OP METAMORPHOSES IN THE CRUSTACEA. 315 



route back again in their very tender age. Scarcely a stronger confirmation than 

 this very circumstance, of the universality of metamorphosis, could be adduced : for 

 if there were any exception, it would be in the terrestrial species ; but no, they are, 

 when first hatched, incapable of living out of water with swimming members ; hence 

 the parent is impelled by instinct to seek that element for its progeny which Nature 

 has designed for the whole of the tribe to which they belong. Having lived amongst 

 West Indian islands, where these facts were constantly before him, neither he, nor any 

 other person, could invent any plausible reason for this curious piece of economy." 



In the fifth and last place are to be noticed Mr. Thompson's general statements. 

 In the Addenda to his second number he states that he has had a confirmation of 

 his views in one of the West Indian land Crabs, and in some other of our most widely 

 separated native genera, authorizing his previous assertion that the greater number 

 of the Crustacea do actually undergo transformations, of which, in addition to the 

 facts adduced in his first memoir, further instances will be given in future memoirs. 

 On the wrapper of his fourth number he has given a list of some of these promised 

 memoirs, in which we find the Paguri, the Shrimp and Prawn, the genera Porcellana, 

 Gegarcinus, Hydrodomus, and other genera of land Crabs and Pinnotheres, all stated 

 to undergo various remarkable metamorphoses ; and in the nineteenth number of 

 the Zoological Journal he states that the newly hatched young of the following Bra- 

 chyurous genera. Cancer, Carcinus, Portunus, Eryphia, Gegarcinus, Thelphusa}, 

 Pinnotheres, and Inachus, have been ascertained to be Zoes by himself; and that the 

 following Macrourous genera are likewise subject to metamorphosis, viz. Pagurus, 

 Porcellana , Galathea, Crangon, Palemon, Homarus, Astacus. ! 



Such are the various circumstances upon which Mr. Thompson has built his theory 

 of metamorphosis. I have given them at rather an inconvenient, but not an unne- 

 cessary length, and as far as possible in his own words, in order that I might be free 

 from any charge of misrepresentation in the observations which I may think it ne- 

 cessary to make upon each of them, with a view to prove that the theory is without 

 foundation. 



For this purpose I propose, in the first place, to enter into a review of Mr. Thomp- 

 son's observations, whence alone I conceive that no sufficient ground is raised for 

 the establishment of the theory in question. In the second place, I propose to col- 

 lect the recent views of the most celebrated crustaceologists, all of whom have ad- 

 vanced opinions to the like effect. And in the third place, I shall bring forward 

 some circumstances observed by myself having a precisely similar tendency. 



In the first place, therefore, I have to endeavour to prove from Mr. Thompson's 

 own statements and figures, that there is not sufficient foundation for the theory of 

 metamorphosis, and for this purpose I shall take in review seriatim the several cir- 

 cumstances which he has mentioned and above alluded to. 



And first with respect to the metamorphosis into Crabs which the Zoes are stated 

 to undergo, against which six arguments may be adduced. 



