MR. Thompson's observations doubtful. 91 



iiiigration of the land crabs of the West Indies to deposit 

 their eggs in the water. Mr. Thompson has subsequently 

 jmblished several memoirs in the Entomological Magazine, 

 and elsewhere, in which he has stated that the eggs of other 

 Decapods jjroduce various kinds of Zoeaj. I have here 

 given Mr. Thompson's observations at some length, because 

 the facts, if fully established, are highly interesting. It is 

 proper, however, to state, that Dr. Rathke has, in a series of 

 microscopic observations, far more elaborate than any hitherto 

 published by Mr. Thomi)son, clearly shown the gradual de- 

 velopement of the cray-fish within the egg, and which, upon 

 bursting into life, possesses all the form of its parent, and 

 has also announced a memoir* in opposition to Mr. Thomp- 

 son ; whilst the Rev. Lansdown Guilding has expressly 

 stated that the land crabs do not undergo any metamorphosis 

 [Mag. Nat. Hist., May, 1835) ; and in a memoir which I have 

 published in the Philosophical Transactions for 1835, I have 

 fully confirmed GuikUng's statement : thus, two examples in 

 the great div^sions of Br achy lira and Macroura are shown to 

 militate against Mr. Thompson's assertion, that the Crustacea 

 universally undergo metamorphosis ; and, as the organization 

 of those two animals is so completely analogous to that of 

 the common crab (the young of which Mr. Thompson affirms 

 to be a Zoea) and the rest of the Decapoda, I cannot but 

 think that Mr. Thompson must have fallen into some funda- 

 mental error in his observations ; at least, it is certain that 

 the researches of Mr. Thompson are made without any of 

 that analytical precision which is so obnously reqidsite in 

 such a matter. It would, indeed, be a remarkable thing, 



* " As to the Decapods, so far as I have examined their developement, 

 I must deny such an assertion [as that made by Mr. Thompson] ; and of 

 them I can say nothing less than that, at the end of tlieir existence in the 

 egg, they have exactly the same aspect, and are as fully developed, as the 

 full-grown individuals."— Rathke. 1837. Annols Nat. Hist. 



