HISTOLOGY AND CYTOLOGY 375 



one side or pole, and this condition is termed telolecithal. Indeed, 

 such a large amount of yolk is present that it results in the active 

 cytoplasm of the ovum being confined to a small area, the germinal 

 disc, which contains the nucleus or germinal vesicle, as it is frequently 

 termed, and is situated at one point of the surface. The question 

 of the amount and distribution of the yolk is not an important 

 matter from the point of view of the fundamental structure of the 

 egg, since it is all non-active food material, and so a question of 

 detail. On the other hand, it is of extreme importance to the 

 changes occurring after fertilisation, since it determines to a large 

 extent the way the early development can proceed. 



With this general description of the germ cell we can leave the 

 study of Cytology and pass on to consider what happens when the 

 germ cells unite in certain species of Chordata. 





