746 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



These several experiments agree in showing that the fecundity of 

 a female is unaffected by the relatedness or unrelatedness of her mate. 

 In other words, the racial fecundity of the male in no case affects the 

 productiveness of his mate, unless he is a wholly sterile animal. 



Certain of the young produced by Cross 1, Pair 2, were bred inter se. 

 Of ten pairs tested, all were fertile, though the record for one was incom- 

 plete on account of an accident. The average number of young produced 

 by the remaining nine pairs was 356. The broods produced by the ten 

 pairs individually were as follows: 



Pair. Young. 



G 7.1 . . . [44] (incomplete) 

 G 7.2 . . . 338 

 G7.3 . . . 408 

 G 7.4 . . . 339 

 G7.5 . . . 359 



Average, 356 young. 



This is a remarkably high average. The A race at this same time 

 (generation 28), and under identical conditions, was producing an average 

 of 95 young to a pair ; and pure D pairs in the previous generation had 

 produced an average of 228 young, while pure D females mated with 

 A males had produced 255 young, 100 less than the average brood of 

 their cross-bred offspring. 



Young from the reciprocal cross, la, Pair 5, were likewise mated 

 inter se. Eight pairs were tested, all fertile. Their broods were as 

 follows : 



Pair. 



G 18.5 

 G 18.6 

 G 18.7 

 G 18.8 

 Average, 252 young. 



The average number of young, 252, is not much greater than the 

 general average for Cross la, though the particular brood (Pair 5, 

 Cross la) from which the parents were derived contained only 163 young, 

 and the average for pure D pairs had previously been found to be 228. 

 On the whole, therefore, this cross, like the reciprocal one previously 

 discussed, seems to have increased the productiveness of the cross-bred 

 offspring, making it greater than that of either parent race when purely 

 mated or when cross-mated. 



Young. 



[66] incomplete. 

 [178] " 



173 

 180 



