DAVIS: SPERMATOGENESIS. 147 
25. ‘lhe monosome does not divide in the first division but divides 
longitudinally and probably equationally in the second. 
26. ‘The spermatids are dimorphic, one-half containing a mono- 
some while the other half lack this element. 
27. ‘The monosome remains compact for some time within the 
nucleus of the spermatids, but later breaks up into fine granules in the 
same manner as the autosomes. 
28. In Dissosteira carolina the Nebenkern is not derived directly 
from the remains of the spindle fibers but is probably formed chiefly 
from the mitochondrion. 
29. In Dissosteira carolina the axial filament is from the first con- 
nected with a distinct centrosome, which is applied to the exterior 
of the nuclear membrane. As the spermatid elongates the Nebenkern 
becomes converted into an envelope surrounding the axial filament. 
30. In Dissosteira carolina the head of the mature spermatozoén 
is formed entirely from the nucleus; the centrosome forms the greater 
part of the small middle-piece; while the tail is composed of a central 
fiber, derived from the axial filament and Nebenkern, surrounded by 
a cytoplasmic envelope. 
31. In Steiroxys trilineata the axial filament is apparently not at 
first connected with a centrosome, which appears in the usual position 
only when the axial filament is well developed. ‘The axial filament is 
from the first surrounded by an envelope of doubtful origin denser 
than the surrounding cytoplasm. ‘The Nebenkern migrates around 
the nucleus and becomes applied to its anterior end. 
32. In Steiroxys trilineata the head of the mature spermatozo6n is 
-formed from the nucleus and the Nebenkern, the latter developing 
into the acrosome; the middle piece is formed chiefly from the cen- 
_ trosome, which divides into four parts; while the tail is composed of 
the central fiber, derived in part from the axial filament, surrounded 
by a cytoplasmic envelope. 
33. Innocase is there evidence that the monosome is extruded from 
the nucleus during metamorphosis or that the spermatids degenerate, 
except in rare instances. ‘Therefore the mature spermatozoa must be 
dimorphic with respect to their chromatin content, although there are 
no visible differences either in form or volume between the two types. 
34. Throughout the entire history of the germ cells there is strong 
evidence for the individuality of the chromosomes. 
