608 FOURTH REPORT — 1834. 



On the Transformations of the Crustacea. By J. O. West- 

 wood, F.L.S. ^c. 



The object of this communication having reference to one of 

 the three queries relative to the annulose animals, proposed by 

 the Association, was to endeavour to prove the correctness of 

 the views of Rathke, and the consequent want of foundation of 

 those of Thompson: 



1st, By a summary of the recent authorities particularly 

 bearing upon the question ; and 2ndly, by a statement of some 

 facts which had come under the notice of the author himself. 



In the former branch of the subject were mentioned the 

 dissertation of Rathke upon the development of the ova of 

 Asellus aquaticus ; the memoir of Dr. Zencker upon the 

 Gammarus Pulex ; and the more generalized memoir of M. H. 

 Milne Edwards, of which a report by M. St. Hilaire has been 

 published in the Annales des Sciences Naturelles, in which, 

 however, the nature of the transformations of the genera Cy- 

 mothoa, Cyamus, and Phronima is particularly noticed. 



From these works, as well as from Mr. Thompson's own 

 memoirs on My.sis and Arte7nia, and Mr. Coldstream's paper 

 upon Limnoria terebrans, (Jamesons Edinburgh Journal, 

 April 1834,) it is evident that although the more typical Crus- 

 tacea {Malacostraca) undergo a series of moultings, whereby 

 an increase of size, and sometimes a slight increase in the 

 number of locomotive organs are obtained, yet there is no 

 violent change of form similar to the metamorphoses of insects; 

 such, in fact, as it is asserted by Mr. Thompson that even the 

 more tyj^ical Crustacea undergo. 



With reference to the second branch of his notice, the 

 author stated that although the land crab of the AVest Indies 

 was that particular species upon whose habits Mr. Thompson 

 more especially dwelt, as indicating the necessity of metamor- 

 phosis in Crustacea, he had obtained from the collection of 

 the Rev. L. Guilding specimens of the ova and young, just 

 hatched, of that species, and which he had himself extracted 

 from beneath the abdomen of a female, where many hundred 

 others were deposited, the young having all the appearance of 

 the pei-fect animal, and not a single zoe being present. He had 

 also obtained from the same collection zoes nearly an inch 

 long, rather too large to admit of the supposition that they 

 would subsequently be transformed into crabs, and dwindle 

 into the size of the young ones just noticed. 



Thus types of all the great divisions of the Malacostraca have 

 been ascertained to undergo no metamorphosis ; 



