FOOD AS A FACTOR IN THE DETERMINATION OF 

 SEX IN AMPHIBIANS. 



HELEN DEAN KING. 



Of the many theories that have been advanced regarding the 

 causes that determine whether an animal shall become male or 

 female, the one that nutrition is a dominant factor in sex deter- 

 mination has received much credence. This theory has been 

 supported by the results of numerous feeding experiments made 

 by different investigators on various classes of animals, and also 

 by statistics compiled by Diising (5) and others with reference to 

 the proportion of males and females in the human race among 

 the offspring of the rich and of the poor. 



Three investigators, Born, Yung and Cuenot, have sought by 

 experimental means to ascertain the relation of nutrition to sex 

 determination in amphibians. Born (1), who was the first inves- 

 tigator in this field, found that in a total of 1,272 young Rana 

 fusca that had been well nourished during the larval period, 1209 

 or about 95 per cent, were females, while in 160 young frogs 

 taken from their natural environment only 52 per cent, were 

 females. From the results of these experiments Born con- 

 cluded that an abundance of food leads to the development 

 of a greater proportion of females. As several investigators 

 have pointed out, Born's results cannot be considered as fur- 

 nishing conclusive evidence regarding the influence of nutrition 

 on sex determination, for the methods employed in the experi- 

 ments did not exclude the possibility that other factors than 

 nutrition influenced the results. No account whatever was taken 

 of the many hundreds of tadpoles that died during the course of 

 the investigations and, as Born himself suggests, there is the pos- 

 sibility that the mortality was greater among the males than 

 among the females. In ascertaining the sex of the young frogs, 

 Born examined the gonads in toto and did not make use of sec- 

 tions in any case : if the genital organs were large, the individual 

 was classed as a female ; if the organs were small, the individual 



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