SEXUAL SELECTION 385 



Mutilla Europcea makes a stridulating noise; and accord- 

 ing to Goureau" both sexes have this power. He attributes 

 the sound to the friction of the third and preceding abdomi- 

 nal segments, and I find that these surfaces are marked with 

 very fine concentric ridges; but so is the projecting thoracic 

 collar, into which the head articulates, and this collar, when 

 scratched with the point of a needle, emits the proper sound. 

 It is rather surprising that both sexes should have the power 

 of stridulating, as the male is winged and the female wing- 

 less. It is notorious that Bees express certain emotions, aa 

 of anger, by the tone of their humming; and, according to 

 H. Muller (p. 80), the males of some species make a peculiar 

 singing noise while pursuing the females. 



Order, Ooleoptera (Beetles).— Many beetles are colored so 

 as to resemble the surfaces which they habitually frequent, 

 and they thus escape detection by their enemies. Other 

 species, for instance, diamond-beetles, are ornamented with 

 splendid colors, which are often arranged in stripes, spots, 

 crosses, and other elegant patterns. Such colors can hardly 

 serve directly as a protection, except in the case of certain 

 ■flower- feeding species; but they may serve as a warning or 

 means of recognition, on the same principle as the phos- 

 phorescence of the glow-worm. As with beetles the colors 

 of the two sexes are generally alike, we have no evidence 

 that they have been gained through sexual selection; but 

 this is at least possible, for they may have been developed 

 in one sex and then transferred to the other; and this view 

 is even in some degree probable in those groups which pos- 

 sess other well-marked secondary sexual characters. Blind 



females ; but these young females would next year produce males ; and will it 

 be pretended that such males would not inherit the characters of their male 

 grandfathers? To take a case with ordinary animals as nearly parallel as pos- 

 sible ; if a female of any white quadruped or bird were crossed by a male of a 

 black breed, and the male and female offspring vrere paired together, will it 

 be pretended that the grandchildren would not inherit a tendency to blackness 

 from their male grandfather? The acquirement of new characters by the sterile 

 worker-bees is a much more difficult case, but I have endeavored to show in 

 my "Origin of Species" how these sterile beings are subjected to the power 

 of natural selection. 



^^ Quoted by Westwood, "Modern Class, of Insects," vol. ii. p. 214. 

 Descent — TOL I. — 17. 



