EFFECTS OF INBEEEDING AND CROSSBREEDING. 



31 



(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 



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S 3 '4- 



Fig. 20.— The percentage born alive, by size of 

 litter (Table 15), 1916-1919. (See Fig. 8 for ex- 

 planation of symbols.) 



2 3-^ 



Fig. 21. — The percentage raised of the young 

 born alive, by size of litter (Table 16), 1916- 

 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 (Cl) to obtain an advance of 70 

 per cent over the inbred ancestry and go beyond the random-bred stock. 



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80 



60 



'PC 



20 



ks 









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CO 



Cfi 









a 







s^ 



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V. 



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=H, 









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CO 



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Fig. 22.— The birth weight of young raised to 33 

 days, by size of litter (Table 19), 1916-1919. 

 (See Fig. 8 for explanation of symbols.) 



I 2 3 -^ S 



Fig. 23.— The rate of gain per day by size of 

 litter (Table 20), 1916-1919. (See Fig. 8 for 

 explanation of symbols.) 



Another important resultps 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, 



