EFFECTS OF INBREEDING AND CROSSBREEDING. 



23 



percentage raised of the young born alive. The superiority of the 

 crossbreds produced by inbred females (CO, CA) over inbreds shows 

 that the heredity of the young counts for a great deal. The still 

 greater superiority of the crossbreds from crossbred parents (CC) 

 shows, however, that the breeding of the dam is also of much impor- 

 tance, as would of course be expected. The effects of renewed in- 

 breeding may be seen in the lower average of Cl as compared with CC 

 and the still lower average of C2. The result of crossing inbred male 

 with crossbred female (AC) is practically the same as the reciprocal 

 cross (CA). One would expect an average as high as CC. There 

 seems to be no explanation other than an extreme chance deviation. 

 The young from crossbreds selected for their rapid gains (CG) did 

 not show as great a percentage advance over the inbreds as the young 



/5 



/O 



I 



■/O 



-/5 



n 













CC 





a30.4- 



CLjGG- 

 C2 



f 









y 





; 



/3 









.^■i*?" 



y 



^s^^-^ 



c/ 





35 



\ 





A 





c/? 







01 

 32- 



39 



A 



A 



^ 











/B7.S- 



^ 



fl 















/ 

















2 



/ 

















Fig. 14.— The weight at 33 days, 191&-1919. Indices correcting for effects of size of litter and seasonal 

 conditions (Table 2). (See Fig. 8 for explanation of symbols.) 



from the subnormal parents in Experiment CL. We again conclude 

 that direct selection is futile in the case of characters of the kuid dealt 

 with here, in which hereditary differences are small compared with 

 those due to environment. 



The comparison of the gains of the inbreds CO, CC, Cl, and B in 

 separate sizes of litter (Fig. 23) confirms the results from the indices. 



WEIGHT AT WEANING. 



This is merely the sum of the birth weight of the young raised and 

 the gain from birth to 33 days (Fig. 14). As it depends largely on 

 the latter factor, no additional points of interest are brought out. 



