THE VITAL PROCESSES. 



walls; this latter corresponds to our stomach. It is 

 separated from the fore and hind portions of the canal by 

 rudimentary valves, 

 which are simple ex- 

 trusions of the wall of 

 one cavity into the 

 opening of the next 

 cavity, and whose 

 loose edges prevent 

 the return of mate- 

 rial. In such insects 

 the food is soft as to 

 its substance and not 

 varied in its nature. 

 Hence there is no 

 need of special gland- 

 ular extensions of the 

 canal. In insects 

 whose food is of more 

 solid nature or more 

 varied in its charac- 

 ter, more modifica- 

 tions of the canal are 

 necessary for the se- 

 cretion of fluids 

 needed in the diges- 



- . 1 FIG. 13. Digestive system of a beetle, Carabus. 



tion of particular por- a> anal gland . c (of fore gut)> crop . c (of hind 



of the food, and gut), colon, merging into rectum; d, evacuating 

 duct of anal gland; g, gastric caeca; i, ileum; m, 

 mid intestine; mt, Malpighian tubes; o, cesoph- 



for the retention of 



the food long enough agus; p, proventriculus; r, reservoir. (Folsom, 



to let it become a f ter Kolbe ^ 



thoroughly permeated with these fluids. In many insects 



this is accomplished by the crop and the proventriculus, 



