ANCEUS. 183 



But we have not run the risk of such imputation, having 

 carefully examined the structure of the female before 

 the ova were developed, while they were in the ovisac, 

 and after the presence of embryos in the ovi-pouch ; we 

 therefore think it possible that exceptions to a common 

 law may exist in this as well as in other things. 



The ovi-pouch of this genus appears not formed by 

 a series of fine scales attached to the coxae, as in the 

 Amphipoda, but by a thin membrane, that is itself the 

 wall of the ventral surface of the animal, which splits into 

 scales when the embryo is ready to take its departure. 



M. Hesse states the period of incubation to be from 

 twenty to twenty-five days, and sometimes less, and he 

 believes that impregnation takes place prior to the last 

 or adult moult of the animal. This is contrary to our 

 anticipation, and, indeed, contrary to the common law of 

 nature. We have certainly dissected adult animals that 

 have not had the trace of ova. We therefore believe 

 that immediately after the animal has undergone the 

 adult moulting, it ceases from its gormandizing and com- 

 mences breeding, and that, consequently, impregnation 

 takes place immediately after the moult. 



Observers must have noticed that in the younger stage 

 — that is, until the animal ceased to have a digestive ap- 

 paratus — the animal, by feeding, distends the posterior 

 portion of the pereion to a considerable extent, whence 

 M. Hesse says that " sometimes they are so gorged with 

 blood that they become as distended as if they were full 

 of eggs." 



It must strike the physiologist as a remarkable circum- 

 stance, that the part which becomes distended by feeding 

 is not the stomach, which in Crustacea exists in the 

 cephalon, but that part which afterwards becomes the 

 reservoir of the future progeny. 



