314 THE DESCENT OF MAM, 



tliat of tlie beetle (fig. 10), the male of which has 

 left mandible much enlarged, so that the mouth is 

 greatly distorted. In another Carabidous beetle, Euryg- 

 nathus,* we have the case, unique as far as known to Mr. 

 Wollaston, of the head of the female being much broader 

 and larger, though in a variable degree, than that of the 

 male. Any number of such cases could be given. They 

 abound in the Lepidoptera; one of the most extraordinary 

 is that certain male butterflies have their fore legs more or 

 less atrophied, with the tibias and tarsi reduced to mere 

 rudimentary knobs. The wings, also, in the two sexes 

 often differ in neuration,f and sometimes considerably in 

 outline, as in the Aricoris epitus, which was shown to me 

 in the British Museum by Mr. A. "Butler. The males of 

 certain South American butterflies have tufts of hair on 

 the margins of the wings and horny excrescences on the 

 disks of the posterior pair.;]: In several British butterflies, 

 as shown by Mr. Wonfor, the males alone are in parts 

 clothed with peculiar scales. 



The use of the bright light of the female glow-worm has 

 been subject to much discussion. The male is feebly 

 luminous, as are the larvae and even the eggs. ^ It has been 

 supposed by some authors that the light serves to frighten 

 away enemies, and by others to guide the male to the 

 female. At last Mr. Belt appears to have solved the 

 difficulty; he finds that all the Lampyridae which he has 

 tried are highly distasteful to insectivorous mammals and 

 birds. Hence it is in accordance with Mr. Bates' view, 

 hereafter to be explained, that many insects mimic the 

 Lampyridae closely, in order to be mistaken for them, and 

 thus to escape destruction. He further believes that the 

 luminous species profit by being at once recognized as 



* " Insecta Madereusia," 1854, p. 20. 



f E. Doubleday, " Annals and Mag. of Nat. Hist.," vol. i, 1848, p. 

 379, I may add that the wings in certain Hymenoptera (see Sliuck- 

 ard, " Fossorial Hymenop.," 1837, pp. 39-43) differ in neuration 

 according to sex. 



:{: H. W. Bates, in "Journal of Proc. Linn. Soc," vol. vi, 1862, p. 

 74. Mr. Wonfor's observations are quoted in "Popular Science 

 Eeview," 1868, p 343. 



" The Naturalist in Nicaragua," 1874, pp. 316-320. On the phos- 

 phorescence of the eggs, see "Annals and Mag. of Nat. Hist.," 1871, 

 Nov., p. 373. 



