372 
Journal o f Agricultural Research 
Vol. XXIX, No. 8 
accumulation of fat in this region, 
tending to push downwards the ventral 
body wall. This produces the ventral 
sagging of the abdominal wall, which 
is characteristic of a laying hen. 
than the leg length. There is less 
sex difference than would be expected 
from the weights. As will be shown 
later, the male comb is far larger and 
the weight of the head in the older 
Fig. 6 .—-Length of head (in centimeters) from tip of bill to the most posterior part of the head, plotted on 
age in days. After about 105 days the head appears shorter in the females 
Head length. —Figure 6 shows the 
increase in length of the head. The 
formula is: F= X°- 36 + 0.007X+ 1.44 
in which Y represents the head length 
in centimeters and X represents the 
age in days. The formula applies to 
male birds is consequently greater 
than the weight of the head in the 
females. A study of Figures 6, 7, and 
10 will suggest that the sex difference 
so evident in the head weight is due 
very largely to the greater weight of 
Fig. 7.—Growth in absolute and percentage weight of the entire head, without feathers, plotted on 
gross body weight. The individual specimens at 2,300 and 2,440 gm. gross body weight were too 
heavy to be included on the chart. A sex difference in head weight appears beyond about 300 gm. 
gross body weight. This difference is accentuated by the increased growth of comb in males above 
1,400 gm. in gross body weight 
the males from 10 to 140 days, then 
the curve is constant at 8.34 cm. For 
the females the formula applies from 
10 to 105 days after which time the 
curve remains constant at 7.5 cm. 
The growth curve of the head length 
resembles the wing length more closely 
the male comb and wattles. The 
linear measurements when plotted on 
age all show a continuous convexity 
superiorly, although the curves show 
different rates of growth and rates 
differing at different ages of the chicks. 
The linear measurements employed 
