1428 THE STORY OF THE UNIVERSE 



brane, of a shape between triangular and oval, with 

 a few fine black lines running through it, and along 

 one edge. But on bringing a greater magnifying 

 power to bear on it, we see that the clear surface is 

 covered with minute short stiff hairs, each of which 

 has an expanded base. And still further, by deli- 

 cate focusing, we find that there are two sets of these 

 hairs, which come into view alternately, those of one 

 row projecting upward toward our eye, those of the 

 other downward. They are placed on both the upper 

 and under surface, and are in fact appendages of two 

 distinct membranes, applied to each other. There 

 is some reason to believe that these hairs are deli- 

 cate organs of touch communicating impressions 

 through the skin to a sensitive layer beneath; at 

 least such seems their function on the body, and 

 we may judge from analogy that it is not different 

 here. 



The black lines are elastic, horny tubes, over 

 which the membranes are spread and stretched, like 

 the silk of an umbrella by its ribs. The upper mem- 

 brane is firmly attached to the tubes (which are 

 called neryures) ; the lower has but a slight adhesion, 

 and is easily stripped from them. The nervures 

 originate in the body, and diverge like a fan to va- 

 rious points of the tip, and to the upper and lower 

 edges; some of them, however, terminate in the sub- 

 stance of the wing without reaching the edge, and 

 some send off cross branches by which two are con- 

 nected together. They generally maintain the same 

 thickness throughout, but there are enlargements 

 where the branches join the main trunks. These 



