664 Sex in Parabiotic Twins 



through large anastomoses (fig. 5), it seems improbable that the substances 

 become removed before they reach the gonads of the co-twin. It appears more 

 likely that the salamander gonad is not an adequate receptor and therefore 

 remains unresponsive to the Triturus substances. 



The fact that in two of the oldest pairs (mac-Tg and jef-T.^) the ovaries of 

 the salamander show some deficiencies may possibly indicate a change of con- 

 ditions governing sex interference on approach of the stage of maturity. How- 

 ever, the observed effects are too slight and the material too meager to permit 

 a definite statement in this respect. Attempts to solve this particular problem 

 by transplanting gonads between larvae of salamanders and newts were un- 

 successful, because the implants failed to develop properly. 



The second result is more complex in its aspects and implications. The 

 fact that the newt gonads in most jeffersonianum and in all tigriniim combina- 

 tions, even the unisexual ones, are extremely reduced could seem to indicate 

 that one deals with a general effect of parabiosis between species of different 

 taxonomic families, rather than with specific sex antagonism. It is easy to 

 show that such an assumption would be untenable. For one thing, in the 

 maculatum combinations, where the antagonism is more moderate, we have 

 a gradation of inhibition types, which definitely depends on sex combinations. 

 Inhibition becomes more and more severe in the following sequence: (a) 

 mac5-T ^, (b) mac$-T $, (c) macJ'-T (^, (d) mac^-T 5. Secondly, inhibition 

 effects happen to be more pronounced in newts combined with salamanders 

 of large gonad and small body size (Jeff, and tig.) than in those joined with 

 salamanders of large bodies and relatively small gonads (mac). Hence, the 

 extent of the reaction in the newts is not correlated with body size of the 

 salamanders. Thirdly, in three pairs in which the salamander member was 

 without gonads (due to early destruction of the gonad-forming body region), 

 the newts had normal and full-sized gonads. The pair jef-T^^ is the most con- 

 vincing case in this regard. Its Triturus member is the only female newt with 

 entirely normal ovaries in the whole set of thirty-nine twins. It is significant 

 that the jeffersonianum member is deficient mainly in the lower body region 

 while its upper parts, the head, and especially also the hypophysis gland, are as 

 well developed as in most other jef-T pairs. The importance of this case gains 

 relief by comparison with pairs like jef-T. Avhere the upper body region of 

 the salamander is deficient, the hypophysis absent, and the testes well de- 

 veloped; in this pair the Triturus gonads are as rudimentary as in all other 

 combinations with male salamanders. The conclusion that the salamander 

 gonads alone are responsible for the inhibitions is unavoidable. The interest- 

 ing suggestion made by C. R. Moore,^° in connection with his work on the 

 opossum, namely that substances issuing from the entire somatic complex 

 rather than from the gonads only may be the humoral agents responsible for 

 free-martin effects, is therefore ruled out as far as the present experiments 

 and materials are concerned. Likewise, the mentioned observations show that 

 the hypophysis gland is not in any specific way involved. In fact, some other 



