METAMORPHOSES. 89 



But it is perfectly 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 develope- 

 ment. 



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 (Mysis), the sea wood-lice (Iso- 

 poda), they are retained in a kind of a 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 exceptions occurring in Cyclops, 

 the young of which were regarded by Muller as belonging to 

 two distinct genera (Amymone and Nauplius), Argulus, and 

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

 tors of this tribe of animals, has assigned it as one of their 

 principal characters, that they undergo no metamorphosis. 

 Mr. J. V. Thompson of Cork, has, however, lately published 

 a series of memoirs, in which he has announced " that the 

 greater number of the Crustacea do actually undergo trans- 

 formations. The circumstance of the Crustacea being sup- 

 posed to pass through no intermediate 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 quite sufficient to render their separation permanent. It 



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