HORMONES IN DIFFERENTIATION OF SEX 



91 





^*V^ .^v- _^' A 





S-.-' / V 



"-^~ .\:!^> 



Fig. 2.11. Stages in the transformation of testis to ovary in the male (punci.ii luii ) imni- 

 ber of an Ambystorna tigrinum-A. punctatum pair, joined in heteroplastic parabiosis (Burns, 

 1935). yl to D show, at successive levels in the same gonad, the degeneration of the medulla 

 by vacuolation of the rete canals and lobules, accompanied by persistence and growth of the 

 cortex. E shows a section through one of the dominant and entirely normal tigrinum ovaries; 

 a gross picture of these ovaries is seen in F. (From R. K. Burns, Anat. Rec, 63, 101-129, 1935.) 



velopinent and delay the beginning of sex 

 differentiation. This appears to be the ease 

 in the first parabiosis experiments (Burns, 

 1925) in which the method of joining inter- 

 fered with feeding and resulted in a severe 

 retardation of growth. Such pairs developed 

 so slowly that sex differentiation was de- 

 layed for weeks and in many cases for 

 months. When it eventually took place 

 members of a pair were almost invariably 

 of the same sex (c/. Humphrey, 1932) al- 

 though there was great variation in the size 

 and stage of differentiation of the gonads. 

 In this experiment the usual physiologic 

 dominance of the male was also disturbed, 

 male-male and female- female pairs appear- 

 ing in nearly equal numbers.^ The manner 



^ The author's interpretation of the results in 

 this experiment has often been questioned by 

 Witschi. However, all but a small part of this ma- 

 terial was subsequently re-examined by Humphrey 

 (1932) whose study confirmed the original conclu- 

 sions except for minor details in\-olving at the 

 most only eight pairs. In Humphrey's opinion 

 there were certain histologic indications that these 



in which extremes of temperatures induce 

 sex reversal in tadpoles through a differen- 

 tial inhibitory effect on the medullary or the 

 cortical component of the embryonic gonad 

 has been referred to earlier. The above re- 

 sult may have a similar physiologic basis 

 if, under prolonged repression, the usually 

 dominant male gonad should prove to be 

 more susceptible to unfavorable conditions 

 than the female. 



3. Administration of Steroid Hormones 



Since sex hormones of adult type became 

 available in pure form their effects on the 

 differentiation of sex have been tested in 

 many species of amphibia. They are readil}' 

 administered in two ways, by injecting di- 

 rectly into the body cavity or, in aqueous so- 

 lution, by adding them to the water in which 

 the larvae are reared. The results on the 

 whole are striking; in certain species there 



pairs were originally heterosexual, although trans- 

 formation had proceeded to the point where a com- 

 plete reversal was imminent. 



