:^o. 644] TRANSFORMATION OF SEX 



195 



anaphase owing to fragmentation of the centrosome and 

 consequent formation of polyasters (Fig. 1). Sometimes 

 aberrant spermatids are formed by suppression of the 

 first and second maturation divisions and growth of axial 

 filaments from the centrosome. Practically all the germ 

 cells of the pro-testis degenerate and disappear while in 

 various stages of maturation— some undergo an oviform 

 type of degeneration, i.e., hypertrophy enormously and 

 take on the superficial characters of oocytes. The ovi- 

 form type of degeneration, however, is more character- 

 istic of the short larval-lived frogs than of R. catesbeiana, 

 for in many animals these large cells appear rarely and 

 in others not at all and this is an important point to keep 

 in mind. This type of degeneration will be discussed in 

 detail in a later paper; suffice to say it gives no clue to 

 the sex of a cell. (See Plates 1 and 2.) 



Some cells of the pro-testis fail to take part in the 

 abortive sexual cycle persisting through the phase of ma- 

 turation and degenerate as spermatogonia. These ele- 

 ments migrate into the sex cords (Fig. 1, g) which have- 

 formed meantime, and form a core of germinal tissue 

 extending through the center of the pro-testis. This core 

 of tissue plus the sex cords is the aiilage of the definitive 

 testis and is quite distinct from the pro-testis, the cells 

 of which are maturating and degenerating, whereas the 

 cells of the forming functional gonad remain as primitive 

 spermatogonia. The definitive testis by rapid growth 

 completely supplants the pro-testis which usually disap- 

 pears some time before metamorphosis. The functional 

 gonad is generally fully formed at metamorphosis when 

 the larvae are two years of age. Some tadpoles, but not 

 all, develop ripe speniiatozda in tlie gonad at metamor- 

 phosis due to a second -rxiial cyclv of the germ cells of 

 the definitive gonad. (Swiiiulc, 'Jl, Jour. Exp. ZooL, 

 Vol. 32.) 



In the frogs with .^hort larva 1-litV tlie saint' ^nrc-H.m 

 of gonads occurs, but in these I'oians the (IcNclopniciital 

 processes are greatly accelerated and the pro-testis ma- 



