APPENDIX II 



human species, about six weeks after fertilization) when the 

 sex glands begin to show the characteristics of the ovary or 

 testis respectively. The accessory sex organs, when they first 

 develop, are capable of being directed toward the pattern of 

 either sex. All the necessary rudimentary tissues for the de- 

 velopment of both the male and the female sex organs are 

 present in every embryo, regardless of the sex of the indi- 

 vidual as determined by fertilization. About the 9th week 

 of embryonic life (in humans) the sex-pattern of the ac- 

 cessory organs begins to be distinguishable, and after that 

 the male organs (epididymis, vas deferens, prostate, seminal 

 vesicles), and the female organs (uterus, vagina) begin to be 

 recognizable to the embryologist, according to the sex of the 

 individual. 



Experiments on a number of species of laboratory animals, 

 done at these early stages, reveal that before the definite 

 characteristics of the accessory organs of the two sexes ap- 

 pear, and to a gradually diminishing degree thereafter, their 

 differentiation may be modified and controlled by treatment 

 with estrogens and androgens. For example, an embryonic 

 animal which is genetically a male (as determined at the 

 time of fertilization) may be made by suitable doses of estro- 

 genic hormone to develop accessory sex organs of female 

 type. Reversal in the opposite direction may be accomplished 

 by subjecting a genetic female to treatment with androgenic 

 hormone. The hormone administered by the experimenter thus 

 overrides and contradicts the influences which normally con- 

 trol the sex-pattern of the accessory organs. 



Such experiments were first done on the relatively accessible 

 embryos of aquatic animals, especially the amphibians. The 

 extensive literature which has grown up on this subject is 

 well reviewed in Sex and Internal Secretions, Baltimore, 1939. 

 Experimentation on mammals has been more difficult be- 

 cause of the inaccessibility of the embryos in the uterus. 

 R. K. Burns, Carl Moore and others have cleverly taken ad- 



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