232 HELEN DEAN KING. 



amount of water in the egg at the time of fertilization has some 

 influence in determining sex; an increase in water content tending 

 to produce a male; a lowering of the water content favoring the 

 development of a female. 



It is, of course, possible to explain these results in other ways 

 besides attributing them to chance or to selective mortality. 

 On the assumption that the male is responsible for sex-deter- 

 mination in Bufo the results of the acid series of experiments 

 can be attributed to the fact that the solution killed more of 

 the female-producing than of the male-producing spermatozoa; 

 why this should occur is not at all clear. The explanation of 

 the relatively high percentages of females among the individuals 

 derived from eggs that were subjected to the action of a salt 

 or of a sugar solution before fertilization must be ascribed, ac- 

 cording to this view, to the fact that the solutions rendered the 

 eggs more resistant to the entrance of one kind of spermatozoa 

 than to the other. This would be, in effect, selective fertilization 

 for which at present there is no evidence, unless we accept the 

 case of the pigeon. According to the investigations of Aristotle, 

 of Fluorens ('64) and of Cuenot ('99) the first of the two eggs 

 laid by the pigeon almost always produces a male. Selective 

 fertilization therefore very probably occurs in the pigeon if the 

 male is responsible for sex in this form. 



That the results of any of these experiments are conclusive, 

 I do not for a moment maintain. They seem to me to be unusual 

 enough, however, to warrant the continuation of investigations 

 along these lines. As they stand the results strongly suggest 

 that sex in Bufo is determined at or near the time of fertilization, 

 and that external factors acting during this period may influence 

 the sex-determining mechanism in such a way as to cause it to 

 produce one sex or the other. The results also seem to indicate 

 that in Bufo sex is determined in the egg, and that it may depend 

 in some way on the relative amount of water in the egg at the 

 time of fertilization. This suggestion, if capable of more general 

 application, does not exclude the possibility that in some cases 

 the spermatozoan may influence sex. It is known that the 

 unfertilized eggs of the bee produce only males, and that fertilized 

 eggs almost invariably develop into females. In this case the 



