DAVIS: SPERMATOGENESIS. 101 
metaphase of the first division the monosome may lie either in the plane 
of the equatorial plate midway between the spindle poles or nearer 
one pole than the other (Plate 4, Fig. 63). Even when it lies in the 
equatorial plane, the monosome can be easily distinguished by its 
rough contour, and also by the fact that it usually lies with its axis 
at an angle to the axis of the spindle. In all cases the monosome is 
attached to spindle fibers from only one pole. ‘The monosome does 
not divide during the first maturation division, but passes bodily to 
one of the poles (Fig. 65). In Figures Ma—Me (p. 96) which are all 
drawn from sections of the same cell, this is conclusively shown. 
Here there can be no doubt that all the chromosomes except one have 
divided into two equal parts, which are moving toward opposite poles 
of the spindle. ‘The other chromosome, the monosome, has no corre- 
sponding mate moving toward the opposite pole. As the monosome 
passes toward the pole the arms of the U separate somewhat, so that 
it has practically the same shape as the autosomes. In the succeeding 
telophase the monosome cannot be distinguished, but in the “‘semi- 
resting’? stage of the secondary spermatocyte it can again be recog- 
nized. During this stage the monosome retains its compact structure 
in striking contrast to the autosomes. During the second maturation 
division the monosome is not distinguishable, since the autosomes also 
have at this-time somewhat rough contours. Figure R (p. 100) is a 
polar view of the equatorial plate of a secondary spermatocyte which 
lacks the monosome, there being only eleven chromosomes present. 
Figure Q is a similar view of a cell with twelve chromosomes, one of 
which is evidently the monosome. During the second division the 
monosome divides along with the autosomes. ‘This is conclusively 
shown in Plate 5, Figures 78 and 79, which are drawn from two sec- 
tions of the same cell. In this case there can be no doubt that there 
are twelve daughter chromosomes passing to each pole of the spindle. 
The question at once arises, are we to consider the division of the 
monosome during the second maturation division longitudinal or 
transverse. Otte (:06) concludes that in Locusta, where the mono- 
some has a somewhat similar history, the division is transverse. At 
first I was inclined to interpret the division in Dissosteira in the same 
way, but on further consideration believe such a conclusion to be un- 
warranted. ‘The peculiar manner in which the monosome becomes 
converted into a loop during the latter part of the growth period can 
be easily interpreted as due to a longitudinal splitting. This interpre- 
tation is supported by the fact that, whereas the autosomes become 
converted into a single chromatin thread, the monosome becomes 
