78 THE VERTEBRATE OVARY AND ITS RELATIONSHIP TO REPRODUCTION 



cular, and the underlying tissues become thin and greatly distended. The 

 tunica albuginea of the ovary and the two thecal layers of the follicle also 

 are involved in this thinning-out process. As the distended papillary area 

 continues to grow thinner, a small amount of blood followed by some of the 

 follicular fluid containing the egg emerges from the follicle and passes into 

 the surrounding area in close proximity to the infundibulum of the Fallopian 

 tube (fig. 48E, F). The entire process is a gradual one and may be described 

 as gently but not violently explosive (Hill, Allen, and Cramer, '35). It is of 

 interest and significance to observe that Burr, Hill, and Allen (35) were able 

 to detect a change in electromotive force preceding and during the known 

 period of ovulation. 



The process of papillary rupture in the rabbit occupies about five seconds; 

 egg discharge with the surrounding liquor folliculi occurs in approximately 

 30 to 60 seconds. After the egg has emerged, the follicle as a whole may 

 collapse. The slit-like opening through which the egg and follicular fluid 

 passed during ovulation soon is filled with a clot composed of coagulated 

 blood and follicular fluid (fig. 48G). 



While the foregoing processes, visible on the ovarian surface, are consum- 

 mated, certain internal changes occur which form a part of the ovulatory pro- 

 cedure. These changes are as follows: At about the time the egg is to be 

 extruded, the follicular fluid reaches its maximum in quantity. This increase 

 produces considerable follicular turgidity which may be associated with an 

 endosmotic effect due to an increase in the salt content of the contained fluid. 

 Shortly before the surface of the follicle ruptures, the cumulus begins to dis- 

 integrate, and the egg lies free in the antral fluid. At about this time the first 

 maturation division of the oocyte occurs in the majority of mammals, and 

 the first polar body is extruded. 



Concerning the internal changes accompanying rupture of the mammalian 

 follicle, passing mention should be made of the theory that bursting blood 

 vessels discharge their contents into the follicular fluid and thus cause suffi- 

 cient pressure to rupture the follicle (Heape, '05). Considerable blood dis- 

 charge into the follicle seems to be present in some forms, e.g., the mare, 

 quite absent in others such as the human, and present slightly in the opossum. 



2) Hormonal Control of the Ovulatory Process. The hormonal mechanism 

 involved in ovulation in the spontaneously-ovulating mammals probably is as 

 follows: The follicle-stimulating hormone causes the growth and development 

 of the follicle or follicles. Estrogen is released by the growing follicles and 

 possibly by other ovarian tissues due to the presence of small amounts of LH, 

 and, in consequence, the estrogenic hormone reaches a higher level in the 

 blood stream (figs. 53; 59). 



In the meantime, it is probable that the corpus luteum hormone, proges- 

 terone, is produced in small amounts. The exact source of this hormone is 

 not clear. It may be produced by old corpora lutea or by the interstitial tissue 



