344 riddle: control of sex ratio 



The observed relation of the time of fertilization to modified 

 sex-ratios in cattle is summarized in Table 9. Thury reported 

 in 1862 that from fertilizations made in the early period of heat 

 in cattle an excess of females were produced; and that later 

 (delayed) fertilizations give rise to an excess (all according to 

 Thury) of males. Similar experiments have been several times 

 repeated and these repetitions have all shown an excess of one 

 or the other sex in accordance with such early or late fertiliza- 

 tion. 10 The facts as reported by the several observers, and the 

 totals, are given in the table. We postpone for a moment a 

 discussion of the situation presented by these data except to 



TABLE 10 

 Time of Fertilization and Sex Ratio in Sheep 



Bell" 



Matings in October, 1899 c? 10:9 26 = 72.0 per cent 9 



Matings time unknown, 



1899 c? 179: 9 166 = 48.0 per cent 9 



Matings after Novem- 

 ber 15, 1899 c? 23: 9 3 = 11.5 per cent 9 



° Records of a neighboring flock supplied to Dr. Bell by Mr. Macrae. 



draw attention to the probability that in late (delayed) fertiliza- 

 tion the ovum takes up water before fertilization and gives an 

 excess of males. 



Connected with these facts obtained from cattle are some par- 

 tially similar data for sheep. From records obtained by Dr. 

 Alexander Graham Bell ('14), made primarily with the object of 

 learning whether certain conditions have an influence on "twin- 

 ning" in sheep, the materials for Table 10 have been taken. 

 Here, again, as in cattle there is probably some evidence for an 

 increased male production from delayed fertilizations. 



Experiments on the frog and the toad have afforded evidence 

 for the control of sex. Richard Hertwig ('06, '12), and later 

 Kuschekewitch ('10), allowed frog's eggs before fertilization to 

 "overripen," a process during which the eggs take up water — 



10 The use of the terms early and late fertilizations assume that some ovula- 

 tion occurs either immediately before, or shortly after, the beginning of heat. 



