48 THE BREEDING OF ANIMALS 



at least three weeks after isolation from the cock. After 

 the end of the third week the vitality of the spermatozoa is 

 apparently reduced, as eggs laid during the fourth and fifth 

 weeks may exhibit at the most abnormal cleavage, which 

 soon ceases. Eggs laid forty days after isolation are cer- 

 tainly unfertilized and do not develop." 1 That the sperma- 

 tozoa may continue to fertilize eggs in the hen for at least 

 twenty days after coition is noted also by Spallanzani. 



The researches of Lewis 2 including records of twenty- 

 five sows showed that in three cases only were the sperm- 

 cells alive and active after twenty hours existence in the 

 female organs of generation. In two cases live sperma- 

 tozoa were collected from the uterus at the end of forty 

 hours. In most cases the sperm-cells taken from the 

 female organs were all dead at the end of sixteen hours 

 after the sow had been bred to a healthy normal boar. 

 The rupture of the Graafian follicles was found to occur 

 almost universally during the last part of the heat. " In 

 no case were the follicles found ruptured during the first 

 twenty-four hours of heat and in most of the cases a 

 period of thirty hours elapsed after the first signs of heat 

 before many of the egg-cells escaped from the ovary." 

 In no case were the Graafian follicles found ruptured in 

 sows which were examined early in the heat. In one sow 

 ovulation did not occur until forty-five hours and in 

 another case seventy hours after the beginning of heat. 

 From the fact that in swine the duration of the vitality 

 of the sperm-cells in the generative organs is so short and 

 that ovulation occurs during the last part of the heat, it 

 is apparent that sows should be bred during the last 

 part of the heat. To be more explicit, the sow should 



1 Spallanzani, "Dissertations," vol. II, 1784. 



2 Loc. cit., p. 7 et seq. 



