236 F. E. CHIDESTER. 



In the male the abdomen is narrow and the intromittent organs 

 or verges are the first pair of abdominal appendages. The paired 

 penes are formed by the everted posterior parts of the efferent 

 ducts. The penes transmit spermatophores down the groove 

 lit the verges into the seminal receptacles of the female. 



In the- virgin female- the abdomen is much like that of the male, 

 except that the telson is narrower. Hay (15) discovered the 

 presence of a pair of hooks which project from the body and fit 

 into a pocket on either side of the abdomen, holding the abdomen 

 tightly flexed against the ventral surface of the carapace. The 

 swimmerets are very small n the virgin female. Crabs moult 

 several times during the summer, according to Herrick (16). 



At the moulting the broad abdomen of the ovigerous female is 

 liberated from its narrow quarters in the old virginal shell, and 

 the female is ready for impregnation. The abdomen of the ovig- 

 erous female is held flexed only by muscular contraction. 



A few days after impregnation, the female may be seen to have 

 two spermatophore plugs projecting slightly from the vaginae 

 and effectually closing the entrance. These plugs are probably 

 secreted by the glands of the male. Andrews has found that the 

 spermatophores of the crayfish are held in the annulus ventralis 

 of the female by plugs secreted by the glands of the male (2). 

 It is not known by me just when the plugs are forced out from 

 the vagina' of the female crab, but probably they are retained 

 until just before the laying. This would be the case if the crabs 

 are to be classed at all with the crayfish in which fertilization is 

 external, and in which the annulus ventralis acts as a temporary 



sperm receptacle. 



SPECIMENS STUDIED. 



I males. 

 M.iles. Virgin. Ovin<-r.m-. With Eggs. 



Blue crabs 3 3 



Rock crabs 3 2 7 i 



Green crabs 2 2 2 



Lady crabs 2 . 2 2 



Iii the above table the virgin females are those that \\ere 

 brought into the laboratory and moulted there. 



Distinction between the ovigerous females showing spermato- 

 phore plugs and tho>e not showing them will be made as tin- 

 experiments are d 



