358 The Spermatogenesis of Bufo Lentiginosus 
perceive a difference in the size of the chromosomes, although this differ- 
ence is not so marked as in the first mitosis because of the smaller size 
of the chromosomes. Many investigators have already noticed a variation 
in the size of the chromosomes in the maturation divisions of the germ- 
cells. Were the reasons for this phenomenon known, they would doubtless 
aid materially in solving many of the vexing problems of heredity. 
In a great majority of the spermatocytes the post-synapsis stages of 
development do not follow the well marked types described above, but 
are irregular and somewhat difficult of analysis. In many cases the 
spireme, instead of breaking into dumbbell or rectangular-shaped seg- 
ments, forms the ring-shaped chromosomes that are so characteristic of 
the prophases of the first maturation mitosis in the spermatocytes of 
other animals. In most of the cases that have been described, the ring- 
shaped chromosome is produced by the longitudinal splitting of a 
chromatin segment which opens through the middle region and remains 
united at the ends, a typical case being that of Gryllotalpa as described 
by vom Rath (45). In Bufo the method of ring formation is somewhat 
peculiar. The spireme formed after the synizesis stage constricts into 
oval segments (Figs. 32-34), and usually, before the constriction is com- 
pleted, the segments open through the middle, thus forming typical 
ring-shaped chromosomes which may remain connected for some time 
(Figs. 31, 32, 33, 36). In Bufo, therefore, the opening in the ring is 
not the space between univalent chromosomes, as maintained by Mont- 
gomery (38) for Desmognathus and Plethodon, but represents the longi- 
tudinal splitting of a bivalent chromosome that is completed in the 
second maturation mitosis. The first maturation mitosis, which is always 
seen at this stage in the dumbbell-shaped chromosomes (Figs. 30, 37, 
38), is not, as a rule, visible in the ring-shaped chromosomes until they 
have entirely separated and condensed into tetrad groups, as do the 
ring-shaped chromosomes in Gryllotalpa (Fig. 39). Before the first 
maturation spindle is formed the ring-shaped chromosomes become scat- 
tered throughout the nucleus (Fig. 40). They are at this time usually 
round or oval in form, but occasionally they are distinctly diamond 
shape (Figs. 32, 40). In only two cases have I ever seen any indication 
of a division of the ring-shaped chromosomes preparatory to the first 
maturation mitosis. One of these cases is shown in Fig. 32, where, at 
the four corners of the diamond, dark lines divide the chromosome into 
four parts, thus plainly indicating that the chromosome has already 
divided for both of the maturation mitoses. 
Tt is apparently a matter of little, if of any, importance which of 
