12 



THE INTERNAL STRUCTURE OF INSECTS 



Fig. 



10. — Spiracles of a grasshopper. 

 Enlarged. Original. 



higher animals, whose 

 blood circulates in ar- 

 teries, veins, and capil- 

 laries. In insects the 

 blood flows freely around 

 the internal organs and 

 through the tissues. 



There is a heart, how- 

 ever, which keeps the 

 blood moving. It is an 

 elongated structure, situ- 

 ated just beneath the 

 upper surface of the in- 

 sect's body, and consists 

 of a series of chambers, 

 each with valves opening 

 from the body cavity 

 into the chamber, and 

 with another valve open- 

 ing into the next chamber 

 toward the front. The 



trachea) are extremely thin walled, 

 and the oxygen that they contain 

 is thus brought to the various 

 tissues. Air circulates slowly in 

 the tracheae. The openings or 

 spiracles are guarded by various 

 devices, such as a fringe of hairs. 



The Circulatory System 



The entire body cavity of an 

 insect is bathed in a yellowish or 

 greenish fluid that we speak of as 

 its blood. There is no closed 

 system of blood vessels, as in the 



Fig. U. 



insect's heart. 

 Original. 



(Diagrammatic.) 



