272 THE THEORY OF THE GENE 



bers (24, 25, 28) have, however, been reported. According 

 to the most recent account, that of Witschi, Rana tem- 

 poraria has 26 chromosomes, including a slightly un- 





•r 



^' 



a 







d 



Fig. 145. 

 Chromosome groups of the frog Eana temporaria. a, Diploid male 

 group. 6 and V anaphase plates of first spermatocyte division each 

 showing thirteen chromosomes, c and c' ditto, d division of XY- 

 chromosome of first spermatocyte, e, separation of X and Y at 

 second spermatocyte division. (After Witschi.) 



equal XY pair in the male (Fig. 145). If this is confirmed, 

 the female is XX (homogametic) and the male XY (het- 

 erogametic). 



Pfluger (1882), Richard Hertwig (1905), and later 

 Kuschakewitsch (1910) have shown that overripe eggs 

 give an increased percentage of males. In so far as these 



