With the ascent in power, the intensity of individuation keeps even pace; and from this we may explain all the characteristic distinctions between this class and that of the vermes. The almost homogeneous jelly of the animalcula infusoria became, by a vital oxydation, granular in the polypi. This granulation formed itself into distinct organs in the molluscæ; while for the snails, which are the next step, the animalized lime, that seemed the sole final cause of the life of the polypi, assumes all the characters of an ulterior purpose. Refined into a horn-like substance, it becomes to the snails the substitute of an organ, and their outward skeleton. Yet how much more manifold and definite, the organization of an insect, than that of the preceding class, the patient researches of Swammerdam and Lyonnet have evinced, to the delight and admiration of every reflecting mind.
In the insect, for the first time, we find the distinct commencement of a separation between the exponents of sensibility and those of irritability; _i.e._ between the _nervous_ and the _muscular_ system. The latter, however, asserts its pre-eminence throughout. The prodigal provision of organs for the purposes of respiration, and the marvellous powers which numerous tribes of insects possess, of accommodating the most corrupted airs, for a longer or shorter period, to the support of their excitability, would of itself lead us to presume, that here the _vis irritabilis_ is the reigning dynasty. There is here no confluence of nerves into one reservoir, as evidence of the independent existence of sensibility _as_ sensibility;--and therefore no counterpoise of a vascular system, as a distinct exponent of the irritable pole. The whole muscularity of these animals, is the organ of irritability; and the nerves themselves are probably feeders of the motory power. The petty rills of sensibility flow into the full expanse of irritability, and there lose themselves. The nerves appertaining to the senses, on the other hand, are indistinct, and comparatively unimportant. The multitude of immovable eyes appear not so much conductors of light, as its ultimate recipient. We are almost tempted to believe that they constitute, rather than subserve, their sensorium.