Inheritance Materials of (icrvi-Cclls 77 



The widely known result reached hy Hertwig and vurlHed 

 and extended by Kuschakewltsch ex})re.ssed in a single sen- 

 tence, is that the number of males and of females ])ro(luced 

 by the eggs of a given female depends upon whether the 

 eggs are fertilized when newly rij)e or when over-ri})e, a great 

 ])redominance of males coming from the latter class. In 

 a tabulation of the results of four sets of experiments \)\ 

 Hertwig " almost every case shows the number of males 

 increased when the time elapsing })etween deposition of the 

 eggs and fertilization was increased, the highest percentage 

 of males in any one lot being 759, fertilization in this in- 

 stance having been twenty-two hours after the fertilization 

 of the last preceding lot. 



In a species of toad, Bufo lentigijwsus, results have been 

 obtained just the reverse of those on the frog, that is, the 

 proportional number of females has been experimentally 

 increased. This was accomplished by fertilizing the eggs 

 in water made slightly alkaline. Since frog eggs are known 

 to absorb water when they remain long in it, as in the case 

 of those which gave rise to a preponderance of males in 

 the Hertwig method of experimenting; and since alkaline 

 solutions extract water from eggs, and likewise cause them 

 to produce a preponderance of females, Miss King drew 

 the obvious conclusion that the quantity of water contained 

 in eggs of these animals may be a factor in determining the 

 sex of the animals developed from the eggs. Although 

 Miss King recognizes that her experiments do not furnish 

 final proof of the conclusion she draws, she believes, rightly 

 it would seem, that they weigh heavily in tliat direction. 

 "As they stand," she writes, "the results strongly suggest 

 that sex in Bufo is determined at or near the time of fer- 

 tilization, and that external factors acting during this ])o- 

 riod 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 Ilufo sex is determinwl in 



