EFFECTS OF INBREEDING AND CROSSBREEDING. oe 
(more than 80 per cent) obtained in the second generation of cross- 
breeding over the average of the inbred families. The record of the 
original random-bred stock is surpassed by nearly 15 per cent by 
00 
8O 
K K 
§ 
1S) Q 
0 ‘ 
20 
o Ss ZF F 
4 Sze OF LITTER SIZE OF £/77ER 
Fic. 20.—The percentage born alive, by size of Fig. 21.—The percentage raised of the young 
litter (Table 15), 1916-1919. (See Fig. 8 for ex- born alive, by size of litter (Table 16), 1916- 
planation of symbols.) 1919. (See Fig. 8 for explanation of symbols.) 
Experiment CC. In fact, it was merely necessary to cross two inbred 
families and obtain a second generation (C1) to obtain an advance of 70 
per cent over the inbred ancestry and go beyond the random-bred stock. 
/ 2 J coal / 2 3 aed foo 
SIZE OF 4/7 7ER SIZE OF L/77LA 
FIG. 22._The birth weight of young raised to 33 Fig. 23.—The rate of gain per day by size of 
days, by size of litter (Table 19), 1916-1919. litter (Table 20), 1916-1919. (See Fig. 8 for 
(See Fig. 8 for explanation of symbols.) explanation of symbols.) 
Another important resultjis seen in comparing the advance of 80 
per cent in Experiment CC with the 16 per cent by which the best 
inbred family differs from the average. Looking at this result alone, 
