246 WILBUR WILLIS SWINGLE 
Just why there should be this difference in time of maturation 
between the male and female sexual cycles of the tadpoles the 
writer is unable to say, though from certain data to be consid- 
ered hereafter, obtained from studies on birds and mammals, it 
would not be surprising if the young female frog some months 
after metamorphosis likewise showed an abortive maturation 
cycle culminating in degeneration of the oocytes.^ This point is 
now under investigation. Bearing in mind, then, this outline 
sketch of the developmental history of the gonads and germ cells 
of both sexes in the bullfrog tadpole, the following detailed 
account of the cellular changes involved in the larval maturation 
cycle of the male becomes more intelligible.^ 
OBSERVATIONS. SEXUAL CYCLE FIRST-YEAR LARVAE. PRIMARY 
AND SECONDARY SPERMATOGONIA 
The primary spermatogonia found in such gonads as shown in 
figures 33 and 34 and text figures 1 A and B are much larger 
than the later generation of cells to which they give rise. In 
general these primary cells are more lightly staining than other 
elements of the gonad, and are peculiar, moreover, in that they 
are usually surrounded by a follicle made up of small, flattened, 
deeply staining stroma or peritoneal elements separating them 
one from another. This is true of this generation of cells in both 
larval and adult frogs. 
The primary spermatogonial nuclei are large and very irregu- 
lar in outline, presenting marked lobulations and indentations — 
the so-called polymorphism of the nucleus. Study of these poly- 
morphic nuclei during early prophase stages of division has led to 
the conclusion that the lobulations and consequent polymorphism 
are due merely to large chromosomal vesicles or to the partial 
fusion of such vesicles, for from each of these lobulations a 
chromosome or pair of chromosomes appear in division pro- 
phases. The resting nucleus contains considerable karyolymph, 
1 Recently the writer has observed typical tetrad formation and a few first- 
maturation spindles and chromosomes in oocytes, of female larvae. Such cells 
degenerate in the act of division just as do the laVal spermatocytes of the male 
tadpole of the first year. 
