496 JEAN REDMAN OLIVER 



Fig. 23 Oblique view of a slightly flattened spermatid. A large clear cyto- 

 plasmic area surrounds the anterior portion of the nucleus, the limits of the head 

 cap not being evident in it. The nucleus is denser, especially its posterior 

 portion. 



Fig. 2-4 Face view of spermatid. The nucleus is uniformly dark, the rodlet 

 has lengthened and nearly reaches the caudal tube. The caudal tube is much 

 longer and its included cytoplasm now stains darker. In the head cap the acro- 

 some is not distinguishable as a separate structure, the two uniting in a heavy 

 line. 



Fig. 25 First appearance of transverse bands across the nucleus. The upper 

 dark area coincides with the portion covered by the head cap. 



Fig. 26 Cross sections of two spermatids at the level of the centrioles showing 

 the flattened elliptical outline of the caudal tube in this view. 



Fig. 27 As the spermatid elongates the cell membrane approaches the wall of 

 the caudal tube in its proximal portion. The proximal centriole is much flattened 

 and scarcely visible. The rodlet has reached the inner surface of the wall of the 

 tube. The insertion of the caudal tube upon the nuclear wall is marked by a 

 circular thickening, knob-like in cross section. 



Fig. 28 Profile view of elongated spermatid. The considerably flattened 

 nucleus shows cross-banding. The head cap has stained black at the tip. The 

 remnant of the sphere has shifted to the distal portion of the cytoplasm, and 

 appears as a faint outline only. 



Fig. 29 The spermatid is still more elongate, the caudal tube has become 

 separated from the nucleus, and is beginning to narrow distally, its contents 

 staining more deeply. Its wall shows a nodule at the anterior end, the cross 

 section of the thickened margin. 



Figs. 30 to 32 and 34 to 35 Third period of spermiogenesis. 



Fig. 30 The separation of the caudal tube from the nucleus has about reached 

 its maximum. The proximal centriole is flat, its rodlet is in contact with the 

 caudal tube. The posterior portion of the distal centriole has wandered down 

 the axial filament, and now forms the annulus, an. The anterior portion of the 

 distal centriole has elongated and bent at right angles with itself, thus forming 

 a transverse and a vertical limb. The cell membrane fuses with the wall of the 

 caudal tube about midway of its length. 



Fig. 31 A spermatid imbedded in the cytoplasmic prolongation of a Sertoli 

 cell; S.C., which is shown only in part. As is usually the case the outline of the 

 cell membrane of the spermatid may be traced readily in its distal portion, but 

 becomes lost when surrounded by the cytoplasm of the Sertoli cell. The outlines 

 of the caudal tube are sharply defined. The annulus, an., is migrating down the 

 axial filament, and the anterior portion, n.p., of the distal centriole is in the act 

 of dividing into two unequal portions. 



Fig. 32 The annulus, an., has now reached the posterior end of the caudal 

 tube, the limit of its migration. The two bodies deri^ved from the division of the 

 proximal half of the distal centriole in figure 31, now lie side by side at the ante- 

 rior end of the caudal tube. The shrinkage of the latter is in progress and the 

 tube is narrowing rapidly. A very characteristic displacement to the left is 

 seen, due apparently to the resistance of the jodlet, which is in contact with 

 the tube at its anterior end. 



