DAVIS: SPERMATOGENESIS. Ill 



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 wliich the Neben- 

 bern is still very irregular. The nucleus has lost its staining 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. The cytoplasm on the 

 side containing the Nebenkern is just beginning to grow out to form 

 the tail of the spermatozoon. 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 



