666 



Sex in Parabiotic Twins 



cessful grafts of gonads in normal animals as compared with the relative ease 

 of getting implants in castrates. In many heterogenous parabiotic twins, the 

 ovaries (or testes) of one twin seem to be able to monopolize the whole supply, 

 thus depriving the co-twin more or less completely of this substance and, 



TABLE 4 



Type of Reactions Produced in the Sex Glands of Male and Female Newts 



{Triturus torosus) by Parabiotic Twins 



F, M, normal sex glands (no reaction); f, m, inhibited yet clearly differentiated sex glands 



(moderate reaction); i, rudimentary and sexually undifferentiated glands (maximal reaction). 



The sex types of the producers of inductive substances are indicated by ss (distinct hermaph- 

 rodite tendency), s (slight hermaphrodite tendency), d (prevailingly gonochoristic) and dd (fully 

 gonochoristic). 



therefore, of the possibility of growing normal gonads. These hypothetical 

 substances are not hypophysial hormones, since sex glands of larval newts 

 grow normally even in the complete absence of the hypophysis gland (Woron- 

 zowa and Blacher,^" Witschi''). Nor can they be sex hormones, for the charac- 

 teristic reactions which these produce in salamanders (Foote") are entirely 

 different from anything observed in the present experimental series 

 (Witschi'"). Since they serve to control the size and the total amount of 

 gonadal tissue in single individuals, as well as in conjoined twins, they may be 

 designated, provisionally, as ovarial and testicular groxoth substances. 



The reactions produced in Triturus testes and ovaries are represented in 

 a summary way in table 4. Their correlation with sex (5, (^) and sex type (ss, 

 s, d, dd) of the parabiotic twins is quite obvious. Comparing the reactions in 

 heterogenous pairs with those obtained in homogenous Triturus twins (two 

 bottom columns), it becomes evident that in the latter the effects are produced 

 only by a mutual cortex-medulla antagonism; whereas in the former the 

 mechanism is complicated by the following factors: 



1. Salamanders do not respond to inductive agents of the newt and, there- 

 fore, continue with the unimpeded output of substances which interfere with 

 gonadal development in the newt. 



