352 THE AMERICAN NATURALIST [Vol. LTV 



lent a do not become fully mature and ready for copula- 

 tion until the fifth season after metamorphosis. The 

 writer has captured two females of Rana catesbiana two 

 seasons after metamorphosis which were yet sexually 

 immature, hence it seems that the females of this species 

 also require a long period of time in which to develop 

 sexual maturity. The developmental history of the male 

 gonads and germ cells is quite different, and when rightly 

 interpreted fails to show female animals transforming 

 into males and vice versa, or abnormal sex ratios. 



It was stated that germ cells of the male larvse begin 

 their maturation cycle simultaneously with those of the 

 females. This is a very unusual condition and probably 

 unique among the vertebrates though common enough 

 in the invertebrates. It will be recalled that in the verte- 

 brates—for example the mammalia, a very long period 

 of time, sometimes years, separates the maturation cycle 

 of the sexes. In many instances in the female, the initial 

 maturation changes preceding the growth period of the 

 oocyte, occur before birth, whereas the same nuclear 

 changes in the male cells do not make their appearance 

 until shortly before the attainment of sexual maturity. 

 It has become the custom for investigators of sexual con- 

 ditions in the Anura to use this fact of the early occur- 

 rence of maturation stages preceding the growth period 

 of the oocyte in the female as a cytological criterion for 

 differentiating the sexes in the larval stages. Unfortu- 

 nately this principle, though true enough for other verte- 

 brates is not applicable to Anurans and the result has 

 been hopeless confusion of the sexes because in this group 

 maturation occurs in larval males. 



From the period of formation of pachytene nuclei, the 

 history of the sexes is quite different in Rana catesbiana 

 and unmistakable if a complete series of larval stages is 

 obtained. In justice to other investigators whose results 

 the writer criticizes as based upon misinterpretation of 

 sexual conditions, it is fair to point out that of all exist- 

 ing species of Anura, Rana catesbiana is apparently the 

 only one in which precocious ripening of the male germ 



