HORMONES IN DIFFERENTIATION OF SEX 



145 



the embryonic gonads is a matter which can 

 be discussed with some assurance only in 

 the case of the mammahan testis. In the 

 testes of adult mammals the interstitial tis- 

 sue has long been recognized as the source 

 of the male hormone and, as was pointed 

 out in the beginning, the marked develop- 

 ment of this tissue in the testes of pig em- 

 bryos led to the first suggestion that a 

 hormone might be involved in sexual differ- 

 entiation (Bouin and Ancel, 1903). In con- 

 nection with the freemartin studies, an 

 examination was made of the gonads of nor- 

 mal calf embryos and fetuses (Bascom, 

 1923) which pointed to the well developed 

 interstitial cells as the probable source of 

 the male hormone. This provided a plausible 

 explanation of the invariable dominance of 

 the male twin, because in fetal ovaries no in- 

 dication of internal secretion could be found 

 until relatively late in gestation ; in the tes- 

 tis, on the contrary, interstitial tissue was 

 seen in increasing amounts from practically 

 the beginning of sex differentiation. 



It is unnecessary to multiply cases in 

 which the presence of interstitial tissue in 

 the embryonic testis coincides with indica- 

 tions of hormone activity. On the other 

 hand, instances in which a reduction in tes- 

 tis activity (as evidenced by the condition 

 of the sex accessories) can be correlated 

 with the status of the interstitial tissue are 

 pertinent. Decapitation of rabbit embryos 

 (Jost, 1951a) is followed by definite re- 

 tardation in the development of certain male 

 accessory structures, although the growth 

 of the embryo as a whole is normal. Exam- 

 ination of the testes in these specimens 

 showed a reduction in size and in the num- 

 ber of interstitial cells; whether there was 

 also cytologic abnormality has not been as- 

 certained. The defects of the sex accessories 

 in the decapitated fetuses resembled those 

 which appear after incomplete or unilateral 

 castration. Structures near the defective tes- 

 tes (epididymides, vasa deferentia) were 

 virtually normal but more distant structures 

 (sinus derivatives, external genitalia) 

 showed failures of development comparable 

 to those produced by complete castration. 

 Inadequacy of the testes to maintain nor- 

 mal development in these cases is appar- 



ently due to a quantitative deficiency of the 

 interstitial tissue and the male hormone. 



A similar reduction of the interstitial tis- 

 sue occurs in decapitated rat fetuses (Wells, 

 1950) and in this instance cytologic changes 

 in the interstitial cells were also seen. In 

 this species, however, no clear effects were 

 observed on the accessory sex organs, as is 

 also the case in fetal mice hypophysecto- 

 mized by irradiation (Raynaud and Frilley, 

 1947; Raynaud, 1950). Negative findings in 

 these cases may be attributable to species 

 differences as to the stage at which the in- 

 terstitial tissue becomes active ; however, it 

 is more probable that the different result is 

 due simply to the longer period of observa- 

 tion in the rabbit, allowing more time for 

 the deficiencies to appear.-- 



Also pertinent in this connection is the 

 behavior of the interstitial tissue of the em- 

 bryonic rat testis transplanted between the 

 lobules of the seminal vesicle of a castrate 

 adult; the interstitium of the grafted testis 

 undergoes a considerably hypertrophy and 

 the epithelium of the host's seminal vesicle 

 gives a corresponding response (Jost, 

 1951b). But when the host is also hypo- 

 physectomized such grafts are deficient in 

 interstitial cells and there is little or no re- 

 sponse by the seminal vesicle (Jost and Co- 

 longe, 1949). The correlation between the 

 state of development of the interstitial cells 

 and the evidences of hormonal activity in 

 these cases is direct and striking (for a re- 

 cent review of this subject see Jost, 1957). 



XII. A Comparison of the Effects of 



Emhryonic and Adult Hormones 



in Sex Differentiation 



A problem has long existed as to whether 

 the hormones or hormone-like substances 

 produced by the embryonic gonads are es- 

 sentially similar in character to adult sex 

 hormones. When the effects of the two types 

 of hormone on the development of embry- 

 onic sex primordia are studied under com- 

 parable conditions the resemblances are in 



"It should be noted that treatment with go- 

 nadotrophins prevents the reduction in the inter- 

 stitial tissue after decapitation, and may even pro- 

 duce hypertrophy of the interstitial cells (Wells, 

 1950, Jost, 1951a). In one instance also a graft of 

 the fetal hypophysis had the same effect (Jost). 



