6 



BttLLETlN 1090, IT. S. DEPARTMENT OE AGBICtTLTURE. 





of in the third generation because a skin disease had become estab- 

 lished in it. These failures can not be ascribed to inbreeding. 



There were thus 23 families with which the inbreeding experiment 

 really started. One of these (Family 15) became extinct in 1911. 

 Family 1 followed in 1914 and Families 3, 11, and 21 in 1915, leaving 

 18 families in existence at the end of 1915. Families 14, 19, and 34 

 became extinct before the middle of 1917. In the summer of 1917 

 several other experiments had become so extensive that it seemed 

 best not to attempt to maintain all of the inbred families. Five 

 families — 2, 13, 32, 35, and 39, were selected for perpetuation, while 

 the others were gradually eliminated. (Pis. I to VI.) The condi- 

 tion of the families in November, 1915, is shown in Table 1. 



Table 1. — Number of matings in each generation of inbreeding in each family on 



November 15, 1915. 



[The original matings are called the zero generation.] 



Family. 



Generation — 



Num- 

 ber of 



6 



7 



8 



9 



10 



11 



12 



13 



14 



15 



mat- 

 ings. 



2 







4 



10 



11 

 4 

 1 

 6 



6 

 3 

 4 

 13 











31 



7 







1 

 6 

 15 



3 



4 

 5 



1 

 1 





12 



9 









1 



17 



13 









39 



14 



1 



1 











2 



17 





1 

 1 



1 

 3 

 3 



7 

 4 

 2 

 1 



3 

 3 



4 

 5 

 2 

 2 

 4 

 3 

 1 

 5 



11 

 6 



18 



6 

 4 

 1 

 1 

 1 

 1 

 6 

 4 



6 



4 



3 



1 



21 



18... 









15 



19 













8 



20 









5 

 4 

 2 









18 



23 







1 









12 



24 . 













7 



31 i 









4 

 12 







15 



32 











7 



1 



27 



34 











2 

 2 

 5 

 



7 



3 



35 









1 

 1 

 1 

 1 



10 

 6 



7 

 14 



11 

 2 

 3 

 2 



8 



1 



38 



36 









25 



38 









1 



1 



19 



39 









42 

















Total 



1 



1 



5 



28 



59 



93 



83 



56 



21 



4 



351 







The 23 families which have been made the basis of analysis were 

 descended from 23 different females, but are not so distinct from one 

 another on the male side. Only nine males were in fact used in the 

 foundation stock. Male 1 was used with Females 1, 2, 3, and 7 to 

 found the families named from these females. Male 13 was the male 

 ancestor of Families 9 and 11 and parts of Families 13 and 14. Male 2 

 was the male ancestor of the remaining lines in Families 13 and 14 

 and all of Family 15. Families 17 to 24 are all descended from 

 Male 3; Families 31 and 32 from Male 9; Families 35 and 36 from 

 Male 11, while Families 34, 38, and 39 had separate male ancestors. 

 It may be seen that Families 13 and 14 are really composite and 

 each might well have been treated as two families. In Family 13 

 the line descended from Male 2, began to decline after three genera- 



