SUPPLEMENTARY NOTES ON TWINS IN CATTLE. 



6 9 



be traced back to the stage of 25 mm. at least. Comparison of 

 these leads to the conviction that in this free-martin ovarian differ- 

 entiation had begun, and that modification did not date from a 

 stage in which the prospective differentiation of the gonad, whether 

 as ovary or testis, is still indistinguishable. However, the work 

 of Chapin (1917) and of Willier (1920) has shown that in later 

 fcetal and post-natal stages nothing remains comparable to the 

 cortex of the ovary. 



v' 



^ifm 



*-*\%*e$ 



e»,S®' 



&&!? 



■•■■■■,. ■ ■.- . ■■■■ . 



\f " «• G •-, ■' '■ 1 . ' •* »• " 



• ..:• - . 



' " ' . : " . : ::: 



Fig. 13. Detail of area designated in Fig. ioc. Normal female No. 54c. 1. 

 Germinal epithelium (cords of Pfluger) ; 2. Albuginea (primary) ; 3 Primary 

 sex-cords (medulla). 



The ostium tubse abdominale of the normal female is conspicu- 

 ous at the anterior end of the mesonephros (Fig. 9). It lies in 

 the same position in the normal male (Fig. 8), though it is less 

 conspicuous. In the free-martin (Fig. 7), on the other hand, it 

 can not be seen in the dissection, and was found in sections a con- 

 siderable distance from the anterior end of the mesonephros, as 

 though the Miillerian duct had failed to grow in length after its 

 formation, and thus its anterior end had become displaced. For 

 the rest there is practically no difference in the ducts in the two 

 sexes ; and naturally none was to be expected, nor was any found, 

 in the free-martin. 



The feature of most general interest in this case is the demon- 

 stration that a specific sex hormone is being produced by the male, 



