ON EGGS OF MARINE ANIMALS 33 



laid is capable of fertilization, but if one cuts up the animals to 

 procure the eggs, one obtains mature eggs, inactive eggs and 

 coelomic corpuscles. (Scott, 1906,) 



The case of Amphitrite, one of the most interesting that 

 I know, recalls the precision of the egg-laying in Echinorhynchus, 

 where only fertilized eggs, among the fertilized and unfertilized 

 which the uterine bell takes up, pass outside the female. 



Phascolosoma gouldii 



Phascolosoma eggs are best when laid. On one occasion only, 

 in 191 1, was I able to fertilize eggs obtained by cutting up 

 the animals to procure gametes. Eggs and sperm thus obtained 

 are mixed with innumerable coelomic corpuscles; shed eggs and 

 sperm are free of them. 



Phascolosoma vulgare and Ph. elongatum 



At Roscoff, Phascolosoma vulgare and Ph. elongatum are best 

 when shed. (For all three forms of Phascolosoma, see Gerould, 

 1907.) 



Cumingia 



Workers who use Cumingia are indebted to Dr. Gilman A. 

 Drew, formerly assistant director of the Marine Biological Labo- 

 ratory, Woods Hole, for the method of obtaining the eggs. 



The animals are collected at low tide, kept in mud, protected 

 from rise in temperature, and brought to the investigator as 

 quickly as possible. They are placed under running water for 

 about fifteen minutes or until wanted. Each animal is now 

 transferred to a separate dish — the females in finger bowls con- 

 taining about 200 cc. of sea-water, the males in dishes of about 

 50 cc. capacity. I distinguish the sexes by the color of the 

 sexual elements seen through the shells: females show a salmon 

 pink, the males a dead white color. If the animals are not dis- 

 turbed, in less than half an hour they set free their eggs and 

 sperm. I pipette the eggs off as soon as they are shed. Insemi- 

 nations should be made from a thin sperm-suspension. 



Ensis 



The eggs of E?isis resemble greatly those of Cumingia. 

 They may be obtained in abundance and with ease, especially 



