378 
SEXUAL SELECTION. 
Part IL 
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 Typhaeus, 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 
67 Westwood, ‘ Modem Class/ vol. i, p. 184. 
08 Wollaston, On certain musical Curculionidse, ‘Annals and Mag. of 
Nat. Hist/ vol. vi. 1860, p. 14. 
fi9 ‘ Zeitschrift fur wiss. Zoolog/ B. xvii. 1867, s. 127. 
