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HELEN DEAN KING. 



dividuals in which sex was ascertained were females, although 

 one half of the eggs had developed in water which had a tem- 

 perature of 22-30° C. while the other half of the eggs had been 

 kept at a temperature of 14-18° C. In the second series (lotB), 

 the eggs were subjected to conditions similar to those under 

 which the eggs of lot A had developed. Only 33.97 per cent, 

 of females was obtained in this series, and more females were 

 found among the individuals which had developed at a tempera- 

 ture of 14-18° C. than among those which had been kept at the 

 higher temperature. The results of these experiments, therefore, 

 do not support Hertwig's contention, and they seem to indicate 

 that temperature, acting during the development of the tadpoles, 

 does not determine sex in Biifo. 



In the series of experiments described above the eggs belong- 

 ing to lot A were fertilized in water which had a temperature of 

 16-18° C. ; the eggs used for lot B, on the other hand, were ferti- 

 hzed in water which had a temperature of only 11-13° C. The 

 results obtained in the experiments suggested the idea that tem- 

 perature, acting at the time that the eggs were fertilized, might 

 determine sex. This suggestion was tested in the spring of 1 908 

 in the following way : a pair of toads were placed in water which 

 was kept at a temperature of 26° C. until the eggs had been 

 deposited and fertilized ; the eggs from a second female were laid 

 and normally fertilized in water which had a temperature of 9° C. 

 There was thus a difference of 17° C. in the temperature of the 

 water in which these two sets of eggs were fertilized. In each 

 series as many individuals as possible were carried through to 

 metamorphosis and their sex ascertained. The results obtained 

 in these experiments are summarized in the following table. 



Table I. 



The average proportion of females among young toads that 

 have recently completed their metamorphosis is 51,62 per cent., 

 judging from the number of females found among the 9,949 



