310 HUMAN PHYSIOLOGY 



2. THE FEMALE SEXUAL PRODUCTS AND THEIR 

 FORMATION 



1. The ovum. The female sexual cell or egg is a 

 spherical cell having a diameter of o. 15-0.2 mm. Its proto- 

 plasm is called egg-yolk; its nucleus, germinal vesicle. It 

 is surrounded by the zona pellucida. In the yolk we can 

 distinguish : 



(1) The real living substance, the protoplasm. 



(2) The dcutoplasin, or yolk granules, which serves as 

 food. 



In the human ovum there is but little deutoplasm in the 

 form of spheres, yolk granules, lying in the protoplasm. In 

 many animals, e.g. birds, much deutoplasm is present. 

 The nucleus of the egg is generally spherical, clear, and with 

 a double contour; it surrounds the germinal spot (macula 

 germinativa). The zona pellucida is 0.02-0.025 mm thick 

 and radially striated. These striations are caused by the 

 numerous perforations of the zona pellucida. 



2. Formation of the ovum. The eggs in the ovary are 

 placed in the Graafian follicle, a spherical vesicle, which in 

 mature condition has a diameter of 10-15 mm. The follicles 

 are imbedded in the connective-tissue stroma of the ovary 

 and are surrounded by a vascular capsule. The inner wall 

 of this capsule is surrounded by the membrana granulosa or 

 germinativa, composed of many layers of epithelial cells. 

 The epithelium forms at one place a great mass of cells, 

 called the discus proligerus, in which lies the ovum. The 

 cavity of the follicle between the discus proligerus and the 

 rest of the wall of the follicle is filled with a yellowish fluid 

 containing proteid. 



The Graafian follicle originates as follows : The surface of 

 the ovary is covered with a cylindrical epithelium (the 

 so-called germinal epithelium) which covers also the tubular 

 invagination of the surface of the ovary. These invagina- 

 tions grow downward and are cut off by the stroma of the 

 ovary. The separated tubes develop into the Graafian 

 follicles. In the germinal epithelium the round egg-cells 



