A substantial number of papers has been published during the last few years, in which the possibility of influencing the sex of the chick embryo is discussed: Kozelka and Gallagher ( '34) ; Dantchakoff ( '38) ; Willier, Gallagher and Koch ( '35, '37) ; Wolff ( '35) ; Wolff and Ginglinger ( '35, '36) ; Wolff and Wolff ( '37) ; Ludwig and von Ries ( '36, '37) ; Gaarenstroom ('37, '38). By injecting oestrogenic substances into the eggs, it has been possible to prevent the left gonads of the genetic male embryo from developing into testes, ovotestes or ovaria being the issue, while the right gonads in most cases showed poor development. Injection of male hormones, insofar as testosterone was used, produced no result, androsterone and dehydroandrosterone on the other hand, like oestrone, caused feminization of the gonads of the genetic male embryos. The belief that the genetic female embryos are masculinized by means of androsterone, was not confirmed definitely. I n order to obtain a satisfactory effect, oestrone should be administered in quantities of 50 to lOOy, of androsterone at least 700 y and of dehydroandrosterone probably still more should be employed. An influence on sex only becomes visible if the injection is carried out during the first 6 days of incubation, after the seventh day it is impossible to obtain any result.The development of the mullerian ducts is likewise influenced by sex hormones. We have studied this effect in 791 embryos and the results are given below. Our examination was carried out in two different ways : 1. Series of eggs were treated with male or oestrogenio substances at different periods of incubation. The injection was made into the albumen, close to the pointed portion of the egg, as already explained in previous reports. Examination of the embryos from the eggs, which took place on the eighteenth day of the incubation period, was made with the naked eye, and where necessary with the aid of a binocular.At this moment it is easy to detect the sex of the embryo.The male embryo has the testes, right and left, high up in the abdomen, in the immediate vicinity of the spinal column ; the female on the left, in the identical spot, has an ovary, whereas on the right side nothing can be seen except a small rudiment. Under the influence of sex hormones a number of embryos develop with gonads on the right side, one-fourth or twothirds the size of those on the left. These we termed intersexes, since intersexuality could be established histologically in many cases. A macroscopic diagnosis of the intersex is very useful, being swiftly made. The females of some breeds of chicks, e.g., the Rhode Island Reds, fairly frequently have a large right gonad by nature, which fact is apt to cause confusion. Nevertheless, we decided to retain the term intersex for all embryos of this kind. Therefore where the Rhode Island Red breed was used, by 'intersexes,' genuine intersexes or females are meant. This will not cause any misconception in judging the result.
2.The second range of tests comprised eggs, trea...
