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. 



s-. 



FIG. 146. Digestive system of a beetle, FIG. 147. Digestive system of Myrme- 



Carabus. a, anal gland; c (of fore gut), crop; leon larva, c, caecum; cr, crop; m, mid 

 c (of hind gut), colon, merging into rectum; intestine; mt, Malpighian tubes; s, spin- 

 d, evacuating duct of anal gland; g, gastric neret. After MEINERT. 

 caeca; i, ileum; m, mid intestine; mt, Mal- 

 pighian tubes; 0, cesophagus; p, proventricu- 

 lus; r, reservoir. After KOLBE. 



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. 



