Oct. 27, 1923 
Otocephaly in Guinea Pigs 
169 
subsequent injury to the offspring (as suggested by Werber ( 11 ) in 
connection with experiments on butyric acid and acetone). 
If the genetic element is of any such kind, females of Family 13 should 
produce as high a percentage of otocephali in outcrosses as in matings 
with brothers. A large number of outcrosses of this kind have been 
made, all of them since 1916, since which time Family 13 has been 
composed exclusively of high producing lines and has produced an 
average of 2.7 per cent otocephali. There have been 711 young from 
crosses in which the dam was of Family 13 and the sire either an inbred 
or a cross between two other inbred families. One otocephalus appeared, 
a frequency of one-seventh of 1 per cent, where some 19 were to be 
expected on the basis of the production of such females mated with 
brothers during this period. The single otocephalus was sired by a 
male from a cross between Families 32 and 39, the former of which 
produced 9 otocephali itself. 
Among 373 young whose sire was of Family 13 but whose dam was of 
another family or unrelated cross, there were no otocephali. There was 
also none among about 3,000 crossbred young, neither of whose parents 
had blood of Family 13. Two, however, were produced by crosses in 
which Family 13 was involved on both sides. One of these was a three- 
quarter-blood, dam of Family 13 and sire from a cross between Families 
13 and 34. There have been 147 three-quarter-blood young whose 
dams were of Families 13 and 189, none otocephalic, from the reciprocal 
type of mating. The other crossbred otocephalus was from a selection 
experiment (CL). Both the sire and dam were one-quarter blood of 
Family 13. Among 234 F 2 young from crosses between Family 13 and 
other families, there were no monsters of this kind. 
This study of the crosses again indicates transmission of the otoce¬ 
phalic tendency from Family 13. It also indicates that it is not a 
maternal character. 
SEX 
Table III shows data on the sexratio among otocephali. Both in Family 
13 and in the other families there have been more than twice as many 
females as males. In all there have been 55 females and 26 males with 
1 undetermined, a sex ratio of 47.3 as compared with approximate 
equality among all the young from the same matings (sex ratio 97.0). 
There is here a departure of 4.8 times the probable error. Such a de¬ 
parture would occur only about once in 800 times by chance. It is 
thus fairly certain that female sex predisposes toward development of 
this defect. A possible explanation is that the level of metabolism is 
lower in female than in male embryos at the critical moment in develop¬ 
ment, rendering them more easily depressed by unfavorable conditions. 
Such an interpretation is in harmony with the views of Whitman and 
Riddle ( 12 ) on the early differentiation of the sexes. 
