THE EXTERNAL ANATOMY OF INSECTS 



89 



specialized example of this type of stridulating organ is possessed by 

 the larvae of Passalus, in which the legs of the third pair are so much 



shortened that the 

 /-^■— ) . larvae appear to 



have only four legs ; 

 each hind leg is a 

 paw-like structure 

 fitted for rasping 

 the file (Fig. loi). 



These insects 

 are social, a pair of 

 beetles and their 

 progeny living to- 

 gether in decaying 

 wood. The adults 

 prepare food for the 

 larvae; and the col- 

 ony is able to keep 

 together by stridu- 

 latory signals. 



d. THE MUSICAL 

 ORGANS OF A CICADA 



Fig. loi. — Stridulating organ of a larva of Passalus; 

 a, b, portions of the metathorax; c, coxa of the 

 second leg; d, file; e, basal part of femur of middle 

 leg; /, hairs with chitinous process at base of each; 

 g, the diminutive third leg modified for scratching 

 the file (From Sharp). 



With the cica- 

 das there exists a 

 type of stridulating 

 organ peculiar to 

 them, and one that is the most complicated organ of sound 

 found in the animal kingdom. Yet, while the cicadas are the 

 most noisy of the insect world, the results obtained by their com- 

 plicated musical apparatus are not comparable with those pro- 

 duced by the comparatively simple vocal organs of birds and of 

 man. 



It is said that in some species of Cicada both sexes stridulate ; but 

 as a rule the females are mute, possessing only vestiges of the musical 

 apparatus. 



The structure of the stridulating organs varies somewhat in 

 details in different species of Cicada; but those of Cicada plebeia, 

 which were described and figured by Carlet ('77), may be taken as an 

 example of the more perfect form. In the male of this species there is 

 a pair of large plates, on the ventral side of the body, that extend back 



