FOOD AS A FACTOR IN THE DETERMINATION OF SEX. 5 1 



acetic, as they had reached a stage of development when it would 

 be possible to ascertain the sex of each individual by means of a 

 histological examination of the gonads. 



In the corresponding lots of the two series of experiments 

 there was a remarkable uniformity in the rate of development of 

 the individuals. In both series the tadpoles fed on the yolk of 

 egg underwent their metamorphosis much sooner than any of 

 the others, the last one in Series II. completing its metamorpho- 

 sis on July II. These tadpoles were only of average size, and 

 none of them ever reached the length attained by many of the 

 tadpoles that were fed on meat. Lecithin, therefore, may cause 

 a more rapid development, but it does not produce individuals of 

 unusual size. The tadpoles fed on meat grew enormously but 

 this increase in size was not accompanied by a more rapid develop- 

 ment ; on the contrary, the development of these tadpoles seemed 

 to be greatly retarded and some 50 of them had not begun meta- 

 morphosis by the middle of July. According to Yung, a purely 

 vegetable diet is insufficient to transform a frog tadpole into a 

 frog. Such a diet does not seem to be equally injurious to toad 

 tadpoles, however, as comparatively few of the individuals that 

 were fed entirely on wheat died during the course .of the experi- 

 ments, and only about 25 of them had not undergone meta- 

 morphosis by July 13. 



As presumably the individuals that were fed on a mixed diet 

 received the kind of food that is obtained by tadpoles living under 

 natural conditions, it might be expected that these individuals 

 would be larger and stronger than the others and that they 

 would undergo metamorphosis more quickly than those receiving 

 food that is only exceptionally, if ever, obtained by tadpoles in a 

 state of nature. Much to my surprise the development of the 

 individuals in Lot C lagged behind that of the tadpoles in the 

 other lots, and large numbers of them died during the course of 

 the experiments. On July 13, there were at least 100 tadpoles 

 in Lot C that had not yet begun their metamorphosis. 



The sex of all of the individuals used in the experiments was 

 ascertained when possible. The results for Series I. are summa- 

 rized in the following- table. 



