112 INTRODUCTION TO 



instrument of motion. From this circumstance, s 

 gradation can be traced, as to the share the uppei 

 wings take in flight from the Coleoptera to the He 

 miptera, and from these to the Orthoptera. The in- 

 sects possessing the greatest powers of flight, must 

 therefore, be sought among those in which the uppei 

 wings are wholly membranous ; and we accordingly 

 find them among the Neuroptera, Hymenoptera, anc 

 Lepidoptera. Every one who has paid the slightest 

 attention to the subject, must have noticed how much 

 more vigorous and sustained is the flight of a dragon 

 fly, a bee, or a butterfly, than that of a beetle, a 

 grasshopper, or a plant-bug. The under wings are 

 in every instance membranous, and are exclusively 

 organs of flight. 



A wing of the latter sort, whether it belong to the 

 superior or inferior pair, has the external appearance 

 of a firm, dry, membrane, usually transparent, anc 

 traversed by numerous salient horny ribs. Although 

 the membrane appears simple, it consists, in reality 

 of two membranous leaves, closely applied to eacl 

 other, and enveloping the ribs just spoken of. This 

 can be made to appear very distinctly when the insec 

 has just emerged from the pupa and immersed in 

 spirits of wine, as the fluid can be introduced betweer 

 the still flaccid membranes, and thus distends then: 

 like a bag. Even this membrane, which appears o 

 the finest and most glossy surface to the naked eye 

 is found under the microscope to be clothed more 01 

 less densely with hairs; and in some gnats* these 



* See the immensely magnified figure of a gnat in Swam- 

 merdanTs Book of Nature, PLATE XXXVI. 



