INFANCY OF CRABS AND CATERPILLARS 239 



adult is assumed, and from thence onward, by a series of 

 moults, the characteristic shape of the shore crab is put on. 

 But this only after a long and numerous series of moults, 

 as seen in our illustration, which shows all the cast-off shells 

 worn by a young crab during a period extending from 

 June 13, 1901, to July 20, 1904, when the captive died, 

 still, so to speak, in infancy. On the average it will be 

 seen, from the first appearance of the crab stage tiU death, 

 there were sixteen moults ; and no one has yet discovered 

 how many moults take place from the hatching of the 

 egg onwards to the end of the megalopa stage. 



But more remarkable is the history of the prawns of 

 the genus Peneeus. So long ago as 1863 Fritz Miiller 

 found that the young of Peneeus left the egg in what is 

 known as the Nau-plius stage — a form of larva hitherto 

 unknown save among those minute Crustacea the Copepoda, 

 and the cirripedes or barnacles. Herein the body is 

 pear-shaped, and there are only three pairs of limbs. 

 These limbs, however, do not answer to legs, but to the 

 antennules, antennae and jaws of later stages of develop- 

 ment ! These organs, in the adult, are about as unlike 

 as can be, yet in the larva they are hardly distinguishable 

 one from another ! 



The antennae of the nauplius in fact serve as jaws till 

 they are eventually replaced, in the adult, by the mandibles. 

 Finally, at this stage of development there is only a single 

 eye, which is placed in the middle of the head. From 

 the nauplius stage this larva passes through a " meta- 

 nauplius " to the " zoea " stage, thus undergoing a series 

 of most striking changes of form. Then follows the 

 " schizopod " stage, which is the last step towards the 

 adult Peneeus^— a. near relation of the highly esteemed pink 

 shrimp ; but the swimmerets, it will be noted, have not 



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