THE INTERNAL ANATOMY OF INSECTS 



111 



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

 specialized organ in which the food is prepared for entrance into 



the more delicate ventriculus ; such an 

 organ is teimed the proventnctdus (Fig. 

 126, pv). The characteristic features 

 of a proventriculus are a remarkable 

 development of the chitinous intima 

 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 larv^a of Corydalus (Fig. 

 127) will serve to illustrate its form. 

 In the proventriculus, the food is both 



Fig. 127. — Cross-section of the 

 proventriculus of a larva of 

 Corydalus. 



masticated and more thoroughly 

 mixed with the digestive fluids. 



The (esophageal valve. — When 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 

 mesenteron, the stomach, the chylific 

 ventricle, the chylestomach, 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 oesophageal valve of a 

 larva of SimuUum; F, fore-intestine: 

 M, mid-intestine; u, point of union 

 of fore-intestine and mid-intestine; 

 p, peritoneal membrane; i, 

 intima of fore-intestine; e, epithe- 

 lium of fore-intestine; pi, peri trophic 

 membrane; m, muscles. 



