174 
Journal of Agricultural Research 
Vol. XXVI, No. a 
Table VI. —The sizes of the litters in which otocephali were born , as compared with those 
of their normal brothers and sisters a 
Size of litter— 
Family 13. 
Others. 
Total. 
Otocephali. 
Normal. 
Otocephali. 
Normal. 
Otocephali. 
Normal. 
I . 
3 
26 
I 
15 
4 
41 
2. 
17 
103 
9 
79 
26 
182 
3 . 
*9 
173 
13 
134 
32 
307 
4. 
11 
141 
8 
72 
19 
213 
e . 
50 
35 
8S 
6. 
1 
11 
I 
II 
Total. 
50 
493 
32 
346 
82 
839 
Average. 
2. 76±. 08 
3-17±- °3 
3. oo±. 12 
3. I9±. 04 
2. 85 ±. 07 
3. i8±. 03 
Difference .. 
0.41 ±0.088 
o.i9±. 125 
°-33±-°75 
« Note that the average size of litter relative to individuals is larger than the average with the litter taken 
as the unit. The average size of litter (litter as unit) was 2.70 and 2.74 in the matings which produced 
otocephali in Family 13 and other stocks, respectively, as compared with 3.14 and 3.15 where the individual 
was the unit. 
mortality op utter mates 
If otocephali are caused by unfavorable conditions, we should expect 
a higher mortality among their normal litter mates than among normals 
from litters which did not include otocephali but which were from the 
same matings. The parallelism in the seasonal fluctuation, in these 
characters, allowing a lag of a month, however, has already been shown. 
The data for the direct relationship between them are presented in 
Tables VII and VIII. A comparison between Family 13 and other 
stocks is given in Table VII. In Table VIII all stocks are combined. 
We find that a distinctly smaller percentage of litter mates were bom 
alive (73.3 ±2.6 per cent, as compared with 80.7 ± 1.0 per cent for non¬ 
litter mates). Similarly, a smaller percentage of litter mates are raised 
of those born alive (73.7±3.0 per cent, as compared with 77.3 ±1.2 
per cent for nonlitter mates). Among the litter mates 54.1 ±2.9 per 
cent of all young bom dead or alive were raised to weaning, as com¬ 
pared with 62.4 ± 1.2 per cent among nonlitter mates. 
One objection which may be raised to these comparisons is that they 
are based on young bom in litters of different sizes. There can be, for 
example, no litter mates of otocephali bom in litters of one. If, however, 
the percentages are compared for corresponding sizes of litter, the same 
results are found. If the averages for each size of litter among the non¬ 
litter mates are weighted by the number of litter mates bom in each 
size, we get grand averages only slightly different; 81.6 per cent bom 
alive, 77.2 per cent raised of those bom alive, and 62.3 per cent raised 
of all young. The difference between litter mates and nonlitter mates 
in total percentage raised is 8.3 ±3.1, or 2.6 times the probable error. 
There can be little doubt that conditions which cause a high mortality 
among normal young have some influence in determining otocephaly. 
Here again, however, the relation is not very great. 
