DAVIS: SPERMATOGENESIS. bt 
However, practically the only evidence for this is the fact that as the 
Nebenkern develops the interzonal filaments gradually disappear. 
Certainly these filaments do not become converted directly into the 
Nebenkern, but if they take part in its formation must first disintegrate. 
Figure 214 (Plate 9) represents a spermatid in a somewhat later 
stage after the Nebenkern is fully formed. In this case the interzonal 
body is still faintly distinguishable, although no trace is left of its 
fibrillar structure. Usually the interzonal body is not recognizable 
at so late a stage. Figure 213 shows a spermatid in which the Neben- 
bern is still very irregular. ‘he nucleus has lost its staiping power to 
a considerable extent, and its appearance is quite different from that 
at a little earlier stage, but is characteristic of this and later stages. 
The entire nucleus has a finely-granular structure without any well 
defined network or differentiation of chromatin and linin. ‘The fine 
granules stain lightly with hematoxylin, so that the nucleus as a whole 
appears grayish, with here and there a few large granules staining 
deeply with hematoxylin. The monosome is still distinguishable as 
a compact, deeply staining body. For some time the further changes 
in the nucleus consist chiefly in the gradual disintegration of the larger 
deeply staining chromatin granules, including the monosome, until 
finally all the chromatin becomes converted into fine granules which 
have lost to a very large extent their affinity for hematoxylin (Figs. 
215-219). In Fig. 214 the monosome has begun to disintegrate, 
while the Nebenkern forms a rounded, homogeneous, deeply staining 
body by the side of the nucleus. It already shows indications of 
dividing into two equal parts by constriction. ‘lhe cytoplasm on the 
side containing the Nebenkern is just beginning to grow out to form 
the tail of the spermatozoén. In Figure 215 the Nebenkern has divided 
into two equal parts. During this and slightly earlier stages it often 
shows near the periphery a very narrow lighter area outside of which 
is a thin envelope of more deeply staining material. Probably this 
appearance is due to faulty fixation, since it is more marked in poorly 
fixed material and since in some cases, especially near the outer walls 
of the follicle, where the cells are most easily acted on by the fixing 
agent, the Nebenkern appears perfectly homogeneous. It is an inter- 
esting fact, which has also been noted by other writers, that the 
spermatids seem to be the most difficult elements in the testis to fix 
properly. 
By the time the Nebenkern has divided, the entire cell has become 
considerably elongated. Applied to the exterior of the nuclear mem- 
brane can be seen a small deeply staining body which is evidently the 
