422 Data on Variation in the Comh of the Domestic Fowl 
either of these things directly in a satisfactory way. At the outstart of the work 
it was felt to be absolutely essential to get some kind of a picture of each in- 
dividual comb. Practical considerations ruled photography out as a means of 
reaching this end. Resort was had to drawing the combs actual size with the 
aid of a camera lucida arranged not to magnify or distort the image. In this 
way one can get an accurate outline of the lateral aspect, or, more correctly, of 
a sagittal section of the comb. It was at first thought that it would be best to 
make such drawings with the comb still attached to the head. Experience 
showed however that this was not the case. More uniform and accurate repre- 
sentation of the base of the comb could be made if it was removed from the head. 
After this was learned all the combs were removed before they were drawn. They 
were cut off with a sharp scalpel, great care being taken to ensure that the cut 
evenly followed the contour of the top of the skull. The severed comb was put 
on a flat surface after removal, and the basal cut edge was made, as nearly as 
possible, a straight line. After the outline of each comb had been drawn, the area 
bounded by the outline of the comb was determined by means of an Amsler polar 
planimeter to tenths of a square centimetre. Our procedure was as follows : the 
area of every comb was measured twice ; if the results of the two measurements 
did not agree, a third measurement was then taken. If this measurement agreed 
with one of the others, it was taken as the final result. If it did not agree with 
either of the other two, an average was taken of the three measurements and 
the average recorded as the area. Every efFoi-t was made to attain accuracy 
in the planimeter measurements, and it is believed that the figures given are 
substantially correct. 
In addition to the comb area, the length of the comb was measured. This was 
done by placing a sliding arm-caliper on the outline drawings, and adjusting it 
so that the arms touched respectively the most anterior and posterior points of 
the comb outline, with the bar of the caliper parallel to the base of the comb. 
It was desired to measure the height of the comb, but attempts to do this directly 
failed. The reason for the failure will be apparent if one examines the figures. 
The top of the comb is an irregular, serrated line. It is quite a matter of accident 
which particular point of region of the comb happens to be highest. If one were 
to measure the height at different points in different combs, it is plain that one 
would not always be measuring morphologically identical or even comparable 
things. Thus, in one case (Fig. 27, Plate I.) the highest part of the comb might 
be at the very posterior end, and in another case well toward the anterior end 
(Fig. 93, Plate III.). Height measurements made on such a plan would have 
no particular significance. Yet comb-height is a very significant thing, parti- 
cularly in cold climates. The tall comb (e.g., the Leghorn type) is much more 
liable to be frozen than is the low Plymouth Rock comb. It is highly important 
to get some measure of height in a study of comb variation. After a careful 
study of the problem we have reached the conclusion that a fairly trustworthy 
and significant measure of comb-height will be obtained if we take the height 
of a rectangle having a length and an area equal to that of the comb. We 
