HOW INSECTS BREATHE. 141 



not at all affected; it remains unchanged as long as the 

 wings can vibrate. If the poisers, lastly, be cut off, this pro- 

 duces no difference of sound .... The spiracle alone re- 

 mains therefore to be considered as the cause and instrument 

 of the sound." Following up these experiments Dr. Bur- 

 meister dissected the spiracle, and found that the posterior 

 lip is formed into a small, flat, halfmoon-shaped plate : " upon 

 this plate (lo. cit., p. 469) there are nine parallel very delicate 

 horny leaves, the superior free sharp edges of "hich are bent 

 somewhat downward." . . . " Upon the air, which is 

 driven with force out of the tracheae, touching these laminae, 

 they are made to vibrate, and sound precisely in the same 

 manner as the vibrating of the glottis of # the larynx." 



Kirby and Spence appear only to have seen some extracts 

 from Chabrier's interesting paper (see Kirby and Spence's 

 Edition, 18-36, p. 488), and say, " after all the friction of the 

 base of the wings against the thorax seems to be the sole 

 cause of the alarming buzz of the gnat as well as that of other 

 Dipt era." 



Yet I cannot but think that Chabrier and Burmeister have 

 conclusively shown these sounds to be connected with the 

 rushing of the air from the spiracles, and therefore entitled to 

 some extent to the name of voice. 



The short description which I have given above applies 

 in essentials to almost all perfect insects, and to the great 

 majority of larvae. Yet many live in water, and require 

 therefore some modification of the respiratory organs to fit 

 them for this abode. 



Although many perfect insects are found only in and about 

 water, there are but few so essentially aquatic as to require 

 any considerable alteration in this respect. 



The Orthoptera or Hymenoptera, as far as Ave know at 

 present, are without exception land animals. Although many 



