At the center of the upper border of Fig. 4, p.s., there 

 is one cell with a large nucleus. This is one of a single 

 row of cells along the side of the tubule which may be called 

 the prlDBtry sperraatogonial cells since they, by division, 

 give rise to a new lot of spermatogonia. Hear the top of Fig. 



3, p«s., we find a similar cell. The cells forming the cres- 

 cent-shaped region are In this case not so far advanced as in J*'ig. 



4. Figure 1 represents a tubule the largest portion of which 

 is filled with spermatids which have already entered upon their 

 transformation into sperms. In the upper portion of the draw- 

 ing we have an early stage in the foimation of a new batch of 

 spermatogonia. There are four large spermatogonial nuclei 

 surrounded by many epithelial nuclei and a considerable amount 

 of cytoplasm. Delicate cell walls cutting O'.t the cytoplasm 

 that belongs to each spermatogonial cell can sometimes be made 

 out at this stage. A later stage in the multiplication of 

 these cells is shown in Fig. 2. A large nucleus, p.s,, near 

 the middle of the convex border of the spermatogonial mass, 

 doubtless marks the position of the row of primary spermatogon- 

 ial cells which will persist unmodified to form, at a later 

 period another lot of spermatogonia. The largest cavity of 

 this tubule contains spermatids well advanced in their trans- 

 formation into sperms. They fill the cavity but only a por- 

 tion of those seen in the cross-section are represented in the 

 drawing. In Fig. 3 the mass of spermatogonial nuclei is still 

 further enlarged. Indeed most of thorn have probably reached 

 the spermatocyte stage. The spermatocytes in the early prophase 

 of the first maturation division are shown in Fig. 4. By put- 



