138 THE CAUSES WHICH PROPAGATE 



constituted by a rig-id and compact skin, or dermis, for their 

 presence. The files, or lima?, also exhibit every degree of 

 perfection, from the pectinate structures found in the Dung* and 

 Burying" Beetles, arising- from coalescence of transverse dermal 

 wrinkles, and presenting regular raised ridges of truncate trian- 

 gular section to the rudimentary and sub-regular shagreening 

 seen in the Lily Beetles and Weevils. The musical organs in 

 our Palaearctic species are usually sexually common; and though 

 commonly employed to produce but a passive plaint of fear 

 resulting on touch, yet in some groups they acquire that spon- 

 taneity of action compatible with the attainment of the higher 

 economic expressions of anger, love, or rivalry, and in these kinds 

 they likewise postulate the existence of auditory organs. The 

 Dung Beetles [Geotrnpes) , a genus of Longhorns, and the Death 

 Watches obtain thus pre-eminence in their respective families. 



In Coleoptera there are either one or two limse develojied at 

 points of similar friction, and the action of stridulation is com- 

 monly the respiratory protrusion and contraction of the abdominal 

 articulations, in respect to which the limse are found on various 

 parts of the segmental surface or on the elytra or coxae. In the 

 Longicornes, one Lamellicorn genus, and in one of the Elateridse, 

 the music results from the action of the depressor and elevator 

 prothoracic muscles, and the single lima in the first is on the 

 mesonotum, in the second on the presternum, and in the third on 

 the prosternal spine. It is surmised likewise in certain genera 

 that stridulation is effected by the action of the elevator and 

 depressor muscles of the hind legs, as in grasshoppers, suggestive 

 limajform structures existing in connection on the abdomen. 



We also see that" -while the Longhorns present a uniform 

 method of stridulation, and have musical organs similarly placed, 

 differentiated by the number and fineness of their striae, in the 

 Lamellicornes the action and limae have considerable diversifica- 

 tion ; and the Ground and Water Beetles manifest considerable 

 latitude in the position of the limae. As regards the periods of 

 music, in those kinds where the stridulation is voluntary, some 

 longhorns creak in sunshine and some of those with lamellated 

 antennae at evening. 



The Geodephaga, or Ground Beetles proper, include those 

 long-legged, flattish, voracious creatures that make us start 



