No. G33] NEOTENY 355 



terion of sex differentiation employed by Witschi, i. e. f 

 that all germ cells in the larval gonads showing pseudo- 

 reduction (leptotene and pachytene stages) are to be re- 

 garded as female, the writer obtains in his set of 2,000 

 animals, !M> per cent, females and only 4 per cent, males. 

 In larvae of 85 mm. length the percentage of males is zero 

 if this criterion of sexual differentiation is employed. 

 The writer has found so far no evidence that the sex 

 ratios of Anure are any different from those of other 

 vertebrates, and is inclined to regard the confusion con- 

 cerning sex differentia lion and development in anurans 

 as a result of interpretating male animals showing pre- 

 cocious maturation changes of the germ cells as females 

 and hermaphrodites. Sex in the frog does not appear 

 to be nearly so labile and easily influenced as some in- 

 vestigators claim. Professor Hertwig's "late fertiliza- 

 tion" experiments are more satisfactorily interpreted on 

 the chromosomal hypothesis of sex determination, than 

 on any other. 



One reason so many workers dealing with anurans 

 have regarded these animals as possessing hermaph- 

 roditic tendencies is the occurrence of "oocytes," so- 

 called, in the testes of larval and adult frogs and the 

 presence of the peculiar ovary-like structure, the organ 

 of Bidder, in the Bufonidoe. The origin of these apparent 

 oocytes in Rana catesbiana has not yet been worked out 

 as completely as the writer could wish ; however, enough 

 data has been collected to warrant a tentative explana- 

 tion of their occurrence in this form and the same data is 

 suggestive as regards the nature of Bidder's organ in 

 the male toad, at least suggestive enough to warrant a 

 reinvestigation of this structure, now generally regarded 

 as a rudimentary ovary. 



In male Rana catesbiana larvae, these large oocyte- 

 like cells are of frequent occurrence, and assume this 

 character while in the pachytene stage. Previous to the 

 growth period they are indistinguishable from the other 

 pachytene male cells of the gonad. During the growth 

 stage, which is later followed by their degeneration and 



