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. ‘lhe 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 interzonal 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 
