LONDON INSECTS 105 



turned into dry chambers filled with hot air, lighter, of 

 course, than the cooler air outside, into which the bird 

 has to rise. 



But, even with this beautiful contrivance for lighten- 

 ing it, the solid inside frame of bones on which beasts, 

 and birds, and fishes are built is a dead weight to lift ; 

 and so in insects, in which the power of flight is carried 

 to a far higher perfection than even in the Swallow or 

 Frigate-bird, different arrangements are made. The 

 heavy skeleton is dispensed with altogether, and instead 

 of it the supports for the body are given by a light, stiff 

 outside skin only; and, instead of having their fluid 

 parts aired as in beasts by little lungs in the middle of 

 the body, they suck in the air through openings, not 

 confined as in men and beasts to mouth and nose, but 

 dotted about the body in many parts, varying in dif- 

 ferent insects back, sides, head, and tail into tubes 

 (trackece they are called) which run backwards and 

 forwards in every direction through trunk and limbs. 



The four powerful, wide-spreading wings of the 

 Dragon-fly, ' the Eagle among insects/ look as if made 

 of the thinnest goldbeater's skin stretched on wire, stiff 

 at the base and front edges of the wing, spreading out 

 into the finest network. Through almost every thread 

 of the lace, and everywhere else through its body, breath 

 passes, so that the Dragon-fly, as one sees it hawking 

 in the fields or over the ponds, is a whiff of living air, 

 imprisoned in a cage of muscle with gripping claws, 

 and a head all eyes and jaw. No wonder with such an 

 outfit, and power to fly backwards and sideways as 



