884 
SEXUAL SELECTION. 
Part II- 
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, when 
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 h 1 
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 / 1 Some natu- 
ralists believe that beetles make this noise to frighten 
away their enemies ; but I cannot think that the quadru- 
peds and birds which are able to devour the larg® r 
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 (Anolium tessdlatuni ) a re 
well known to auswer eacli other’s ticking, or, as I ha ve 
74 M. P. de la Brulerie, as quoted in 1 Journal of Travel,’ A. Murr®)’ 
vol. i. 1808, p. 13o. 
