DATA ON VAKIATION IN THE COMB OF THE 
DOMESTIC FOWL*. 
By RAYMOND PEARL and MAUD DEWITT PEARL. 
1. Much of the evidence adduced in support of Mendel's law as a general 
method of inheritance has been derived from breeding experiments with the 
domestic fowl. The woi'k of Bateson, Hurst, and Davenport has served to make 
it a classical object of research in this field. One of the most obvious of the 
" unit characters " of poultry is the form of the comb. All students of inheritance 
in this group have included the study of the comb in their work. The behaviour 
of the various comb types in inheritance is frequently cited as a well-nigh perfect 
example of typical allelomorphism. The different comb types — single, pea, rose, 
etc. — are commonly said not to blend in cross-breeding, but instead to be inherited 
in a strictly alternative manner and in accordance with Mendel's law. 
In spite of the extensive use of comb form in poultry as a character in the 
study of inheritance there has been, so far as we are aware, no particular study 
ever made of the degree and character of variation within each of the several 
known types of comb. About a year ago an opportunity was afforded one of us 
to carry on extensive breeding experiments with poultry. The plans made for 
the prosecution of such experiments included the investigation of the inheritance 
of comb characteristics. It was felt to be highly desirable in connection with this 
work to gain some sort of idea of the degi-ee and manner in which there was 
variation within each of the several comb types. Such questions as the following 
suggest themselves : How far from the normal in any direction may the single 
comb, for example, be expected to depart in pure bred birds? What degree of 
variation, biometrically considered, do the various comb characters exhibit ? The 
work of Weldon on peasf and on Lychnis J has demonstrated the importance of 
such studies in relation to the analytical investigation of Mendelian phenomena. 
All studies of this kind take their point of departure in an attempt to analyze 
* Papers from the Biological Laboratory of the Maine Agricultural Experiment Station. Orono, 
Maine, U.S.A., No. 8. 
t Biometrika, "Vol. i. pp. 228 — 254. 
J Ibid. Vol. II. pp. 44 — 55. 
