82 GENERAL ZOOLOGY 



Back flow of the blood is prevented by a series of little 

 valves which allow only movement toward the head. After 

 the blood traverses the sinuses (where it bathes all the 

 internal organs, so that they may absorb nourishment from 

 it and shed excretions into it), it flows into the pericardial 

 chamber and enters the heart through several pairs of 

 lateral ostia. If more food is digested and absorbed than 

 can be utilized, it is converted into fatty substances and 

 stored in the two elongated "fat bodies" on either side 

 of the heart. 



The blood of a grasshopper, or. of any tracheate arthro- 

 pod, does not carry oxygen or carbon dioxide as it does in 

 most animals. The trachea form separate channels for 

 carrying air and the respiratory system is, therefore, en- 

 tirely independent of the circulatory system. This is an 

 admirable scheme, for each system is free to carry on its 

 own work. It has the disadvantage, or course, of requiring 

 two separate systems of conducting tubes in all parts of the 

 body. The grasshopper's tracheal system has good-sized 

 air-sacs (Fig. 36), which indicate that it is well fitted for 

 flight.. When a grasshopper breathes rapidly the abdomen 

 is rhythmically shortened and lengthened. By such move- 

 ments air is forced in and out of the spiracles on the sides 

 of the thorax and abdomen. A tracheal tube will not col- 

 lapse, for the walls have an elastic strand in them which, 

 though not continuous, is closely coiled like a wire spring 

 and keeps them expanded. The tracheal tubes divide into 

 very fine branches which go to every part of the body. 

 They extend to the tips of the legs, are closely wrapped 

 about all the internal organs and even penetrate into them. 

 Oxygen is thus always at hand to help in metabolism. 



The excretions' resulting from metabolic processes in the 

 grasshopper's body are eliminated through Malpighian 

 tubules which open into the intestine (midgut) just behind 

 the stomach. These tubules are closed at the free end. 

 They are very slender and swing freely about in all direc- 

 tions in the blood sinuses. Waste products are absorbed 



