40 



THE AMERICAN NATURALIST 



[Vol. LV 



was a cross between families 35 and 2 and whose dam 

 was of family 13, was entered once under each of the 

 former families and twice under family 13. The aver- 

 ages of the entries under each family in this tabulation 

 are given in Table XIII. It will be seen that in each 

 group of experiments, family 35 has a distinct lead over 



TABLE XIII 



the others as ancestral to resistant crossbreds. Family 

 39 and the other families which entered into the ancestry 

 of the crossbreds appear to rank with the more sus- 

 ceptible families 13 to 32. It will be seen that the rank 

 of families 35, 2, 13 and 32 as ancestors of resistant 

 crossbreds is the same as their own rank in resistance. 

 These results are brought out more clearly in a tabula- 

 tion in which all of the crossbreds are classified as half- 

 blood, quarter-blood and zero-blood of family 35. The 

 last class may be divided into half-blood, quarter-blood 

 and zero-blood of family 2. The results in comparison 

 with those for family 35, 2 and the others combined are 

 given in table XIV. 



The half-bloods of family 35 are distinctly superior 

 to family 35 itself, and thus much superior to their other 

 ancestral families.^ In the three groups of experiments 



* The preliminary study of another large series of animals (lots 15 to 21) 

 shows that while the order among the crossbreds, as related to the presence 

 of the blood of family 35 has been maintained, the advantage of the half- 

 half -bloods slightly less. The order of the inbred families it may be added 

 remains exactly as described. 



