56 BULLETIlSr 1090, U. S, DEPAETMENT OF AGRICULTUEE. 



absence of appreciable correlation between first and second periods 

 among the five families in contrast with the significant correlatior 

 found in dealing with all 22 families (Table 3) is of course due to thej 

 large part played by Families 2 and 35 among the 5 families. Ilj 

 strengthens the evidence for inheritance to find that even these^ 

 families became fairly well settled in relation to the other families 

 during the second period. 



Considering the separate characters the evidence for differentiation 

 in weight is most consistent. There is close agreement between 

 rank in weight at all ages and in both sexes. The only important 

 exception is that Family 32 appears to produce heavy young rela- 

 tive to its adult weight. 



The rank of the families in both size and frequency of litters 

 appears to have become fairly well settled in the second period. 

 Because of the negative correlation present in the five families 

 between these elements of fertility there is not much differentiation 

 in the product, the number of young produced per year. The 

 perfect correlation in 1916-1919 between adult weight and size of 

 litter is noteworthy. It will be remembered that significant correla- 

 tions were fomid among the 22 families between birth weight or gain 

 and size of litter in the second period. The possible explanation 

 suggested in that case, namely that the three best families in both 

 weight and size of litter were all derived from one male ancestor, has 

 no application among the five families considered here. There is 

 undoubtedly an indication of a direct physiological relation between 

 weight and size of litter, apart, of course, from the direct (negative) 

 effect of size of litter on the early weights, for which due correction is 

 made by the use of indexes. 



There is good evidence for differentiation in both percentage born 

 alive and percentage raised of those born alive. Just as in the case 

 of the two elements of fertility, there happens to be a negative correla- 

 tion between the two characters among the five families, with the 

 consequence that there is no very clear-cut differentiation in their 

 product, the percentage raised of all births. 



The longevity of the males and females born 1915-1918 was obtained 

 by taking each interval of three months in age separately and finding 

 the death rate among those not disposed of during the period in 

 question. The most noteworthy feature is the marked superiority 

 of Family 2 shown by both sexes. There was not much differentia- 

 tion among the other families, 



A comparison of ranks in different characters during the third period 

 confirms the conclusion drawn from study of the 22 families in the 

 earlier periods, namely, that there is not differentiation in general 

 vigor, but differentiation in each characteristic separately. The 

 number of young raised per year by a mating is perhaps the best single 



