Oct. 27, 1923 
Otocephaly in Guinea Pigs 
171 
TABLE IV .—The birth rank of otocephali in relation to that of all young from matings 
which produced otocephali , excluding two matings which produced only one litter 
each 
Rank of litters. 
Total. 
Last 
re¬ 
cord¬ 
ed. 
z 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
Otocephali. 
17 
XX 
17 
10 
6 
7 
3 
1 
4 
X 
X 
X 
79 
xo 
Total. 
*45 
X 55 
161 
136 
103 
80 
48 
36 
23 
IS 
10 
4 
916 
165 
Per cent. 
ix- 7 
7 -x 
10.6 
7-4 
5-8 
8.7 
6-3 
8.8 
17. 4 
6.7 
xo. 0 
25.0 
8.6 
6.1 
The impression which one obtains from the table is that birth rank 
is of very little importance. An otocephalus is about as likely to be 
born in one litter as another. It is true that first litters show some ex¬ 
cess over second litters, but the excess over third litters is insignificant. 
The percentage in last litters from these matings (third to twelfth litter) 
was a trifle less than in the whole population (6.1 per cent as compared 
with 8.6 per cent). 
First litters are born predominantly in winter when conditions are 
unfavorable, the majority of matings being made in summer, half a 
year earlier. Any slight tendency toward excess of otocephali in first 
litters may be due to this cause. We conclude that there is no demon¬ 
strable difference due to birth rank. 
SEASONAL FLUCTUATIONS 
The number of otocephali born in each month in comparison with all 
young from the same matings is shown in Table V. It will be noticed 
that there is no very conspicuous difference among different months r 
but that a somewhat higher percentage of otocephali are born in the 
months from January to April, inclusive, than during the rest of the 
year. During these four months Family 13 produced 42 per cent of its 
otocephali while the same matings were producing only 27 per cent of 
their total young. Similarly, the other stocks produced 44 per cent of 
their otocephali while only 30 per cent of their young were being born. 
The application of the x 2 test to the number born in each month, 
assuming 8.9 per cent as the expected figure in each case, gives the prob¬ 
ability of 0.363 that the distribution is random. If, however, the year 
is broken into four-month periods for application of this test, the prob¬ 
ability becomes only 0.013. Thus there is a distinct indication that 
more otocephali are born following the unfavorable winter conditions 
than in the rest of the year, but it is only an indication. 
Table V. —The month of birth of otocephali in relation to that of all young from matings 
which produced otocephali 
Month of birth. 
TotaL 
Jan. 
Feb. 
Mar. 
Apr. 
May 
June 
July 
Aug. 
Sept. 
Oct. 
Nov. 
Dec. 
Otocephali. 
8 
XI 
7 
9 
7 
5 
6 
5 
8 
6 
3 
7 
82 
Total.. 
ss 
83 
7 i 
50 
84 
88 
86 
89 
80 
67 
70 
98 
92X 
Per cent. 
14-5 
13-3 
9.9 
18.0 
8-3 
5*7 
7.0 
5-6 
10.0 
9.0 
4-3 
7 -i 
8.9 
