OF THE WINGS AND LEGS. 165 



To understand the structure of the head of an insect, it 

 is essential to examine it, to handle it, to dissect it, 

 then the foregoing description will probably prove useful ; 

 but no description, without ocular demonstration, can be 

 made perfectly clear. The structure of an insect's mouth 

 will be pretty well understood by a comparison with our 

 own, if we suppose it possible for both our upper and lower 

 jaw to be divided down the middle, and the two halves of 

 each to move from side to side, meeting in front, the lips 

 and tongue remaining as they are. Our upper lip cor- 

 responds, then, precisely to the labrum of insects ; our 

 lower lip to the labium ; our upper jaw, divided, to the 

 mandibles ; our lower jaw, divided, to the maxilla ; our 

 tongue, to their tongue ; and, when both mouths are closely 

 shut, the parts in each occupy similar places. The mouth 

 of Ripipteryx at p. 159 aptly illustrates this. 



Wings and Legs. The wings and legs of insects are 

 situated in equal numbers on each side of a right line 

 drawn down the back; they constitute five pairs, four 

 wings and six legs. 



The fore wings or proala arise from the sides of the 

 mesotliorax ; they vary in composition, covering and form, 

 and their variations afford excellent distinguishing charac- 

 ters : fore wings are called scaly or squamosa, when they 

 are membranaceous, and covered with a coat of minute 

 scales placed in rows ; the edges of the scales in one row 

 covering the insertions of those in the next, like the scales 

 of a fish, or the tiles of a house : these wings are used 

 principally in flight ; the wings have this character in the 

 butterfly : they are membranaceous or membranacecB when 

 composed of a delicate transparent membrane, which is 

 upheld and moved by various strong nervures, traversing 

 it in various directions : in the fly, these fore wings alone 

 perform the office of flight; in the bee, they have the 



