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1. An experimental study on the effects of gonad grafts in the embryo chick was undertaken in an attempt to reproduce the results obtained by Minoura and to define the bearing of this experiment on Lillie's theory of the free-martin in cattle. 2. Eggs from a sex-linked cross were used so as to be able to identify the original sex of the embryos. 3. In the majority of cases the egg received the graft at the seventh day of incubation and was examined at the seventeenth day, at which stage the progress of sexual differentiation is almost as complete as at the time of hatching. 4. In all 540 embryos were operated on. Of this number 233 received testis grafts and 168 ovary grafts. Other tissues grafted were thyroid, adrenal, pancreas, spleen, gall-bladder, liver, Wolffian body, kidney, lung, lens, and heart. 5. The age of the grafted tissue varied from the fourteenth day of incubation up to ten weeks old. 6. Of the gonad grafts, 150 survived the operation, 71 ♂ and 79 ♀. 47 ♀ chicks were obtained after testis grafts, and 27 ♂ chicks were obtained after ovary grafts. Healthy active testis grafts were found in 20 ♀ and 5 ovary grafts in ♂. 7. The sex ratio in the surviving chicks showed no deviation from the normal. 8. Macroscopical examination of the urogenital system showed no deviation from the typical structure consonant with the sex of the chick as determined by its plumage colour. 9. Microscopical examination of the gonads revealed no abnormalities in histological structure. 10. These results lend no confirmation to the view that the process of sexual differentiation in the chick can be profoundly modified by the specific physiological activity of a gonad graft of the opposite sex. 11. Minoura's interpretation of his results are criticised. 12. The grafting of gonad tissue in the embryo chick does not reproduce experimentally the conditions existing in the bovine free-martin in that in the former the embryo is exposed to the specific action of the grafted gonad alone, whereas in the latter the female co-twin is exposed to the action of all the internal secretions from the male.

Gonad Grafts in Embryonic Chicks and Their Relation to Sexual Differentiation