198 THE AMERICAN NATURALIST [Vol. LYI 



in the course of the abortive and degenerate sexual cycle 

 of an embrj-onic pro-testis? 



The work of Witschi on the problem of sex in anurans 

 can be summarized thus : He has described in great de- 

 tail and with admirable exactness the process of develop- 

 ment of the pro-testis or Bidder's organ in the short 

 larval-lived frogs, its degeneration and final replacement 

 by the definitive gonad. This process he calls transfor- 

 mation of females into males. The experimental investi- 

 gations of Witschi upon sex transformation by environ- 

 mental influences consists of this: By means of such 

 agents as heat or cold, etc., he has simply modified the 

 normal course of development of the pro-testis — Bid- 

 der's organ, thereby accelerating or delaying the devel- 

 opment of the definitive testis. The experimental results 

 show that it is possible to modify the developmental rate 

 of the embryonic testis. Similar experiments carried out 

 with regard to other larval structures would unquestion- 

 ably give similar developmental modification. Cold hin- 

 ders metamorphosis and all the normal structural changes 

 metamorphosis implies. All of these environmental influ- 

 ences are interferences with the normal cycle of the go- 

 nads, by which the development of the definitive gonad 

 out of the pro-testis is accelerated, retarded, or possibly 

 prevented entirely. The following quotation from Wit- 

 schi '14, page 10, is significant in this connection: 



Bei seinen Untersuchungen war es Hertwig aufgefallen, das unter 

 dem Einfluss verschiedener Aussenbedingungeii sich nicht nur die 

 Geschlechtsziffern, sondern oft auch in ganz auffalliger Weise der 

 Ehythmus. in Welchem die Keimdriisen und manche andere Orgaiie 

 sieh anleg-eii und entwickeln. 



It is probable, judging from certain experiments re- 

 ported, that the degree of development attained by the 

 larval gonadic rudiment, its position in relation to the 

 definitive gonads, its period of persistence, non-formation 

 in some forms, and such like, may vary in different frog 

 species and is determined by heritable factors. For ex- 

 ample, in Bufo, the structure jjersists throughout life in 



