594 



Ontogeny of Endocrine Correlation 



stage). If the embryos are of opposite sex 

 and vascular connections are established 

 between them, the female partner is modified 

 in the male direction, forming the freemar- 

 tin. Since the structural changes are limited 

 to the production of male sex characters in 

 the female co-twin, it has been inferred that 

 the gonads of the male co-twin not only 

 produce but release male sex hormones into 

 the common blood stream at a very early 

 stage. (For certain shortcomings in the 

 purely hormonal interpretation of the free- 

 martin condition see Owen et al., '46; Moore, 

 '47; and Anderson et al., '51.) 



2. In the chick, by implanting fragments 

 of a sexually differentiated gonad (6- to 

 11-day embryo) into the coelom of a host 

 embryo of 50 hours (preceding by about 

 two days the time of origin of the gonad 

 primordia), Wolff ('47) succeeded in bring- 

 ing about an approximation of grafted tissue 

 and host gonads. If of opposite sex, the 

 grafted tissue modifies the direction of sex 

 development of the reproductive organs of 

 the host. Ovarian tissue causes the formation 

 of ovarian cortex on the left testis; testis 

 tissue has little effect on the left ovary but 

 inhibits or completely suppresses the Miiller- 

 ian ducts. The degree of sex transformation 

 is dependent upon the vohime of the graft 

 and the distance between graft and host 

 gonads. In general, the closer the graft, the 

 greater is the degree of effect. Similar re- 

 sults are obtained by cultivating in vitro 

 duck gonads of sexually indifferent stages 

 in juxtaposition. If left gonads of opposite 

 sex constitution are in more or less intimate 

 contact, the testis is modified into an ovo- 

 testis by the ovary (Wolff and Haffen, '52). 

 Since the effects produced in hosts by grafts 

 of embryonic testicular or ovarian tissue and 

 in explants of associated left gonads of oppo- 

 site sex are identical in character with effects 

 produced by the injection of synthetic sex 

 hormones, it is apparent that the embryonic 

 differentiated gonads produce sex hormones 

 (for further details and argument see Wil- 

 lier, '39, '52). 



3. In the rat, according to lost ('50), a 

 fetal testis (15 to 16 days old) grafted upon 

 the atrophied seminal vesicles of an adult 

 castrate produces within five days an in- 

 tense but local activation of the seminal 

 epithelium identical in character to the 

 effects of injecting testosterone. Tissues other 

 than testis fail to produce the effect. Al- 

 though androgenic activity of the fetal testis 

 is shown, the activity seems to depend upon 

 gonadotrophic stimulation, particularly since 



an embryonic testis graft has little or no 

 effect on the seminal epithelium in hypo- 

 physectomized and castrated adult rats. 



4. Castration by localized x-irradiation 

 of a duck or chick embryo during the sex- 

 ually indifferent stage indicates that hor- 

 mone secretions of the early differentiated 

 gonad are essential in determining the di- 

 rection of differentiation of other sex struc- 

 tures. An asexual or neutral type is obtained 

 following such precocious castration (Wolff 

 and Wolff, '51). In both males and females 

 the genital tubercle and syrinx (duck only) 

 assume the male shape and oviducts persist. 

 These results imply that in the normal em- 

 bryo (a) the female form of the genital 

 tubercle and syrinx is conditioned by the 

 presence of ovarian hormone and {b) the 

 retrogression of the oviducts is dependent 

 upon the presence of testicular hormone. 

 These findings are in agreement with the 

 results of injecting sex hormones, male hor- 

 mones suppressing oviducts in genetic fe- 

 males and female hormones stimulating ovi- 

 ducts in genetic males. (For a more complete 

 analysis of the time and manner of release 

 of sex hormones in bird embryos, see Willier, 

 '52.) 



Similarly, the effects of surgical castration 

 of the rabbit fetus indicate that the direction 

 of differentiation of gonoducts and accessory 

 sex structures is influenced by hormonal 

 secretions of the embryonic gonads (lost, 

 '47, '50). If the gonads are removed from 

 fetuses of either sex before the initiation of 

 structural sexual differentiation (18 to 19 

 days of gestation) the entire genital tract 

 is feminine in form. In males the develop- 

 ment of the Wolffian ducts and prostatic 

 buds is entirely suppressed, the oviducts per- 

 sist, and the external genitalia are feminine 

 in form. The Wolffian body retrogresses as 

 in normal females. However, castration of 

 male fetuses at sixccessively later stages (20 

 to 24 days of gestation) brings out the ad- 

 ditional point that sex structures, already 

 acted upon by testicular hormones, retain 

 the male type although usually in an unde- 

 veloped state. Synthetic androgens admin- 

 istered to castrates have a reparative influ- 

 ence on sex structures which simulates that 

 of the embryonic testis hormones. In cas- 

 trated females, on the other hand, the genital 

 tract retains a feminine form essentially like 

 that of control females of the same age. 

 Apparently, then, the embryonic testis pro- 

 duces male sex hormones which control the 

 development of the male form of the ex- 

 ternal genitalia and Wolffian bodies, the 



