“I 
SEX-DETERMINATION IN AMPHIBIANS 32 
2. EXPERIMENTS ON THE FERTILIZED EGG 
If the sex of an embryo is not definitely fixed by the character 
of the spermatozoan that fertilizes the egg, it is possible that the 
zygote is a sex-hybrid and that external conditions, acting during 
the early stages of development, may turn the balance in favor of 
one sex or the other. 
Several different experiments were made this year to see whe- 
ther changing the water content of the zygote would have any 
effect on the sex ratio. ‘These experiments may be divided into 
two groups: (A) those in which an attempt was made to cause 
the eggs to absorb an increased amount of water during the fer- 
tilization period; (B) those in which eggs were made to lose water 
during this time. 
With increased absorption of water 
According to Loeb (’06), eggs can be made to take up water 
by placing them in weak solutions of acid or of alkali, the quantity 
of water absorbed depending on the strength of the solution used. 
Former experiments have shown that the eggs of Bufo are very 
sensitive to the action of acid and of alkaline solutions, and that 
it is not possible to subject them to the action of a solution stronger 
than 0.01 per cent without rendering the great majority incapable 
of development. Last year seven lots of eggs, from four different 
females, were fertilized in weak solutions of acetic acid (0.0025 
per cent to 0.01 per cent), and in every instance the percentage of 
females obtained was from 10 per cent to 20 per cent lower than 
that in the control lot. Unfortunately no definite conclusions 
could be drawn from these experiments, since in every case the 
mortality was very great both at the time that the eggs were fer- 
tilized and during the growth of the tadpoles. 
I planned to repeat these experiments on a large scale this past 
spring in the hope that definite conclusions would be possible 
from the results obtained. To my great surprise, however, I 
found that it was not possible to obtain any considerable number 
of eggs that would develop normally after being fertilized in solu- 
tions of acetic acid. Altogether twenty batches of eggs, from 
