12 INTRODUCTION. 



C0PEIN.5) the mandibular ridges are represented by irregular 

 tubercles and the apparatus seems comparatively imperfect. It 

 has not yet been ascertained what sound, if any, is produced by thest- . 

 In the larva? of the Stag-beetles (Lucanid.?;) a highly chitinised 

 area appears at the base of each intermediate leg, and, when 

 examined, this is seen to be closely studded with short pointed 

 tubercles. If a living larva is held in the lingers it will be found 

 to draw the hind leg sharply across this part of the preceding 

 one and at the part of the former where the contact occurs may be 

 seen another very hard chitinous surface. The trochanter is 

 drawn out into a long straight file and its inner edge is provided 

 with a series of microscopic sharp-edged ridges placed transversely. 

 If the insect be held near the ear the vibrations set up by the 

 friction of the studded plate against these ridges can be distinctly 

 heard. In the genus G'eotn/pcs (ScARAB.EiD.i;) sound is produced 

 by similar means, but here the hind leg is considerably shortened 

 and the joints appear solidified, while from base to tip runs a row 

 of sharp horny teeth. Corresponding with these, the horny area 

 at the base of the second pair of legs is furnished with tine close 

 ridges, so that the functions of the two parts are rever.-ed. The 

 shrunken hind leg has quite lost its original function, for its 

 direction is changed and it is inclined forwards, resting upon the 

 preceding limb and always ready to make music. The last stage 

 in this remarkable transformation of an organ of locomotion into 

 one of vocalisation is found in the Passalid.e. The larvae of this 

 family are quite active, less unwieldy in form, and provided with 

 better-proportioned legs tlian other Lamellicorn larva>. Tlie latter, 

 however, seem to be only four in niunl)er. 'J he last pair are so 

 much reduced as to be scarcely visible without a lens, w hich reveals 

 them in a form resembling tiny scales. These leg-vestiges are 

 ])rovided with several hooked claws at the margin or lower surface 

 and lie close to the body upon a microscopically ridged plate like 

 that of Geoii-u2>cs (fig. 7). 



Fig. 7. — Larva of l\ii^a/i($, and enlarged detail of part of middle leg and 

 reduced hind leg. 



In the adult Passalid.t the legs are all perfectly normal, and 

 stridulation is accomplished by the friction between the wings and 

 the upper surface of the abdomen. A small area upon eacli wing 

 is studded beneath with peculiar hard short spines and against 



