INTERNAL ANATO.MY OF S(iUJLLA. 
413 
are large and columnar in form. The cytoplasm contains 
numerous small granules, is somewhat denser in the region 
next the hmmococele, and shows a faint striation parallel with 
the cell length. The portion of the cytoplasm bordering the 
lumen is, as above stated, characteristically striped. The 
nuclei are always situated near the striated border, and are 
large, with conspicuous chromatin granules. These less 
granular columnar dorsal cells pass gradually into the more 
granular and often flatter cells found towards the duct end of 
the gland (Text-fig. 7). The ventral cells chiefly differ from 
the dorsal in that the granules contained in the cytoplasm 
are more numerous and are much larger and that there are 
no striatious in the general cytoplasm. It should also be 
mentioned that the cells composing the part of the kidney 
actually in contact with the end-sac are flat and small (Text- 
fig. 5), and that these gradually merge into the colnmnar 
kidney-cells already described. 
Histology of the Duct. 
The duct region of the gland is distinguishable as a whole 
from the region of the kidney by the spacious lumen (a few 
wall invaginations only being present in the upper part of the 
duct) and by the character of the cells composing its wall. 
The character of the cells of the duct, indeed, enables this 
region to be distinguished with the greatest precision from 
the adjoining region of the gland proper, since, as can be seen 
in Text-fig. 4, there exist no cells intermediate in character 
between those composing the duct, on the one hand, and those 
composing the kidney on the other. We saw that the region 
of the gland proper could be sharply distinguished by the 
same means from the region of the end-sac, the cells of the 
latter being quite distinct in character. 
The duct region of the gland can (PI. 28, fig. 3) be sub- 
divided into three sub-regions : (1) The upper duct, (2) the 
bladder, and (3) the duct aperture to the exterior. In the 
subregion of the upper duct the lumen is wide, contains a 
