ON EGGS OF MARINE ANIMALS 35 



readily if taken from the animal. There is no scarcity of Mactra 

 in the Woods Hole region. This i§ a beautiful egg admirably 

 suited for experimental work. 



Pecte7i 



Pecten is monoecious and, in my experience at least, seems 

 to be self-fertilizable. In battery jars each of which contained 

 a single individual I have repeatedly found fertilized eggs which 

 developed into veligers. With suitable food one could doubtless 

 carry these animals through to sexual maturity. This might 

 well repay the effort. 



Crepidula 



Of the three Woods Hole species of Crepidula — plana, forni- 

 cata, and convexa — plana is most commonly used for embryo- 

 logical work. Conklin's studies were made for the most part 

 on the egg of C. plana. 



The breeding season for C. fornicata in the Woods Hole 

 region lasts from early summer to about the middle of August, 

 that of C. plana begins somewhat later and lasts longer. The 

 egg-laying season of C. convexa covers about the same period as 

 that of C. plana. (Conklin, 1897.) 



The fertilized eggs in all three species are laid in capsules. 

 This fact guarantees normal eggs. To obtain the eggs one 

 simply removes and punctures the capsules found beneath the 

 snail. All eggs produced by one female are laid at about the 

 same time. Development from egg-laying to the escape of 

 the veligers is very slow, taking about four weeks in the case of 

 C. fornicata and somewhat longer in C. convexa and C. plana 

 (Conklin, loc. cit.). For problems on determinate cleavage this 

 is an excellent egg. 



Aplysia 



Both at Naples and at Roscoff the large nudibranch, Aplysia., 

 is very common. After having been collected, the animals are 

 placed in pairs in large aquarium jars under gently flowing sea- 

 water. For the early stages of development, it is necessary to 

 keep the animals under observation, especially once copulation 

 has begun, in order to remove the eggs for study and expier- 



