370 THE DESCENT OF MAN 



the females are wingless; the sexes differ in the forna of 

 their bodies, elytra, antenna, and tarsi; but, as the signifi- 

 cation of these differences are 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 com- 

 monly differ much in color; 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 colored; and 

 as these insects emit an extremely nauseous odor, their 

 conspicuous colors may serve as a signal that they are un- 

 palatable to insectivorous animals. In some few cases their 

 colors appear td be directly protective; thus Prof. Hoffmann 

 informs me that he could hardly distinguish a small pink 

 and green species from the buds on the trunks of lime-trees, 

 which this insect frequents. 



Some species of Eeduvidae make a stridulating noise; 

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

 effected by the movement of the neck within the pro- 

 thoracic cavity. According to Westring, Reduvius person- 

 atus also stridulates. But I have no reason to suppose that 

 this is a sexual character, excepting that with non-social 

 insects there seems to be no use for sound-producing organs, 

 unless it be as a sexual call. 



Order, Homoptera. — Every one who has wandered in a 

 tropical forest must have been astonished at the din made 

 by the male Cicadae. The females are mute; as the Grecian 

 poet Xenarohus 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 in cages for the sake of their song, so that it must be 



^ Westwood, "Modern Clasa. of Insects," vol. ii. p. 473. 



