GEEM CELLS OF ANURANS 277 
to the urodeles, with the exception of the bullfrog larvae described 
here. In other anurans permanent retention of larval characters 
may be experimentally produced by prolonging the larval life 
by thyroid extirpation; the retention of the larval somatic charac- 
ters has no effect upon the germ cells. Similar results were 
obtained by the writer (Swingle, '17-'18), where it was shown 
that acceleration of metamorphosis by thyroid feeding does not 
accelerate the normal course of events in the germ-cell cycle. 
It appears possible that the precocious seasonal ripening of the 
male tadpoles germ cells is a recapitulation, just as the tadpole soma 
is possibly a recapitulation of an earher phylogenetic stage when 
the present-day Anura were more Uke the Urodela than they are at 
present, both in regard to body form and sexual conditions. It 
would be interesting to know whether or not larval urodeles show 
any such precocious sexuality as described here for anurans. It 
is not improbable that other vertebrates with larval periods of 
development, such as some of the eels and petromyzonts, will be 
found to present analogous conditions to those described for 
the bullfrog larva. In fact, judging by certain facts to be pre- 
sented hereafter, it seems likely that all the vertebrates present 
some such precocity of the germ-cell cycle as described here. If 
the phenomena described here are in any way rooted in past 
phylogenetic conditions, it is a much more remote past than 
anything represented by any living Urodele type. 
6. Is there a precocious sexual cycle in other anurans? 
This question must be answered at once in the affirmative. 
In Rana catesbeiana the larval period is the longest of any 
other anuran known, and, as a consequence, the precocious sexual 
cycle of the tadpole is carried farther than in other frogs. There 
is no question but that if other anurans presented conditions in 
their germ-cell cycle as marked and unmistakable as those in the 
bullfrog, such conditions would have been reported years ago. 
One could not easily overlook cysts of spermatocytes in v/hich the 
tetrads are of sufficient size to permit counting with a one-sixth 
Leitz objective and a no. 5 ocular. Although conditions in other 
frog species are not so plain and easy of interpretation as those 
presented by the bullfrog larvae, yet nevertheless such species 
