THE 



AMERICAN NATURALIST 



Vol. LVI. May- June, 1922 No. 644 



IS THERE A TRANSFOEMATION OF SEX IN 

 FROGS? 



PEOFESSOR W. W. SWINGLE 



OsBORX Zoological Laboratory, Yale University 



This paper is a reply to the recent article of Dr. Emil 

 Witschi which appeared in a late issue of the Naturalist 

 (Vol. LV, No. 641). Witschi is quite convinced that the 

 problem of sex development and differentiation in frogs 

 has been settled, and that nothing further remains to be 

 said. However, the writer feels that instead of being 

 solved, the time has come for a revision of the entire 

 question of sex development in Anurans, and that the 

 subject is ripe for a reinterpretation upon a more ra- 

 tional basis than that accorded to it heretofore. 



The first portion of the paper will be devoted to a brief 

 exposition of the writer's interpretation of sex in frog 

 larvffi based upon data obtained from a study of the bull- 

 frog. The second part of the paper is a reply to certain 

 questions raised by Dr. Witschi. 



In larval males of the bullfrog two gonads are formed, 

 just as there are two kidneys formed, a pro-testis or em- 

 bryonic sex gland destined to degenerate and disappear 

 in ontogenetic development and a definite or functional 

 testis which replaces it. The germinal elements of the 

 pro-testis arise in the entoderm and migrate into the 

 germ ridges early in embryonic life. The cells multiply 

 rapidly and together with the mesodermal elements of 

 the germ glands form paired ridges projecting into the 

 ccelomic cavity. While the tadpole is very immature and 

 has yet a year of larval life before metamorphosing, the 

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