620 



THE SENSES AND SENSORY ORGANS. 



the semicircular canals and cochlea of a Vertebrate ; and vibra- 

 tions of this fluid would be an efficient cause acting upon the 

 chordotonal elements of the halter. The vibrations of this 

 fluid would necessarily be greatly intensified by the varying 

 pressure on the elastic capitellum of the halter. 



I think it probable that some such action occurs as that 

 which I have indicated. The halteres appear to me to be 

 microphones of a most efficient kind, which probably enable 

 these insects to perceive sounds the intensity of which is far 

 less than those which affect the human ear. 



12. THE WING ORGANS. 



The wings of most Insects contain organs which are similar 

 to the chordotonal organs of the halteres of the Diptera. 

 These were discovered by Braxton Hicks [292], and have been 

 more fully described by Graber [285]. 



Fie. 81. The wing organs of Clytus and Chrysopa, after Graber [285]. A> the 

 trachea and nerve of the submarginal nervure of the wing of Clytus, seen as a 

 transparent object ; />, surface view of three of the organs from the same ; 

 C, group of pores on the base of the submarginal nervure of the wing of Chry- 

 sopa ; a, bands uniting the organs with the integument ; c/i, chordotonal thread ; 

 ;/, nerve ; /, pore or vesicle ; tr, trachea. 



After investigating these organs in various insects, Graber 

 obtained a very satisfactory preparation from the subcostal 

 nervure of the wing of Clytus, which he describes in the fol- 

 lowing terms : ' I observed a group of closely-packed and rela- 

 tively small pores on that part of the subcostal nervure which 



