CASTLE. — INBREEDING, CROSS-BREEDING, AND SELECTION. 745 



duced 255 young by A mates, and 228 young by D mates (see page 743). 

 The sterility of Pair 1 in Cross la was probably inherent in the A male, 

 as will subsequently appear. 



Average, 161 young. 



Average, 212 young. 



The A females employed in Cross 2 seem to have been more productive 

 than those employed in Cross 1. Further, the F females of Cross 2a 

 were less productive than the D females employed in Cross la. Ac- 

 cordingly the averages for the reciprocal crosses, 2 and 2a, are not so 

 unlike as are those for Crosses 1 and la. Nevertheless, in one case as 

 in the other, the A females are much the less productive. 



Cross 3. A ? X stock-jar <f (p. 735). 



In a third cross (Cross 3), the reciprocal of which was not performed, 

 A females were mated with males from the stock-jar (p. 735). They 

 showed about the same productiveness (125) in this case as when mated 

 with their own brothers (128), or with D males (129, Cross 1). 



A control cross (Cross 4), made at the same time as the foregoing, 

 between F females and D males, produced an average of 219 young, 

 which agrees closely with the average, 212, produced by F females 

 when mated with A males (Cross 2a). 



Cross 4. F 9 X D <?. 

 Pair 1 .... 199 young. 

 Pair 2 .... 256 " 

 Pair 3 .... 263 " 

 Pair 4 .... 159 " 



Average, 219 young. 



