COMMON RIVER CRAYFISH. 239 



subject of the moult of Crustacea ; and to Rathke the 

 subject of his observations on the growth and development 

 of the embryo. The general facts thus observed, and their 

 bearing upon the two interesting subjects to Avhich they 

 refer, will be found treated of in the Introduction to this 

 work. 



Their food consists of aquatic mollusca, the larva? of 

 insects, and even of small fish ; and they also do not 

 refuse any dead animals which may lie within their reach 

 in the water. They generally appear to require the 

 continual renewal of the respiratory fluid ; and hence 

 are generally found inhabiting running streams and 

 rivers, in which they conceal themselves in holes in the 

 banks. They change their crust annually, towards the 

 end of spring, and, like all their congeners, they grow 

 rapidly for a time after this change, and become fleshy 

 and full. 



My friend, Mr. Ball of Dublin, has favoured me with 

 the following amusing and graphic account of an indivi- 

 dual of this species, which he kept in confinement : " I 

 once had a domesticated cray-fish, Astacus fuviatilis, 

 which I kept in a glass pan, in water not more than 

 an inch and a half deep ; previous experiments having 

 shewn that in deeper water, probably for want of suffi- 

 cient aeration, this animal would not live long. By 

 degrees my prisoner became very bold ; and when I held 

 my fingers at the edge of the vessel, he assailed them 

 with promptness and energy. About a year after I had 

 him, I perceived, as I thought, a second cray-fish with him ; 

 on examination, I found it to be his old coat, which he had 

 left in a most perfect state. My friend had now lost his 

 heroism, and fluttered about in the greatest agitation. 

 He was quite soft ; and every time I entered the room. 



