in.] METAMORPHOSES OF INSECTS. 53 



forms, and O. F. Miiller gave them the name of Nau- 

 plius. So also, the second or Zoe'a form (Fig. 38) was 

 at first supposed to be a mature animal, until its true 

 nature was discovered by Vaughan Thompson. 



The Zoe'a form of larva differs from the perfect 

 prawn or crab in the absence of the middle portion of 

 the body and its appendages. The mandibles have 

 no palpi, the maxillipeds or foot-jaws are used as 

 feet, whereas in the mature form they serve as jaws. 

 Branchiae are either wanting or rudimentary, respira- 

 tion being principally effected through the walls of 

 the carapace. The abdomen and tail are destitute of 

 articulate appendages. The development of Zoe'a 

 into the perfect animal has been well described by 

 Mr. Spence Bate 1 in the case of the common crab 

 ( Ca rein us 111 cenas) . 



All crabs, as far as we know, with the exception of 

 a species of land crab (Gegarcinus\ described by 

 Westwood, pass through a stage more or less re- 

 sembling that shown in Fig. 38. On the other hand, 

 the great group of Edriopthalma, comprising Amphi- 

 poda (shore-hoppers, &c.) and Isopoda (wood-lice, &c.) 

 pass through no such metamorphosis ; the develop- 

 ment is direct, as in the Orthoptera. It is true that 

 one species, Tanais Dulongii, though a typical Isopod 

 in form and general character, is said to retain in some 

 points, and especially in the mode of respiration, 

 some peculiarities of the Zoe'a type ; but this is quite 

 .an exceptional case. In Mysis, says F. Miiller, 2 

 " there is still a trace of the Nauplius stage ; being 



1 Philosophical Transactions, 1859, p. 589. 



2 "Facts for Darwin," Eng. Trans, p. 127. 



