ON OUK 1'RESENT KNOWLEDGE 01' THE CRUSTACEA. 53 



the appendages are not very much larger at the extremity than they are at 

 the points of articulation. 



Tho late Mr. Couch, who, at his place of residence, had valuable oppor- 

 tunities for studying marine animals under various conditions, gave much 

 attention to this subject. 



In the Report of the Royal Polytechnic Society for Cornwall for tho year 

 1843 is a communication on tho process of exuviation in Crabs and Lobsters, 

 by J. Couch, Esq., and again, in the Journal of the same Society, is a paper 

 giving an account of "A particular Description of some circumstances 

 hitherto little known connected with the process of Exuviation in the 

 common Edible Crab," by Jonathan Couch, Esq., E.L.S. &c. (1852). This 

 last memoir chiefly refers to the manner in which the animal withdraws the 

 large claws from the old shell. 



Bell says, in his Introduction to his ' History of the British 

 Stalk-eyed Crustacea,' p. xxxv, that " It is impossible to imagine 

 that the crust of the legs, especially of the great claws of the larger 

 species, could be cast off unless it were susceptible of being longitudi- 

 nally split ; and Reaumur states that such is actually the case, each of tho 

 segments being composed of two longitudinal pieces, which, after separating, 

 to allow of the passage of the soft limb, close again so accurately that it is 

 very difficult in the last crust to discover the line of division. When the 

 animal has disembarrassed itself of the crust, the latter is found absolutely 

 entire, and has exactly the form which it possessed previous to the opera- 

 tion." 



In the ' Annals of Nat. Hist.' 2nd ser. vol. x. p. 210, Mr. Gosse, in his ac- 

 count of the exuviation in Maia squinado, states that the animals withdrew 

 the legs, first one and then another, until they were quite out, as if 

 from boots. The joints as they came oirt were a great deal larger than the 

 cases from which they proceeded. It 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. 



It is this point which the late Mr. Jonathan Couch took up in his last 

 memoir alluded to. He Avrites : — " That in my former studies of this process 

 I had myself overlooked or misapprehended the mode by which the claw- 

 legs were withdrawn from the loosened crust, is in the first place to be ascribed 

 to the fact that my attention was chiefly occupied with what was going on 

 in the body and its immediate organs, the eyes, antennse, and inward frame ; 

 and in the next place to the circumstance that the portions of the legs 

 which alone answer to Reaumur's description in any degree are by their 

 situation hidden below the under portion of the carapace, to which they arc 

 pressed close by the principal joints of the legs themselves, so that they could 

 not have been attended to without a greater degree of violence than I judged 

 myself warranted in using with due regard to the other observations I was 

 desirous of carrying out. 



" It was evident, from an inspection of the proceeding in this specimen," — 

 a female (technically a bon crab) of the stage of growth only one degree 

 short of the full size, — " that Mr. Gosse's statement relative to the withdrawal 

 of the smaller legs is correct, and therefore the language quoted from Re'aumur 

 will not correctly express what takes place in the Common Crab ; nor, I be- 

 lieve, for reasons presently to be assigned, even in the species on which his 

 observations were made — the River Crayfish. The bony covering, where 

 this remarkable process takes place, is not simply divided by splitting, but by 

 a far more complicated action, which yet is beautifully expressive of tho 



