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INTRODUCTION TO 
our relief; and solves the difficulty by affirming that 
membranous wings are desiccated branchise ana- 
logous to the branchiae of fishes ; and, moreover, that 
elytra are the analogues of the shells of bivalve 
mollusca ! ! Mr. Kirby is disposed to consider them 
as having some relation to the membranous expan- 
sions found in certain Saurian reptiles of the genus 
Draco ; but wisely refrains from doing more than 
merely throwing out the hint that such may be the 
case. It is surely more natural to regard them with 
M. Audouin, as organs sui generis, destined to exer- 
cise a particular function, and undergoing sucb modi- 
fications as best adapt them for fulfilling that function 
in every variety of circumstances.* 
As the wings occupy the superior portion of the 
thorax, and serve for aerial motion, so the legs are 
appropriated to the lower, and furnish the means of 
moving on the earth and in the water. Their num- 
ber never exceeds or falls short of six ; this rule 
being so invariable, that any articulated animal found 
not to conform with it, may at once be concluded 
not to belong to the class. Their position has been 
already indicated ; a pair being appropriated to each 
of the three principal divisions of the thorax, and 
their distance from each other at the points of in- 
sertion depends on the greater or less extension of 
these divisions on their inferior or sternal face. They 
are distinguished as the fore, middle, and hind legs. 
The joint which unites the leg with the body is 
* See Lacord. Intro, a V Entom. I. 409. 
