GERMINAL VESICLE AND FIRST EMBRYONIC NUCLEUS. 173 



disappeared. Nothing is easier than to make this observa- 

 tion on the ova of the starfish, since the eggs continue to 

 develop on the object-slide, and the changes which they 

 undergo take place under the very eye of the observer. 

 Eight or ten times have I seen the series of modifications 

 which lead to the disappearance of the vesicle of Purkinje 

 evolve themselves under my very eyes. The succession of 

 these phenomena is the same, whether one observes a fecun- 

 dated ovum or follows them in a non-fecundated one. The 

 whole series of these changes is completed in the same time 

 in either case. I believe, however, that fecundation is often 

 the immediate cause of the disappearance of the germinal 

 vesicle, in this sense, that in a ripe ovum the germinal vesicle 

 disappears from the time that the ovum is placed in the 

 presence of the sperm, whilst that element might have still 

 remained for some time if the ovum had not been fecun- 

 dated. This appears to me to be shown by the following 

 observation : if we place in two glasses ova from the same 

 ovary, and fecundate those in the one, carefully preventing 

 the sperm from becoming mixed with the contents of the 

 other, an hour after the fecundation all the mature ova of 

 the first glass will have lost their vesicle, whilst most of those 

 in the second still show it perfectly distinct. If amongst the 

 fecundated ova one be chosen which shows a quite super- 

 ficial germinal vesicle, we may be almost certain to see 

 the germinal vesicle disappear in less than an hour. But it 

 is not so if we select from amongst the non-fecundated ova 

 one which presents similar conditions. 



Let us now see the series of modifications that are observed. 



1. At first the little granular mass which is situated by the 

 side of the nucleolus, and which is composed of nucleoplasma 

 and pseudo-nucleoli, becomes less and less apparent ; soon it 

 becomes impossible to distinguish it ; the germinal vesicle 

 now contains only an entirely homogeneous and transparent 

 liquid ; with no other granule than the spot of Wagner or 

 nucleolus. 



2. The contour of the germinal vesicle becomes paler ; the 

 same is the case with the nucleolus, the substance of which 

 appears to become less and less refractile. At the same 

 time the nucleolar vacuoles become united with a single 

 central vacuole, which appears as a clear spot, circumscribed 

 by an irregular ring formed of a highly refractile substance. 

 The nucleolus becomes very irregular, its surface is now 

 knobbed, and the projections are separated from each other 

 by fissures. The nucleolus resembles a small raspberry-like 

 mass. 



