494 JEAN REDMAN OLIVER 



the distal centriole the axial filament extends through and beyond the cytoplasm 

 of the spermatid. In the distal cytoplasm are a few deeply staining rounded 

 masses. The nucleus is shifting toward the proximal end of the cell. 



Fig. 12 Similar to figure 11, but slightly more advanced. 



Fig. 13 The proximal centriole has fused with the nuclear membrane and is 

 apparently within the nucleus itself. At the right of the latter the remnant of 

 the sphere is seen. 



Fig. 14 A stage similar to the preceding one save that the acrosome is more 

 clearly seen. The nucleus has shifted still further toward the proximal end of 

 the cell, its chromatin is finely divided, and the whole nucleus begins to stain a 

 more uniform dark color. 



Fig. 15 The nucleus is at the periphery of the cell, enveloped only by the cell 

 membrane, which is itself indistinguishable. The proximal centriole is not yet 

 in contact with the nuclear wall. 



Figs. 16 to 29 Second period of spermiogenesis 



Fig. 16 A slightly smaller spermatid than usual, probably due to the plane of 

 the section. The earliest appearance of the caudal tube filaments is shown. 

 The centrioles and axial filament were not included in the plane of the section. 

 Nucleus at the proximal pole of the cell, its chromatin now reduced to fine gran- 

 ules, the whole structure staining dark. 



Fig. 17 A similar stage to the foregoing except that the centrioles and axial 

 filament are shown. The latter extends out obliquely between the filaments, 

 crossing two of them. 



Fig. 18 Early stage of formation of filaments of caudal tube. The axial fila- 

 ment from the distal centriole passed out from the plane of the section before 

 reaching the cell boundary. 



Fig. 19 The general dark tone which the riucleus takes on at this stage is here 

 represented. Many scattered small granules of chromatin are still visible. Four 

 of the filaments to form the caudal tube are visible in this focus. 



Fig. 20 The nucleus has become more elliptical and more homogeneous. The 

 filaments have fused together into a hyaline caudal tube, the sides of which are 

 distinguishable as sharply defined lines. From the proximal centriole a delicate 

 rodlet has grown outward and backward. The distal centriole has increased in 

 size. Beyond the opposite pole of the nucleus the thickened head cap appears, 

 the acrosome showing as a heavy line. 



Fig. 21 The nucleus presents the form of a double pyramid, its anterior por- 

 tion lighter and more granular than the posterior part, which is dense and dark. 

 A short rodlet projects from the anterior centriole. The posterior centriole 

 shows a constriction as if dividing. The portion of the nucleus included within 

 the caudal tube often has concave outlines for a short time, as here shown in this 

 stage. 



Fig. 22 Differentiation of nuclear areas not clearly shown. The nucleus is 

 covered by a thick head cap with well defined acrosome. The distal centriole 

 has divided into an anterior and a posterior half. 



