No. I.] THE EMBRYOLOGY OF CREPIDULA. 15 



turbans' living there. They appear to breed throughout the 

 whole year." 



2. B7'eeding Habits. 



The breeding season of C. fornicata lasts on the New Eng- 

 land coast from early summer until about August 15. A large 

 proportion of the individuals of this species, examined late in 

 June, were found to have laid their eggs, while none were found 

 with eggs later than the middle of August, though many from 

 widely separated localities were examined. At that time, how- 

 ever, the shells from all these localities were covered by the 

 very small young, or spat, of this species. It may be worth 

 while to remark that the breeding season is always earlier with 

 those individuals found on the shells of Limuli than with those 

 which exist in chains on the sea bottom. This is due, I think, 

 to the fact that in early summer the Limuli are found on 

 shallow, sandy beaches, where the temperature of the water is 

 higher than at a depth of one to six fathoms, where the others 

 are found. The breeding season of C. plana begins somewhat 

 later and lasts longer than that of C. fornicata ; several of the 

 former species were found with newly laid eggs as late as 

 September 7. The egg-laying season of C. convexa lasts 

 through nearly the same period as that of C. plana. 



As is well known, the sexes are separate in these gastero- 

 pods, and the males are fewer in number and smaller than the 

 adult females. Chains of Crepidulas are sometimes found in 

 which there is not a male individual, while isolated females, 

 with from ten to twenty thousand perfectly fertilized eggs, are 

 of frequent occurrence. Considering the sedentary character 

 of these moUusks, the manner of sexual union is an interesting 

 question. There is no doubt that the spermatozoa mingle 

 with the ova before the egg capsules are formed within the 

 oviduct of the female, and yet the mature females are abso- 

 lutely fixed to one spot, and the largest males have very little, 

 if any, power of movement. The smaller the individual is, 

 however, the greater its power of locomotion. The young of 

 both sexes are freely motile, but as they grow larger they lose 

 this power. In C. plana all the males are much smaller than 



