408 THE ALIMENTARY CANAL OF THE IMAGO. 
The Proventriculus (Pl. XXIV., Figs. 2 and 3) is ovoid, flattened 
above and below. It may be described as an intussusception of 
the stomodeum .into the mesenteron, and, except in form, it 
differs but little from the same organ in the larva. It consists 
of a thick cellular plug, perforated by the proventricular branch 
of the cesophagus in its centre and grooved around its edge, 
surrounded by the wall of the proventriculus, which presents a 
thick ridge fitting into the groove in the plug. 
The outer wall of the proventriculus is continuous with the 
anterior edge of the groove in the plug, on the one hand, and 
with the wall of the chyle stomach, from which it is separated 
by a sphincter, on the other; it is covered by a continuous 
layer of radiating muscles, which arise from the junction of the 
cesophagus with the plug. 
Both the central plug and the thickened ring of the outer 
wall consist of a tissue which is almost cartilaginous, formed 
by the fibrillation of the epithelial cells (see p. 280). 
The distribution of the tracheal vessels to the proventriculus 
is very remarkable. A tracheal ring surrounds the proventri- 
cular cesophagus, and is deeply imbedded in the plug; and 
from a dozen to eighteen radial vessels arise from this ring and 
arch over the outer surface of the proventriculus. These 
vessels are continued as parallel vessels over the outer surface 
of the chyle stomach. The ring receives air from longitudinal 
tracheze which lie close to the cesophagus, and it gives off 
DESCRIPTION OF PLATE XXIV. 
The alimentary canal of the Imago : 
Fic. 1.—The alimentary canal from the proventriculus to the rectum, removed from 
the body. The chyle stomach is seen from its side, but the rest of the alimentary 
canal is represented from its dorsal aspect : ch, chyle stomach; 7, crop + 
di, distal intestine ; #7, Malpighian vessels ; a, oesophagus ; A 2, proximal in- 
testine ; 7 g, proventricular ganglion ; 7, rectum ; 7 f, rectal papille ; 7, trachez ; 
tr s, tracheal sacs, 
Fic, 2.—A vertical submedian section through the proventriculus and part of the 
chyle stomach ; fz, proventriculus. 
Fic. 3.—A median vertical section of the proventriculus. 
Fic. 4.—A section through the rectal valve. 
Fic. 5.—A transverse section of the intestine about two millimetres above the rectal 
valve. 
