EXTERNAL ANATOMY OF INSECTS. 399 



through every puncture : or take the elytra of Geotrupes 

 stercorarius, or any common beetle in which these or- 

 gans have punctate striae, 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 a . It is not improbable that in the case last 

 mentioned these pores may be of use, as the spiracles are 

 usually 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 ascer- 

 tained with respect to the hive-bee b , 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 c , are usually more par- 

 ticularly exposed to it, are well clothed with hair; and 

 in those articulations of insects where much friction takes 

 place, we may often observe a dense fringe or coating of 

 the same substance. This you may see in the common 



a Plate XXVIII. Fig. 1, 2. 



h Huber Now. Obs. ii. 317. c Vol. I. p. 5Q2— . 



