17 



December 28, 1830. 



W. Yarrell, Esq. in the Chair. 



The form of a circular letter, to be addressed to the heads of 

 Menageries and Museums in foreign countries, was submitted to 

 the Committee, and approved of. 



A letter was read, addressed to the Secretary of the Society by 

 J. V. Thompson, Esq., dated " Cork, Dec. 16, 1830." In it Mr. 

 Thompson urges, in support of the universality of a metamorphosis 

 among the Crustacea, that he has ascertained the newly hatched 

 animal to be a Zoea in eight genera of the Brachyura, viz. Cancer, 

 Carcinus, Por tunas, Eriphia, Gecarcinus, ThelphusaP, Pinnotheres, 

 and Inachus ; and in seven Macrourous genera, viz. Pagurus, Por- 

 cellana, Galathea, Crangon, Palcemon, Homarus, and Astacus. 

 " These embrace all our most familiar native genera of the Deca- 

 poda." The Lobster, or Astacus marinus, Mr. Thompson states, 

 " does actually undergo a metamorphosis, but less in degree than in 

 any other of the above-enumerated genera, and consisting in a 

 change from a cheliferous Schizopode to a Decapode ; in its first stage 

 being what I would call a modified Zoea with a frontal spine, spatu- 

 late tail, and wanting the subabdominal fins ; in short, such an ani- 

 mal as would never be considered what it really is, was it not 

 obtained by hatching the spawn of the Lobster." In the other 

 indigenous species of Astacus, Ast. fluviatilis, the River Crawfish, it 

 would appear from the excellent treatise of M. Rathke on the 

 development of its eggs, that the young are hatched in a form 

 according with that of the fully grown animal. Mr. Thompson, 

 however, suspects that some source of error may exist in these 

 observations. " If it should be found otherwise, it can only be 

 regarded as one solitary exception to the generality of metamor- 

 phoses, and will render it necessary to consider these two ani- 

 mals for the future as the types of two distinct genera." In il- 

 lustration of the change of form observed by him in the limbs of 

 the Lobster, Mr. Thompson inclosed a sketch of the " cheliferous 

 member of its larva," which is presented as divided to its base, and 

 consisting of, 1 . a cheliferous portion ; 2. a portion of equal length 

 with the preceding and terminated by natatory cilia (described as 

 the outer division of the limb, or future flagrum) ; and 3. a short 

 rudiment of one of the future branchice. 



A specimen of the Labrus maculatus, Bloch, presented to the So- 

 ciety by Sir A. Carlisle, was exhibited. When quite recent, its rich 

 [No. II.] Zool. Soc. Proceedings of Comm. of Science, &c. 



)j> vm 



