46 HELEN DEAN KING. 



which is not present in the testis. Altogether the gonads of about 

 600 individuals were examined histologically and in only about 

 50 cases was it impossible to distinguish one sex from the other. 

 The methods used in carrying out the experiments and in 

 ascertaining the sex of the individuals have been given in consid- 

 erable detail in order to indicate the precautions that were taken 

 to avoid the most probable sources of error that might have had 

 an influence on the results. 



The Normal Proportion of the Sexes in Bufo lentiginosus. 



Cuenot has collected the statistics that have been published 

 regarding the normal proportion of the sexes in various species 

 of Rana, and his table shows that the number of females varies 

 from 49 per cent, to 86.8 per cent, in different cases. Pfliiger 

 (9) and von Griesheim (7), who have most carefully investigated 

 this subject, find that not only does the proportion of females 

 vary somewhat in lots of frogs taken from different localities, but 

 that there is also a marked difference in the proportion of females 

 in lots of frogs taken from the same locality in different years. 

 The normal proportion of the sexes in Rana seems, therefore, to 

 be a variable one depending on the locality and on the year. 

 In the great majority of cases there seems to be a greater num- 

 ber of females than of males, not only among adult frogs but 

 also among the young just after metamorphosis : the excess 

 varies from 1.05 per cent, to 73 per cent, in different cases. 



I have not been able to find any statistics regarding the normal 

 proportion of the sexes in other amphibians. Fischer-Sigwart 

 (6) has noticed an excess of males among Hyla aborea during the 

 breeding season, and Boulenger (2) has stated that there is an 

 excess of males among the common European toads, Bufo vul- 

 garis and Bufo clamata : neither investigator gives any statistics in 

 support of his statement. For some years past I have been col- 

 lecting adult toads during the breeding season and also during 

 the summer months, and I have always found an excess of males 

 in this species. Unfortunately I have kept no records regarding 

 the proportion of the sexes among adults. 



In order to determine the relative proportion of the sexes in 

 young toads that have recently completed their metamorphosis, 



