and also in reistance to tuberculosis. It was @5ncluded from a 
consideration of he various lines of evidencey’that the inbreeding 
was in some way respoisible for at least.ag part of the decline. 
In Part Il? a detailed study was made of the 23 separate inbred 
families. It was shown that marked hereditary differentiation 
had been brought out among them early in the course of the inbreed- 
ing and that the differences had increased later. There had been 
also an automatic differentiation and fixation of the more obvious 
characteristics, such as color, pattern, and tendency toward poly- 
dactylism and toward the production of particular types of monsters. 
It was found that the various elements of vigor and weakness had 
become fixed in almost every possible combination in the various 
families, there being no evidence for hereditary differences in general 
vigor. 
The purpose of the present paper is to present the results of crosses 
between the inbred families. 
THE INBRED FAMILIES. 
Of the 17 inbred families still in existence in 1916, only 5 have been 
retained to the present. It seemed necessary to eliminate the others 
in order to make room for the crossbreeding experiments and to 
obtain sufficient numbers from these five. Families 2, 13, 32, 35, 
and 39 were the ones retained, partly because they occupied a large 
number of pens, and partly because of contrasting characteristics. 
Family 39, for example, had the least white in the coat, while Family 
13 had the most. Family 32 had a peculiar intense golden agouti. 
Families 2 and 13 were at opposite extremes in weight and also 
contrasted in size of litter. 
CROSSBREEDING EXPERIMENTS. 
The control stock, Experiment B, has been maintained, as from the 
first, by matings between individuals less closely related than second 
cousins. 
Since 1916 a large number of first crosses have been made between 
different families. These constitute Experiment CO. The young are 
crossbred but the parents are inbred. 
Some of the progeny from Experiment CO have been mated with 
others from a different cross, thus bringing together four inbred 
families. This is Experiment CC. Both parents and young are cross- | 
bred in this case. | 
Other animals from Experiment CO have been mated brother with | 
sister. This is Experiment C1. The parents are crossbred but the | 
young are to some extent inbred. 
2 U.S. Department of Agriculture Bulletin 1090. 
