CASTLE. — INBREEDING, CROSS-BREEDING, AND SELECTION. 765 



(5) The grandchildren produced by either of the reciprocal crosses 

 between the A series and the M or N series vary much in productiveness. 

 Some are sterile or of low productiveness like mothers of the pure A 

 race. These occur oftenest among the young of cross-bred pairs of low 



TABLE XV. 



AM2 167 ? sterile St. St. 198 201 189 126 146 



productiveness. Others are as productive as the uncrossed M or N 

 races. 



(6) It follows from the facts stated in 3-5 that a tendency to low 

 productiveness and sterility on the part of the female may be transmitted 

 through either sex as a racial character. When so transmitted it con- 



TABLE XVI. 



A N Series. 



(Cross 6, page 747 ; see also Table XVII.) 



^1 36.17 ? x N5 $ 



[52] i [367] 



go -g gm -g gt» 



^4iVl 11 55 114 55 59 43 302 



forms imperfectly with Mendel's law of alternative inheritance. Fertility 

 is commonly dominant over low productiveness, but not invariably. See 

 Table XV, A M 2, in which generation half the pairs are sterile. This 

 case is exceptional. Low productiveness commonly skips a generation 

 following a cross, but may be transmitted directly through the female 

 parent. Its reappearance after skipping a generation is not certain. If 

 selection is made from the most fertile cross-bred broods, low productive- 



