428 Data on Variation in the Comb of the Domestic Fowl 
From these tables the following facts are to be noted : 
(1) The average area of the combs of the females of the race of Barred 
Plymouth Rocks here discussed is in round numbers 5^ square centimetres. The 
average length of comb is a little over 5 cm. This indicates an average calculated 
height of 10^ mm. On account of the way in which the combs were removed (cf. 
p. 422), this represents the average height above the top of the skull, 
(2) There is a high degree of variation, both absolute and relative, in regard 
to each of the size characters studied. The Barred Plymouth Rock female ac- 
cording to the American Standard of Perfection* has the comb "small, proportional 
to the size of the specimen, set firmly on the head, straight and upright, evenly 
serrated, having five well-defined points, those in front and at rear being somewhat 
smaller and shorter than the other three." The drawings and figures here pre- 
sented show that in the absence of special selection in regard to comb size, the 
character shows a range of variation all the way from the condition shown in 
large combed types like the Leghorns to the very smallest of single combs (cf. 
for extremes. Figs. 85 and 93 of Plate III.). 
(3) The amount or degree of variation, whether measured absolutely or 
relatively, is not the same for the characters measured. The area shows the 
highest and the length the lowest coefficient of variation. This relation is to 
be expected from the form of the comb. The chief factor in determining variation 
in area is the shape of the serrated portion of the comb. The figures of Plates 
I. to III. show how variable in shape the combs are. It must be remembered that 
the comb characters studied are not independent variables f. 
5. We may turn next to the consideration of variation in the shape or form 
of the comb. In the typical single comb such as is shown, for example in 
Diagram A, there are to be distinguished four regions or parts which are 
morphologically distinct. 
a 
Diagram A. Outline of a typical single comb removed from the head. The dotted lines indicate 
distinct regions of the comb. The comb outline of this figure is a copy of Figure 2, Plate I. 
These regions may be designated as follows : 
(1) A basal region (Diagram A, a) forming the attachment of the comb 
to the top of the skull. From the base springs the vane, or upright portion. In 
the vane are to be distinguished three portions as follows : 
* Published by American Poultry Association, 1906. 
t The value of v is directly deducible from that of v , and v , when we know the correlation of area 
and length. We find for length and area correlation c . , = '845, from /■ , = (i; '^ + v.'^ -v.'^)l{2v .v.). 
AL AL ^ A L H ' A L' 
