SPERMATOGENESIS IN THE ALBINO RAT 139 



Figure 3, from 11 -day-old material, shows that two distinct 

 changes have occurred, in addition to a slight increase in the 

 diameter of the tubule. These are 1) a marked increase in the 

 number of the cells and, 2) the presence of a new type of cell, 

 which I call Type B, seen more enlarged in figure 9. It is char- 

 acterized by its spherical form and the densely staining, sharply- 

 defined masses of chromatin. Its origin is shown in figure 5. 

 The cells marked D.C. are cells of type A in division. Two 

 characteristic daughter cells appear at B. They are plainly 

 type B, though small. They grow rapidly in size, and since 

 many are produced simultaneously they may form practically 

 all of the outer cell layer, as in (figure 6. The orientation of the 

 division plane may be as shown in figure 6 or as in figure 5 — 

 either longitudinal or radial. In either case the cells soon 

 migrate inward, as seen in the upper part of figure 7. The 

 lower part of that figure and figures 5, 6, and 8 show that the 

 subsequent growth changes occur at deeper levels, or nearer the 

 lumen. 



Cells of type B transform to cells of type C (figs. 4 and 10) by 

 the chromatin masses becoming more diffuse, which thus lose 

 their sharply defined edges, as seen in section, and assume a 

 woolly appearance. 



The next stage of development is seen in figure 1 1 . Here the 

 spireme has evidently begun its differentiation, as seen by the 

 presence of a thread made of small, woolly, lightly-staining chro- 

 matin masses. These by approximating toward each other, and 

 condensing, pass to the leptotene stage through the condition 

 shown in figure 12. 



Leptotene stage (fig. 13). The lower part of figure 7 shows this 

 condition of the tubule when the tissue is not sufficiently de- 

 stained, as the nuclei reveal no structural details unless destained 

 to a point at which the cells of type A have lost all color. The 

 spireme in this, as well as in the stage shown in figures 11 and 12, 

 is apparently of the segmented type, though perhaps determina- 

 tion of this point is questionable owing to the small size of the 

 cells and the large quantity of chromatin present. The leptotene 

 stage is characterized by the extreme fineness of the thread, 

 which now appears narrowest in its history, yet stains deeply. 



