ACTIVITIES OF THE OVARY 83 



peratures which obtain in the spring, the egg may remain there for 3 to 5 

 days without producing abnormahties. If kept at very cool temperatures, 

 the period may be extended. Among the mammals the viability after ovulation 

 varies considerably. In the mare, fertilization must occur within about 2 to 4 

 hours; rabbit, 2 to 4 hours (Hammond and Marshall, '25); rat, about 10 

 hours; mouse, 12 to 24 hours (Long, '12; Charlton, '17); opossum, probably 

 within the first hour or so because of the deposition of the albuminous coating 

 in the oviduct; fox, probably only a few hours; sow, about 24 hours or less; 

 man, probably 24 hours or less. In the guinea pig, functional degeneration 

 may begin within 4 to 8 hours after ovulation (Blandau and Young, '39). 



11. History of the Egg Follicle after Ovulation 

 a. Follicles Which Do Not Develop a Post-ovulatory Body 



The changes which occur within the egg follicle after the egg has departed 

 are most variable in different vertebrate species. In most of the fish group 

 the ovary as a whole shrinks to a fraction of its previous size, and many 

 very small, immature eggs, interstitial tissue, and collapsed,, contracted, empty 

 follicles make up its composition. Similarly, in frogs, toads, and salamanders 

 the collapsed follicle which follows ovulation does not develop an organized 

 structure. The thecal tissue contracts into a small rounded form within which 

 are a few follicle cells (fig. 45B). These bodies soon disappear. 



In many snakes and in turtles, the follicle collapses after ovulation, and it 

 is questionable whether organized bodies develop in the site of the ovulated 

 follicle. A similar condition appears to be the case in birds. However, Pearl 

 and Boring ('18) described an abbreviated form of a corpus luteum in the 

 hen in both discharged and atretic follicles. Also, Rothschild and Fraps ('44) 

 found that the removal of the recently ruptured follicle or of this follicle to- 

 gether with the oldest maturing follicle, at a time when the egg which origi- 

 nated from the ruptured follicle is in the oviduct, retarded the laying of the 

 egg from 1 to 7 days. Removal of other portions of the ovary in control 

 hens "practically never" resulted in egg-laying retardation. The ruptured fol- 

 licle, therefore, is believed, by these investigators, to have some influence on 

 the time of lay of the egg. Whether the hormone progesterone or something 

 similar to it may be produced by the ruptured follicle of the hen is ques- 

 tionable, although present evidence appears to suggest that it does (Neher 

 and Fraps, '50). 



b. Follicles Which Develop a Post-ovulatory Body; Formation of the 



Corpus Luteum 



Post-ovulatory bodies or corpora lutea (yellow bodies) develop in the 

 ovaries of elasmobranch fishes which give birth to their young alive. Also 

 in viviparous snakes of the genera Matrix, Storeria, and Thamnophis, it has 



