Chap. X. Thysanura. 279 



which are not known to fight together, of which the males 

 exceed the females in size ; and the meaning of this fact is not 

 known ; but in some of these cases, as with the huge Dynastes 

 and Megasoma, we can at least see that there would be no 

 necessity for the males to be smaller than the females, in order 

 to be matured before them, for these beetles are not short-lived, 

 and there would be ample time for the pairing of the sexes. So 

 again, male dragon-flies (Libellulidse) are sometimes sensibly 

 larger, and never smaller, than the females;" and as Mr. 

 MacLachlan believes, they do not generally pair with the females 

 until a week or fortnight has elapsed, and until they have 

 assumed their proper masculine colours. But the most curious 

 case, shewing on what complex and easily-overlooked relations, 

 so trifling a character as difference in size between the sexes 

 may depend, is that of the aculeate Hymenoptera ; for Mr. F. 

 Smith informs me that throughout nearly the whole of this 

 large group, the males, in accordance with the general rule, are 

 smaller than the females, and emerge about a week before them ; 

 but amongst the Bees, the males of A'pis mellifica, Anthidium 

 munkutum, and Anthophora acervorum, and amongst the Fossores, 

 the males of the Methoca idmeumonides, are larger than the 

 females. The explanation of this anomaly is that a marriage 

 flight is absolutely necessary with these species, and the male 

 requires great strength and size in order to carry the female 

 through the air. Increased size has here been acquired in op- 

 position to the usual relation between size and the period of 

 development, for the males, though larger, emerge bufore the 

 smaller females. 



We will now review the several Orders, selecting such facts 

 as more particularly concern us. The Lepidoptera (Butterflies 

 and Moths) will be retained for a separate chapter. 



Order, Thysanura. — The members of this lowly organized 

 order are wingless, dull-coloured, minute insects, with ugly, 

 almost misshapen heads and bodies. Their sexes do not differ ; 

 but they are interesting as shewing us that the males pay 

 sedulous court to the females even low down in the animal 

 scale. Sir J. Lubbock " says : " it is very amusing to see these 

 " little creatures (Smynthurus luteus) coquetting together. The 

 " male, which is much smaller than the female, runs round her, 

 " and they butt one another, standing face to face, and moving 



'* For this and other statements sec p. 344. 

 on the size of the sexes, see Kirby " 'Transact. liatean See.' Tol 



jud Spence, ibid, vol iii. p. 300 ; xivi. 1868, p. 296. 

 en the durttioD of life in insects. 



