Ontogeny of Endocrine Correlation 



595 



formation of the prostate, the persistence of 

 the Wolffian ducts, and the retrogression of 

 the oviducts. In genetic females the further 

 development of the ovidvicts is conditioned 

 by ovarian sex hormones. < 



More recently Wells and Fralick ('51) 

 have shown for the fetal rat that surgical 

 removal of the testes on the twentieth day 

 of gestation selectively retards the growth of 

 the seminal vesicles and bulbo-urethral 

 glands and, further, that such specific cas- 

 tration effects are prevented by the adminis- 

 tration of testosterone propionate. From the 

 growth responses thus given by the accessory 

 sex organs it is at once clear that for at 

 least a few days prior to birth the testes are 

 active in the production and release of 

 androgenic hormone. 



In summary, the embryonic gonads from 

 the time of onset of morphological sex differ- 

 entiation are active in the production and/ 

 or release of specific sex hormones. The hor- 

 mones are liberated in quantities at least 

 sufficient for effective action through the 

 vascular ciixidation as judged from the na- 

 ture of the responses, especially those of the 

 terminal sex receptors. (For a further treat- 

 ment of the subject see Burns, '49; Jost, 

 '50; Moore, '50.) 



ONSET OF GONADOTROPHIC ACTIVITY 

 OF ANTERIOR PITUITARY 



The evidence just presented for the exist- 

 ence and action of sex hormones early in 

 embryonic development naturally poses a 

 two-fold problem of (1) the extent to which 

 their production and release are dependent 

 upon gonadotrophic stimulation and (2) the 

 time that the anterior pituitary begins to 

 secrete gonadotrophic substances as well as 

 to release them into the blood circulation 

 of the embryo (see Table 27). Whether 

 functional activity of the gonad during em- 

 bryonic life is dependent upon gonadotrophic 

 hormones is a problem which is as yet only 

 beginning to be resolved. The most complete 

 and satisfactory analysis yet made is that of 

 Jost ('48, '51b) on the rabbit fetus. If the 

 male fetus is decapitated at the time of 

 initial strvictural sexual differentiation (about 

 the nineteenth day of gestation) the inter- 

 stitial tissue of the testis is distinctly reduced 

 as compared with normal controls of the 

 same age. Moreover, testicular hormones are 

 quantitatively deficient, as is indicated by 

 the feminization of the external genitalia 

 and by the arrested development of the 

 prostatic buds as shown in Figure 212. Since 



similar effects on the prostate and external 

 genitalia are produced in males castrated 

 at 21 to 22 days, it is inferred that the re- 

 moval of the hypophysis affects the produc- 

 tion of male hormone by the testis. The 

 effects of hypophysectomy are attributed to 

 the absence of specific hormones, since if 

 at the time of decapitation gonadotrophic 

 hormone is administered no signs of in- 

 sufficient testicular secretions are found. 

 These results are interpreted as indicating 

 that the anterior pituitary of the rabbit fetus 

 is active in producing and releasing gonado- 

 trophic hormones either at the time of or 

 shortly after the onset of testis differentia- 

 tion. They are apparently released in suffi- 

 cient quantities to be physiologically effective 

 in maintaining testicular hormone production 

 at a level adequate for regvilating the devel- 

 opment of such sex characters as the prostate 

 and external genitalia during their initial 

 stages of growth and differentiation. 



In other species of vertebrate embryos the 

 evidence thus far available is inconclusive 

 on whether secretions of the anterior lobe are 

 essential for the early development and func- 

 tion of the gonad. In general, so far as results 

 on different species can be compared, re- 

 moval of the anterior lobe has little or no 

 effect on the early morphological develop- 

 ment of the gonads. Two examples suffice 

 to illustrate this point. In the anuran embryo 

 removal of the anterior lobe at the time of 

 its ingrowth has no apparent effect on the 

 growth of the gonads; their development 

 continvies a normal course to the stage which 

 is attained in controls at the time of meta- 

 morphosis (Smith, '39, p. 942). In the chick 

 embryo after hypophysectomy at 33 to 38 

 hours primary morphological sex differentia- 

 tion pi'oceeds in a normal manner until about 

 the thirteenth day, when reductions in inter- 

 tubular tissue of the testis and in ovarian 

 cortex are first noted; however, the gonoducts 

 in both sexes develop normally both in time 

 and manner (Fugo, '40). On the contrary, 

 Wolff and Stoll ("37) report that the entire 

 course of sex-differentiation of gonads and 

 e:onoducts is normal up to the time of hatch- 

 ing in the cyclocephalic chick embryo with- 

 out hypophysis produced by local x-irradia- 

 tion at the 12- to 15-somite stage. By the 

 iniection of estradiol into such pituitarvles<; 

 chick embryos intersexual males are produced 

 as readily as in normal male embryos (Wolff. 

 '37). It seems, therefore, that the functional 

 processes concerned in sex-inversion are 

 wholly independent of hypophyseal action. 

 Whether the gonad during early stages of 



