230 HELEN DEAN KING. 



are overripe when fertilized, tend to produce males because they 

 are relatively richer in nuclear substance; females, on the other 

 hand, are produced when the egg is relatively poor in nuclear 

 substance at the time that it is fertilized. 



It is very probable that the eggs of the frog normally absorb 

 a slight amount of water during their passage down the oviducts 

 and while they were retained in the uteri. If the eggs remain 

 in the uteri two or three days beyond the time that they would 

 normally have been deposited and fertilized it is not improbable 

 that they continue to absorb water during this time. Over- 

 ripe eggs, therefore, would contain relatively more water than 

 those that were laid at the normal time. The sex ratios found 

 when such eggs are fertilized accord very well with those that 

 I have obtained by fertilizing the eggs of Bufo in acid solutions. 

 In both cases it seems probable that the water contents of the 

 eggs at the time they were fertilized was higher than usual; 

 and one is strongly inclined to attribute the great excess of males 

 to this cause. 



Experiments made two years ago with the eggs of Bufo to 

 ascertain whether delaying fertilization would produce an alter- 

 ation in the sex ratio (King, '09) gave negative results. The 

 eggs of Bufo are not as favorable as are those of Rana for experi- 

 ments of this kind, as it is not possible to delay the deposition of 

 the eggs more than a few hours. In the experiments referred to 

 a female was killed as she was about to deposit her eggs. The 

 body was not opened until seven hours later when the eggs were 

 artificially fertilized. Post-mortem changes had evidently begun 

 as, although the majority of the eggs segmented in a more or 

 less regular manner, many of them failed to develop beyond the 

 gastrulation stage. The sex ratios were practically normal in 

 the lot of individuals in which sex was ascertained. In the light 

 of these recent experiments the negative results that were obtained 

 can perhaps be atributed to the fact that either the eggs were 

 unable to absorb water during the time that they remained in 

 the uteri of the dead female, or that they were not kept a suffi- 

 ciently long time to enable them to take up enough water to pro- 

 duce any effect on the sex-determining process. 



Unfortunately there is one source of error in all of the experi- 



