EXTERNAL ANATOMY OF INSECTS. 635 



sent a large surface to the action of the atmosphere with- 

 out incommoding the insect when it has not occasion to 

 use them. 



With respect to this head, insects may be divided into 

 two classes — namely, those whose wings in repose are 

 covered by wing-cases harder than the wings themselves, 

 and those that have no such protection. In the former 

 the wings, though the rule admits several exceptions, have 

 more folds than in the latter. As the different mode of 

 folding the wings has been assumed for a characteristic 

 of the earlier Orders, I shall explain to you with as much 

 brevity as possible how each is circumstanced in this re- 

 spect, beginning as usual with the Coleoptera. 



There are two principal folds of the wing in this Order, 

 which may be named the anal and the apical: the for- 

 mer is when the Anal Area or part of it is folded on the 

 under surface of the base of the wing; this fold is always 

 more or less longitudinal: the latter •, the apical fold, is 

 by means of the commissura or joint of the postcosta lately 

 mentioned: which in Hister, Staphylinus, &c, for obvious 

 reasons a is nearer the base of the wing ; in NecrophO- 

 rus in the middle ; in Dynastes Aloeus beyond the mid- 

 dle 15 ; in Tenebrio Molitor near the apex; and in Dytiscus 

 marginalis there appears to be no joint at all ; but the 

 fact is, that in this insect the postcosta, — the termination 

 of which really forms the joint, the costa itself being only 

 flexible at that point, — stands at a greater distance from 

 the latter at its end. Well, at this joint the above fold 

 is made, the apex of the wing, being first folded longi- 

 tudinally, turning under and inwards, and forming an 



1 Insects with short elytra of course must fold their wings nearer 

 the base than those with Ions ones, b Plate X. Fig. 4. o" . 



