86 



THE EGGS OF MAMMALS 



for some 4 (in fertile matings) to 7 (in infertile matings) 

 hours, during which time the ascending sperms are collect- 

 ing in its lower layers (see Figure 28). The accumulation 

 of sperms so effected ensures that sufficient shall be available 

 to fertilise the ova as they emerge from the plug. As the 

 sperms are put in progressively later than normal in relation 

 to the time of ovulation, the accumulation of sperms be- 

 comes progressively less and the chances of all the ova 



FALLOPIAN TUBE 



PLUG CONTAINING OVA 



Fig. 28. Diagram illustrating how the chances of the ova becoming fertilized 

 are reduced as the interval between mating and ovulation is reduced, a = 

 amount of sperm swarm which would accumulate if mating were made at the 

 ordinary time — 10 hours before ovulation, b = amount of sperm swarm 

 which would accumulate if mating were made 4 hours before ovulation. (From 

 the Journal of Ex-perimental Biology.) 



becoming fertilised are reduced in proportion to the time 

 the fertile mating is delayed with reference to the time of 

 o\ailation. 



^^The ascent of the sperms can be represented as a curve 

 (see Figure 28 and Hammond and Asdell, 1926) or as a 

 swarm (in the statistical sense). The apex of the sperm 

 swarm (shown, in order to assist visualisation of the prob- 

 lem, very diagrammatically in Figure 28) reaches the top 

 of the tube just at the time the plug is formed, i.e., at ovu- 

 lation, and so during the time that the plug exists (about 

 4 hours) it dams up but few sperms as compared with a 

 normal mating made 10 hours before ovulation when the 

 sperm swarm has ascended further (to the point a in Fig- 

 ure 28).'^ 



