1430 THE STORY OF THE UNIVERSE 



no hindrance to the sliding of the front over the 

 hind pair. 



The wings of many insects are interesting on ac- 

 count of the organs with which they are clothed. A 

 familiar example is furnished by the common gnat. 

 There is the same general structure as before two 

 clear elastic membranes stretched over slender horny 

 tubular nervures, and studded on both surfaces with 

 short spine-like hairs, which in this case, however, 

 are excessively numerous and minute. But along 

 the nervures, and along other lines which run (gen- 

 erally) parallel with the front margin, and also along 

 the whole margin, there are set long leaf-like scales 

 of very curious appearance and structure. 



There are, however, other insects which display 

 these or similar appendages in far greater profusion, 

 and in much variety of form and appearance. In 

 the fissures of cliffs that border the seashore may 

 often be found some wingless but active insects, 

 which are endowed with the power of leaping in 

 great perfection. From their hinder extremity being 

 furnished with long projecting bristles, they are 

 sometimes called bristle-tails, but naturalists desig- 

 nate the genus Machilis. If you can get one suffi- 

 ciently still to examine it, you will be delighted with 

 the lustre of its clothing, which appears dusted all 

 over with a metallic powder of rich colors red, 

 brown, orange, and yellow, foiled by dull lead-gray 

 in places. 



If you touch one of these nimble leapers, though 

 ever so slightly, you will see the result on your 

 finger-ends, for they will be found covered with a 



