XXXVI INTRODUCTION. 



was evident that, in this instance, neither were the shells 

 split to afford a lateral passage for the limbs, nor were the 

 limbs reduced to tenuity by emaciation." The new in- 

 tegument is at first soft and membranous, but speedily 

 becomes encrusted with calcareous matter, and as hard 

 as the former. The additional size which is gained by 

 each moult is very striking, and I have often felt, on 

 seeing a newly-emancipated crab by the side of the shell 

 which it had just shed, that, were not the fact absolutely 

 ascertained by observation, it would appear physically im- 

 possible that the larger body could have so recently been 

 contained within so small a case. Reaumur supposed 

 that even the hairs with which the surface is in many 

 species furnished, were contained within the cast crust; 

 but Dr. Milne Edwards asserts that such is not the case ; 

 stating that they are not at first obvious on the surface of 

 the new shell, but " sont rentres a 1'interieur, comme le 

 doigt d'un gant qui serait retourne sur lui-meme ! " If we 

 open, says this author, a Maia a short time before the 

 commencement of the moult, we find between the exist- 

 ing shell and the " chorion " a membranous layer, which 

 resembles condensed cellular tissue, and which becomes 

 thicker and more solid, as the period of moult approaches; 

 it is evidently secreted by the chorion, and is moulded 

 upon the shell which covers it. In the common crab 

 (Cancer Pagurus], and some others of similar form, it 

 would appear that the carapace, instead of being cast 

 entire, divides at the junction of the epimera with the 

 dorsal piece or tergum ; a fact which I have often seen in 

 many species, particularly in the larger Grapsidoe, which, 

 from their form, could not possibly withdraw the body 

 without such a separation. 



