Transvestia

influence them to differentiate in a male direction. The order of events here is that, (1) the presence of a "Y" chromosome determines that the fertilized egg will be a male and in the early fetal stages those cells are formed and gather together in a group to form what becomes the testis. (2) While this is going on and up to the 19th day the cells which will give rise to the genital tract are being differentiated from more primitive cells and be- coming located in the right part of the developing embryo. At this point they have the "potential" (remember this word?) to develop either typical male structures or typical female structures. Left to themselves (that is if the fetal testis is re- moved) they will go in the female direction. But when these cells with this dual potential are ex- posed to androgens from the fetal testis, they are somehow prevented from going in their regular path of development and forced to form penis, scrotum, seminal vesicles, and the rest of the male equip- ment. (3) By the 18th or 19th day the brain is evidently not differentiated far enough for the fetal androgen to have much affect on its develop- ment because there is a further 5 or 6 days (almost 1/3 of the gestational period) during which the absence of androgen in the operated animals makes no lasting difference. But about the 25th day it becomes critical for androgen to be present in order to modify the neuronic development of certain areas of the brain in such a way that sexual stimuli to the mature animal will bring about typical male responses regardless of the genital structures.

Now do you begin to see the significance? There are evidently 2 locations where the androgen works, and two critical times for it to work to bring about two essential aspects of maleness; a) the specific ancestral cells of the genital struct- ures; and the specific male-behaviour-controlling area or "circuits" in the brain; b) approximately 18 days for the anatomical effects and approximately 24-25 days for the cerebral effects, and c) the fact