INSECTS : WINGS AND THEIR APPENDAGES. 



7a 



general structure as before, — two clear elastic membranes 

 stretched over slender horny tubular nervures, and stud- 

 ded on both surfaces with short spine-like hairs, which 

 in this case, however, are very numerous and minute. 

 But, along the nervures, and along other lines which run 

 (generally) parallel with the front margin, and also along 

 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. Erom 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 towards 

 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 or 



SCALES ON A GNAT'S WING. 



