Chap. X. INSECTS. 345 



less atrophied, with the tibiee and tarsi reduced to mere 

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

 often differ in neuration, 10 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 excres- 

 cences on the discs of the posterior pair. 11 In several 

 British butterflies, the males alone, as shewn by Mr. 

 Wonfor. are in parts clothed with peculiar scales. 



The purpose of the luminosity in the female glow- 

 worm is likewise not understood ; for it is very doubtful 

 whether the primary use of the light is to guide the 

 male to the female. It is no serious objection to this 

 latter belief that the males emit a feeble light; for 

 secondary sexual characters proper to one sex are often 

 developed in a slight degree in the other sex. It is a 

 more valid objection that the larvse shine, and in some 

 species brilliantly : Fritz Miiller informs me that the 

 most luminous insect which he ever beheld in Brazil, 

 was the larva of some beetle. Both sexes of certain 

 luminous species of Elater emit light. Kirby and 

 Spence suspect that the phosphorescence serves to 

 frighten and drive away enemies. 



Difference in Size between the Sexes. — With insects 

 of all kinds the males are commonly smaller than the 

 females ; 12 and this difference can often be detected, 

 even in the larval state. So considerable is the difference 



10 E. Doubleday, 'Annals and Mag. of Nat. Hist.' vol. i. 1848, p. 371*. 

 I may add that the wings in certain Hymen optera (see Shuckard, 

 Tossorial Hymenup.' 18:37, p. 39-43) differ in neuration according to 

 sex. 



11 H. W. Bates, in ' Journal of Proc. Linn. Soc." vol. vi. 1862, 

 Mr. Wonfor 's observations are quoted in ' Popidar Science, 

 1868, p. 343. /<^Q° S H 6 



12 Kirliv and Spence, ' Introduction to Entomologv,' vol/^H\*Zo9. A .^ 4 



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