512 WARO NAKAHARA 
m-chromosome. Two other small segments, which are often 
seen joined together (fig. 26), can be interpreted as representing 
the X- and Y-chromosomes. 
Excepting the X- and Y-segments (and the m-segment, of 
which nothing definite was observed), halves of each segment 
bend toward each other, until they come to lie closely side by 
side. This interpretation of the process of tetrad formation 
may receive justification through a comparison of figures 24 
to 33. 
The tetrads thus formed now arrange themselves on the 
equatorial plate of the spindle (fig. 33). Polar view of the plate 
shows five chromosomes as distinct bodies (figs. 35 to 37). The 
X and Y are joined to each other and appear as a single body. 
Of the remaining four, one is decidedly smaller than the others 
and undoubtedly identifiable with the m-chromosome. Three 
others, although they vary more or less in their appearances, 
may therefore be considered as representing the three pairs of 
the diploid chromosomes (two pairs of V’s and a pair of rods 
in the spermatogonial group). Looking from the side, it will 
be seen that the X and Y separate with the division of the biva- 
lents (figs. 34, 38 to 40). Figures 41 to 44 show the anaphase 
of the first division and the prophase of the second, in which 
there is no resting stage. 
If the process of ring and tetrad formation be that of an open- 
ing out of a split chromosome, as it is frequently interpreted, 
the space enclosed by a ring must correspond to the longitudinal 
split in the zygotene thread. That this interpretation does not 
hold in the case of Perla may easily be seen from a comparison 
of figures 21, 27, 33, and 34. The longitudinal split of the 
zygotene spireme persists as such in the ring and even in the 
chromosome on the metaphase plate, and may be best inter- 
preted as a precocious split for the second spermatocytic division, 
which follows the first division without the ‘resting stage.’ It 
has nothing to do with the space enclosed by a ring, which is 
secondarily formed when the two arms of a bivalent segment 
become joined. 
