Germinal Basis of Thyroxin and Female Hormone Effect on Barb Origin in Saddle Feathers

Abstract

The subcutaneous injection of thyroxin or female hormone into the Brown Leghorn male or capon brings about modifications in saddle feathers which, on the basis of c-isochrone relations, signify the origin and growth of definitive barb primordia in a previously undifferentiated ventral field of the germ (Fraps and Juhn, 1 Fraps 2 ). With sufficient concentration of thyroxin, a greater or lesser number of barb apices appear to arise practically simultaneously. Female hormone brings about only slight changes of a similar nature in breast feathers, suggesting that the ventral regions of these germs normally carry a full complement of barb primordia. The only direct observation bearing on this indicated difference in germinal organization was made by Lillie and Juhn, 3 who noted that the unoccupied ventral region of saddle feather germs appeared to be considerably wider than the comparable region in breast germs; Lillie and Juhn, however, attributed this difference largely to the lowness of ridges in saddle germs. A comparison of breast and saddle feather germs prepared before and following injection of thyroxin has therefore been made with a view toward establishing the embryonic basis of the ventral differentiations indicated by c-isochrone analyses of regenerated feathers.

Figs. 1-5 represent, rather schematically, the ventral regions of regenerating germs split along their dorsal faces and spread into the plane of the paper. Apical levels are cut away (excepting in Fig. 1), as are also the undifferentiated germ bases. The sloping lines indicate barbs and barb primordia visible in the several preparations. Increasing diameters of barb bases with increasing distances of bases from sites of origin are not shown in the figures, nor are differences in slopes of barb primordia in different germs or regions. The essential relations illustrated by the several figures follow.