Oct. 27, 1923 
Otocephaly in Guinea Pigs 
165 
DISTRIBUTION WITHIN FAMILY 13 
A detailed study of the history of Family 13 brings out additional 
points of interest. The lines of descent are shown in figure 2. The 
otocephali are represented by circles. 
The features which stand out in the chart are the clusters of otocephali 
in certain lines and their absence in other important subfamilies. The 
original female of Family 13 was mated twice. No otocephali appeared 
among the 404 descendants of her first mate (a line not shown in figure 
1). All the otocephali descend from a mating in the second generation 
of the other line (13-2-5). Another second-generation mating (13-2-7) 
left 199 descendants, but none were otocephalic. Four subfamilies may 
be recognized as springing from 13-2-5 in the third or fourth generation. 
Two of these (13-4-9, 13-3-13) with 196 and 301 young, respectively, 
produced no otocephali. One with 150 young (13-3-11) produced two 
after an inteiVal of seven generations from 13-2-5. The other sub¬ 
family (from 13-4-18) was a very small one in the early generations. It 
produced its first otocephalus in the eighth generation. It began to 
expand with the seventh generation until it displaced all other lines. 
All its branches produced otocephali relatively freely in comparison 
with other inbred families. The general tendency seems to have been 
the production of about 1 per cent. At several points, however, branches 
arose in which the tendency seemed to increase to a noteworthy extent. 
The first cluster of this kind traces to 13-13-1. This mating and its 
descendants, even excluding the most prolific branch, of which we will 
have more to say, produced 9 among 212 young, or more than 4 per cent. 
A veritable epidemic of otocephaly began with mating 13-19-1 in the 
sixth generation from 13-13-1. The six matings of this group have 
