636 THE PHYSIOLOGY OF REPRODUCTION 



says that the hypotypical ovarian state leads to at least temporary 

 sterility. 



Follicular atrophy is, however, a normal process probably in all 

 the higher animals (see p. 153), and it is only when it becomes 

 excessive that it is a cause of sterility, since the number of young 

 ova and follicles is far larger than that of the young which could 

 develop. Thus the human ovary is said to contain 20,000 oocytes 

 at puberty, or sufficient to admit of forty ova being discharged every 

 month throughout the reproductive period of life. In the rat there 

 are, according to Arai, 1 35,100 ova at birth, but these are reduced 

 by degeneration to 11,000 after twenty-three days and 6000 by 

 the sixty-third day. Moreover, according to Robinson, 2 in the ferret 

 the smaller follicles are necessary for providing nourishment for the 

 larger developing ones. 



. Moreover, Hammond 3 has shown that in the domestic animals, 

 and especially in the pig and tame rabbit, fecundity is apt to be 

 conditioned rather by the factors controlling development in iitcro 

 than by the production of ova. The number of eggs matured is 

 frequently in excess of the nutrition available for them, and this 

 leads them to atrophy, sometimes while still contained in the ovarian 

 follicles, but also very frequently as newly fertilised ova or partially 

 developed embryos. 



The effect of external conditions on the rate of follicular ripening 

 in the rabbit has also been studied by Hammond, who states that in 

 the wild state the number of eggs discharged increases from January 

 to April and then decreases. This is similar to what occurs in the 

 domestic fowl. With tame rabbits the effect is not so marked owing 

 to the more uniform conditions under which they are kept. The 

 average number of eggs shed at one period was found to be 5'74 in 

 wild rabbits and 10*3 in domesticated rabbits, but in the latter 

 atrophic foetuses are much more common (see below, p. 656). 



INFLUENCE OF THE MALE PARENT 



It has been suggested that in some males there is a want of 

 vigour on the part of the spermatozoa which either prevents them 

 from conjugating with ova or causes abortion of the fertilised ovum 

 or foetus owing to its being endowed with a reduced vitality. 

 Stephenson 4 refers to cases of bulls which had at one time been 



1 Aral, "On the Post-Natal Development of the Ovary, etc.," Amer. Jour, 

 of Anat., vol. xxvii., 1920. 



2 Robinson (A.), "The Formation, etc., of the Graafian Follicle in the Ferret, 

 etc.," Trans. Roy. Soc. Edin., vol. Hi., 1918. 



:t Hammond, " Further Observations on the Factors controlling Fertility 

 and Foetal Atrophy," Jour. Agric. Science, vol. xi., 1921. 



4 Stephenson, " Abortion in Cows," Jour. Roy. Agric. Soc. vol. xxi. 

 (2nd series), 1885. 



