Growth Rates of Successive Feathers from Single Follicles in the Juvenile Brown Leghorn. ∗

Abstract

The juvenile plumages of the Brown Leghorn of both sexes pass through a series of changes in pigmentation during successive regenerations. These changes are particularly notable in the feathers which are present at hatching, or emerge shortly after hatching. In the wings and tails, for example, the first feathers to appear are stippled or mottled. The second generation of these feathers shows marked changes towards the adult pattern. In pigmentation, third generation feathers are practically identical with homologous feathers of the adult.

It has been shown previously from this laboratory that there is a direct relation between the concentration of female hormone or thyroxin required for reaction and rate of growth of feathers. (Juhn and Gustavson, 1 Juhn, Faulkner and Gustavson, 2 Lillie and Juhn 3 ). There is also a definite range of growth rates characteristic of the feather tracts, and of individual feathers within the tract (Juhn, Faulkner and Gustavson, 1931). These growth relations known to exist in the adult suggest that the juvenile pattern types and changes in these types may be correlated with changes in rates of feather growth during successive juvenile regenerations. In order to test this assumption, we have determined the rates of growth of feathers from a number of tracts in Brown Leghorn chicks. Measurements of length of feathers were begun as soon as possible after hatching, or appearance of feathers, and continued over 2 (in some cases 3) successive regenerations. In all cases which we have studied the rate of growth of the first feather from a given follicle is lowest; second and in many instances third generation feathers grow at increasing rates.

The changes in rates of growth of successive feathers from a single follicle are well illustrated by the main tail feathers.