THE THORAX. 99 



narrow appendage extending from the internal margin. This form is 

 found chiefly in the posterior wings of the butterflies (Pap. Machaon, 

 Podalirius, &c.). 



DIGITATE (digitata, PI. XV. f. 14) is a wing, which has its other- 

 wise undivided surface indented with deep incisions between the ribs 

 or veins (Orneodes). 



Besides these outlines, which are peculiar to the wings, we likewise 

 find in them the majority of the differences mentioned in 18. 



The same applies to the differences of margin ; we therefore refer 

 to 20. 



The surface of the true wings is subjected to but few changes ; in 

 general it is a smooth skin, with here and there some hair spread over 

 it (in many Diptera, for example, Psychoda}. In one order, however, 

 (the Lepidoptera) , the general law prevails for their being clothed with 

 flattened scales (alee squamosas). 



The situation of the wings in repose is much more various in pecu- 

 liarities. We proceed to the consideration of these differences, and 

 thereby form a conclusion to the investigation we have here made upon 

 these organs. 



EVEN (alee planet), are those wings which, in a state of repose, 

 preserve the same extension as when in motion. 



Opposed to them are the FOLDED wings (plicatce). By this term 

 we understand such as are longitudinally folded in repose, like a fan, 

 and expand only during flight into a uniform surface (Orthoptera) . 

 We consider such wings as RE-FOLDED (replicatce) , when their apex 

 falls back upon the base. 



CONVOLUTED wings (al. convolutce] , are such which embrace the 

 body from above downwards, and enclose it as in a tube (Crambus). 



INCUMBENT (incumbentes), when, lying parallely upon each other, 

 they cover the abdomen above (Tenthredo). 



CROSSED (cruciaice), are those incumbent wings which pass over 

 each other only at their apex (many Bees, the hemelytra of the Hemi- 

 ptera heteroptera). 



HORIZONTAL (horizontales}, whose direction is in the same plane 

 with that of the body. The reverse of these are the ERECT wings 

 (erectce), whose line of direction is perpendicular to the plane of the 

 body (Papilio). 



EXTENDED (extensce), form also in their direction a right angle with 

 the body, but lie in the same plane with it ; from these we must dis- 



H 2 



