m. 645] FECUNDITY IN THE GUINEA PIG 353 



females, the male will often go directly to the female in 

 rut. Sometimes, however, he will mistakenly pursue the 

 one that is not in heat, although repelled by sharp bites 

 and other negations, only to wheel suddenly and mount 

 the receptive female. The pursuit of the wrong animal 

 may only serve to stimulate him, but in some instances it 

 was necessary to remove her before he would turn his at- 

 tentions to the one in rut. Puzzling sexual idiosyncrasies 

 also were noted. Instances were observed, for example, 

 in which a male would not under any circumstances mate 

 with a certain female which was in heat, although he was 

 persistent in the case of others. On the other hand, some 

 females also were noticed to repulse a certain. male, al- 

 though accepting others. 



It will be seen from Table I that 106 matings resulted 

 in 61 pregnancies, or 57.5 per cent. Draper, '20, reported 

 that only 40 i3er cent, of the animals bred by him became 

 pregnant. Since Stockard and Papanicolaou found 95.4 

 per cent, out of 88 pigs pregnant, considerable variation 

 would seem to exist. The large discrepancy between their 

 results and ours may be due to the fact that the latter 

 were working with uniformly young, selected animals or 

 that the males were left to remain with the females, in- 

 stead of being removed after several copulations. 



In the many matings not followed by pregnancies, the 

 next cestrous cycle was prolonged. This is shown by the 

 accompanying chart. 



