THE OVUM 



767 



It is marked by striae, which are thought by some anatomists to indicate 

 the presence of small pores ; but the large single opening called a mi- 

 cropyle, which is found in many of the osseous fishes and in mollusks, 

 has not been demonstrated in the human ovum. 



Between the zona pellucida and the vitellus, is a narrow space, about 

 2W07 of an mch 0-3 P) m d iameter - This is called the perivitelline 

 space. 



The vitellus is contained within the zona pellucida. It presents a clear 



outer zone 



to ToVo 



an 



(4 to ^ /*) m diameter. This can not 



be distinguished from the protoplasmic zone, except in perfectly fresh 



Zona pellucida . .^Vv^&i 



Perivitelline Space 



Celts of the discus 

 iroligerus 



Corona radiata 



Germinal Vesicle, 

 with two germinal 

 &$) s P ts 





1&--.. Deutoplasmic 

 Z 



Fig. 206. Deutoplasm-forming ovum from a Graafian follicle of a woman twenty-seven years 



old, X 160 (Nagel). 



This ovum was taken from a fresh ovary removed from the living subject. 



ova. It is composed of clear protoplasm without granules and repre- 

 sents that portion of the protoplasm of the vitellus which is not at any 

 time converted into deutoplasm. Within the clear zone, is the proto- 

 plasmic zone (formative yolk). This presents very fine granules, and 



the zone is ^sVo to T^oo ^ an mc ^ (10 to 21 ft) in thickness. Occupy- 

 ing the central portion of the vitellus, is the deutoplasm (nutritive yolk), 

 forming a mass about -\- of an inch (82 to 87 ft) in diameter. The 

 deutoplasm presents granules of different sizes and different refractive 

 power. Treated with eosin, the protoplasm becomes rose-colored, but 

 the deutoplasm is unaffected. As the ovum reaches its final stage of 

 development, the protoplasmic zone, as far as that portion which forms 

 the so-called outer zone, is gradually changed into deutoplasm. In 



