94 



ENTOMOLOGY 



which is present in many insects, especially Orthoptera and Coleoptera 

 (Fig. 146), and is usually found in such mandibulate insects as feed upon 

 hard substances. The proventriculus is lined with chitinous teeth or 

 ridges for straining the food, and has powerful circular muscles to squeeze 

 the food back into the stomach, as well as longitudinal muscles for re- 

 laxing, or opening, the gizzard. 

 Some authors maintain that the 

 proventriculus not only serves as 

 a strainer, but also helps to com- 

 minute the food, like the gizzard 

 of a bird. 



FIG. 146. Digestive system of a beetle, 

 Carabns. a, anal gland; c (of fore gut), crop; 

 c (of hind gut), colon, merging into rectum; 

 d, evacuating duct of anal gland; g, gastric 

 caeca; /, ileum; in, mid intestine; mt, Mal- 

 pighian tubes; o, oesophagus; p, proventricu- 

 lus; r, reservoir. After KOLBE. 



FIG. 147. Digestive system of Mynnc- 



Icon larva, c, caecum; cr, crop; m, mid 



intestine; ;;//, Malpighian tubes; s, spin- 

 neret. After MEINERT. 



In most insects a cardiac valve guards the entrance to the stomach, 

 preventing the return of food to the gullet. This valve (Figs. 144, 149) 

 is an intrusion of the stomodaeum into the mesenteron, forming a circular 

 lip which permits food to pass backward, but closes upon pressure from 

 behind. 



