FORE-GUT, MID-GUT, AND HIND-GUT. 61 
true skin which lies beneath it. The wall of the stomach 
is a soft pale membrane containing variously disposed 
muscular fibres ; and, beyond the pylorus, it is continued 
into the wall of the intestine. 
It has already been mentioned that the intestine is 
a slender and thin-walled tube, which passes straight 
through the body almost without change, except that it 
becomes a little wider and thicker-walled near the vent. 
Immediately behind the pyloric valves, its surface is quite 
smooth and soft (figs. 9, 10, and 12, mg), and its floor 
presents a relatively large aperture, the termination of 
the bile duct (fig. 12, bd, fig. 10, hp.), on each side. The 
roof is, as it were, pushed out into a short median pouch 
or cecum (ce). Behind this, its character suddenly 
changes, and six squarish elevations, covered with a 
chitinous cuticle, encircle the cavity of the intestine (r). 
From each of these, a longitudinal ridge, corresponding 
with a fold of the wall of the intestine, takes its rise, and 
passes, with a slight spiral twist, to its extremity (hg). 
Each of these ridges is beset with small papille, and the 
chitinous lining is continued over the whole to the vent, 
where it passes into the general cuticle of the integu- 
ment, just as the lining of the stomach is continuous 
with the cuticle of the integument at the mot'-h. The 
alimentary canal may, therefore, be distinguished into 
a fore and a hind-gut (hg), which have a thick internal 
lining-of cuticular membrane; and a very short mid- 
gut (mg), which has no thick cuticular layer. It will be of 
