404 Ralph S. Li Hie 



3 h. 45 m. later they were warmed to 35° for the periods indi- 

 cated. 



In the unfertilized unwarmed control at 6:23 p.m. the eggs 

 remained quite uncoagulated; warming has thus hastened the 

 coagulative change in the mature eggs, and especially in those with 

 membranes, which uniformly showed the most advanced disinte- 

 gration. 



What are the conditions of this varying susceptibility to the 

 above form of treatment at these different periods in the life of 

 the unfertilized egg ^ One event, occurring shortly after the 

 removal of the egg from the animal to normal oxygen-containing 

 sea-water, seems of fundamental significance, viz: the dissolution 

 of the membrane of the immature egg-nucleus or germinal vesicle. 

 This event naturally must precede the maturation divisions that 

 follow; but quite apart from this it seems to form the condition of 

 a profound change in the properties of the egg-cytoplasm, Delage-* 

 has found that enucleate egg-fragments of Asterias are insuscepti- 

 ble to fertilization before the germinal vesicle has undergone visible 

 change; but that very soon after its membrane has begun to show 

 indication of dissolution, merogonic fertilization first becomes 

 possible; a little later, when the membrane has become invisible — 

 although the area of the former germinal vesicle may still be seen, 

 often with nucleolus intact — the fragments of cytoplasm are com- 

 pletely and readily fertilizable. These observations demonstrate 

 that the essential feature of maturation, so far as the cytoplasm is 

 concerned, is not the separation of the polar bodies, but simply the 

 removal of the barrier between the nuclear and the cytoplasmic 



2' Delage: Archives de zoologie experimental et generale, Ser. Ill, T. 9, p. 285, 1901. 



