GERM GLANDS AND GERM CELLS OF FROG LARVAE 551 



The larger size of the germ glands of the control animals is 

 clearly shown in the text figures. 



Sexual differentiation had not taken place in the starved larvae 

 but had in the algae-fed controls. 



At this stage of the work, considerable difficulty was experi- 

 enced in determining the sex of the young tadpoles. The germ 

 glands and germ cells of young frog larvae are so much alike in 

 early stages that it is mpossible to differentiate the sexes with 

 certainty. Although there is a considerable mass of literature 

 regarding the question of sex differentiation in the anurans, each 

 investigator who has dealt with the problem seems to have set 

 aside as untrustworthy the view of previous workers in the field, 

 and to have each promulgated a new sex criterion of his own. 

 I have found that only one or two of the many morphological 

 features of the gonads advocated as sex criteria by the various 

 authors, are trustworthy, when applied to very immature gonads. 



The criterion of sex differentiation adopted for the smaller 

 sizes of tadpoles was that advanced by King ('08) for Bufo and 

 confirmed by Witschi ('15) for Rana temporaria. Both of these 

 authors worked with young larvae, and found that in the germ 

 glands of those animals destined to develop into males, the germ 

 cells are scattered more evenly throughout the gland. Con- 

 versely, in the immature ovary which usually has a lumen, the 

 germinal cells remain near the germinal epithelium, which is 

 generally much thicker than in the males. 



Conditions very similar to those described by King and Witschi 

 for Bufo and Rana temporaria were noted in the larvae of Rana 

 pipiens, and seemed to warrant the adoption of their criterion for 

 sex differentiation in the larval stage of this amphibian. 



May 15, another series of fed and unfed tadpoles was killed 

 and sectioned. The nine day interval of starvation intervening 

 between this series and that of May 6, had sufficed to bring about 

 striking differences between the starved and control animals. 



The algae-fed animals averaged 40 mm. in length; the largest 

 animal of the lot attained a length of 46 mm. All of the controls 

 showed marked growth and development of the hind limbs into 

 their two primary divisions; also the toes had differentiated. 



