384 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 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, bv 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. 74 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 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 tessellation) are 

 well known to answer each other's ticking, or, as I have 



7* M. P. de la Brulerie, as quoted in 'Journal of Travel,' A. Murray, 

 vol. i. 1868, p. 135. 



