GERM CELLS OF ANURANS 267 
The age of these animals could only be estimated by their size 
and developmental stage, and were probably about two years old. 
Some of the tadpoles would have undergone metamorphosis within 
a short time but for the lateness of the season. The writer has 
known for several years that young male bullfrogs sh.ortly after 
metamorphosis are sexually mature, though in regard to size they 
are pygmies compared to the adults and. it is difficult to see how 
they could possibly copulate with mature females. The female 
Rana catesbeiana apparently does not become sexually mature 
and ready for copulation until several years after metamorphosis, 
and in this respect resembles the European frogs, such as Rana 
esculenta. According to the observations of R. Hertwig, Witschi, 
and others, the female of Rana temporaria and Rana esculenta 
does not become fully mature and ready for copulation until the 
fifth season after metamorphosis. Despite the fact that the 
females are sexually immature, the young male bullfrog apparently 
ripens his sexual products continuously, beginning with the first 
year of larval life, though the first-year sexual cycle is abortive. 
The writer has observed somewhat similar phenomena in the 
leopard frog, Rana pipiens. It is not uncommon to find very 
small immature looking individuals of this species with sp6rm in 
their testes. It has been known for several years that prolonga- 
tion of the larval life of tadpoles of this species by thyroid extirpa- 
tion does not prevent the normal seasonal ripening of their sex 
products. Such ripening corresponds to the second larval sexual 
cycle in Rana catesbeiana, for it is probable that the tadpoles 
of this species (i.e., Rana pipiens) undergo a very precocious and 
abbreviated maturation cycle very early in larval life. This 
early cycle in Rana pipiens would correspond to the first sexual 
cycle of Rana catesbeiana; the prolonging of the larval life of 
the leopard-frog tadpoles leads to the second seasonal ripening 
and production of normal spermatozoa just as in the bullfrog, 
though in the latter species the period of larval existence covers 
the second seasonal ripening of the germ cells. 
The germ-cell cycle of the second year in Rana catesbeiana 
larvae, as was previously stated, is normal in every way, hence no 
description will be given of the process here. The secondary 
