238 WILBUE WILLIS SWINGLE 
for a later paper, which will be a consideration of the develop- 
mental history of the male and female sex glands, neoteny, Bid- 
der's organ, and an attempt at a reinterpretation of the problems 
stated in the hght of certain phenomena described below. The 
writer regards the second part of this work as perhaps the most 
interesting from a theoretical standpoint and as comprising the 
main portion; however, for sake of clarity in presentation, divi- 
sion of the subject has been found essential. It is necessary to 
give in detail the normal germ-cell cycle before discussing its 
aberrations or more unusual modifications. 
MATERIAL AND METHODS 
During the course of the work only one species of anuran has 
been employed to any extent, i.e., Rana catesbeiana. Other 
forms have been examined for comparison with the bullfrog, but 
not for the phase of the problem treated in this paper, so they 
need not concern us here. Rana catesbeiana in its larval stage 
has no equal among other frogs in respect to the peculiar fitness 
of its germ cells for this sort of study. The sex cells of the Uro- 
dela have long been noted for their size and fitness for cytologi- 
cal study, whereas the cells of adult frogs and toads have received 
scant attention. Yet it is a fact that the germ cells of larval 
bullfrogs, in regard to the size of cells and chromosomes, are 
little surpassed by even the best urodele material, and in this 
respect they more nearly resemble the caudate forms than the 
conditions presented by adults of their own species. In the 
adult frog or in newly metamorphosed animals the size of cells, 
nuclei, and chromosomes is distinctly less than in the larvae. 
The germ cells of sexually mature bullfrogs are in this respect 
like those of a different animal group when compared with larval 
stages. The explanation of this peculiarity will be discussed in 
its proper place. 
Another interesting feature about the bullfrog that makes it an 
especially favorable object for study is its remarkable long larval 
life. This species usually spends several seasons as a larva, and 
is a tadpole for approximately two years. Sometimes these ani- 
mals pass through almost three years as tadpoles, though this is 
