CRUSTACEANS 



In our inland counties the rude forefathers of the hamlet were con- 

 tent with a classification of the animal kingdom in which crustaceans 

 had no share. Apart from a few birds and mammals, aquatic creatures 

 were conveniently grouped as fishes, frogs, and water-fleas. Hermit- 

 crabs that ascend mountains, robber-crabs that climb cocoa-nut palms, 

 river-crabs such as are known in Eastern Europe, and that mischievously 

 abound in Himalayan rice-fields, subtle and audacious land-crabs, like 

 those for which the West Indies are notorious, have no representatives in 

 England. Though our coasts and shores are rich in Brachyura, not a 

 single species either normal or abnormal has ventured to explore and 

 settle beyond the limits which are reached by sea-water. On the other 

 hand, the Macrura, or long-tailed Malacostraca, are represented by a 

 species of no mean interest, the river crayfish. In this, indeed, English- 

 men of the present generation have reason to feel a particular pride. It 

 was made the subject of an introduction to zoology at large by their 

 celebrated countryman, the late Professor Huxley. Wishing to exemplify 

 the general truths respecting the development of his favourite science 

 by the study of a special case, he selected the common crayfish as an 

 animal which, he says, ' taking it altogether, is better fitted for my 

 purpose than any other.' ' It has a further historical importance. In 

 the class of Crustacea there is scarcely any peculiarity more striking or 

 more general than that of exuviation, the sloughing of the outer coat in 

 its entirety. This ecdysis, or putting off of the hardened external 

 cuticular layer, by which the growing crustacean at intervals of its life is 

 enabled to expand its dimensions, has been often studied, but it was first 

 thoroughly investigated by Reaumur in the case of the crayfish. 



Since these animals are superficially, in everything but size, un- 

 commonly like lobsters, it is natural to ask in what the difference consists. 

 Really the distinctions are rather numerous. The rostrum or beak of 

 the crayfish has a single tooth on each lateral margin, that of the lobster 

 has on each side three teeth. In both forms the tail-part or pleon has 

 six articulated segments and a terminal plate called the telson, but this 

 last piece is cut across by a transverse suture or quasi-articulation in the 

 crayfish, and not so in the lobster. In the lobster all the part in front of 

 the pleon, though representing the fourteen segments proper to the head 

 and trunk, is in fact consolidated, but in the crayfish the last of the four- 



1 The Crajfish, an Introduction to the study of Zoology, International Scientific Series, vol. xxviii. 3rd 

 ed. p. 5 (1881). 



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