DAVIS: SPERMATOGENESIS. 69 



The appearance of the secondary spermatogonia in all generations 

 is practically the same except in size, the later generations being 

 much smaller than the earlier. This is, of course, due to the fact that 

 the growth of the cells does not keep pace with the divisions, which 

 succeed each other rapidly. There is, however, a considerable growth, 

 since cysts containing the later generations of spermatogonia are much 

 larger than those composed of earlier generations. The secondary 

 spermatogonia of the earlier generations are even larger than the pri- 

 mary spermatogonia and the amount of cytoplasm is usually relatively 

 greater (Plate 4, Fig. 68). In a section through one of the smaller 

 cysts the spermatogonia are seen to have a radiate arrangement around 

 a common center. Each cell is roughly conical with the nucleus ec- 

 centrically situated in the broad base near the cyst wall. Extending 

 through the cytoplasm at the apex of each cell, and connecting it with 

 one or more adjoining cells, can usually be distinguished a very finely 

 granular, nearly homogeneous mass staining deeply with Bordeaux. 

 This is the remnant of the interzonal filaments, which often persist 

 for several generations, although naturally those of the last division 

 are most prominent. Following Mark and Copeland (:06), I shall 

 speak of these as the inierzonal bodies. In addition to the interzonal 

 bodies there is in the cytoplasm of this part of the cell a more or less 

 diffuse finely granular material staining with Bordeaux, which is 

 apparently to be considered mitochondrion. It is never very abundant 

 or conspicuous in the spermatogonia of this species, and in some cases 

 it is almost impossible to distinguish it at all. 



In the later generations the spermatogonia lose this regular arrange- 

 ment and the cysts are seen to be made up of large numbers of irregu- 

 larly arranged, rounded or polygonal cells crowded closely together; 

 all being connected with one another by means of the persistent inter- 

 zonal bodies. 



Usually the cells of each cyst are all in approximately the same stage, 

 but in the later generations rarely the cells of one side of a cyst may be 

 considerably in advance of the others. 



Turning now to a more detailed description of the secondary sperma- 

 togonia, we find that during the so-called resting stage the nuclei 

 have practically the same structure as in the primary spermatogonia, 

 except that they are more chromatic, especially in the later generations, 

 and often more irregular in shape (Plate 1, Fig. 6). There is no 

 continuous spireme formed in preparation for division, but the chro- 

 matin becomes aggregated into a number of long, much convoluted 

 threads, which rapidly shorten and thicken into contorted rods of 



