246 



THE MECHANICAL FUNCTIONS. 



converted into thick opaque, and hard plates, (e,) adapted to 

 cover the folded membranous wings when the insect is not 

 flying, and thus securing them from injurious impressions, 

 to which they might otherwise be exposed from heat, miois- 

 ture, or the contact of external bodies. These wing cases, 

 or elytra^ as they are termed, are never themselves em- 

 ployed as wings, but remain raised and m.otionless during 

 the flight of the insect. They probably, however, contri- 

 bute to direct the course of flight, by variously modifying 

 the resistance of the air.* 



In the Orthoptera, (Fig. 159,) the coverings of the wings, 

 or tegmina, instead of being of a horny texture, are soft and 

 flexible, or semi-membranous. The wings themselves, being 

 broader than their coverings, are, when not in use, folded 

 longitudinally, like a fan. 



In the new Order of Rhipiptera of Latreille,t which in- 

 cludes only two genera, the tegmina are anomalous both in 



160 



159 



162 



their situation and shape; being fixed at the base of the an- 

 terior legs, very long and narrow, and apparently incapable 

 of protecting the wings. The wings themselves are of am- 



* The Elytra of insects have been regarded, by Oken, as corresponding to 

 the bivalve shells of the Mollusca, a notion which seems to be founded upon 

 a fanciful and strained analogy. 



f The Strepsipiera of Kirby. See Transactions of the Linnjean Society, 

 XI. 86. 



