266 WILBUR WILLIS SWINGLE 
the gonads at this time, and especially in certain individuals, 
that a great many of the definitive sex cells appear to arise by an 
actual transformation of mesothelial elements into germ cells. 
This question is still under investigation, for it is exceedingly 
difficult to determine definitely whether this is or is not the case 
from morphological data alone. Certainly in my material there 
is very suggestive morphological evidence that such transforma- 
tions may possibly occur, but whether such transformations actu- 
ally do occur is an entirely different thing. 
Another factor to be considered in regard to the reduction in 
cell size of the first-year germ cells is the fact that the entire gonad 
undergoes a striking diminution in size during the second year of 
growth, taking on the character of the adult testis. There is a 
great loss of water from the tissues at the time of metamorphosis 
and consequent shrinkage of the cells of the animal in volume. 
The size of the chromosomes depends upon the volume of the 
surrounding cytoplasm and of the nucleus, hence the smaller size 
of the second maturation cycle tetrads. These tetrads are of the 
short dumpy type found normally in adult frogs and toads (figs. 
120 to 128). 
The interesting fact that the sex products of the first larval sex- 
ual ripening are all abortive, while those of the second larval cycle 
are normal is something of a puzzle, and the only explanation 
occurring to the writer is based upon the phylogenetic history of 
Anura and will be discussed later in this paper along with some 
data of a somewhat similar nature regarding mammals and birds. 
There is one type of cell in the gonads of second-year larvae 
and metamorphosed frogs that may remain about equal in size to 
the germ cells of the younger larvae^ — the primary spermatogonia. 
This type of cell is large in frogs and larvae of any age. 
During the month of August, 1919, several very large tadpoles 
were captured with a total length of 140 to 160 mm. Examina- 
tion of the testes of male individuals showed many normal sper- 
matocyte divisions, spermatids in all stages of development, and 
a few mature spermatozoa. At this time the efferent ducts of 
the testis were not yet fully developed. The gonads were ex- 
tremely small and immature looking. Female gonads of larvae 
of similar size showed only oocytes undergoing growth. 
