GERM CELLS OF ANURANS 243 
formed in the gonads, the so-called secondary genital spaces, lined 
by small non-sexual cells which have migrated into the gland from 
the mesonephros by way of the mesentery. At this stage the 
gonads of both sexes are hollow sacs (surrounded by peritoneum, 
the so-called germinal epithelium), the walls of which consist of 
one, two, or three layers of sex cells, depending upon the stage 
studied (figs. 33 and 34). 
In female larvae the cavity is later obliterated by growth of 
the oocytes. In male animals, these secondary genital spaces 
persist until shortly before metamorphosis, when they also are 
obliterated, chiefly by increased division of the germ cells, and the 
ingrowth of cells from the mesonephros, which form anastomos- 
ing cords throughout the testis, the future rete or efferent ducts 
(fig. 35 shows the obliteration of the testis cavity). 
4. In young first-season tadpoles, the sexes are indistinguish- 
able, though later males and females are easily separated by 
microscopic examination. The female glands grow very fast and 
greatly enlarge, owing to oocyte formation, becoming irregular, in 
outline. On the other hand, the male gonads remain small, are 
fairly regular in outline, but do not generally assume the shape 
characteristic of the adult testis until some months previous to 
metamorphosis, i.e., until the larvae are about two years of age 
(fig. 35). Also text figure 1, C. 
5. The germ cells of larvae, taken in summer of the second 
season, both male and female are found to be undergoing simul- 
taneous maturation changes. This is a most unusual phenome- 
non, and so far as the writer is aware, uniciue among the verte- 
brates, though common enough perhaps among the invertebrates. 
In no other group of the Chordata has anything analogous to the 
simultaneous maturation changes of male and female germ cells 
of larval anurans, such as here described, been reported, although 
on certain theoretical grounds based on a study of the sexual 
cycle of the larval bullfrog, the writer ventures to suggest that 
analogous phenomena are likely to be found in the myxinoids, 
larval petromyzonts, and eels. 
The early maturation stages preceding the growth period of the 
oocyte in female animals, such as leptotene, amphitene, pachy- 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 32, NO. 2 
