SEX-REVERSAL IN PARABIOTIC TWINS OF THE 

 AMERICAN WOOD-FROG. 1 



EMIL WITSCHI, 

 UNIVERSITY OF BASEL, SWITZERLAND. 



On the basis of his work on the free-martin F. R. Lillie (1917) 

 expressed the view, "that sex-determination in mammals is not 

 irreversible predestination, and that with known methods and 

 principles of physiology we can investigate the possible range of 

 reversibility." Numerous investigators followed this suggestion 

 in an effort to determine the nature of the sex-differentiating 

 factors. 



Parabiosis experiments which were first performed in rats by 

 Morpurgo in 1908, were carried out by Matsuyama (1919), 

 Yatsu (1921) and Pfeiffer and Zacherl (1926). These authors 

 obtained almost identical results in so far as there was no sex- 

 change observed. Parabiosis here does not even prevent copu- 

 lation or suppress fertility in either sex. Yatsu describes some 

 pathological changes taking place in the ovaries and the uteri of 

 the female, while the male co-twin is never impaired in the least 

 by the female. But as the castrated male exerts the same 

 influence as the normal one, it seems improbable, that we have 

 to do in this case with a specific action of male differentiating 

 factors. 



The experiments were then extended upon birds and am- 

 phibians, in which the embryos are accessible for the experiment 

 long before their sexual differentiation. Minoura (1921) first 

 reported some intersexual features in the female chick embryos, 

 caused by implanted pieces of the testes of adult cocks. But 

 Greenwood (1925), when repeating that experiment did not find 

 such influences. Recently Willier (1925) grafted embryonic 



1 The experiments were carried out in the Osborn Zoological Laboratory, Yale 

 University. The microscopical study of the material was continued at the Marine 

 Biological Laboratory, Woods Hole, Mass. The writer takes this opportunity of 

 expressing his obligation to these institutions and feels also very much indebted to 

 the International Education Board for the grant of a fellowship. 



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