Hormonal basis of sexual differentiation in the Japanese quail.

On the 10th day of incubation, Japanese quail eggs either were injected with testosterone propionate (TP), estradiol benzoate (EB), or oil, or were not injected. When sexually mature, all birds were examined for a variety of sexually dimorphic behavioral and physical characteristics, both masculine and feminine. They were then exposed to a short photoperiod (causing gonadal regression), treated with either TP or EB, and examined again. Either androgen or estrogen administered before hatching demasculinized males, but did not masculinize females or defeminize either sex. In contrast, early sex hormones masculinize and/or or defeminize mammals. This difference is discussed in relation to other differences in avian and mammalian sexuality.