28 HELEN DEAN KING. 



was made to study the determination of sex in Bufo. The work 

 was carried on in the vivarium of the University of Pennsylvania 

 where the splendid facilities at my command permitted the use of 

 relatively large numbers of individuals in each experiment and the 

 rearing of them under exceptionally favorable conditions. 



In all of the experiments in this series the tadpoles were kept 

 in large glass aquaria or in cement tanks which were supplied 

 with running water. Each tank contained a sloping bank of 

 sand and gravel and also a quantity of water plants. With the 

 exception of the one experiment in which the influence of starva- 

 tion on the determination of sex was being studied, all of the 

 tadpoles used in these investigations received similar food, viz., 

 water plants and minute organisms in abundance and occasionally 

 fine pieces of cooked meat or cereal. According to my observa- 

 tions tadpoles of Bufo invariably prefer an animal to a vegetable 

 diet and they readily devour the dead bodies of their companions. 

 To this latter fact can be attributed the loss of many individuals dur- 

 ing the course of these experiments. Since there is no apparent 

 relation between mortality and sex among tadpoles reared under 

 artificial conditions, as shown by the investigations of Pfiuger ('82), 

 and also by my former work, the individuals in which sex was 

 not ascertained are disregarded in considering the results of these 

 experiments, although the total number of individuals with which 

 each experiment started is given in most cases. The methods 

 used in ascertaining the sex of the individuals were similar to 

 those previously employed (King, '07). Whenever possible 

 the bodies of tadpoles that died were preserved and the sex ascer- 

 tained by means of sections. As there is considerable individual 

 variation in the size and also in the development of the gonads, 

 even after the metamorphosis of the toads, it was necessary to 

 section the genital organs of nearly one fourth of the total num- 

 ber of individuals in order to ascertain their sex. 



I. EXPERIMENTS TO DETERMINE THE SEX RATIO OF THE INDI- 

 VIDUALS THAT DEVELOP FROM THE EGGS OF THE RIGHT 

 OVARY AND OF THOSE FROM THE LEFT OVARY. 



If sex is determined in the ovary, as many investigators be- 

 lieve, it is possible that the individuals developing from the eggs 



