388 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



they are also no doubt in birds, by which the male 

 may attract the female. 



They are so commonly developed in the Ortliop- 

 tera (grasshoppers and crickets), that the arrange- 

 ment which obtains in one member of this order may 

 be conveniently taken as a type. In Macrolyristes 



imperator (Fig. 

 165 ; A and B) 

 we observe that 

 the hinder bor- 

 der of the right 

 wing (s) is thick- 

 ened in such a 

 way as to act as 

 a cord, and that 

 another part of 

 the wing (ni) is 

 converted into a 

 tense membrane. 

 The left wing (B) 

 has its lower 

 surface rough- 

 ened like a file 

 along one line ; 

 this file is 

 brought to rub 

 upon the thick 

 cord (s) of the 

 right wing, and 



so sets the membrane (w) in vibration ; vibrations are, 

 of course, conveyed to the air, and, being regular and 

 definite, they set up vibrations in the air which, on- strik- 

 ing the auditory nerve, give rise to the sensation of more 

 or less musical sounds. Somewhat similar structures 

 are to be found on the wings of the locust, and in the 

 field cricket ; in the latter the two wings are similar 

 in structure, and their movement on one another can, 



B 



Fig. 165. The Soimcl-prochicing Organ of the 

 Orthopterous insect Maorolyristes imperator. 



A, Upper view of right wing ; s, cord ; m, membrane ; 

 is, lower view of left wing ; b, roughened edge. 



