SEXUAL SELECTION 367 



of the females J and this again would naturally follow, as 

 Mr. A. R. Wallace has remarked," through natural selec- 

 tion; for the smaller males would be first matured, and thus 

 would procreate a large number of offspring which would 

 inherit the reduced size of their male parents, while the 

 larger males, from being matured later, would leave fewer 

 offspring. 



There are, however, exceptions to the rule of male insects 

 being smaller than the females, and some of these exceptions 

 are intelligible. Size and strength would be an advantage 

 to the males which fight for the possession of the females; 

 and in these cases, as with the stag-beetle (Luoanus), the 

 males are larger than the females. There are, however, 

 other beetles which are not known to fight together, of 

 which the males exceed the females in size, and the mean- 

 ing 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 colors. But the most curious case, 

 showing 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 gen- 

 eral rule, are smaller than the females, and emerge about 

 a week before them; but among the Bees, the males of Apis 

 mellifica, Anthidium manicatum, and Anthophora acervorum, 



" "Journal of Proc. Ent. Soc," Feb. 4, 1867, p. Ixxi. 

 " For this and other statements on the size of the sexes, see Kirby and 

 Spence, ibid., vol. iii. p. 300; on the duration of life in insects, see p. 344. 



