THE INSECTS 



235 



Breathing Organs. Observation of the abdomen of a living 

 grasshopper shows a frequent movement of the abdomen. Along 

 the side of the abdomen in eight of the segments (in the red-legged 

 grasshopper) are found tiny openings called spiracles. A large 

 spiracle may easily be found in the middle segment of the thorax. 

 These spiracles open into little tubes called trachece. The tracheae 

 carry air to all parts of the body. By the movements of the abdo- 

 men just noted, air is drawn into and forced out of the tracheae. 

 The tracheae divide and 

 subdivide like branches of 

 a tree, so that all the body 

 cavity is reached by their 

 fine endings. Some even 

 pass outward into the veins 

 of the wings. Each of these 

 tubes contains air. The 

 blood of an insect does not 

 circulate through a system 

 of closed blood tubes as in 

 man, but instead it more or 

 less completely fills that 

 part of the body cavity which is not filled with other organs. 

 Oxygen is thus brought in contact with the blood by means of 

 the tracheae. 



Muscular Activity. Insects have the most powerful muscles of 

 any animals of their size. Relatively, an enormous amount of 

 energy is released during the jumping or flying of a grasshopper. 

 The tracheae pass directly into the muscles and other tissues. 

 Here oxygen is passed into the tissues, and oxidation takes place 

 when work is done. 



Food-Taking and Blood-Making. The grasshopper is provided 

 with two pairs of jaws, a forklike ventral-lying pair, the maxillce, and 

 a pair of hard cutting jaws, the mandibles. These parts are covered when 

 not in use by two flaps, the upper and lower lips. The plant food taken by the 

 grasshopper is held in place in the mouth by means of the little jaws, or the 

 maxillae, while it is cut into small pieces by the mandibles. Just behind 

 the mouth is a large crop into which empty the contents of the salivary 

 glands. It is this fluid mixed with digested food that we call the " grass- 

 hopper's molasses." After the food is digested by the action of the 



Cross section through the body of an insect: 

 a, food tube; h, heart; n, nerve cord; t, 

 tracheae opening at t by spiracle. 



