GERMINAL VESICLE AND FIRST EMBRYONIC NUCLEUS. 175 



the nuclear substance which is still enclosed in the wrinkled 

 membrane of the germinal vesicle, the other is formed by 

 a drop of nuclear fluid expressed and projecting into the 

 vitellus. 



6. The extravasated drop is flattened against the vesicle, 

 in the neighbourhood of the hole by which it made its 

 exit. The nuclear mass then reassumes a more or less rounded 

 form. But in this clear mass one distinguishes an irregular 

 line, which separates the intravesicular from the extravesi- 

 cular portion of the nuclear substance. 



This line is produced by the membrane which separates 

 the two parts of the nuclear substance which has become 

 very thin. This line at last completely disappears, proving 

 that the membrane is entirely disolved in the nuclear sub- 

 stance. There then no longer remains any portion of the 

 germinal vesicle, except a clear spot, whose ill-defined 

 contours become more and more irregular. The spot 

 becomes smaller and smaller, and ends by disappearing 

 completely. It seems as if the clear and homogeneous 

 matter of the germinal vesicle became granular from the 

 periphery to the centre. This appearance is probably the 

 result of the progressive dissolution of the nuclear sub- 

 tance by the vitelline protoplasm. 



The successive phenomena which precede the comj)lete 

 disappearance of the germinal vesicle are these : 1. The 

 solution of the nucleoplasmic mass and of the pseudo- 

 nucleoli in the nuclear juice ; 2. The breaking up of the 

 germinal spot into fragments, and the progressive solution 

 of these fragments in the nuclear substance ; 3. The per- 

 foration of the membrane followed by the partial expulsion 

 of the contents of the nucleus ; 4. The complete solution 

 of the membrane in the juice of the germinal vesicle ; 5, 

 lastly, the solution of the nuclear substance in the vitelline 

 protoplasm. 



The modifications which I have shown to exist in the 

 nucleolus, the reduction of the vacuoles into a single vesicle, 

 the changes in the form of that element, and its breaking 

 into fragments cannot be explained unless we admit the 

 contractility of the nucleolar substance. This view is more- 

 over in conformity with the conclusion which one has been 

 able to draw from the amoeboid movements which have 

 been seen to be executed by the nucleoli of other cells. 



The facts which 1 have just related have not been 

 observed by M. Hertwig in .his Toxopneustes lividus. M. 

 Hertwig thinks, on the contrary, without however, being 

 able to affirm it from direct observations, that in that 



