THE VITAL PROCESSES. 27 



swallowed until it can be thoroughly mixed with the 

 digestive fluid. 



The stomach of an insect, instead of serving as does 

 our stomach, as a means of separating the solid foods 

 into minute portions as well as mixing them with the pep- 

 sin, is more like an intestine; it has not the capacity for 

 strong muscular action, such as has the preventriculus or 

 gizzard. Considerable secretion of digestive fluids takes 

 place here, as well as the absorption of the prepared food 

 mass. 



The portion of the canal behind the stomach is, in 

 some insects, modified into regions much like the divisions 

 of the large intestine of the human animal, and named 

 like them, colon, ileum, and rectum. In the primitive 

 insect there are no such divisions apparent ; and in many 

 others the colon or first division is absent. In human 

 alimentation the food current, in process of elaboration, 

 is supplied by the mesenteries with the amoeboid cells, 

 which play so important a part in the maintenance of the 

 health of the body by devouring the microbes of various 

 diseases. In many insects this function seems to be 

 performed by cells of the lining wall of the stomach, which 

 become free by constriction and float out free in the food 

 current. 



The excretory function of the kidneys seems to be 

 discharged by the Malpighian tubes of the insect, which 

 open into the intestine behind the stomach. . In the 

 human animal there is no aeration of the food current 

 until, after having been gathered from the capillaries of 

 the stomach and the intestines, from the lacteals, and 

 from the liver, into the right side of the heart, it is sent 

 to the lungs where it is oxygenated, and, being returned to 

 the left side of the heart, it is sent to all the waiting tissues 



