Kaymond Pearl and Maud Dewitt Pearl 
427 
from the others in that the base of the comb is less straight, and the comb is 
canted at an angle as a whole. This condition results from the fact that these 
combs were drawn without removal from the bird's head. It will be noted that 
measurements from them are not included in Table I. 
An examination of these plates shows at once the extraordinary degree of 
variation which exists within a single comb type, even in the most homogeneous 
material. It is appaient that this variation involves both size and form of comb. 
We may first turn to a discussion of the variation in size shown in these combs. 
4. The distributions of frequency for the 81 birds and the three characters 
measured are given in Table II. 
TABLE II. 
Frequency Distributions for Variation in Area, Length, and Calculated 
Height of Female Barred Plymouth Rock Combs. 
Area 
Length 
Calculated Height 
Sq. cm. 
Frequency 
Mm. 
Frequency 
Mm. 
Frequency 
0-5— 1-4 
1 
32— ,34-9 
1 
,3-5_ 4-4 
2 
1-5— 2-4 
5 
35—37-9 
5 
4-5— 5-4 
3 
2-5— 3-4 
3 
38-40-9 
1 
5-5— 6-4 
1 
3-5— 4-4 
18 
41-43-9 
6 
6-5— 7-4 
2 
4-5— 5-4 
21 
44—46-9 
11 
7-5— 8-4 
14 
5-5— 6-4 
8 
47—49-9 
15 
8-5— 9-4 
11 
6-5— 7-4 
9 
50—52-9 
10 
9-5-10-4 
9 
7-5— 8-4 
8 
53—55-9 
13 
10-5—11-4 
10 
8-5— 9-4 
5 
56—58-9 
8 
11-5—12-4 
6 
9-5— 10-4 
1 
59-61-9 
6 
12-5—13-4 
6 
10-5— 11-4 
0 
62—64-9 
3 
13-5—14-4 
11 
11-5— 12-4 
0 
65-67-9 
1 
14-5-15-4 
4 
12-5— 13-4 
2 
68—70-9 
0 
15-.5— 16-4 
0 
71—73-9 
1 
16-5—17-4 
0 
17-5—18-4 
1 
18-5-19-4 
0 
19-5- 20-4 
1 
The chief variation constants for these distributions are given in Table III. 
TABLE III. 
Constants of Variation in Size Characters of Single Conibs. 
Character 
Mean 
Standard Deviation 
Coefficient of Variation 
Area 
Length ... 
Calculated Height 
5-59 + -17 cm} 
50-80 ±-56 mm. 
10-57 ± -23 mm. 
2- 24±-12cm.2 
7-45 + -39 mm. 
3- 03 + -16 mm. 
39-97 + 2-44 7„ 
14-67+ -79 7, 
28-66 + 1-64 7, 
54—2 
