324 HELEN DEAN KING 
Taking the sex ratio for any lot of individuals as the number of 
males to each 100 females, it is found that the toads derived from 
eggs that were subjected to the action of the salt solution before 
fertilization give a much lower sex ratio than that occurring among 
the individuals developed from eggs which had been treated with 
sugar solution (table 1). If this difference can be attributed to 
the fact that the osmotic action of salt is several times greater 
than that of sugar, it follows that the more water that is extracted 
from the egg just before fertilization the greater becomes its 
tendency to produce a female rather thanamale. On this assump- 
tion it is the egg, and not the sperm, that contains the sex-deter- 
mining mechanism. In Bufo, therefore, as in the sea-urchins 
according to the recent investigations of Baltzer (’09), the female 
is heterozygous as regards sex and the male is homozygous. 
The above interpretation of these results is not the only one 
that can be given, although it seems to me to be the most plausible. 
Selective mortality cannot be held responsible for the sex ratios 
obtained, since in none of the experiments was the mortality 
sufficiently great, either at the time that the eggs were fertilized 
or during the development of the tadpoles, to have appreciably 
affected the results. There are two possible explanations for 
these results that do not involve the admission that external fac- 
tors can influence sex. It is conceivable that subjecting eggs to 
the action of hypertonic solution just before their fertilization 
may have rendered them more easily penetrated by spermatozoa 
that were female-producing than by those that were male-pro- 
ducing, assuming that the spermatozoan determines sex as the 
current chromosome sex theory demands. This means, however, 
that fertilization must here be considered as selective, though 
Wilson (’10) has recently shown that selective fertilization is most 
improbable in any form. A study of the spermatogenesis of 
Bufo (King, ’07) has not shown any dimorphism of the spermato- 
zoa that might be associated with sex-determination; neither has 
such a dimorphism been found in the spermatozoa of any am- 
phibian so far investigated. It seems somewhat absurd, there- 
fore, to assume the existence of dimorphic spermatozoa in Bufo 
