30 



BULLETIIT 1121, U. S. DEPAKTMENT OF AGRICULTUEE. 



sires) from large litters (CL) or from small litters (CG) is without 



TOTAL FERTILITY. 



The number of young born per mating year (Fig. 18) is merely the 

 product of the two elements of fertility, frequency and size of litter, 



60 



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20 















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11.50 

 ,CG 











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y 



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 2 

 /3 



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32 



39 

 OI 



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CO 











-20 



Pig. 18.— Young per mating per year, 1916-1919. Effects of seasonal conditions eliminated (Table 2). 

 (See Fig. 8 for explanation of symbols.) 



which we have discussed separately. It is interesting to find that 

 the dam has more influence on total fertility than the sire, in spite 

 of the greater influence of the latter on frequency of litter. Selection 



SO 



60 



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 20 















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7.23 

















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A 







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if 



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35 

 2 



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32 



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 OI 



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-20 



Tig. 19.— Young raised per mating per year, 1916-1919. Effects of seasonal conditions eliminated (Table 

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



of parents on the basis of size of litter is shown to be wholly without 

 effect. 



The best single measure which we have of the reproductive efficiency 

 of the experiments is the number of young raised per year. This is 

 the product of the young born per year and the percentage raised to 

 33 days (actual, not index) . Figure 19 shows the tremendous advance 



