INTRODUCTION. xlv 



of depositing her eggs in the water, where, in the more 

 typical forms, the young undergo the transformations 

 essential to the whole group, the changes take place in 

 the oviduct; so may not the young of the land crab, 

 whose habits require them to be speedily in a condition 

 to leave the coast where they are hatched, formally un- 

 dergo the metamorphosis within the egg ? This being 

 granted, it would be as reasonable to deny the pheno- 

 menon of transformation in the amphibia generally, be- 

 cause the young of the salamander are brought forth in 

 the perfect state, as to deny its occurrence in the Crusta- 

 cea, on the analogous exceptional case of the terrestrial 

 Gecarcmus.* 



I do not consider it necessary to examine at any detail 

 the " six arguments" which Mr.Westwood adduces "against 

 the metamorphosis into crabs which the Zoes are stated 

 to undergo," since the facts, exactly as related by Mr. 

 Thompson, have been so fully confirmed by subsequent 

 observers. Indeed, I prefer referring to the whole of 

 Mr. Westwood's elaborate examination of the question, 

 for the information of those who may have the curiosity 

 to see how much may plausibly be urged against the 

 truth of a theory, so irrefragably supported by facts. It 

 is sufficient to say that Mr. Westwood does not attempt 

 to bring forward a single investigation or observation of 

 his own in support of his views, with the exception of 

 that of the land crab, already mentioned.i* 



* Mr. Thompson, in the case of Gecarcinus, as in that of some other West- 

 Indian species, depended for his information upon some specimens of female 

 crabs with matured ova being sent to him in spirits. The ambiguous character 

 of such, observations may warrant us in eliminating them at once from the 

 question. 



t I have thought it necessary to examine Mr. Westwood's objections at 



