398 EXTERNAL ANATOMY OF INSECTS. 
shield of the cockchafer (Melolontha vulgaris), and after 
removing the muscle &c., hold it against the light, with 
the inner side towards the eye, you will see the light 
through every puncture: or take the elytra of Geotrupes 
stercorarius, or any common beetle in which these organs 
have punctate striz, and examine them under a lens on 
the inside, and you will see distinctly that the punctures 
pass through the elytrum, and the membrane that lines 
it*. It is not improbable that in the case last mention- 
ed these pores may be of use, as the spiracles are usu- 
ally closely covered by the elytra, for the better trans- 
mission of the air to those respiratory organs. Whe- 
ther the pores in the other parts of the body are for 
transpiration, is more than I shall venture to affirm ; but 
as insects sometimes perspire, at least this has been as- 
certained with respect to the hive-bee’, this must be by 
the means of some pores. 
iv. The integument of insects is often clothed, either 
partially or generally, with pubescence, or hairs of vari- 
ous kinds—a circumstance which seems to have more 
than one object. In Parnus, Heterocerus, Gerris, Argy- 
roneta aquatica, and some other aquatic insects, the end 
in view seems to be to keep the water from wetting the 
crust; and in this case the covering of hairs is dense, 
silky, and decumbent. Another object is preventing 
friction from being injurious: thus humble-bees, that 
from their mode of nidification®, are usually more par- 
ticularly exposed to it, are well clothed with hair; and 
in those articulations of insects where much friction takes 
® Pirate XXVIII. Fic. 1, 2. 
> Huber Nouv. Obs. ii. 317. © Vor. I. p. 498—. 
