Effects of Thyroxin and Female Hormone on One Phase of Saddle Feather Development

Abstract

The c-isochrone has been defined by Fraps and Juhn 1 as the locus of points in the regenerated feather representing a given level of cell division around the annular collar of the feather germ. This locus appears as a constant configuration in each vane-half of the grown feather and is symmetrical with respect to a common transverse shaft level. If the barbs of either vane-half are in parallel array (at any uniform angle with the shaft), the c-isochrone is a straight line from shaft to margin, equidistant on shaft and a given barb from the point of union of that barb with the shaft. In Fig. 1, for example, barbs are laid out at right angles to the shaft, AB (apex of the feather at A), and the c-isochrone must form in this particular construction an angle of 45° with the shaft. Since the apex of the feather forms first, an apical-most c-isochrone, Am of Fig. 1, drawn from apices of the two barbs uniting at their bases to form the shaft (when these are in alignment with the shaft) identifies elements represented in the collar at the onset of feather growth. Successive c-isochrones taken at regular intervals in apico-basal order determine similarly the number of barbs simultaneously represented in the collar of the germ and are the source of other data treated by Juhn and Fraps 2 in the formation of a number of developmental relations. The subcutaneous injection of thyroxin or female hormone into the Brown Leghorn male or capon causes, among other things, marked changes in the contours of certain feathers, notably those of the saddle tracts. What appeared to be a limiting effect of thyroxin on contour was taken by Fraps and Juhn as evidence for the constant configuration of the c-isochrone itself, a deduction resting entirely upon the existence of an open ventral field in saddle feather germs.