274 THE THEORY OF THE GENE 



schi has pointed out that the overripe eggs undergo an 

 unusual type of cleavage, and that a few embryos that he 

 examined show internal defects, but the relation of these 

 defects to the transformation of females into males is not 

 apparent. 



The possibility of transforming individuals having an 

 undifferentiated or juvenile hermaphroditic gonad (or 

 progonad) into females by external agencies is furnished 

 by the following evidence from Witschi's experiments 

 (1914-1915). 



Tadpoles of the Ursprungtal race, that is, probably a 

 differentiated race, gave, at 10° C, 23 males and 44 fe- 

 males; at 15° C, 1315 and 140 5 ; and at 21° C, 115 5 

 and 104 2 . The sex of the tadpoles of this race is appar- 

 ently not affected by temperature. 



On the other hand, tadpoles of the Irschenhausen race 

 reared at 20° C. gave 241 undifferentiated females, and 6 

 lots reared at 10° C. gave 25 $ and 438 2 . From this re- 

 sult Witschi concludes that cold is a male determining 

 factor, but it should not be overlooked that many of these 

 so-called females would later develop into male frogs. 

 In a later account of these experiments he states that 

 ''cold changes the males into protogynous juvenile her- 

 maphrodites as is in general normal for undifferentiated 

 races." 



It seems questionable, therefore, whether there is any- 

 thing more here than a retardation of the definitive male 

 condition. 



In so far as it is possible to reach a provisional conclu- 

 sion from the evidence available at present, it appears that 

 in the undifferentiated races the germ-cells, that are pres- 

 ent in half the individuals that would normally become 

 females, may be changed over into sperm-cells, or else 

 be replaced by cells from a different source that, in turn, 

 become sperm-cells. In other words, the balance of the 



