738 



SPERM, OVA, AND PREGNANCY 



was found to meet with great resistance ; the 

 more slowly the pressure was built up, the 

 lower the peak pressure required to open the 

 isthmian and uterotubal constrictions. The 

 reciuired pressures generally were higher in 

 those animals receiving estrogen. 



D. NUMBER OF SPERM AT THE SITE 

 OF FERTILIZATION 



In the few species subjected to careful in- 

 vestigation, the number of spermatozoa re- 

 covered from the ampulla, or what is re- 

 garded as the site of fertilization, at the 

 approximate time of fertilization, is sur- 

 prisingly low. A summary of available evi- 

 dence is included in Table 13.7. Whereas 

 these data represent, in some instances, only 

 single determinations and, in others, mean 

 values within a very wide range, they show 

 quite clearly that only a minute fraction of 

 the inseminate is present in the vicinity of 

 the ova when fertilization occurs. In some of 

 these studies (Moricard and Bossu, 1951; 

 Blandau and Odor, 1949), search failed to 

 reveal many more sperm than the number of 

 eggs undergoing fertilization. The presence 

 of so few sperm at this critical point is evi- 

 dence enough against the once-popular view 

 that a sperm "swarm" is essential for ferti- 

 lization — either to denude the ova of their 



TABLE 13.7 



Number of spermatozoa found at the site of 



fertilization in several mammals 



TABLE 13.8 

 Sperm survival times in, the female tract 



* Ovarian third of oviduct. 

 t Entire ampulla. 



cumulous auras by hyaluronidase or to sup- 

 ply some ingredient for sperm penetration. 

 Conversely, Braden and Austin (1954) have 

 suggested that an accomplishment of the fil- 

 tering out of the overwhelming majority of 

 sperm during transport is to so limit the 

 number of male gametes present that mul- 

 tiple sperm penetration of the ova is reduced, 

 thereby preventing polyspermy and anoma- 

 lous development. 



E. DUR.\TIO\ OF FERTILIZING CAPACITY 



The retention of fertilizing capacity by 

 mammalian spermatozoa is relatively lim- 

 ited (Table 13.8). As in the male tract, the 

 capacity for fertilization is lost more 

 promptly than is their ability to move. In 

 the female guinea pig, for example, motility 

 of sperm continues for as long as 40 hours 

 after mating, whereas fertilizing capacity is 

 lost about 22 hours after copulation (Yo- 

 chem, 1929; Soderw^all and Young, 1940); 

 in the mouse these periods are approximately 

 I3Y2 and 6 hours, respectively (Merton, 

 19391)). In the consideration of sperm sur- 

 vival in parts of the tract other than the fer- 

 tilization site, sperm motility is the most 

 convenient, although not necessarily the 

 only, criterion of longevity. 



The values presented in Table 13.8 are the 

 most accurate available, but the degree of 

 precision with which such data can be ob- 



