No. 2.] THE OOGENESIS OF BUFO LENTIGINOSUS. SOE 
ovary; the others, as far as I can determine, are actively 
concerned in the formation of the ovarian walls, the cyst 
membranes and the zona pellucida. 
According to the observations of Bouin there are fewer 
primordial germ-cells in a tadpole of Rana temporaria that 
is 33 mm. long than in one 20 mm. long. As the difference 
in numbers is considered too great to be attributed to indi- 
vidual variation, Bouin believes that a reduction in the num- 
ber of primordial germ-cells is brought about at this stage of 
development through an expulsion of a large number of these 
cells from the ovary into the body-cavity. He calls this pro- 
cess “ponte d’ovules primordiaux,” and he considers that it 
is analogous to that which occurs in the adult frog when the 
ripe eggs are expelled from the ovary. Bouin suggests that 
this process may take place so that “‘la glande, qui évolue dans 
le sens male, élimine les éléments qui seraient inutiles a son 
développement ultérieur.” None of the other investigators 
who have worked on the development of the sex-glands in 
amphibians have described such a reduction in the number 
of primordial germ-cells and there is nothing similar to it 
to be found in Bufo. The expulsion of primordial germ-cells 
from the ovary is, therefore, either a process that is peculiar 
to Rana temporaria, or it is one which takes place so quickly 
in other species that it has escaped the attention of the in- 
vestigators working in this field. 
As the tadpole approaches metamorphosis, the ovary in- 
creases in size very rapidly and it usually appears lobed when 
examined in toto under a low power of the microscope. This 
lobed appearance of the young ovary furnishes a means by 
which it can be distinguished from the testis without making 
use of sections. 
Ill. THe SECONDARY OOGONIA. 
Soon after metamorphosis the primary odgonia give rise to 
a new generation of cells, the secondary odgonia, which are 
aggregated into cysts or “cell nests” that are arranged much 
