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116 our relief; and solves the difficulty by affirming that membranous wings are desiccated branchiæ analogous to the branchiæ 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 expansions 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 exercise a particular function, and undergoing such modifications 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 aërial motion, so the legs are appropriated to the lower, and furnish the means of moving on the earth and in the water. Their number 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 insertion 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