SENSE ORGANS. 



217 



We all know the cheerful chirp of the " cricket on the 

 hearth," the insistent, contradictory, answering cry of 

 the katydid, the deafening clatter of the cicada. ■ The 

 organs by which these noises are made are very various 

 and interesting. Most of these sonant insects belong to 

 the grasshopper order (orthopter). In these the anterior 

 pair of wings are somewhat hard, with strong stiff ribs 

 and tense membrane between. Sometimes the hind leg 

 is rubbed against ridges on the stiff edges of the front 

 wings. These wirelike ribs are especially stiff in the 

 overlapping parts on the back. Sometimes these parts 

 in the two wings are rubbed together with a rapid vibra- 

 tory motion, the stiff membrane between them acting as 

 resonators. Often a kind of rasp 

 is added to produce more effect 

 (Fig. 139). 



But the most elaborate con- 

 trivance is found in the cicada, a 

 homopter. Fig. 140, A, is the un- 



■ vcp 



Fig. 140. — A, view of the under side of a cicada (natural size) ; the legs are 

 removed on one side : vcp, ventral cover plate. B, section a little en- 

 larged : vm, vertical membrane ; m, muscle ; dr, drumhead [ vr, ventral 

 resonator. (After Lloyd-Morgan.) 



der side of the insect, natural size. Lifting up the ven- 

 tral cover plates, vcp, a tense membrane is disclosed (vr). 

 This is a resonant membrane. Beyond this there is an 

 enormous cavity, almost filling the whole body, and di- 

 vided into two by a thin vertical septum (vm, Fig. 140, B). 



