The gonads of chick embryos subjected to multiple doses of thyroxine

Abstract

Eggs of White Plymouth Rock and White Leghorn breeds were injected four times with doses of thyroxine totalling 17.75 and 25.0 μg and embryos killed on the 18th day of incubation. The injections were made on the following days of incubation: 0, 7, 10, 14; 4, 7, 10, 14; 10, 12, 14, 16. Males exposed to thyroxine numbered 6 with 9 controls; females 9, with 5 controls. At autopsy, embryos were weighed, gonads removed, weighed and prepared for histological study. In the testes, diameters of seminiferous cords and of nuclei of spermatogonia and number of spermatogonia per millimeter of cord were determined. In the ovaries, widths of cortex and of germinal epithelium were measured. In addition, sections of both testes and ovaries were examined for details of structure. At autopsy on the 18th day of incubation, there appeared to be no significant differences between the gonads of the thyroxine-exposed embryos and those of their controls. Thus, within the limits of this experiment the data offer no evidence of a thyroid-gonad interdependence during the development of the chick embryo.