4o8 THE ALLMEXTARY L'AXAL OF THE LMAud 



The Proventriculus (PI. XXI\'., Figs. 2 and 3) is ovoid, flattened 

 above and below. It may be described as an intussusception of 

 the stomodseum 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 oesophagus 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 

 oesophagus 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 oesophagus, 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 

 tracheae which lie close to the oesophagus, and it gives off 



IIM i<>\ OF L'I.AI i. XXIV. 



The alimentary canal of the Imago : 



!'!<;. I. The alimentary canal from the proventriculus to the rectum, remove. 1 from 



the body. The chyle stomach is seen from its side, hut the rest of the alimentary 



canal is represented from its dorsal aspect : c/i, chyle stomach ; ft; crop ; 



<//, distal intestine; mm, Malpighian vessels; <r, usophagus ; //, proximal in- 



testine j/.v, proventricular ganglion ; ;-, rectum ; ;/>, rectal papillae ; />', trach e ; 



tr s, tracheal sacs. 

 l-'ic. 2. A vertical subim-dinn Fec'.ion through the proventriculus and part of the 



chyle stomach ; pv, proventriculus. 



Kn;. 3. A median vertical section of the proventriculus. 

 Fi<;. 4. A section through the rectal valve. 

 Fir,. 5. A transverse section of the intestine about two millimetres above the rectal 



valve. 



