UNIVERSITY] 







ELEMENTS OF HISTOLOGY. 



CHAPTER I. 



CELLS. 



1. THE ripe ovum (Fig. 1) of man and mammals is 

 a minute spherical clump of a soft, gelatinous, trans- 

 parent, granular-looking substance, containing nume- 

 rous minute particles yolk 

 globules. It is invested 

 by a vertically-striated deli- 

 cate membrane, called the 

 zona pellucida. Inside this 

 clump, and situated more 

 or less excentrically, is a 

 vesicle the germinal vesicle 

 and inside this, one or more 

 solid spots the germinal 

 spot or spots. The gela- 

 tinous transparent substance 

 of the ovum, containing a 

 very large percentage of proteid material, is called 

 Protoplasm. Before and immediately after fertilisa- 

 tion, the protoplasm of the ovum shows distinct move- 

 ment, consisting in contraction and expansion. These 

 movements are spontaneous i.e., not caused by any 

 directly visible external influence. 



The diameter of the ripe ovum in man and domestic 

 animals varies between ^J^ and yi^- of an inch. But 

 before it ripens the ovum is considerably smaller in 



Fig. 1. Ripe Ovum of Cat. 



a, Zona pellucida ; ft, perminal 

 vesicle ; c, protoplasm. 



