GERM CELLS OF ANURANS 287 
reproduction, and then degenerate? The evidence from the 
maturation cycle of the tadpole is again suggestive on this point. 
In the tadpole we may assume, in so far as it is safe to assume 
anything in biology, that the abortive and precocious sexual cycle 
is possibly a case of phylogenetic regression to ancestral condi- 
tions when the Anura were permanently of the caudate type and 
lived and reproduced normally as Urodele-like creatures. The 
carrying over into the ontogeny of the anuran larva's sexual cycle 
of this phylogenetic vestige is not surprising, considering the 
heavy impress of phylogeny upon the tadpole soma. Though 
this explanation may be involved with much plausibility to 
explain the larval sexual conditions of the bullfrog, is it in 
any sense adequate to account for the apparently analogous 
germ cj^cle of the Sauropsida and mammals, forms which do not 
have a larval period? I believe the same explanation appUes 
to these forms also, and that the precocious developmental cycle 
and degeneration of the primordial germ cells described in the 
Amniota differ not in kind, but merely in the degree to which 
the maturation cycle is carried from the larval sexual cycle of 
the Anura. 
In the Amniota we cannot speak of a precocious and abortive 
larval germ-cell cycle, but we can speak of an abortive embryonic 
sexual cycle, which, like that of the^tadpole, possibly bears the im- 
press of past phylogenetic conditions. And why not? If the em- 
bryo of the higher vertebrates can develop gill clefts and a thousand 
and one other evanescent phylogenetic vestiges in the course of 
somatic development, it should not be regarded as extraordinary 
if the germ-cell cycle likewise presented similar ^ancestral remi- 
niscences,' and did a little recapitulating on its own account. 
However, it must be confessed that 'phylogeny,' 'recapitula- 
tion,' 'ancestral reminiscences,' and other vague and more or less 
mystical terms of a kindred nature are after all merely conveni- 
ent pegs upon which to hang our ignorance. There are immediate 
physicochemical reasons for the degeneration of the primordial 
germ cells or their abortive sexual cycle, but what these reasons 
are is unknown, and in view of a better or more plausible, hypo- 
thesis to account for this phenomenon, the one presented above 
is advanced tentatively. 
