890 THE DEVELOPING ENDOCRINE GLANDS 



enlarge, and the bird after a few abortive attempts, learned to give the genuine 

 crow of a rooster. ... It was often seen scratching on the ground and calling the 

 flock to an alleged morsel of food, and though it was never seen to tread hens it 

 would strut and make advances after the manner of cocks. . . . The female be- 

 havior of the bird was as follows. For years it would sing like a laying hen. On 

 two occasions it adopted incubator chicks, caring for them day and night and 

 clucking like a normal hen. ... On one occasion it dropped an egg, which though 

 small and elongated, showed the bird to be in possession of functional ovary and 

 oviduct. 



Its internal anatomy demonstrated the presence of a left ovotestis and a 

 right testis. An oviduct was present on the left side and a vas deferens on 

 both sides. The right testis contained tubules, and within the tubules were 

 ripe sperm. The ovotestis on the left side contained a cortex studded "with 

 oocytes of every size up to a diameter of 20 mm." and "not unlike the ovary 

 of a normal hen approaching the laying season" (Hartman and Hamilton, '22). 

 Seminiferous tubules also were present in the ovotestis which was filled with 

 sperm. 



An interesting example of complete sex reversal was produced experimen- 

 tally in the axolotl, Siredon (Anibystoma) mexicanum, by Humphrey ('41). 

 In doing so, Humphrey orthotopically implanted an embryonic testis of 

 Ambystoma tigrinum into an axolotl embryo of similar age. After the ovary 

 on the opposite side of the host (i.e., the young axolotl) had changed to a 

 testis, the implanted testis was removed. Somewhat later, the sexually reversed 

 female axolotl was bred with other females with success. The Fj and Fj gen- 

 erations suggest that the female axolotl is heterogametic whereas the male 

 is homogametic, with a possible XY or ZW condition in the female and an XX 

 (or ZZ) arrangement in the male. It is interesting to observe that Humphrey 

 obtained YY (or WW) females which were fertile. 



Many other studies have been made along the lines of experimental trans- 

 formation of sex. Of these, the careful studies of Witschi ('39) are illumi- 

 nating. The method, employed by Witschi, was to join two embryos of opposite 

 sex before the period of sex differentiation. In his studies, he used toad, 

 frog, and urodele embryos. Three different results were obtained, in which 

 the medulla or developing testicular rudiment tended to dominate and sup- 

 press the cortex or developing female sex field. For example, in toads, it was 

 evident that the medulla suppressed the cortex only if the two fields came into 

 actual contact; in frogs, the effect of suppression was inversely proportional 

 to the distance of the two sex fields from each other; on the other hand, in 

 urodeles, the substance produced by the medulla evidently circulated in the 

 blood stream and produced its effects at a distance (fig. 368E-G). Witschi 

 postulated the presence of two, not readily diffusible, "activator" substances, 

 cortexin, formed by the cortex, and meduUarin, elaborated by the medulla, 

 to account for the results in the toad and frog embryos, and, in urodeles, 

 he assumed a hormonal substance to be present. 



