undoubtedly be able to bring young to birth.

Transvestia

But let's go back to the beginning and examine what happens if the operated animal was a genetic male. The operation of removing the gonads--in this case the testes--must be done at what is called the critical period (for this particular effect)-- about the 18th or 19th day. NOW, and hear this- this operated male will be born with all the same type of sexual apparatus as the operated female and will to all intents and purposes be a spayed female. Without further treatment his (hers?) subsequent behaviour will be just like the operated female. BUT, if he is given injections of male hormone (and- rogens) up to about the 25th day of development he will at maturity display all the characteristic male reproductive activity including mounting, pelvic thrusts and ejaculatory activity, (though obviously without actual ejaculation because there is nothing to ejaculate), even though his (hers?) genital ana- tomy is typically female. If androgens are not given until maturity however, it does not cause such typi- cal male-type reactions.

If this "pseudo female" (amusingly termed a "fale" for femininized male by those involved in this work) is given estrogen at maturity it will behave like a normal female and if an ovary is surgically implanted it can be made to ovulate like a female.

That is facinating you say, but what is the great significance. Just this, and it has immense significance. The fact that surgical removal of the male sex gland which normally produces androgen at a critical time in the differentiation and develo- pment of the genital tract produces female genitalia means that the rat (and this can be extropolated to the mammalian class collectively) is essentially a female type organism to begin with. Only when fetal androgen is elaborated in the fetal testis does it act on the undifferentiated primal structures to

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