G8 INTERNAL STRUCTURE. 



The illustration, Fi,^. 40, is a longitudinal section 

 through a male grasshopper [Locusta viridissima L.), and 

 shows most of the organs mentioned hereafter. 



B}^ fastening a locust, with the back uppermost under 

 water and by cutting wath a pair of fine-pointed scissors 

 through the integument along the dorsal surface of the ab- 

 domen, the internal organs can be studied. Just below the 

 integument on the dorsal surface of the abdomen, is seen a 

 delicate tube, the /zeart. Just below the integument is a layer 

 of small flat muscles, the abdominal muscles. By removing 

 the dorsal integument of the thorax the large alary muscles, 

 w^hich move the wings, can be seen filling the dorsal portion 

 of the meso- and metathorax. The muscles of the opposite 

 sides of the body are sharply separated, and a thin chitinous 

 partition runs down from the constriction betw^eenthemeso- 

 and metathorax, and separates the muscles of the wing- 

 covers from those of the wings ; a similar partition covers 

 the posterior face of the wing-muscles. The space between 

 the muscles of the abdomen and the viscera is filled with a 

 loose network of light-colored substance, the corpus adi- 

 posum. 



Running inward from the spiracles on the sides of the 

 thoracic and abdominal segments are seen the tracheae, rather 

 tough transparent tubes, which divide into smaller branches 

 passing to the various organs of the body. A spiral elastic 

 fiber is coiled around the wall of each tracheal tube, which 

 by its elasticity keeps the tube permanently open. 



The Respiratory System.— In holding a locust between 

 our fingers we can readily observe its mode of breathing. 

 The portion of the side of the body between the stigmata 

 and the pleura (Fig. 36), contracts and expands, the contrac- 

 tion causing the spiracles to open. About 65 contractions 

 per minute can be counted. This movement is caused b^^the 

 fact that the sternal portion of the abdomen moves much 

 more decidedly than the tergal one. 



Air Sacks.— Insects possessing great powers of flight are 



