Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget .. . flying, and thus securing them frominjurious impressions to which they might other-wise be exposed from heat, moisture, or thecontact of external bodies. These wing cases,or elytra as they are termed, are never themselvesemployed as wings, but remain raised and motion-less during the flight of the insect. They pro-bably, however, contribute to direct the courseof flight, by variously modifying the resistanceof the air.* In the Orthoptera, (Fig. 159), the coverings ofthe wings, or tegmina, i
Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget .. . flying, and thus securing them frominjurious impressions to which they might other-wise be exposed from heat, moisture, or thecontact of external bodies. These wing cases,or elytra as they are termed, are never themselvesemployed as wings, but remain raised and motion-less during the flight of the insect. They pro-bably, however, contribute to direct the courseof flight, by variously modifying the resistanceof the air.* In the Orthoptera, (Fig. 159), the coverings ofthe wings, or tegmina, instead of being of aliorny texture, are soft and flexible, or semi-membranous. The wings themselves, being * The Elytra of insects have been regarded by Oken as cor-responding to the bivalve shells of the Mollusca, a notion whichseems to be founded upon a fanciful and strained analogy. 350 THE MECHANICAL FUNCTIONS. broader than their coverings, are, when not inuse, folded longitudinally, like a fan. In the new Order of Rkipiptera of Latreille,*which includes only two genera, the tegmina are 160 159.
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