262 THE THEORY OF THE GENE 



experiments were not made with the same male for the 

 same sets of eggs, the results are doubtful. Hertwig him- 

 self points out there are many resemblances between the 

 effect of cold and that of overripening. Many embryos 

 are deformed. Witschi has confirmed Hertwig 's results 

 (with the Irschenhausen race). Eggs estimated to be 80 

 to 100 hours overripe gave 74 $ , 21 2 , 20 indifferent tad- 

 poles. 3 



Oscar Hertwig compared the sex ratio of normal and 

 delayed eggs (67 hours' interval) with the following re- 

 sults. Larvae 49 days old (just before metamorphosis) 

 that came from normal fertilization gave 46 indiffer- 

 ent 5 ; those from 'delayed fertilization, 38 indifferent 2 

 and 39 $ . The normal frogs about 150 days old were 

 differentiated females, indifferent females as to gonads, 

 and males (numbers not given), and from the delayed 

 eggs 45 indifferent 2 and 313 $ . Yearling frogs gave 

 6 2 and 1 $ (normal fertilization) and 1 2 and 7 $ (de- 

 layed fertilization). The overripeness here would seem 

 to hasten the male differentiation and in the second place 

 transform the indifferent individuals (here ranked undif- 

 ferentiated females) into males. 



The interpretation of the results produced by over- 

 ripening the eggs is still very obscure. Taken at their 

 face value they seem to show that individuals that would 

 normally become females may become males. As yet no 

 genetic tests have been made of the sex-determining 

 properties of the spermatozoa of individuals obtained in 

 this way. Theoretically, these should be homogametic. It 

 seems improbable that such individuals could live and 

 function under natural conditions, for, although over- 

 ripeness must not infrequently occur, normal males giv- 

 ing 100 per cent females are practically unknown. Wit- 



3 There was 20 per cent mortality in the tadpoles and 35 per cent in the 

 young frogs. 



