No. 2] THE OOGENESIS OF BUFO LENTIGINOSUS. 375 
derived from peritoneal cells at any stage of development. The 
peritoneal cells in the genital ridge vary considerably in size 
and some may be nearly twice as large as others. In all cases, 
however, the cell contains comparatively little protoplasm and 
no yolk; while the nucleus maintains a characteristic appear- 
ance and stains very deeply, thus standing out in sharp contrast 
to the larger, more irregular, and more faintly staining nuclei 
of the germ-cells. 
The development of the genital ridge proceeds from before 
backward. Ina section of the anterior part of the ridge there 
are usually from 5-8 large germ-cells (Fig. 3), while in a 
more posterior section there are rarely more than three of 
these cells. In older tadpoles the difference in the rate of 
development of the different parts of the genital ridge is even 
more strongly marked, since the anterior portion of the ridge 
may have taken on its definite character as an ovary or a testis 
while the posterior portion remains in an apparently indifferent 
state. 
When a tadpole is ten or eleven days old, the yolk spherules 
begin to disappear from the cells of the genital ridge. and the 
structure of the germ-cells can then be more clearly seen (Fig. 
4). At this time the germ-cells are more rounded than they 
were at an earlier period and, as they contain fewer and 
smaller yolk spherules, the polymorphic nucleus is usually 
found in the centre of the cell. With the exception of the 
large plasmosomes, the nuclear contents still show little capac- 
ity for staining either with plasma or with chromatin stains. 
By this time many peritoneal cells have become flattened 
against the germ-cells and have thus assumed the role of fol- 
licle cells. The boundaries of these follicle cells become very. 
indistinct, and in many cases the cytoplasm seems to disappear 
entirely leaving the deeply staining nuclei in contact with the 
germ-cell. 
In early stages of development the germ-cells are not al- 
ways confined to the genital ridge. At the right, in Fig. 4, 
is a cell (Y) which lies considerably outside of the germinal 
area and directly under the Wolffian tubule; in Fig. 5, at the 
