EFFECTS OF INBREEDING AND CEOSSBREEDING. 



25 



It will be se.en that the first cross (CO) results in an increase of 12 

 or 13 per cent in adult weight, but that at least half of this is lost 



/3 







CO 











/ 



\, 





t 





/ 



X 



\ 



C/ 





35 













6776 y%64/— 



32 



j^ 1 



9 

























/o 



is 



-6 



ViG. 15.— Adult weight, 1917-1920. Comparison between inbred famiKes (2, 13, 32, 35, 39), total inbreds 

 (A), random-bred stock (B), first cross (CO), and first generation of renewed inbreeding (Cl). Percentage 

 differences for males and females averaged. (See Table 9.) 



on renewing inbreeding (Cl). Figure 15 brings out these points 



graphically. 



FREQUENCY OP LITTERS. 



It is conceivable that the heredity of the fetuses might make a 

 difference in the number of htters completely absorbed or aborted at 



Fig. 16.— Regularity in producing litters (litters per mating per year), 1916-1919. Effects of seasonal con- 

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



an early stage, and thus make a difference in the frequency of recorded 

 litters. As it turns out, however, the frequency of litter (Fig. 16) is 

 6448— 22— Bull. 1121 4 



