CRUSTACEA. 



185 



the covering of all the most delicate organs, such as 

 tci; yes, antennae, and even branchia: is shed at the 

 same time, we find nut less grounds for astonishment 

 and wonder. The minute Crustacea, whose growth is 

 very rapid, change their coats at very short intervals 

 of time. Thus Jurine observed that the young 

 Daphnes moulted eight, times in seventeen days, but 

 amongst the large species, such as the crabs and 

 lobsters, this only occurs otiee a year. When, there- 

 lore, at the end of the spring, the Cnmlnccn having 

 previously obtained such an increased supply of 

 food, as to make their shells too confined for the 

 increased size of their internal organs, they cast 

 their entire skeleton as we may term it. Previous to 

 doing this, they appear sick, languid and restless, 

 seeking some secluded place, in which they may 

 securely remain until their new covering shall have 

 attained a sufficient consistence. In easting their 

 shells it is difficult, at first sight, to conceive how it is 

 possible that the enclosed claw, for instance, can be 

 so completely drawn out of the old covering, through I 

 the narrow part by which it is attached to the body, : 

 so as to leave the shell of the claw entire, and attached 

 to the cxtivia of the body, in which state they are 

 constantly found. The new shell, however, is at first 

 quite soft and membranaceous, so that we may thereby 

 account for this, circnhrttance, without adopting the 

 opinion of the fisherman, that the lobster pines so 

 much before moulting, that the Mesh of its large claw \ 

 is reduced to the size of a goose quill, which enables, ! 

 it to draw its parts through the joints and narrow 

 passage next the body. Still it is evident, that the 

 forcing of the inclosed claw, even if ever so soft, 

 through so narrow a passage mu^t IK; exceedingly 

 painful. It is to Reaumur that we are indebted for 

 our knowledge of the precise circumstances connected 

 with this curious phenomenon, that distinguished author 

 having imprisoned several cravfish about to moult in 

 pots pierced with holes placed in running water. It 

 is said that it is easy to perceive when the period of 

 moulting is approaching, by pressing the backs of the 

 animals, when the shells yields readily to the pressure 

 of the finger, not offering that, resistance which is 

 common to them. The animals then beat their legs with 

 violence against each other, the body is in a complete 

 agitation, the membranes between the segments being 

 greatly distended, so that the shell is raised consi- 

 derably from the abdomen, the membrane bursting 

 which connects them. By degrees the entire shell 

 and external covering is shed, and in the course of 

 two or three days, or even twenty-four hours, the new 

 skin has acquired its proper consistence. 



Another circumstance of a still more remarkable 

 nature, occurs in the animals we are now treating 

 upon, namely, the reproduction of the claws and legs 

 when accidentally broken off. In some species, indeed, 

 the limbs are so slightly attached, that the least 

 touch causes them to shed them. In like manner it 

 is said that lobsters fear thunder, and are apt to cast 

 their claws on a great clap, and that they will do the 

 same on the firing of cannon ; so that when men of 

 war meet a lobster boat, a jocular threat is used, that 

 if the master does not sell good lobsters they will 

 salute him. In the course of a (lay or two the naked 

 skin exposed by the wound, is found to be covered 

 with a reddish pellicle, which soon assumes a convex 

 surface, grows longer, becomes conical, increases in 

 size, and splitting, exposes to view a soft body, com- 

 posed of the same number of parts as had been lost. 



This soon gains the consistence of the remainder of 

 the body, but never acquires the size of the limb lost 

 although at every subsequent moulting of the skin, 

 its size increases more rapidly than that of the rest of 

 the limbs. 



This curious phenomenon involves, in a singular 

 manner, the principles upon which the moulting of 

 the skin of the annulosa takes place. We are taught 

 that the wings of a butterfly exist in the caterpillar 

 state, and that the legs of the larva of a grasshopper 

 envelope the legs of the perfect insect ; if, therefore, 

 we admit the theory of Swammerdam, founded upon 

 these statements, that every larva at it first exclu- 

 sion, contains within itself the germ of the future 

 imago and of all its envelopes, which, successively 

 presenting themselves, are thrown off, presenting to 

 view the next internal envelope, we shall be com- 

 pelled to establish another theory tor the Crustacea, 

 similar to that of Dr. Heroldt that the successive 

 skins of the larva, pupa case, imago, and its parts and 

 organs, do not pre-exist as germs, but are formed 

 successively from the rete mucosum. Reaumur has, 

 indeed, attempted to explain the causes of this re-pro- 

 duction of limbs ; inquiring, if, at the base of each leg, 

 there may not be a provision of new legs, as in 

 children there is a tooth under the milk tooth ! 

 We are surprised that so acute a reasoner as Reau- 

 mur should not have perceived the incorrectness of 

 such a supposition. It is perfectly natural that the 

 milk teeth are one day destined to fall, and it is 

 natural that their places should be occupied by fresh 

 teeth, which are accordingly provided. But it is per- 

 fectly unnatural merely accidental that the lobster 

 should lose its claws ; and it is equally unnatural to 

 suppose, that nature should have provided a series of 

 organs which, in the majority of instances, would be 

 totally useless, depending only upon accident for their 

 casual development. 



The female Crustacea, after impregnation, deposit 

 a vast number of eggs, which, in many instances, are 

 retained beneath the abdominal portion of the body, 

 whilst in some, as in the opossum shrimps (fifytit), 

 the sea wood-lice (Isopoda), they are retained in a 

 kind of sub-thoracic pouch, and in others they are 

 placed in a membranaceous bag, or pair of bags, 

 dependent from the base of the abdomen, as in the 

 Cyclops, Branchipus, &c. It has been generally stated 

 in all works upon this class, that with a very few 

 exceptions, the young, when hatched from the eggs, 

 closely resemble their parents in form ; these ex- 

 ceptions occurring in Cyclops, the young of which 

 were regarded by Muller as belonging to two dis- 

 tinct genera (Amymome and Nauplius], Argidiis, and 

 Branchipus. Indeed, Dr. Leach, one of the chief 

 investigators of this tribe of animals, has assigned it 

 as one of their principal characters, thai they undergo 

 no metamorphosis. Mr. J. V. Thomson of Cork has, 

 however, lately published a series of memoirs, in 

 which he has announced as an " important discoccry, 

 that the greater number of the Crustacea do actually 

 undergo transformations. The circumstance of the 

 Crustacea being supposed to pass through no inter- 

 mediate form, has been brought forward heretofore as 

 one of the arguments for their separation from insects ; 

 but although the fallacy of that opinion may diminish 

 the number of characteristics which distinguish these 

 two tribes of animals as distinct classes, there yet 

 remains those depending on the anatomical structure 

 of their respiratory and circulating systems, which are 



