OP METAMORPHOSES IN THE CRUSTACEA. 313 



generally received opinion amongst naturalists, that the transformations of the Crus- 

 tacea consist merely in the periodical shedding of the outer envelope, without any 

 metamorphosis being undergone or additional organs acquired. 



The object of the following pages is therefore to endeavour to ascertain whether 

 this opinion be correct or not ; and in order to do this satisfactorily we shall be 

 obliged to test such observations which may negative its correctness, by the applica- 

 tion of those general principles which, as we have seen, regulate the transformations 

 or other changes of the Annulosa. 



The non-existence of transformations in the Crustacea in general has been asserted 

 "by every crustaceologist, with the exception of a recent author, John V. Thompson, 

 Esq., F.L.S., (the accuracy of whose beautiful figures deserves the highest praise,) and 

 by whom, in the first and succeeding numbers of the Zoological Researches, the dis- 

 coveiy that the greater number of the Crustacea do actually undergo metamorphoses 

 of a very peculiar kind, and of a totally different description from those of insects, 

 has been announced. " So little has this been suspected by naturalists," observes this 

 author*, "that the contrary has been assigned as one of the distinctive characters 

 of the class, and been used as an argument for their separation from insects." 



Mr. Thompson's views are founded upon some circumstances exhibited by some of 

 the most singular animals hitherto ascertained to belong to the class, (which consti- 

 tute the genus Zoea of Bosc,) as recorded by Slabber or Mr. Thompson himself, as 

 well as upon some other circumstances respecting other portions of the class. These 

 consist. 



In the first place, in a supposed change which the Zoes are reputed to undergo ; 

 respecting which Mr. Thompson (after alluding to the observations of Slabber, which 

 he thinks erroneous,) thus expresses himself: "After keeping a full-grown Zoe for 

 more than a month, it died in the act of changing its skin and of passing into a new 

 form, but one by no means similar to that expected [from the previous observations 

 of Slabber], as appears evidently by its disengaged members, which are changed in 

 number as well as in form, and now correspond with those of the Decapoda (Crabs, 

 &c.), viz. five pair, the anterior of them furnished with a large claw or pincer : the 

 metamorphosis not having been completed, prevented any knowledge being acquired 

 of its general form ; enough, however, has been gained to show that the distinctive 

 characters of Zoea and of Slabber's changed Zoea were entirely lost ; that the mem- 

 bers, from being natatory and cleft (as shall shortly be shown), become simple and 

 adapted to crawling only. On the 1st of May another large Zoea was taken, and 

 dying towards the end of the month without having the strength to disengage itself 

 from the exuvium, presented precisely the same results with the former^-." In the 

 account of the figures of this full-grown Zoe, "behind the corselet the rudiments 

 of the limbs of the perfect animal, or Crab," are described as " beginning to show 

 themselves J;" but on comparing this figure with that of the newly hatched "Zoe, 



* Zool. lUustr., p. 7. t Ibid., pp. 8, 9. X Ibid., p. 33. 



2 s2 



