S84 
SEXUAL SELECTION. 
Part IL 
become, in proceeding towards the apex, more and more 
confluent, regular, and naked ; so that three-fourths of 
the segment is covered with extremely fine parallel 
ribs, which are quite absent in the female. In the 
females, however, of all three species of Oryctes, w T hen 
the abdomen of a softened specimen is pushed back- 
wards and forwards, a slight grating or stridulating 
sound can be produced. 
In the case of the Heliopathes and Oryctes there can 
hardly be a doubt that the males stridulate in order to 
call or to excite the females ; but with most beetles the 
stridulation apparently serves both sexes as a mutual 
call. This view is not rendered improbable from beetles 
stridulating under various emotions ; we know that birds 
use their voices for many purposes besides singing to 
their mates. The great Chiasognathus stridulates in 
anger or defiance ; many species do the same from dis- 
tress or fear, when held so that they cannot escape ; 
Messrs. Wollaston and Crotch were able, by striking 
the hollow stems of trees in the Canary Islands, to dis- 
cover the presence of beetles belonging to the genus 
Acalles by their stridulation. Lastly the male Ateu- 
chus stridulates to encourage the female in her work, 
and from distress when she is removed .' 4 Some natu- 
ralists believe that beetles make this noise to frighten 
aw r av their enemies ; but I cannot think that the quadru- 
peds and birds which are able to devour the larger 
beetles with their extremely hard coats, would be fright- 
ened by so slight a grating sound. The belief that 
the stridulation serves as a sexual call is supported 
by the fact that death-ticks ( Anobium tesselatum ) are 
well known to answer each other’s ticking, or, as I have 
74 M. P. de la Brulerie, as quoted in ‘ Journal of Travel,’ A. Murray, 
yol. i. 18G8, p. 135. 
