No. 644] TRANSFORMATION OF SEX 



201 



was the most marked of any animal yet observed, several 

 cysts of unmistakable spermatocji;es and spermatids were 

 observed. Tliey arose from the maturating cells of what 

 Witschi regards as the female part of the gonad — in 

 reality the pro-testis, and were of the cell type character- 

 istic of the adult frog. This observation shows two 

 things clearly: (1) That the direct descendants of the 

 male primordial germ cells {pro-testis elements) can pro- 

 duce practicaUy mature germ cells; (2) that the sper- 

 matocytes of the structure regarded hy the writer as a 

 pro-testis are really male cells, and that the structure in 

 so-called sexually intermediate frogs and tadpoles is in 

 no sense to he regarded as female in character. 



Another point is of interest here — the writer has 

 never observed direct testicular development in R. cates- 

 heiana, though it probably occurs in some strains; the 

 indirect method alone has been found, e.g., first a pro- 

 testis is formed which is later supplanted by the defin- 

 itive gonad. In the bullfrog, which has the longest 

 larval life of any anuran, the pro-testis persists longer 

 than in other forms, sometimes two years before giving 

 place to the definitive gonad. What the writer calls a 

 pro-testis of so-called sexually intermediate tadpoles is 

 according to Witschi a transitory ovary. If this is true 

 why is it that despite its persistence for such a long time, 

 relatively few oocyte-like cells are found in B. catesbei- 

 ana and in many individuals none, throughout a two- 

 year period, but instead the structure produces sperma- 

 tocytes and sometimes spermatids! Why is it, if this 

 structure is an ovar\^ in the so-called females that later 

 transform into males, that the shorter the larval life of 

 male anurans, the more the pro-testis in its structure and 

 behavior resembles the Bidder's organ characteristic of 

 male toads, due to rapid oviform degeneration of its 

 cells; the longer the larval life, e.g., Rana catesbeiana, 

 the more the germinal elements undergo a normal sexual 

 cycle characteristic of male cells ? The answer is, because 

 in forms with extraordinary prolonged lar\^al lives the 



