GERM CELLS OF ANURANS 237 
of 1918. To Professors Allen and W. R. B. Robertson, of the 
Department of Zoology, the- University of Kansas, I" am also 
indebted for aid in collecting tadpoles and newly metamorphosed 
bullfrogs at various times. 
DIVISION OF THE PROBLEM 
The subject of sex in larval anurans is such a complex one 
and the literature on the question so vast, that no attempt will 
be made to deal with all the aspects of the problem in this paper. 
Instead, the material has been so arranged that different phases 
will be taken up and discussed separately in a series of papers. 
This paper is concerned chiefly with the more usual phases of the 
sexual cycle of the male Rana catesbeiana, both in the larvae 
and newly metamophosed animals, with especial reference to 
chromosomal conditions. The broader questions of hermaphro- 
ditism, alleged to exist normally as a developmental phase of 
anurans, reversal of sexuality, anomalous sex ratios and their 
experimental modification, Bidder's organ, and other interesting 
problems will not be touched upon here, save perhaps inciden- 
tally, and then only in the briefest fashion. It will be recalled 
that Pfliiger reported years ago, that there occur normally in 
newly metamorphosed frogs three kinds of individuals, males, 
females, and hermaphrodites, the two latter forms much more 
numerous in early stages than the males. In the course of fur- 
ther development the hermaphrodites become either definitely 
male or female, as the sex ratio for adult frogs is approxunately 
50-50. The investigations of R. Hertwig, Kuschakewitsch, and 
Witschi not only confirmed Pfliiger's work, but extended it by 
showing that anurans apparently first develop solely as females 
and sexual intermediates, the males only later differentiating 
from the females and hermaphroditic forms. Moreover, these 
investigators described in great detail modification of the sex 
ratios by environmental changes, such as extremes of tempera- 
ture and late fertilization. All of these alleged facts have given 
rise to the behef that anurans in their sexual development differ 
greatly from other vertebrates. These questions are reserved 
