I.] 



THE OVARIAN OVUM. 



13 



The rest of the ovum is known as the yolk. This 

 consists of two elements, the white yolk- and the yellow 

 yolk-spheres, which are distributed respectively very 

 much in the same way as in the laid egg, the yellow 

 yolk forming the main mass of the ovum, and the white 

 yolk being gathered underneath and around the disc 

 (Fig. t, w. y), and also forming a flask-shaped mass in 

 the interior. The delicate membrane surrounding tlie 

 whole is the vitelline membrane. 



The youngest ova in the ovary of a fowl, in common 

 with those of all other animals, present the characters 

 of a simple cell. Such a cell is diagrammatically repre- 

 sented in Fig. 5. 



It is seen to consist of a naked protoplasmic body 

 containing in its interior a nucleus the germinal vesi- 

 cle which in its turn envelopes 

 a nucleolus constituting what is 

 known as the germinal spot. 

 Such young ova are enclosed in 

 a capsule of epithelium, named 

 the follicle or follicular mem- 

 brane, and are irregularly scat- 

 tered in the stroma of the ovary. 

 The difference between such 

 an immature ovum and the ripe 

 ovum just described is very great, 

 but throughout its growth the 

 ovum retains the characters of a 

 cell, so that the mature ova- 

 rian ovum, equally with the 

 youngest ovum in the ovary, is a single cell. 

 The most striking changes which takes place in the 



Fig. 5. 



Diagram of the 

 Ovum. (From Gegen- 

 baur.) 



a. Granular proto- 

 plasm, h. Nucleus (ger- 

 minal vesicle), c. Nu- 

 cleolus (germinal spot). 



