10 E. E. JUST. 



Without going into details, it may be said at the outset that 

 the egg of Nereis gradually loses its power of being fertilized and 

 eventually reaches the condition of the Platynereis egg where in- 

 semination induces maturation only. I cite a single experiment. 



June 28, 9:10 P.M. Dishes of eggs Nos. i, 2, and 3 were set 

 aside. The next day at 2 :io P.M. each dish of eggs was drained 

 and divided into two lots — A and B. Lot A in each case was 

 inseminated in the water- which had stood over the eggs for seven- 

 teen hours. Lot B of each dish was inseminated in fresh sea- 

 water. No eggs in either lot of No. i developed beyond matur- 

 tion. In Lots A and B of Nos. 2 and 3, .1 per cent, or less went 

 as far as the two-cell stage. Some eggs in all the dishes were in 

 the germinal vesicle stage. No trochophores were found. 



Eggs were frequently tied in bags of filter paper and placed 

 in a beaker under running water for twelve hours. In other 

 cases they were washed by changing the water at odd times during 

 the day. It was found that eggs differ greatly with respect to 

 the time that they must remain in sea-water before they lose 

 their fertilizing power, but it may be clearly proved that washing 

 or staling of Nereis eggs renders them incapable of being fertilized. 

 This stage may be reached after three hours in seawater (cf. 

 Just, '12): 



This varying susceptibility proved very disappointing because 

 I had suspected, not, of course, the degree of susceptibility present 

 in Platynereis, but perhaps such as could be expressed more 

 definitely. 



Because of these results with washed and stale egg insemina- 

 tion, when the warm sea-water experiments were continued during 

 the July Nereis "run" I was certainly unprepared for the results 

 obtained. The following experiments are typical of a large 

 number performed almost daily during the July and August 

 "runs": 



{a) July II, 9:50 A.M. Eggs from one female divided into 

 two lots; one lot put in sea- water. This lot transferred from the 

 sea-water to warmed sea-water (35° C). The eggs form jelly in 

 the warm sea-water and make a mass which has to be shaken to 

 obtain samples. 10:55, many have formed jelly and maturated, 

 but most retain jelly with germinal vesicle intact. Some of 



