INITIATION OF DEVELOPMENT IN NEREIS. 5 



earlier ones) partially broken down. The cytoplasm is normal 

 in color and the membranes normal. 



1:35 P.M., many eggs are in cleavage. 



4:00 P.M., many eggs are in late cleavage. 



June 25, 9:00 A.M. The dishes show a good per cent, of very 

 fine "swimmers." The cleavage seems almost normal. 



Thirty-five minutes' exposure gives by far the highest per- 

 centage of swimming forms. As in all the experiments of this 

 group, some eggs remain in the germinal vesicle stage with 

 cortex intact. 



If eggs be warmed in "egg-water" (sea-water charged by eggs 

 that have remained in it for several hours) the results are no 

 different. 



To sum up, we find that eggs of Nereis cut out in warm sea- 

 water and exposed to temperatures ranging from 33° to 35° C. 

 develop with cleavage which is closely similar to the normal. 

 Some eggs remain in the germinal vesicle stage. For the best 

 percentage of swimming forms the optimum exposure at 35° is 

 twenty-five minutes; at 33°, is thirty-five minutes. 



2. Experiments with Dry Eggs. 



Many of the experiments with dry eggs were run with the 

 washed egg series. In the majority of cases eggs from one female 

 thoroughly dried on clean filter paper were received in a dry 

 watch glass.^ These eggs were divided into two lots; one lot 

 warmed in sea-water at the given temperature and the other 

 washed by changing the sea-water several times, allowed to 

 settle, and after draining placed in the warm sea-water. 



A large number of experiments was made with dry eggs, in the 

 attempt to determine the quantitative relations early found to 

 control the number of eggs developing. Thus, with smaller 

 quantities of warm sea-water every single egg quickly forms jelly 

 and at least ninety-eight per cent, cleave, but with larger quan- 

 tities of warm sea-water the percentages are lower. 



As Miss Allyn found for Chcetopterus cleavage appears to in- 



1 With dry eggs one must be careful for the mere drying will initiate changes as 

 I have found. Eggs left on filter paper for from five to twenty minutes form jelly, 

 a small per cent, cleave and a few swim. 



