260 WILBUK WILLIS SWINGLE 
years as a larva, and each year is* marked by a seasonal ripening 
of sexual products. Attempts of first-year tadpoles to ripen 
their sex products is abortive; the second year's attempt is suc- 
cessful (plate 15) at the time of metamorphosis. 
The heterotypic mitosis of first-year larval spermatocytes 
First maturation division metaphases are very abundant in 
first-year larvae, especially in young larvae 45 to 60 mm. total 
length which have passed through one winter as larvae. In such 
animals entire cysts are found with completely formed tetrads 
and spindles all ready for division, and many in the act of divid- 
ing; yet, oddly enough, careful examination of many hundreds of 
sections of such larval gonads fails to show stages of the first 
maturation mitosis beyond very early anaphases (plates 9, 10, 
11). This is an interesting fact, and it is strange to see entire 
cysts of apparently normal spermatocytes in metaphase or early 
anaphase, and yet never find telophases of such divisions, inter- 
kinesis stages, or any indications of secondary spermatocytes. 
Cells which have developed thus far in a perfectly normal man- 
ner, save for precocity of the maturation cycle and are apparently 
in possession of the requisite mechanism for cell division, are 
unable to complete the process. During late prophase and meta- 
phase the achromatic elements, that is, the machinery of cell divi- 
sion and chromosomal separation, break down and the tetrads go 
to pieces before the telophase. It is rare to find complete 
separation of the homologous components of the tetrads. Some- 
times the smaller ring elements do separate (figs. 29 and 30) and 
in rare cases an early anaphase is reached. In general the degen- 
erative processes set in shortly after the time of spindle formation 
when the chromosomes are arranged in a typical metaphase plate, 
their long axis parallel to the long axis of the spindle, or else 
when they are scattered irregularly through the cytoplasm, fol- 
lowing the disappearance of the nuclear wall (figs. 100 to 110). 
The spermatocytes may even go to pieces in late diakinesis, 
though such cases are not common. 
