SEX-REVERSAL IN PARABIOTIC TWINS. 



139 



Controls were reared under identical laboratory conditions. 

 Sex-differentiation was in full course by the 22d day, in a lot 

 of larvse, preserved at this time. The animals metamorphosed 

 between the 44th and the 59th day. The species proved to 



FIG. i. Parabiotic twins TSi. Newly metamorphosed. The left side animal 

 with the pigmented ventral surface is an European Temporaria, the right side 

 animal is an American Syhatica. 



belong to the differentiated sex type. Among these 196 controls 

 were 100 females and 96 males a very close approximation to a 

 i : i ratio (expectation calling for 98 : 98 with a probable error 

 of 4-7)- 



We should therefore expect, that by chance combination, 

 the 56 twins considered in this paper would consist of the 

 following zygotic groups 14 of of + 140? 9 + 14 9 of + 14 9 9 

 (the probable error being 2.2). Preliminary observations on 

 a part of this material seemed to indicate that in the hetero- 

 geneous combinations the sex of one animal is not influenced by 

 that of the other, and a statement to this effect was made in an 

 evening lecture at the Woods Hole Laboratory this summer. 





