
• [8]. — — ATTACHMENT OF YOUNG TO SWIMMERET OF MOTHER • 41
• [9]. — — STRUCTURE OF THE STOMACH • 53
• [10]. — — LONGITUDINAL SECTION OF THE STOMACH • 56
• [11]. — — ROOF OF THE STOMACH, FROM WITHIN • 60
• [12]. — — DISSECTION FROM THE SIDE (male) • 62
• [13]. — — ALIMENTARY CANAL FROM ABOVE • 65
• [14]. — — BLOOD CORPUSCLES • 68
• [15]. — — TRANSVERSE SECTION OF THORAX • 70
• [16]. — — THE HEART • 72
• [17]. — — STRUCTURE OF THE GILLS • 76
• [18]. — — THE GREEN GLAND • 83
• [19]. — — MUSCULAR TISSUE • 91
• [20]. — — MUSCLES OF CHELA • 93
• [21]. — — ARTICULATION OF ABDOMINAL SOMITES • 97
• [22]. — — MUSCULAR SYSTEM • 100
• [23]. — — NERVE FIBRES • 102
• [24]. — — NERVE GANGLIA • 103
• [25]. — — NERVOUS SYSTEM • 104
• [26]. — — OLFACTORY AND AUDITORY ORGANS • 114
• [27]. — — AUDITORY SAC • 117
• [28]. — — STRUCTURE OF EYE • 119
• [29]. — — DIAGRAM OF EYE • 123
• [30]. — — FEMALE REPRODUCTIVE ORGANS • 129
• [31]. — — MALE REPRODUCTIVE ORGANS • 130
• [32]. — — STRUCTURE OF OVARY • 131
• [33]. — — STRUCTURE OF TESTIS • 132
• [34]. — — SPERMATOZOA • 134
• [35]. — — THE LAST THORACIC STERNUM IN THE MALE AND FEMALE • 136
• [36]. — — TRANSVERSE SECTION OF ABDOMEN • 142
• [37]. — — ABDOMINAL APPENDAGES • 144
• [38]. — — CONNECTION BETWEEN THORAX AND ABDOMEN • 151
• [39]. — — CEPHALOTHORACIC STERNA AND ENDOPHRAGMAL SYSTEM • 153
• [40]. — — OPHTHALMIC AND ANTENNULARY SOMITES • 156
• [41]. — — THE ROSTRUM • 157
• [42]. — — A SEGMENT OF THE ENDOPHRAGMAL SYSTEM • 159
• [43]. — — LONGITUDINAL SECTION OF CEPHALOTHORAX • 162
• [44]. — — THE THIRD MAXILLIPEDE • 164
• [45]. — — THE FIRST AND SECOND MAXILLIPEDES • 166
• [46]. — — THE SECOND AMBULATORY LEG • 169
• [47]. — — THE MANDIBLE AND MAXILLÆ • 171
• [48]. — — THE EYE-STALK, ANTENNULE, AND ANTENNA • 172
• [49]. — — BLOOD CORPUSCLES • 176
• [50]. — — EPITHELIUM • 178
• [51]. — — CONNECTIVE TISSUE • 179
• [52]. — — MUSCULAR TISSUE • 181
• [53]. — — MUSCULAR TISSUE • 182
• [54]. — — NERVE GANGLIA • 188
• [55]. — — NERVE FIBRES • 189
• [56]. — — CUTICULAR TISSUE • 191
• [57]. — — SECTIONS OF EMBRYOS • 208
• [58]. — — EARLIER STAGES OF DEVELOPMENT • 210
• [59]. — — LATER STAGES OF DEVELOPMENT • 216
• [60]. — — NEWLY HATCHED YOUNG • 220
• [61]. Astacus torrentium, Astacus nobilis, and Astacus nigrescens. COMPARATIVE VIEWS OF THE CARAPACE, THIRD ABDOMINAL SOMITE, AND TELSON • 233
• [62]. — —, — —, and — — COMPARATIVE VIEWS OF THE FIRST AND SECOND ABDOMINAL APPENDAGES OF THE MALE • 245
• [63]. Cambarus Clarkii • 248
• [64]. Parastacus brasiliensis • 250
• [65]. Astacoides madagascarensis • 251
• [66]. DIAGRAM OF THE MORPHOLOGICAL RELATIONS OF THE Astacidæ • 253
• [67]. Homarus vulgaris • 258
• [68]. Parastacus, Nephrops, and Palæmon. PODOBRANCHIÆ • 259
• [69]. Nephrops norvegicus • 260
• [70]. Palinurus vulgaris • 262
• [71]. Palæmon jamaicensis • 269
• [72]. Cancer pagurus • 273
• [73]. Penæus • 281
• [74]. Cancer pagurus. DEVELOPMENT • 282
• [75]. Astacus leptodactylis • 301
• [76]. Australian Crayfish • 307
• [77]. MAP OF THE DISTRIBUTION OF CRAYFISHES • 309
• [78]. Cambarus. WALKING LEG • 312
• [79]. Palæmon jamaicensis • 329
• [80]. Pseudastacus pustulosus and Eryma modestiformis • 340
• [81]. Hoploparia longimana • 342

THE CRAYFISH:
AN INTRODUCTION TO THE STUDY OF ZOOLOGY.

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CHAPTER I. THE NATURAL HISTORY OF THE COMMON CRAYFISH
(Astacus fluviatilis.)

MANY persons seem to believe that what is termed Science is of a widely different nature from ordinary knowledge, and that the methods by which scientific truths are ascertained involve mental operations of a recondite and mysterious nature, comprehensible only by the initiated, and as distinct in their character as in their subject matter, from the processes by which we discriminate between fact and fancy in ordinary life.

But any one who looks into the matter attentively will soon perceive that there is no solid foundation for the belief that the realm of science is thus shut off from that of common sense; or that the mode of investigation which yields such wonderful results to the scientific investigator, is different in kind from that which is employed {2} for the commonest purposes of everyday existence. Common sense is science exactly in so far as it fulfils the ideal of common sense; that is, sees facts as they are, or, at any rate, without the distortion of prejudice, and reasons from them in accordance with the dictates of sound judgment. And science is simply common sense at its best; that is, rigidly accurate in observation, and merciless to fallacy in logic.

Whoso will question the validity of the conclusions of sound science, must be prepared to carry his scepticism a long way; for it may be safely affirmed, that there is hardly any of those decisions of common sense on which men stake their all in practical life, which can justify itself so thoroughly on common sense principles, as the broad truths of science can be justified.

The conclusion drawn from due consideration of the nature of the case is verified by historical inquiry; and the historian of every science traces back its roots to the primary stock of common information possessed by all mankind.

In its earliest development knowledge is self-sown. Impressions force themselves upon men’s senses whether they will or not, and often against their will. The amount of interest which these impressions awaken is determined by the coarser pains and pleasures which they carry in their train, or by mere curiosity; and reason deals with the materials supplied to it as far as that interest carries it, and no farther. Such common {3} knowledge is rather brought than sought; and such ratiocination is little more than the working of a blind intellectual instinct.