84 



THE EGGS OF MAMMALS 



rabbit OMilates at 10 hours after copulation and the ferret 

 at about 30 hours, Hammond and his coworkers undertook 

 a series of matings using an initial sterile mating to initiate 

 the o\ailation stimulus and then fertile mating to permit 

 sperm access to ova at successively later intervals. In the 



+10 



+ 5 +4 +3 +2 +1 -1 -2 

 OVULATION 



AVERAGE 

 UTTER SIZE 



^c OF MATINGS 

 WHICH WERE 

 FERTILE 

 NUMBER OF 

 YOUNG PER 

 MATING 



HOURS INTERVAL BEFORE (I-) OR AFTER (-) OVULATION 



Fig. 27. Fertility of matings made at different intervals of time before or 

 after mating (all strains). (From the Journal of Experimental Biology.) 



most extensive series of rabbit matings (Hammond, 1934) 

 employed three inbred strains of rabbits in order that homo- 

 geneous conditions of fertility might exist in his experi- 

 ments. The data of his experiments are given in Table XIV, 

 and a graphical representation in Figure 27. 



It is at once obvious from these data that matings to 

 fertile bucks made after the 5th hour following a sterile 

 mating show a decline both in absolute (per cent of fertile 

 matings) and relative fertihty (number of young produced). 

 WTien matings are made to fertile bucks at twelve hours 

 after the sterile copulation, i.e., at two hours after o\ailation 

 minimum fertility is attained. 



