394 HARRY H. CHARLTON 



up. The nucleus appears round in polar view, but oval if looked 

 at from the side. Later the nucleus becomes spherical, the 

 chromatin appearing finely granular and congregated at the 

 boundaries of the nucleus leaving an open center (fig. 66). One- 

 half the cells show an idiochromosome nucleolus which usually 

 presents a spherical part extending into the nuclear cavity and 

 a flattened area against the inner surface of the nuclear mem- 

 brane, while the other cells do not possess an idiochromosome 

 nucleolus. 



The methods of fixation and staining have a great deal to do 

 with the structures observed in the spermatid. When strong 

 Flemming is used for fixing followed by Heidenhain's iron 

 haematoxylin, the cytoplasm of the early spermatid contains 

 such a mass of intensely staining material that the nuclear 

 membrane is made out only with difficulty. The same stain 

 after Bouin's fluid brings out the nucleus and centrosomes, but 

 not the cell inclusions. 



At the very first, the cytoplasmic structures are somewhat 

 loosely aggregated around the nucleus, but particularly between 

 the nucleus and the last division plane, The centrosome can 

 easily be followed from the telophase; located at first on the cell 

 wall of the dividing second spermatocyte, it later moves inward, 

 occupying the space between the cell wall and the nucleus 

 (fig. 65). 



As it moves around to get between the nebenkern and the 

 nucleus, it turns 90 and comes to lie with one end on the nuclear 

 membrane and the other against or near the cell wall (figs. 66 

 and 67). The rod-shaped centrosome now frequently shows a 

 granule or enlargement at the nuclear end. 



The nebenkern has meanwhile formed a broad ring of densely 

 staining granular material in the center of which spindle remains 

 of the last division appear and on either side two spherical bodies 

 become visible (fig. 69), exactly like those seen in the two matura- 

 tion divisions, and undoubtedly represent old spindles. In 

 cross-section they appear as rings with their boundaries staining 

 in varying degrees, often looking like crescents, and may possess 

 a darker staining center. Looked at from the side, they take 

 the form of rods with faintly stained material between them. 



