SOUNDS OF INSECTS. 



93 



three, towards the top of the head. We know nothing certain 

 of the manner in which these organs act upon the light that 

 falls upon them ; nor of the mechanism of vision amongst 

 Insects. 



611. Several Insects possess, in common with the higher 

 animals, the faculty of producing 

 sounds : but in general their song is 

 not connected with the movements of 

 the air in the respiratory apparatus, 

 as amongst the former ; and depends 

 upon the rubbing of certain parts of 

 the body against each other, or on 

 the movements produced in certain 

 special instruments, by the contrac- 

 tion of muscles. Thus the monoto- 

 nous and deafening noise of the Cicada 

 results from the alternate tension and 

 relaxation of an elastic membrane, 

 placed like the skin of a drum upon 

 the base of the abdomen ; amongst 

 the Crickets, there are certain parts 

 of the wings, which, when rubbed 

 against each other, vibrate with in- 

 tensity, and which have a very curious structure for this purpose ; 

 but the humming of Flies appears to depend upon the rapid exit 



of the air through 

 the thoracic spira- 

 cles, during the 

 violent movement 

 of flight. Again, 

 there are some In- 

 sects that utter a 

 kind of cry, the 

 manner of produc- 

 ing which is not well known ; such is the Sphinx Atropos, 

 known under the name of the Death's-head Moth. (ANIM. 

 PHYSIOL. 676679). 



Fio. 311 CICADA. 



Fio. 312. SPHINX ATROPOS. 



