Class Insecta 525 



ground food is passed on into the stomach. In the stomach digestion is 

 probably completed with the aid of enzymes secreted by the gastric 

 caeca. Absorption probably occurs in the stomach; in the rectum, ex- 

 cess water is reabsorbed. 



At the constriction where the stomach and large intestine join are 

 located numerous threadlike Malpightan tubules. These constitute the 

 excretory system of the grasshopper. There are a great number of 

 these tubules which extend out into the hemocoel. The distal ends are 

 closed, but osmotic pressures remove the salts and uric acid from the 

 blood of the hemocoel. The wastes are discharged into the intestine 

 to pass out with the feces. 



From the paired spiracle openings along the sides of the abdomen 

 and thorax, the tracheae lead into the body. These tracheae branch 

 and rebranch into tracheoles. The walls of the tracheae secrete an 

 inner lining of chitin which is cast off with the exoskeleton during 

 ecdysis. The principal tracheal tubes have spiral threads for strengthen- 

 ing of the walls. Longitudinal vessels or trunks connect the spiracles 

 and provide additional air passageways. 



The movement of air through this complex of tubules is not a pas- 

 sive process. It is actually pumped through by a series of several 

 bladderlike structures (air sacs) which attach to points on the tracheae 

 near the spiracles. During inspiration, the four anterior ones are 

 opened and the posterior six are closed. Air thus enters through the 

 anterior spiracles. During expiration, the anterior four close and the 

 posterior six open. Air passes out through the posterior spiracles. 

 The air is dissolved in liquid present in the ends of the tracheoles. 



The heart is a slender tubular organ which lies against the dorsal 

 wall of the abdominal exoskeleton. It is located in a very small 

 pericardial cavity. In the heart are a series of small valves or osfia 

 through which blood enters. As the heart contracts, it forces blood 

 into a small dorsal aorta which passes anteriorly to the head. Here 

 the blood passes into the hemocoel and circulates through the body 

 spaces, finally returning to the pericardial cavity. The blood is color- 

 less, but contains some amoebocytes which remove foreign bodies. The 

 blood principally acts as a circulating medium for food and wastes. The 

 much-branched tracheal system takes care of respiration. 



The spaces between the organs are largely filled with a mass of 

 cells, the fat body, which is important in the storage of food. This is 

 particularly important during molting periods when the animal can 

 take in very little nourishment. 



