176 
Journal of Agricultural Research 
Vol. XXVI, No. 4 
Table IX .—The average weight at birth of otocephali, their litter mates and their brothers 
and sisters of other litters , in Family 13, other stocks, and the total a 
Family 13. 
Other stocks. 
Total. 
Number. 
! Average size of lit¬ 
ter. 
Average 
weight. 
Number. 
Average size of lit¬ 
ter. 
Average 
weight. 
<u 
Average size of lit¬ 
ter. 
Average 
weight. 
Standard deviation. 
Actual. 
Adjusted. 
Actual. 
I 
Adjusted, j 
Actual. 
Adjusted. 
Gm. 
Gm. 
Gm. 
Gm. 
Gm. 
Gm. 
Gm. 
Otocephali. 
so 
2. 76 
66. 7 
64.2 
3 X 
3.00 
71 -3 
71-3 
81 
2.85 
68.5 
67. o±i. 4 
18.7 
Litter mates. 
7 S 
3-37 
7 i -3 
74 -i 
60 
3-43 
73 -o 
77-4 
135 
3 - 34 
72.1 
75.6±i. 1 
18.8 
Nonlitter mates. 
418 
3-16 
74*4 
76.1 
286 
3 -14 
77*3 
78. 7 
704 
3-*5 
75*6 
77 - i±o. 5 
20.4 
0 Owing to the important effect of size of litter on birth weight, an average birth weight adjusted to an 
average size of litter of three is given as well as the actual figures. 
Corrected or not corrected, there is not much difference between the 
average weights of litter mates and nonlitter mates, although the former 
are slightly lighter according to both (corrected, litter mates 75.6 ±1.1 
gm. nonlitter mates 77.1 ±0.5). Here, again, we have a slight indi¬ 
cation that unfavorable conditions cause otocephaly, but in this case 
the difference is statistically of no significance. 
The otocephali themselves are about 11 per cent lighter in weight 
than their normal litter mates. This difference, however, is to a large 
extent accounted for by their small heads. Taken as a class they show 
no evidence of malnutrition. 
The direct search for indications of an environmental factor in deter¬ 
mining otocephaly has led to rather meager results, although all lines of 
evidence agree in indicating that unfavorable environmental conditions 
have some influence. 
There is one consideration which might well have discouraged such a 
search from the first. If otocephaly is determined by external factors 
of such nature as to act on litter mates alike, we should expect to find 
in many cases more than one otocephalus in a litter. There have been 
only six such cases and three of these are among descendants of the 
line from mating 13-19-1, in which the high frequency of otocephali 
(21.5 per cent) makes the chance occurrence of two in a litter a frequent 
probability. Of these six cases two were litters of two, both otocephali, 
while the others were in litters of three, two otocephali and one normal. 
Expressed in another way, otocephali have had 12 otocephalic litter 
mates (each pair counted twice) in a total of 152 litter mates, or 7.9 per 
cent otocephalic. They have had 64 otocephalic brothers and sisters 
among 1,107 in other litters, or 5.6 per cent. There is thus no appreciable 
tendency for otocephali to occur in the same litters, and, as we have 
previously seen, very little tendency for them to occur in the same mat¬ 
ings, unless the whole line to which they belong is characterized by pro¬ 
ducing a high percentage. All environmental factors which act alike 
on litter mates, through effect on the condition of the dam or otherwise, 
are at once ruled out as factors of more than very secondary importance. 
The case is parallel to that of the piebald pattern in guinea pigs, which 
is determined nearly 60 per cent by nongenetic factors, but to no ap- 
appreciable extent by factors which act on litter mates alike ( 14 ). 
