6 ANIMAL BIOLOGY 



in the location of its organ of hearing. Look on the side 

 of the first segment of the abdomen and you will find an 

 oval aperture covered with membrane; this is furnished 

 with a delicate apparatus which is stimulated by the vi- 

 brations of the air and thus makes its possessor aware of 

 the presence of sound. As animals which hear usually 

 have some means of making a noise themselves, we find 

 that grasshoppers are frequently furnished with an instru- 

 ment for the production of song, although it is present 

 only in the male sex. This instrument consists in most 

 cases of a series of fine teeth on the inner side of the femur. 

 As this apparatus is rubbed over one of the veins of 

 the wing cases it produces a shrill note. If one carefully 

 approaches a singing grasshopper he may see the femur 

 drawn across the wing cover, producing a sound much as 

 the violinist does by drawing his bow over a string. 

 The musical sound probably serves, like the songs of 

 birds, as a means of bringing the sexes together. 



After this study of the external parts of the grasshopper 

 let us consider briefly some of the features of its internal 

 structure. The part of the body concerned with the 

 digestion of food is the alimentary canal which is a tube 

 leading from the mouth to the posterior end of the body. 

 Different parts of this tube differ in structure and in 

 function. Leading from the mouth is a short and narrow 

 division called the esophagus. Connected with a promi- 

 nence at the anterior end of the esophagus are the salivary 

 glands whose function is to secrete and pour into the 

 alimentary canal a fluid which aids in digestion. Pos- 

 teriorly the esophagus leads to a crop lined internally with 

 rows of chitinous teeth which probably serve to grind 

 up the food. Behind the crop is a large, thin-walled 

 stomach at the anterior end of which open a number of 

 tubes called gastric caeca. The stomach passes into the 



