24 



THE CLASS OF INSECTS. 



during flight. The median area (Fig. 31 a) is the largest. It is 

 in the grasshoppers and crickets sometimes modified to form a 



musical organ, 



being 



drum-like, as in the 

 (Ecanthus (Fig. 30), or 

 rasp-like, as iu Arcliyp- 

 tera (Fig. 3 la). The 

 internal area (c) is the 

 smallest, and less dis- 

 tinctly marked than the 



two other regions ; the musical file-like or- 

 gan of Orchelimum vulgare, a common grass- 

 hopper (Fig. 32 d) is situated on this area. 



The limits of the edges of the wing vary 

 in almost every genus, and their comparative length affords 

 excellent generic characters. The front edge (Fig. 29) is called 

 the costal, its termina- 

 tion in the outer angle 

 of the wing is called 

 the apex; the outer edge 

 is situated between the 

 apex and the inner an- 

 gle, between which and 

 the base of the wing is 

 the inner, or internal, 

 edge. These distinc- 

 tions are of most use 

 in describing the butter- 

 flies and moths. 



The Appendages of 

 Fig. 3i a. tf ie H ea d. These organs 



are divided into two groups, 



the first of which comprise the 



sensory organs, i. e. the ocelli, 



eyes, and antennae, which are attached to the region in front 



of the mouth, or preoral region of the head. The second 



group consists of the sensorio-digestive appendages, combining 



the power of finding and seizing the food and preparing it for 



digestion. They are inserted behind 

 to the postoral region of the head. 



the mouth and belong 



