350 SEXUAL SELECTION. Part II. 



of these differences is quite unknown, they may be here 

 passed over. The females are generally larger and more 

 robust than the males. With British, and, as far as 

 Mr. Douglas knows, with exotic species, the sexes do 

 not commonly differ much in colour; but in about six 

 British species the male is considerably darker than the 

 female, and in about four other species the female is 

 darker than the male. Both sexes of some species are 

 beautifully marked with vermilion and black. It is 

 doubtful whether these colours serve as a protection. 

 If in any species the males had differed from the females 

 in an analogous manner, we might have been justified 

 in attributing such conspicuous colours to sexual selec- 

 tion with transference to both sexes. 



Some species of Keduvidae make a stridulating noise ; 

 and, in the case of Pirates stridulus, this is said 21 to 

 be effected by the movement of the neck within the 

 pro-thoracic cavity. According to Westring, Beduvius 

 personatus also stridulates. But I have not been able 

 to learn any particulars about these insects ; nor have I 

 any reason to suppose that they differ sexually in this 

 respect. 



Order, Homojrfera. — Every one who has wandered in 

 a tropical forest must have been astonished at the din 

 made by the male Cicadaa. The females are mute ; 

 as the Grecian poet Xenarchus says, " Happy the 

 " Cicadas live, since they all have voiceless wives." 

 The noise thus made could be plainly heard on board 

 the " Beagle," when anchored at a quarter of a mile 

 from the shore of Brazil ; and Captain Hancock says 

 it can be heard at the distance of a mile. The Greeks 

 formerly kept, and the Chinese now keep, these insects 



21 Westwocd, ' Modern Class, of Insects,' vol. ii. p. 473. 



