92 EVENINGS AT THE MICROSCOPE 



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

 very curious appearance ,and structure. 



Confining our attention to one of these lines, suppose 

 one of the nervures, we see that its course is marked on 

 the upper membrane by five rows of minute elevated 

 warts, arranged obliquely with one another. From each 

 of these warts springs a slender stem which gradually 

 dilates into a thin leaf-shaped plate of transparent sub- 

 stance, having from four to eight or ten longitudinal ribs. 

 They project in a radiating manner, all inclined toward 

 the tip of the wing. The same line on the under-surface 

 carries the like number of leaf-like plates, corresponding 

 in arrangement, structure, form and direction with those 

 on the upper side. The margins of the wing all round 

 are furnished with similar organs, with this difference, 

 that whereas the plates along the lines are as it were cut 

 off abruptly at their greatest diameter, the marginal ones 

 converge again with a gracefully curved outline, to a fine 

 point: a form which is seen to the greatest advantage 

 along the hind edge of the wing, while those of the front 

 margin are thicker, and more densely crowded. 



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 sea- shore may often be found some wing- 

 less but active Insects, which are endowed with the power 

 of leaping in great perfection. From their hinder extrem- 

 ity being furnished with long projecting bristles, they are 

 sometimes called Bristle- tails, but naturalists designate the 

 genus Machilis. If you can get one sufficiently still to 

 examine it, you will be delighted with the lustre of its 

 clothing, which appears dusted all over with a metallic 



