Abstract
I. The Male. A series of experiments was carried out to determine the nature of the control of the sex characters, particularly plumage, of the English Sparrow. Previous studies have established that the secondary sexual characters, including plumage, of various breeds of domestic fowl, ducks and pheasants are under the influence of the gonads.
In the first experiment 52 male birds (35 adult and 17 immature) were castrated. At the time of the operation feathers were plucked from areas showing sexual dimorphism. The regenerated feathers were always of the male type. The capon assumes the normal male plumage and in this respect is similar to domestic fowl.
The bill of the adult male during the breeding season is blue-black in color but during late August and early September the bill becomes a light horn color. This light color is retained during the winter but with the approach of the breeding season the bill again takes on the black color. When a male with a black bill is castrated the color changes to a light shade, characteristic of the winter condition when the gonads are inactive. The color change becomes noticeable at the base of the mandible 10-14 days after the operation. Three weeks later the bill has completely changed color.
In the second series daily intramuscular injections of female sex hormone (prepared from the urine of pregnant women) were given 12 capons. The dosage varied from 1/2 to 10 rat units per day for a period of 30 days, a given capon receiving the same dose each day. Feathers were plucked at the time the injections were started. The regenerated feathers were of the normal male type. Experiments using Brown Leghorn and Sebright Bantam capons demonstrated that 1-2 1/2 rat units of female sex hormone per 100 gm. of body weight given daily for a period of 30 days influenced regenerating feathers toward femaleness.
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