356 GENERATION. 



ner ; and sometimes a third makes its appearance. As soon 

 as the globules are perfectly formed, they all become de- 

 tached from the vitellus, but remain adherent to each other, 

 gradually fusing to form a single rounded, very faintly gran- 

 ular mass ; and it is opposite this globule that the first fur- 

 row of segmentation of the vitellus is observed. The com- 

 plete formation of the polar globules and their fusion into 

 one occupy three hours. It is probable that the polar globule 

 is formed in the mammalia in the manner above indicated. 

 "Weil has lately described, in the fecundated ovum of the rab- 

 bit, before segmentation of the vitellus, a body which is un- 

 doubtedly analogous to this globule. 1 Sometimes the polar 

 globule is formed in ova that have not been fecundated. 



Vitelline Nucleus. A short time after the complete for- 

 mation of the polar globule, the germinal vesicle having dis- 

 appeared, the deformed vitellus resumes its original rounded 

 appearance, and fills again the cavity of the vitelline mem- 

 brane. At this time, the extreme periphery of the vitellus 

 becomes clearer ; the granules collect in a large zone around 

 the centre, and, in the centre itself, a clear, rounded body 

 makes its appearance, which is called the nucleus of the vitel- 

 lus. This mass is viscid, amorphous, without granules, and 

 is entirely different from the germinal vesicle, having no nu- 

 cleolus at first, a nucleolus, however, appearing in the nuclei 

 which result from its segmentation. The formation of the 

 nucleus of the vitellus is a positive evidence of fecundation. 

 It appears from fifteen to thirty hours after fecundation. 2 



Segmentation of the Vitellus. Almost immediately fol- 

 lowing the phenomena we have just described, the vitellus 

 begins to undergo the remarkable process of segmentation, 

 by which it is divided into numerous small cells. This pro- 



1 WEIL, Bdtrage zur Kentniss der Befruchtung und Entwicklung des Kanin- 

 cheneies. Medizinische Jahrbucher, Wien, 1873, S. 24. 



2 ROBIN, Note sur la production du noyau vitellin. Journal de la physiologic, 

 Paris, 1862, tome v., p. 314. 



