356 The Spermatogenesis of Bufo Lentiginosus 
ments into the reduced number of chromosomes. ‘The “ synapsis ” stage, 
to use the term introduced by Moore (41) to designate the stage in 
which the pseudo-reduction in the number of chromosomes occurs, is in 
Bufo co-incident with the synizesis stage as it is in Triton, elasmo- 
branchs, and various other forms. 
A section through a spermatocyte as the cell is emerging from the 
synizesis stage is shown in Fig. 24. Against one side of the nucleus is a 
dense irregular mass of chromatin from which extend the loops of an 
apparently continuous spireme. This spireme differs from that found in 
the spermatocytes at the end of the growth period, in that it is shorter, 
thicker, and instead of being granular is very “ mossy ” in appearance. 
A shghtly later stage in which the mass of chromatin against the 
nuclear membrane has still further decreased is shown in Fig. 25. At 
the end of the synizesis stage the nucleus contains a deeply staining, 
apparently continuous spireme (Fig. 26) which has a much smoother 
outline than the spiremes shown in Figs. 24 and 25. I have never found 
any indications of a longitudinal splitting of the spireme that is so char- 
acteristic of the post-synapsis stages in the spermatocytes of the Urodela. 
Soon after the stage shown in Fig. 26, the spireme shortens some- 
what and, consequently, becomes considerably thicker than before (Fig. 
27). Subsequently certain portions of the spireme stain much more 
lightly than the rest, these lighter staining regions marking the location 
of the transverse divisions by which the spireme is later broken into 
the reduced number of chromatin segments (Fig. 28). The next step 
in the process of separating the chromosomes is seen in Fig. 29, where 
the spireme is found to be constricted at various places. In many cases, 
before this first constriction of the spireme is completed, a second constric- 
tion appears through the middle of each segment so that the chromosomes 
that are finally produced from the spireme have the shape of dumbbells 
(Fig. 30). Itis very probable that the constriction in each segment marks 
the line of union of the two chromosomes that were united end to end in 
synapsis; and, as will be shown later, this constriction also marks the loca- 
tion and the direction of the division of the chromosomes in the first mat- 
uration mitosis of the spermatocytes. When the chromosomes have the 
shape of dumbbells at the stage of Fig. 30, they undergo no further 
changes in form until the anaphase of the first maturation mitosis. 
There is no indication of the second division in this type of chromosome 
until the late anaphase when the chromosomes are again constricted into 
dumbbells (Fig. 51). If one traces the various steps in the develop- 
ment of the chromosomes from the stage represented by Fig. 27 until 
