38 HELEN DEAN KING. 



this second experiment were laid as this knowledge might help to 

 explain the reason for the extraordinary excess of males. 



Hertwig repeated this experiment in 1906 using eggs of Rana 

 temporaria. None of the tadpoles developing at a temperature 

 of 20 C. lived to undergo metamorphosis and therefore their 

 sex could not be ascertained. Out of 340 larvae developing at 

 a temperature of 10 C., 74 lived to undergo metamorphosis. 

 Of this number 38 were males, 23 females, and in 11 the sex 

 was not ascertained although the individuals were probably males. 

 Hertwig's conclusion from this experiment is that cold favors the 

 development of males as heat favors the development of females. 



The following series of experiments was made to study the 

 influence of temperature on the determination of sex in Btifo. 

 Five hundred eggs laid and normally fertilized in the laboratory 

 on the morning of March 31, 1907, were divided into two lots : 

 one lot of 250 eggs was placed in a greenhouse, heated by steam, 

 where the temperature of the water in which the tadpoles were 

 developing varied from 23 30 C.; the remaining 250 eggs 

 were placed in a tank in an unheated basement room where the 

 temperature of the water in which the tadpoles lived ranged from 

 14- 1 8 C. during the daytime and was probably much colder 

 at night. Both lots of tadpoles were given similar food and all 

 of the conditions, excepting the temperature, were made as 

 nearly alike as possible. For convenience in description this set 

 of 500 eggs will be called Lot A. An unusually high tempera- 

 ture has apparently as injurious an effect on the eggs of Bufo as 

 it has on the eggs of Rana since a great many of the tadpoles 

 that were kept in water with a temperature of 23 30 C. died 

 before it was possible to ascertain their sex. The tadpoles that 

 lived developed very rapidly and many of them had completed 

 their metamorphosis by the first of June. The tadpoles kept in 

 the cold water were vigorous and healthy, and comparatively few 

 of them died. Their development was very slow, however, as 

 compared with that of the individuals living in the warm water. 

 At the end of May the largest of the tadpoles in this lot had a 

 body length of but 8 mm. and their hind legs were still very 

 small. None of these tadpoles underwent metamorphosis until 

 the third week in June. 



