INSECTS 1445 



third joint projects obliquely a stiff bristle or style, 

 which tapers to a fine point. It is densely hairy 

 throughout; and is more beset with longer hairs on 

 two opposite sides, which decrease regularly in length 

 from the base, making a wide and pointed plume. 



Such are a few examples of what are presumed to 

 be the ears of insects ; let us now turn our attention to 

 their eyes. And we can scarcely select a more bril- 

 liant, or a larger example, than is presented by this 

 fine dragon-fly (^Eshna), which I just now caught as 

 it was hawking to and fro in my garden. How gor- 

 geously beautiful are these two great hemispheres 

 that almost compose the head, each shining with a 

 soft satiny lustre of azure hue, surrounded by olive- 

 green, and marked with undefined black spots, which 

 change their place as you move the insect round! 



Each of these hemispheres is a compound eye. I 

 put the insect in the stage-forceps, and bring a low 

 power to bear upon it with reflected light. You see 

 an infinite number of hexagons, of the most accurate 

 symmetry and regularity of arrangement. Into those 

 which are in the centre of the field of view, the eye 

 can penetrate far down, and you perceive that they 

 are tubes; of those which recede from the centre, 

 you discern more and more of the sides; while, by 

 delicate adjustment of the focus, you can see that 

 each tube is not open, but is covered with a convex 

 arch of some glassy medium polished and transparent 

 as crystal. There are, according to the computations 

 of accurate naturalists, not fewer than 24,000 of these 

 convex lenses in the two eyes of such a large species 

 of dragon-fly as this. Every one of these 24,000 



