710 Mr. Gilbert J. Arrow on 



system, but in certain cases by a degree of social organiza- 

 tion which was until quite recently hardly suspected, 

 although the elaborate instincts of certain members of the 

 group attracted attention in very early times and procured 

 from the ancient Egyptians peculiar honours for the 

 Sacred Scaraba^us and other beetles of the same family. 



The usual type of stridulating organ in the Lamelli- 

 cornia is the same as tliat now known to occur in nearly 

 all the large groups of Coleoptera and consisting of a 

 highly-chitinized plate, the surface of which is broken up 

 into a number of extremely fine parallel ridges capable of 

 being set in vibration by being sciaped by one or more sharp 

 edges situated upon another part of the body. Practically 

 all the musical organs described by Mr. Gahan, although 

 varying to an extraordinary extent in their situation in 

 different beetles, are of this pattern; but structures of 

 somewhat greater variety have come to light in Lamelli- 

 corns, so that it is necessary to modify to some extent our 

 ideas of the elements necessary for sound-production in 

 Coleoptera. In a wide sense, however, all the instruments 

 coming within the scope of the present paper are of the 

 " stringed " type and consist essentially of two parts, of 

 wliich I shall call the more delicate and regular one by 

 whose vibrations the sound is immediately produced, the 

 " strididatory plate " or " stridulatory area," and the less 

 complex one which excites these vibrations, the " plectrum." 

 In other groups of beetles instruments of percussion occur, 

 and in one Lamellicorn, the common Cockchafer, one 

 author * has described a vocal apparatus of the " reed " 

 type, but I have not been able to find any confirmation of 

 this discovery. 



The stridulatory area and plectrum do not generally 

 need any very fine adjustment for the performance of their 

 function, but in order to secure contact one of them 

 commonly covers much more space than the other. When 

 the stridulatory nrea is narrow or confined to small 

 tubercular elevations the plectrum usually extends 

 considerably beyond it, and, on the other hand, if a broad 

 area is found covered with the vibratory ridges the 

 plectrum will probably be more or less minute. The 

 musical quality of the vibrations produced by these 

 structures depends upon their extreme hardness and 

 rigidity, and these are commonly indicated by a black or 

 * Landois, Tliierstimmen, jj. 110. 



