164 
Journal of Agricultural Research 
Vol. XXVI, No. 4 
Inbreeding resulted in a decline in vigor on the average in all respects, 
including the weight at birth and later ages, size and frequency of litters, 
and the mortality at birth and . later. The families differed greatly in 
the degree of the decline. It might be thought that the families which 
declined the most in vigor would produce the most monsters. It happens, 
however, that Family 13, with by far the highest percentage of otocephali, 
was also the most vigorous on the whole of the 23 families up to 1915. 3 
It has always been among the best three in weight at all ages and in size 
of litter, and is the only family which was better than the average in all 
respects studied. Among the five families now on hand it still produces 
the heaviest pigs and the largest litters. The two weakest families in 
nearly all respects were No. 1 and 15, which produced no otocephali or 
monsters of any sort except for one clubfoot (ectromelus) in Family 15. 
It is clear that the production of otocephali is not merely a manifestation 
of lack of vigor. 
The conclusion which is forced upon us is that there is an important 
hereditary basis to otocephaly. The part which inbreeding plays here, 
as in other cases, is merely to bring clearly to light 'the hereditary differ¬ 
ences between different strains. Indeed, the fact that one high-grade 
otocephalus appeared in the control stock B indicates that the tendency 
was probably present before the inbreeding commenced. 
DISTRIBUTION BY GENERATIONS 
The distribution of the otocephali within Family 13 and within Family 
32, which stood second in their production, is of interest. In the former 
the first otocephalus appeared in 1908, in the second generation of 
inbreeding, but there were no others until one came in the eighth gene¬ 
ration in 1912. Twenty-five of the 50 in this family appeared in the 
seventeenth and later generations and no fewer than 17 in the two most 
advanced generations, the twentieth and twenty-first. This again sug¬ 
gests the traditional cumulative effect of inbreeding. The history of 
Family 32, however, happens to be nearly the reverse. The nine otoce¬ 
phali were produced in the third to the eighth generations among 1,040 
young. Not one has appeared since the eighth generation (1,516 young), 
in contrast with 48 in Family 13 in these generations, although the two 
families have run roughly parallel in number of young and generations 
of inbreeding. Family 32 has now (1922) reached the twenty-first 
generation. The other families show no tendency toward increasing 
appearance of otocephali. Only 1 out of 19 has appeared since the 
thirteenth generation, although one of these families has reached the 
twenty-fourth generation. 
Under the system of brother-sister mating, each family tends to split 
up into subfamilies. The subfamily which happens to advance most 
rapidly in inbreeding tends to displace the others. The apparently 
contradictory results in Family 13 and the others, relative to distribu¬ 
tion by generations, are readily reconciled by the hypothesis that there is 
segregation of the hereditary factors for otocephaly, and that it is largely 
chance whether the subfamily which receives such factors to the greatest 
extent is the one which pushes ahead most rapidly. 
1 The data for Family 4 have not been analyzed. 
