170 Journal of Agricultural Research voi. xxvi, no. 4 
Table III. —The number of males , females, and young of undetermined sex , and the sex 
ratio among the otocephali in the litters and from the matings containing the latter 
(otocephali included in the latter classes) 
Family 13. 
Others. 
Total. 
9 
?<* 
Sex 
ratio. 
d 
9 
la 
Sex 
ratio. 
<? 
9 
?o 
Sex 
ratio. 
Otocephali. 
16 
33 
1 
Per 
cent. 
48. 5 
10 
22 
O 
Per 
cent . 
45-5 
26 
55 
I 
Per 
cent. 
47-3 
Litters with 
otocephali. 
55 
66 
4 
83-3 
44 
48 
O 
9 1 * 7 
99 
114 
4 
86.8 
Matings with 
otocephali. 
253 
279 
11 
9 °. 7 
194 
182 
2 
106. 6 
447 
461 
13 
97.0 
• Undetermined. 
ENVIRONMENTAL CONDITIONS 
The data have been studied carefully for indications of the effects of 
environmental factors. The size of litter, birth weight, and mortality 
at birth and from birth to weaning are characters which are greatly 
affected by external conditions. The month of birth is important, since 
conditions have usually been distinctly poorer in winter than during 
the rest of the year. The possibility that birth rank (first, second, 
third litter, etc.) may play a part has also been investigated. 
In these studies a control is necessary. The averages for the char¬ 
acters listed above have varied greatly from year to year in all stocks, 
depending largely on how the guinea-pig colony has passed through the 
winter. There has also been a decline, due to inbreeding. Thus the 
records of stocks producing young at approximately the same time 
should be used as a control. The best plan has appeared to be to com¬ 
pare the otocephali with their litter mates and both of these classes 
with the young produced by other litters from the same matings. 
Family 13 has been dealt with separately from the other stocks. It 
will be noticed that its records are usually somewhat lower. This may 
appear to contradict the statement previously made that Family 13 was 
the most vigorous of the inbred families, notably in size of litter and 
weight. The explanation is that most of the otocephali of this family 
came in the later years, when there had been a decline due to inbreeding 
and, in certain of which, conditions were at the poorest (as judged by 
the control stock) while most of the other otocephali came in early 
years when there was less inbreeding and conditions were better. In 
any given year, Family 13 stands out as the best of the inbred families 
in these respects. 
BIRTH RANK 
Table IV summarizes the data on birth rank, showing the birth rank 
of otocephali in relation to that of all young from matings which pro¬ 
duced them, with the omission, however, of two matings which pro¬ 
duced only one litter each (containing five young, of which three were 
otocephali). All matings included produced at least three litters. A 
fair comparison can accordingly be made of the percentage of oto¬ 
cephali in first, second, and third litters. A slightly smaller percentage 
is to be expected in the fourth and later litters for obvious statistical 
reasons. 
