14 



PRACTICAL ZOOLOGY 



sent in the common Carolina locust. Next, the partially digested 

 food enters the stomach or ventriculus (Fig. 3, vent), where it is 

 acted upon by juices secreted by six spindle-shaped pouches 

 (Fig. 3, gas.c) which open into the anterior end of the stomach. 

 From the stomach food passes into the intestine (not all of this 

 is shown in Fig. 3), the final portion of which is known as the 

 rectum (Fig. 3, red). The digested food is absorbed by the 



walls of the alimentary canal 

 and the undigested material 

 passes out of the body 

 through the anal opening 

 (Fig. 3, an). 



Circulation. — The di- 

 gested food absorbed by 

 the intestinal wall enters 

 the blood which fills the 

 body cavity, and is car- 

 ried in the blood stream 

 to all parts of the body, 

 where it is assimilated ; that 

 is, is changed into living 

 matter to take the place of 

 that which is continually, 

 being used up by the activi- 

 ties of the animal. The 

 blood is a fluid containing 

 corpuscles. These corpus- 

 cles are not reddish in color, 

 as in human beings, but are 

 usually colorless. The fluid of the blood is also generally color- 

 less, but it is sometimes yellowish or greenish. It has just 

 recently been discovered that the sex of many young insects 

 (caterpillars) can be determined by the color of the blood, that 

 of the males being yellow, and that of the females green. 



The circulatory system of the insect is very simple and there 



Fig. 4. — Diagram of an insect show- 

 ing the heart (h), aorta (a), and direction 

 of the blood-flow (by arrows). (After 

 Kolbe.) 



