496 COMPARATIVE ANATOMY AND' PHYSIOLOGY. 



organ by means of which they can be carried with 



safety to the body of 

 the female, and here, 

 as in so many of their 

 other organs, we find 

 the crayfish convert- 

 ing some of its ap- 

 pendages into a suit- 

 able apparatus ; the 

 appendages of the 

 first two segments of 

 the abdomen, that is, 

 of the two segments 

 which lie immedi- 

 ately behind that on 

 the base of the ap- 

 pendages of which 

 are placed the male 

 orifices, have their 

 terminal portions 

 converted into styli- 

 form processes, with 

 their edges so folded 

 on themselves as to 

 form each a half- 

 canal. 



In the ovary we 

 find here, as in so 

 many other cases, 

 that one cell in a 

 special set (ovisac) 

 grows to a compara- 

 tively large size at 

 the expense of those 

 that surround and 

 form a coat for it ; 



when this ovum escapes from the ruptured ovisac it 



Fig. 206. Figures of the Male (A) and Fe- 

 male (B) Organs of Astacusfluviatilis. 



ov, Ovary ; od, oviduct ; od', its orifice ; t, testis ; 

 vd, vas deferens ; vd', its orifice. (After 

 Huxley.) 



