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Memoir on the Metamorphoses in the Macrourae or Long-tailed 

 Crustacea, exemplified in the Praxvn {PalcBmon serratus). 

 By W. V. Thompson, Esq., F. L. S., Deputy Inspector- 

 General of Hospitals. (Communicated by Sir James Mac- 

 Grigok, Bart. M. D., F. R. S., &c.) With a Plate. 



Having in my Zoological Researches, and in subsequent 

 memoirs, fully developed the metamorphoses in the Brachyurae 

 or crabs, I am happy to have it in my power to make known 

 similar changes in the Macrourae, and which have been traced 

 in the prawn in a very satisfactory manner, as well as in the 

 shrimp, and some others of this tribe of the Crustacea ; in all of 

 which the larva, although different from that of the crabs, is 

 nevertheless a Shizopoda, generally of a totally different aspect 

 from the parent animal, and provided at first with a very limited 

 number of cleft members, commonly two or three pair, perfectly 

 analogous to those of the Zoe ; these larvae, it must be farther 

 observed, do not, in their subsequent stages, become MegalopcB, 

 like those of the crabs, but appear to undergo a successive de- 

 velopment, probably embracing several stages. 



For several seasons previous to 1828, I had repeatedly met 

 with* animals in the harbour of Cove, so exactly similar to 

 Slabber's metamorphosed Zoe (Zool. Res. pi. 1. fig. 1, h), and 

 scarcely doubting the accuracy of his observations at that time, 

 that I wished for an opportunity of verifying the fact by similar 

 attentions bestowed upon some zoea, the result of which turning 

 out so contrary to my just expectations, (as given Zool. Res. 

 mem. 1st, p. 8), it still remained a desideratum to know what 

 this nondescript really was ; the most probable conjecture being 

 that it might prove the intermediate stage of some of the Ma- 

 crourae. 



The summer of 1828 put me in possession of this interesting 

 information ; for by hatching the ova of the prawn, it was dis- 

 covered to be the first stage of that animal ! numbers of them 

 being excluded while actually under observation (as represented 

 Fig. 1.) ; thus proving that the Macrourae are also subject to 

 metamorphosis, but that the larva bears no farther relation to 



VOL. xxr. NO. xLii. — OCTOBER 1836. a 



