THE GRASSHOPPER 15 



is no complex arrangement of tubes, as in human beings. Near 

 the upper part of the body is a rather long contractile tube 

 called the heart (Fig. 3, ht), into which the blood surrounding it 

 flows through pairs of openings. By contractions, the blood is 

 forced forward out of the heart and into the spaces of the body in 

 which the various internal organs lie. All of these organs are 

 in this way continually bathed with a fresh supply of blood, as 

 illustrated by the arrows in Figure 4. 



FUNCTIONS OF BLOOD. --In man the blood carries food 

 material, waste substances, and oxygen from one part of the 

 body to another, but in insects there is a complex system of 

 tubules, known as tracheae, which carry oxygen directly from the 

 outside to the various parts of the body and so the blood is 

 relieved of this duty. 



Respiration. - - We are accustomed to think of breathing as 

 taking place through the nose or mouth, but in insects air is 

 taken in through pores, called spiracles, or stigmata, which occur 

 at intervals on the sides of the body. The grasshopper is pro- 

 vided with ten pairs of these breathing pores; two in the thorax 

 and eight in the abdomen. Connected with these openings are 

 the tubes within the body which branch many times, becoming 

 very minute. The taking in and forcing out of air, a process 

 known as respiration, is brought about by regular expansions 

 and contractions of the abdomen. In certain grasshoppers 

 there had been found to be from thirty-four to ninety-two 

 respiratory movements per minute. Such a system as that 

 just described is in the grasshopper and many other insects 

 assisted by rows of air sacs; thus an abundant supply of oxygen 

 is assured at all times, a fact that in part accounts for the re- 

 markably rapid growth of these animals. 



Excretion. - Waste matters in solution that result from the 

 breaking down of the living matter during the activities of the 

 insect are collected by a group of long thin tubes which are coiled 

 about in the body cavity (Fig. 3) and enter the forward end of 

 the intestine. These tubes, of which there may be as many as 



