240 



ERNEST E. JUST. 



nucleus intact until inseminated or otherwise stimulated as for 

 instance, by squirting forcibly through a pipette. 



Two or three minutes after insemination, a jelly is rhythmically 

 extruded from the cortical protoplasm. In ten minutes the 

 germinal vesicle breaks down, development is initiated. 



Males and females captured in the evening while swimming at 

 the surface of Eel Pond were kept in separate dishes until morning 

 when they were transferred to fresh clean sea-water. To get an 

 abundance of eggs and of sperm for an experiment, it was merely 

 necessary to cut open a female and a male. The cut animals 



FIG. i. Egg of Nereis at time of insemination; polar view. 

 FIG. 2. Maturation stage; second membrane formed; oil drops at vegetative 

 pole. 



were removed from the dishes at once; moreover, every other 

 precaution was taken to avoid abnormalities superinduced 

 through toxic influences, mechanical shock, etc. In several 

 watch glasses of sea water in which India ink had been ground 

 up eggs were put together with a minute quantity of sea water 

 containing very few spermatozoa. The time of insemination \\ .1^ 

 noted and the numbered dishes observed to the second cleavage. 

 This method was varied somewhat as I shall later note. 



Kinged slides also were used; eggs placed on these in SIM water 

 and ink were inseminated. Sometimes a cover slip was placed 

 on the eggs. Finally, for the later observations a very few eggs 

 were placed on slides and the cover slips supported with glass rods. 



