ACTIVITIES OF THE OVARY 



75 



While one Graafian follicle in only one ovary is generally developed in 

 the human, monkey, cow, ewe, elephant, etc., at each reproductive period, 

 a multiple condition is found in many other mammals. Each ovary in the 

 opossum may ripen seven or more follicles, in the bitch (female dog) from 

 2 to 7 follicles, and in the sow from 4 to 10 follicles at each reproductive period. 



b. Structure of the Prototherian Egg Follicle 



The follicle of the prototherian mammals contains a relatively large egg, 

 while the surrounding fluid and follicular tissue in comparison is small in 

 quantity (fig. 46). In these mammals the egg fills most of the follicular cavity, 

 with the exception of a small fluid-filled space intervening between it and 

 the zona pellucida which lies contiguous to the granulosa cells. Internal and 

 external thecal tissues surround the granulosa cells as in the Graafian follicle 

 of the higher mammals. 



c. Egg Follicles of Other Vertebrates 



The fully-developed egg follicle in most vertebrates is similar to that found 

 in the prototherian mammals in that the egg tends to fill the entire follicle. 

 The general structural relationships also are similar (figs. 45, 47). 



6. Ovulatory Process; Possible Factors Controlling Ovulation 



The following description of the ovulatory process in the mammal and in 

 other vertebrates should not be construed as a description of the mechanism, 

 as the exact mechanism is unknown. However, a certain amount of general 

 information has been obtained concerning ovulation and the factors involved. 

 Much of this information has been obtained from studies of the ovulatory 



THECA INTERNA 



CONTRACTED FOLLICLE 

 AFTER EGG DISCHARGE 



OC ES S 



I ON 



Fig. 45. (A) Young egg follicle of Cryptohranchus alleganiensis, a urodele. (From 

 Noble: "Biology of the Amphibia," New York, McGraw-Hill, after Smith.) (B) Dia- 

 grammatic representation of ovarian events in the frog resulting in egg discharge. (From 

 Turner: "General Endocrinology," Philadelphia, W. B. Saunders, slightly modified.) 



