FERTILIZATION AND CLEAVAGE 



85 



In order to make quite certain that the cause of the 

 smaller litters produced after the experimental matings made 

 late in relation to ovulation was due to the ova not being 

 fertilized and not to any interference with the process of 

 ovulation or other causes, a few does so mated were killed 

 during pregnancy and the number of corpora lutea {i.e., 

 ova shed) compared with the number of foetuses present. 

 The results are given in Table XV, and demonstrate that 

 there is a decrease in the number of ova fertilized in the 

 later matings. This implies that the sperm reach the portion 

 of the tubes containing the ova at a time when these ova 

 are for some reason no longer fertilizable. 



TABLE XV 

 The Percentages of Rabbit Ova Fertilized in Matings Made at Vari- 

 ous Times before and after Ovulation. (From Hammond, 1934) 



On the basis of Heape's (1905) observations that rabbit 

 sperm reach the tops of the tubes in about 4 hours after 

 coitus, Hammond concludes that rabbit ova can remain 

 fertilizable for at most 6 hours after o^Tllation, by allowing 

 a 2-hour postovulatory interval in the matings made at 

 12 hours after the ovulation-inducing mating. This period 

 coincides approximately with the time {i.e., 7 hours) that 

 it takes for the ova of sterile matings to begin to separate 

 from the follicle cell mass and start their free travel down 

 the tubes. Hammond concludes therefore that the presence 

 of the plug of massed ova is necessary for fertiUzation. He 

 reasons as follows: 



'^The plug, of liquor folliculi and detritus, containing the 

 ova dams up the top of the Fallopian tube and remains there 



