STEUCTURE AND BIOLOGY OF SCHIZONEUEA LANIGERA. 681 
valve (fig. 48), which prevents the regurgitation of plant 
juices from the mid-gut to the oesophagus. 
A band of connective tissue (c. t.) extends from the oesopha- 
gus across the shoulder of the oesophageal valve, forming 
a kind of ligament which is continuous with the connective- 
tissue coat of the oesophagus and stomach. 
The stomach forms a thick-walled sac with a wide lumen, 
which is usually filled with plant juices. Its wall consists of 
an epithelial layer of large, conical cells, the free ends of 
which bulge into the cavity of the sac (fig. 40). Externally 
there is a thin layer of connective-tissue. Towards the 
posterior end of the stomach the lumen decreases in size, and 
the cells become flatter. 
At the base of each cell is a prominent deeply-staining 
nucleus, which is embedded in a mass of granular secretion. 
The granules are also densely crowded throughout the cyto- 
plasm. It is probable that these cells function as digestive 
glands, and pour digestive secretions into the lumen of the 
stomach. Along the free end of the cells there is a well- 
defined margin, which, bordering the lumen, stains deeply 
with eosin. 
At its posterior end the stomach narrows considerably, and 
becomes continuous with the coiled intestine. The structure of 
the walls of the latter closely resembles that of the stomach, 
but the cells are not so conical, and the granular elements 
in the cytoplasm not so dense. The lumen of the intestine 
is greatly reduced, and usually tri-radiate or irregular in 
section. 
When seen in fresh prepai’ations the mid-gut is whitish- 
grey in colour, semi-transparent, with the large nuclei of the 
epithelial cells showing conspicuously through the walls. 
The general course taken by the intestine may be described 
as follows (figs. 5 and 35). 
The stomach extends obliquely in the median line to about 
the third or fourth abdominal segment, where it leads into 
the intestine (f.), which turns abruptly on itself in an antero- 
ventral direction. In the posterior half of the thorax the 
