. 1386 NATURAL HISTORY OF WASPS. 
There is little to add with respect to the use of 
the spiracle as a respiratory larynx. Insect functions 
require that these little creatures should have perfect 
control over the ingress and egress of air, and the ap- 
paratus for this purpose is as simple as it is effectual. 
Flies have a screen of hairs across their stigmata, to 
prevent the introduction of extraneous matters, but 
wasps and bees have no further protection than that 
which their hairy body supplies: their habits of life 
probably rendering any such arrangement unneces- 
sary. But with regard to the functions of the spiracle 
as a vocal larynx, there is much more to be said, and 
the interest of the subject will be, I am sure, a suffi- 
cient excuse for extending the inquiry beyond the 
range of the Hymenoptera. We can have no better 
guide than Dr. Landois* in this survey. 
Speaking generally, insects produce sound in one 
of two ways, namely, either by attrition of their 
horny covering, or by a current of air setting mem- 
branes placed for this special purpose in vibration” 
Instances of the first kind of instrument, so to say, 
are found in the grasshopper, the cricket, the death’s- 
head moth, and the death-watch beetle. The grass- 
hopper rubs his thighs against the sides of the 
abdomen, the filed ridges of the legs and the sound- 
chambers beneath the abdominal scales being mu- 
tually adapted to each other, so as to develop the 
sound. House crickets make their loud chirping by 
rubbing the finely ribbed nervure of one wing against 
the other wing. And the death’s-head moth rubs its 
* See also on all this subject, Kirby and Spence, ‘ Introduction to 
Entomology,’ 7th ed. p. 493. 
v 
