INITIATION OF DEVELOPMENT IN NEREIS. II 



these eggs again subjected to heat; no results. July 12. Very 

 fgw, I in 1000, swimming. 



(b) July 15, 3:20 P.M. Eggs cut out and washed, put in 6 

 c.c. of sea-water warmed at 35° C. Samples taken at five-minute 

 intervals for forty minutes. Next day: Majority are in germinal 

 vesicle stage, at least seventy-five per cent. Less than one per 

 cent, swimming. 



(c) July 16, 9:35 A.M. Eggs washed ten times evening before 

 and five times during this morning. Two series: A inseminated, 

 B in warmed sea-water at 3 :50 samples taken (ten in all) at five- 

 minute intervals. Uninseminated control. 



July 17, 1 :30 P.M. No development in uninseminated control 

 (few have cytolyzed). Inseminated eggs show that few have 

 formed jelly (ten to fifteen per cent.) . One per cent, have cleaved 

 and some of these swim. Of the warmed eggs at least ninety-five 

 per cent, are in the germinal vesicle stage with cortex intact. 

 Less than one per cent, have formed polar bodies. ' 



(d) July 16, 10:30 A.M. Eggs from a dried female divided in 

 two lots; one lot washed in 100 c.c. of sea-water by changing the 

 water four times. 10:40 A.M. In warmed sea-water, 34° C. 

 Samples out at five-minute intervals for sixty minutes. 



2:00 P.M. At least ninety per cent, in the germinal vesicle 

 stage, small per cent, form jelly and divide. Next day, none 

 swim. 



I was tempted to discredit my June experiments after the first 

 of these findings, I could only convince myself after running 

 series after series of washed and dry eggs along with eggs cut out 

 directly into warmed sea-water. Most workers in inseminating 

 eggs obtain the sexual products in separate dishes, and add sperm. 

 Such procedure succeeds admirably with Nereis giving one 

 hundred per cent, of cleavage. But if eggs be cut out of Nereis 

 in sea-water, divided in two lots, and washed once or twice, one 

 lot being inseminated and the other warmed we get the surprising 

 result that while every single inseminated egg develops, few of the 

 warmed go beyond maturation. If the water over the eggs be 

 changed a few times in ten minutes, ninety per cent, warmed in 

 sea-water fail even to maturate. 



This must mean that the egg of Nereis is so susceptible to 



