292 WILBUR WILLIS SWINGLE 
6. All increase in the number of germ cells in male larvae up to 
the 40-mm. stage is beyond question, by mitotic division of the 
preexisting sexual elements derived from the primordial germ 
cells of the entoderm ridge. A 40-mm. larva is about one year 
of age. 
7. At the 40-mm. stage, despite the fact the tadpole is an imma- 
ture larva and the gonads mere hollow sacs and in no way re- 
semble testes, the germ cells enter maturation and pass through 
every stage of the maturation cycle in a normal manner, up to 
the first maturation division. In the act of division, the sperma- 
tocytes go to pieces and are resorbed. 
8. Practically all of the germ cells derived from the primordial 
sex cells pass through this abortive maturation cycle and degen- 
erate. A very few germ cells lineal descendants of the primordial 
embryonic sex-cell line persist unchanged, i.e., remain as sperma- 
togonia through the maturation cycle and do not degenerate. 
Later these few cells give rise to a second generation of smaller 
germ cells. 
9. This second generation of germ cells shortly before meta- 
morphosis of the larvae undergoes a second sexual cycle, charac- 
terized by the production of normal spermatozoa. Thus there 
are two larval sexual cycles: one occurring in immature larva of 
40 to 60 mm. and ending in degeneration, the other appearing 
shortly before metamorphosis, i.e., in larvae 140 mm. total length 
and ending in the production of normal sex products. 
10. In the interval between the first and second larval sexual 
cycles following the degeneration of large numbers of maturation 
cells the gonads become filled with small cells which, because of 
their size, nuclear structure, and staining capacity, appear as 
transition stages between mesothelial cells (germinal epithelium 
and sex cord elements) and true germ cells. The later history 
of these cells shows them to be germ cells, but their origin is open 
to two interpretations and is not as clear as could be desired. 
The writer considers these cells as small germ-cell descendants 
of the primordial sexual elements, and not as transformed germi- 
nal epithelium elements, but admits that the evidence from his 
material is equally strong in support of the germinal epithelium 
view-point. 
