414 
W. X. F. WOODLAND. 
large quantity of excretory products, and is only slightly 
invaded by a relatively few simple wall-involutions (PL 28, 
fig. 3). The character of the cells forming the duct wall is 
shown in Text-fig. 4. The cytoplasm is faintly stained on the 
side situated next the lumen, but denser in appearance next 
the htemocoele and is throughout faintly granular. The 
nuclei are large and spherical. In shape the cells are very 
irregular, and are quite devoid of the conspicuous striated 
border so characteristic of the cells of the gland proj^er. The 
nuclei, like those of the gland-cells, are situated at one end 
of the cell, but unlike those of the kidney, are situated next 
the htemocoele and not next the lumen. Text-fig. 4 shows well 
the respective characters of the duct- and gland-cells and the 
abrupt transition from the one type to the other. Judging 
from the character of the cells of the duct, it seems probable 
that they take little or no share in the process of excretion. 
In the sub-region of the bladder the lumen is more spacious 
than in any other part of the gland and invaginations of the 
wall are quite absent. The cells of the walls ai-e short, 
columnar or cubical in form (Text-fig. 8), and the cytoplasm 
is uniformly pale and faintly granular ; there is no polar 
diherentiation as in the cells of the upper duct. The nuclei 
are situated at the ends of the cells remote from the lumen. 
It is perhaps important to notice that the walls of the bladder 
near the external opening (Text-fig. 8) are devoid of the 
double layer of investing squamous epithelium found on the 
exterior of all other parts of the gland — a fact possibly of signifi- 
cance in connection with the question as to the g’erm-layer 
origin of the gland to be discussed later. 
The bladder rapidly becomes narrow at its lower end to 
open to the exterior (Text-fig. 8). A notable feature of this 
external opening is the modification of the cells lining the 
inner and posterior side of the duct. As will be seen from 
fig. 3 (Pi. 28) and Text-fig. 8, the cells in the position stated 
become enormously elongated in a direction approximately 
parallel with the length of the duct to form a conspicuous 
clump of columnar cells continuous at the upper end with the 
