48 HELEN DEAN KING. 



produce relatively more males. Yung maintains that nitroge- 

 nous food is highly favorable to the development of females ; while 

 Schultze (n) states that food of this character has no influence 

 whatever in determining sex. 



It was intended, when the experiments began, to test both of 

 the possibilities mentioned above. Among the 300 individuals of 

 Series I., that were poorly nourished the mortality was so great 

 during the first month of the experiment that it was necessary to 

 abandon, for the time, the study of the possible influence of mal- 

 nutrition on sex determination. The investigations were there- 

 fore confined to an attempt to ascertain whether an abundant 

 nutrition or the character of the food received by the larvae has 

 any influence in determinating sex. The lot of 300 tadpoles 

 which had received little food was therefore discarded, and all of 

 the remaining individuals received an abundance of the particular 

 kind of food whose influence was being investigated. 



In Series I., 300 tadpoles (Lot A) were fed exclusively on a 

 meat diet consisting of small pieces of cooked lamb or beef; 300 

 tadpoles (Lot B) were nourished on a purely vegetable food con- 

 sisting of a cooked wheat cereal ; a third set of 300 individuals 

 (Lot C) received a mixed diet composed of water plants {Nitella 

 and Spirogyrd) and minute organisms on decayed leaves and bits 

 of wood taken from a pond in which toads breed each spring. 

 Lot C presumably received food similar in character to that 

 normally obtained by amphibian larvae. 



According to experiments made by Danilewsky (4), lecithin has 

 a marked influence on the development of frog embryos : tad- 

 poles fed on it show a great increase in size and in weight over 

 control tadpoles that have not received lecithin as food. Dani- 

 lewsky's experiments were not continued until the tadpoles 

 underwent metamorphosis, and therefore his results do not indi- 

 cate whether the increase in the size of the tadpoles was due to a 

 more rapid development or whether it was the direct effect of the 

 lecithin in producing abnormally large individuals. As it is con- 

 ceivable that ta more rapid development or an abnormal increase 

 in size might possibly be factors that would influence the sex of 

 an individual, a fourth set of 300 tadpoles (Lot D) in Series I. 

 were fed exclusively on the yolk of hen's egg which, according 



