THE BEGINNINGS OF LIFE. 



201 



be understood that his opinions are in accordance with 

 those of other naturalists. The second stage in the 

 formation of the ovum has to do with the deposit of the 

 vitelline or yolk-substance around the germinal vesicle. 



FIG. 12. 

 Early forms of ova in Ascaris mystax. (Thomson.) 



a. Molecular condition. 



b, c. Germinal vesicles becoming surrounded by yolk granules. 

 d, e. Irregular forms of ova due to tight packing. 



/. Later stage showing first traces of vitelline membrane. 



Dr. Thomson says: c The granules of the yolk-sub- 

 stance very soon collect round the exterior of the germi- 

 nal vesicles 1 . These granules appear at first to be 



1 In some cases, however, the order is different. The germinal 

 vesicle may at first be surrounded by more or less of a clear viscous 

 material in which granules, after a time, make their appearance. Thus 

 Professor Thomson tells us (loc. cit. p. 133) that 'In most animals 



