GERM CELLS OF ANURANS 241 
1918, from a pool in Douglas County, Kansas; 1700 larvae meas- 
uring from 60 to 165 mm. total length were taken from a pond on 
the University Campus at Princeton during the months of July, 
August, and October, 1919. Only a comparatively small num- 
ber of animals from these various groups were examined micro- 
scopically, the remainder were preserved for a study of the sex 
ratios and so-called hermaphroditism at various developmental 
stages — phases of the subject not dealt with here, but which make 
up the subject-matter of a later communication. 
The size or length of tadpoles is not a good criterion of their 
age because of the size variability shown by anuran larvae of 
similar age, reared under identical environmental conditions. The 
writer was, until last year (1919), unable to get the eggs of the 
bullfrog in sufficient quantity to rear the tadpoles artificially. 
Hence the age of the older larvae given in this account is only 
approximate, for they are classified according to size and stage of 
development, as first- and second-year tadpoles. 
RESUME OF A FEW OF THE MORE IMPORTANT POINTS IN THE 
DEVELOPMENTAL HISTORY OF THE GERM GLANDS AND 
GERM CELLS OF RANA CATESBEIANA LARVAE 
A brief summary of the developmental history of the gonads 
and sex cells may prove useful in elucidating some of the peculi- 
arities of the sexual cycle described later in the paper. Only 
a few of the more important stages will be considered here, and 
then only in a very brief and sketchy way. 
1. The primordial germ cells of the embryo are first distin- 
guishable from other yolk-laden entoderm cells as a ridge just 
dorsal to the cavity of the archenteron and ventral to the 
aorta, separating the two lateral plates of mesoderm (text fig. 2, 
A) . The medial growth of the two lateral plates and formation 
of the mesentery together with probably an active migration 
dorsally of the germ cells themselves, cuts off this germ-cell ridge 
from the underlying entoderm (text fig. 2, B and C). As devel- 
opment proceeds this median ridge of germ cells splits longitudi- 
nally and the cells of the two halves then migrate laterally on 
either side to form two independent ridges invested with a cov- 
