4O HELEN DEAN KING. 



cent, of females. Just as striking a difference is shown in the 

 case of the individuals that were reared in cold water. Lot A 

 produced 61.58 per cent, of females, while Lot B, developing 

 under similar conditions, gave but 37.60 per cent, of females. 

 The very different sex ratios obtained with lots of eggs subjected 

 to the same temperature conditions seem to indicate that sex in 

 Bufo is not determined by the temperature of the water in which 

 the tadpoles develop. 



If sex is already determined in the egg and not influenced by 

 external factors there is probably a considerable variation in the 

 sex ratios of lots of eggs laid by different females. It might, 

 therefore, be possible to explain the above results on the assump- 

 tion that, by chance, batches of eggs were taken for the experi- 

 ment which gave the extremes of possible normal variations in 

 the sex ratio. This explanation is hardly a satisfactory one, 

 especially in light of the results obtained in the experiment about 

 to be described. The batch of eggs from which the individuals 

 used in Lot A were taken was laid in water which ranged from 

 16 1 8 C. during the two hours or more in which the eggs were 

 being deposited and fertilized. The eggs used in Lot B, on the 

 other hand, were laid in water which had a temperature of from 

 ii 13 C. during the period of their deposition. The results 

 of the experiment at once suggested the idea that the tempera- 

 ture of the water at the time that the eggs were fertilized might 

 possibly have some influence on sex ; a high temperature favoring 

 the development of females, a low temperature that of males. 

 The following experiment was made to determine the value of 

 this suggestion. 



On April 5, 1908, a pair of toads were placed in water which 

 remained at a temperature of about 26 C. during the time that 

 the eggs were being deposited and fertilized. All of the eggs 

 that were laid fertilized readily at this temperature and all seg- 

 mented in a normal manner. For convenience in description 

 this set of eggs will be called Lot C. On the same date another 

 pair of toads were placed in water which had a temperature of 

 about 9 C. during the period in which the eggs were being de- 

 posited. All of the eggs in this set, which will be called Lot D, 

 were also fertilized and all developed normally. There was, 



