228 HEREDITY AND SEX 



(6) We come now to the most perplexing case on 

 record. In frogs the normal sex ratio is approximate 

 equality. Professor Richard Hertwig has found that 

 if the deposition of the eggs is prevented for two to 

 three days (after the eggs have reached the uterus) 

 the proportion of males is enormously increased — 

 in the extreme case all the offspring may be males. 

 By critical experiments Hertwig has shown that the 

 results are not due to the age of the spermatozoa, al- 

 though in general he is inclined to attribute certain 

 differences in sex-determination to the sperm as well 

 as to the eggs. 



The evidence obtained by his pupil, Kuschakewitsch, 

 goes clearly to show that the high male sex ratio is 

 not due to a differential mortality of one sex. 



In the following table four experiments (a, h, c, d) 

 are summarized. The interval between each record 



a) 47 9 : 32 ^ 9 : 97 ^ 



/^\ /^^\ /^^\ 



b) 34 9:47^ 65^:77^ 156 9:194^ 7 9:48^ 



c)64 9: 6U 101^:139^ 115 9:169^ 



/IK /'K /'N 



d) 55 9:52^ 148 9:87^ 719:70^ 17 9:129^ 



is written above in hours. In all cases an excess of 

 males is found if the eggs have been kept for several 

 hours before fertilization. In the first (a), second (6), 

 and fourth (d) cases the excess of males is very great. 

 Hertwig attempts to bring his results into line with 



