378 SEXUAL SELECTION. Part II. 



many have the power of stridulating when excited ; many 

 are furnished with the most extraordinary horns, appa- 

 rently for the sake of ornament ; some which are diurnal 

 in their habits are gorgeously coloured ; and, lastly, 

 several of the largest beetles in the world belong to this 

 family, which was placed by Linnaeus and Fabricius at 

 the head of the Order of the Coleoptera. 67 



Stridulating organs. — Beetles belonging to many 

 and widely distinct families possess these organs. The 

 sound can sometimes be heard at the distance of several 

 feet or even yards, 68 but is not comparable with that 

 produced by the Orthoptera. The part which may be 

 called the rasp generally consists of a narrow slightly- 

 raised surface, crossed by very fine, parallel ribs, some- 

 times so fine as to cause iridescent colours, and having 

 a very elegant appearance under the microscope. In 

 some cases, for instance, with Typhoeus, it could be 

 plainly seen that extremely minute, bristly, scale-like 

 prominences, which cover the whole surrounding sur- 

 face in approximately parallel lines, give rise to the 

 ribs of the rasp by becoming confluent and straight, and 

 at the same time more prominent and smooth. A hard 

 ridge on any adjoining part of the body, which in some 

 cases is specially modified for the purpose, serves as the 

 scraper for the rasp. The scraper is rapidly moved across 

 the rasp, or conversely the rasp across the scraper. 



These organs are situated in widely different posi- 

 tions. In the carrion-beetles (Necrophorus) two parallel 

 rasps (r, fig. 24) stand on the dorsal surface of the fifth 

 abdominal segment, each rasp being crossed, as described 

 by Landois, 69 by from 126 to 140 fine ribs. These 



6 ' Westwood, ' Modern Class.' vol. i. p. 184. 



68 Wollaston, On certain musical Curculioiiidse, 'Annals and Mag. of 

 Nat. Hist.' vol. vi. 1860, p. 14. 



,;, J ' Zeitschrift fur wiss~ Zoolog.' B. xvii. 1867, s. 127. 



