278 WILBUR WILLIS SWINGLE 
apparently show essentially identical phenomena as described 
by myself. The trouble heretofore has been one of interpre- 
tation. In Rana temporaria and Rana esculenta tadpoles the 
same precocity of the sexual cycle, as is presented by the bull- 
frog has been described many times by various investigators 
of these European frogs, but has been interpreted in a manner 
entirely different from the explanation here given. The fig- 
ures and descriptions of Bouin, Kuschakewitsch, Witschi, Schmidt- 
Marcel, and others on the history and development of the germ 
cells of these frogs plainly indicate the precocious maturation 
process in the larvae. However, the ripening of the tadpole 
germ cells of the species studied goes only up to and including 
the pachytene, according to their figures. These writers proba- 
bly misinterpreted the sexual conditions, and this has led to some 
bizarre theories of sex differentiation in frog larvae. According 
to the interpretation of this school, all larvae whose germ cells 
presented auxospireme, i.e., leptotene and pachvtene maturation 
stages, are to be regarded as females, because it is only female 
animals that show such maturation changes in larval or embry- 
onic life. Similar maturation stages of male sex cells do not 
occur until near the period of sexual maturity, according to them. 
In the anurans studied by these writers the precocity of the sex- 
ual cycle is very marked, and the germ cells do not go beyond 
the pachytene and form tetrads and first-maturation spindles as 
normally occurs in Rana catesbeiana. Consequently they were 
not aware that the male larvae exhibits a precocious maturation 
cycle coincident with that of the females, when the cells of the 
latter go through the early stages of oocyte formation. As a 
consequence of this developmental peculiarity, i.e., curtailment of 
the maturation cycle to the early stages of the process, without 
exception these writers, being unable to differentiate male from 
female, concluded that all frog tadpoles first develop as females, 
then later half of the female tadpoles must transform into males, 
because the sex ratio of adult frogs is approximately 50-50. 
Their conclusions were logical enough, even though probably 
erroneous, considering their premise that early maturation stages, 
leptotene and pachytene, are solely characteristic of female 
animals, when found in immature or embryonic forms. From a 
