74 THE VERTEBRATE OVARY AND ITS RELATIONSHIP TO REPRODUCTION 



effects upon the growth of the oviduct (Romanoff and Romanoff, '49, pp. 

 242-244). In the frog, Rana pipiens, mammalian pituitary gonadotrophins 

 are able to effect ovulation (Wright and Hisaw, '46). Pituitary gonadotrophins 

 have been shown also to have profound stimulative effects on the ovaries of 

 fishes, salamanders, and reptiles. 



5. Structure of the Vertebrate, Mature Egg Follicle 



As a result of the differentiation and growth induced by the gonadotrophic 

 hormones of the anterior lobe of the hypophysis described in the preceding 

 paragraphs, the egg follicle reaches a state of maturity (fig. 43C). This state 

 is achieved when the follicle is about to rupture with the resultant discharge 

 of the egg. The size of the mature egg follicle varies greatly in different meta- 

 therian and eutherian mammals, although the size of the follicle is not related 

 to the size of the egg. On the other hand the size of the mature egg follicle 

 in prototherian mammals and in other vertebrate species shows great diver- 

 gences, being dependent in this group upon the size of the egg at the time 

 of ovulation (fig. 46). 



a. Structure of the Mature Follicle in Metalherian and Eutherian 



Mammals* 



The structural pattern of the mature Graafian follicle in the human is 

 strikingly similar to the follicles in other members of this group. It is a vesicular 

 structure with a diameter approximating five millimeters. Externally, the fol- 

 licle is composed of two connective-tissue layers, an inner cellular layer con- 

 taining blood capillaries, the theca interna, and an external, fibrous layer, 

 the theca externa (figs. 43C, 44). These two layers are not clearly separable. 

 Passing inward from the theca interna is the basement membrane. Resting 

 upon this membrane are several layers of epithelial cells comprising the 

 membrana granulosa. The latter membrane borders the cavity or antrum of 

 the follicle, which is filled with the liquor folliculi. This liquid is under con- 

 siderable pressure in the follicle at the time of egg discharge or ovulation. 



Projecting inward into the antrum on one side is a small, mound-like 

 mass of granulosa cells, the cumulus oophorus (fig. 43C). Within this hillock 

 of epithelium, is the egg, which measures in the human about 130 p. to 140 /x 

 in diameter. In the opossum, the fully developed Graafian follicle is about 

 1.25 by 2 mm. in diameter, while the slightly oval egg approximates 120 by 

 135 IX. The egg of the rat and mouse is small, having a diameter of 75 ^i, 

 while that of the dog is about 140 y^\ sow, 120 to 140 n\ rabbit, 120 to 130 /x; 

 monkey, 1 10 to 120 ^; deer, 1 15 /x; cat, 120 to 130 /x; mare, 135 /x; arma- 

 dillo, 80 /x (Hartman, '29). 



* According to Strauss, '39, the mature Graafian follicle of Ericulus is not a vesicular 

 structure, as in other higher mammals, but is filled with a loose meshwork of granulosa 

 cells. 



