THE INTERNAL ANATOMY OF INSECTS 



111 



Fig. 127. — Cross-section of the 

 proventriculus of a larva of 

 Corydalus. 



mediately in front of the mid-intestine or ventriculus, is a highly 

 speciaHzed organ in which the food is prepared for entrance into 

 the more delicate ventriculus ; such an 

 organ is termed the proventriculus (Fig. 

 126, pv). The characteristic features 

 of a proventriculus are a remarkable 

 development of the chitinous mtima 

 into folds and teeth and a great in- 

 crease in the size of the muscles of this 

 region. The details of the structure 

 of this organ vary greatly in different 

 insects; a cross-section of the proven- 

 triculus of the larva of Corydalus (Fig. 

 127) will serve to illustrate its form. 

 In the proventriculus, the food is both 

 masticated and more thoroughly 

 mixed with the digestive fluids. 



The oesophageal valve.—Wh&n the 

 fore-intestine projects into the mid- 

 intestine, as shown in Figure 128, 

 the folded end of the fore-intestine 

 is termed the (esophageal valve. 



C. THE MID-INTESTINE 



The mid-intestine is the inter- 

 mediate of the three principal 

 divisions of the alimentary canal, 

 which are distinguished by differ- 

 ences in their embryological origins, 

 as stated above. The mid-intestine 

 is termed by different writers the 

 mese liter on, the stomach, the chylific 

 ventricle, the chyle stomach, and the 

 ventriculus. 



The layers of the mid-intestine. — 

 The structure of the mid-intestine 

 differs markedly from that of the 

 fore-intestine. In the mid-intestine 

 there is no chitinous intima, and the 

 relative positions of the circular and 

 longitudinal muscles are reversed. 



Fig. 128. — The cesophageal valve of a 

 larva of Simulium; F, fore-intestine: 

 M, mid-intestine; u, point of uriion 

 of fore-intestine and mid-intestiner 

 p, peritoneal membrane; i, 

 intima of fore- intestine; e, epithe- 

 Hum of fore-intestine; pt, peritrophic 

 membrane; m, muscles. 



