1 82 Evolution and Adaptation 



female is dark purple ; but it is difficult to say which sex is 

 the more ornamented." 



In other families of bees, differences in the color of the 

 sexes have been recorded, and since the males have been seen 

 fighting for the possession (?) of the females, and since bees 

 are known to recognize differences in color, Darwin believes 

 that : — 



" In some species the more beautiful males appear to have 

 been selected by the females ; and in others the more beauti- 

 ful females by the males. Consequently in certain genera, 

 the males of the several species differ much in appearance, 

 whilst the females are almost indistinguishable ; in other 

 genera the reverse occurs. H. Muller believes that the 

 colors gained by one sex through sexual selection have often 

 been transferred in a variable degree to the other sex, just as 

 the pollen-collecting apparatus of the female has often been 

 transferred to the male, to whom it is absolutely useless." 



Although in beetles the sexes are generally colored alike, 

 yet in some of the longicorns there are exceptions to the rule. 

 " Most of these insects are large and splendidly colored. The 

 males in the genus Pyrodes, which I saw in Mr. Bates's 

 collection, are generally redder .but rather duller than the 

 females, the latter being colored of a more or less splendid 

 golden-green. On the other hand, in one species the male 

 is golden-green, the female being richly tinted with red and 

 purple. In the genus Esmeralda the sexes differ so greatly 

 in color that they have been ranked as distinct species ; in 

 one species both are of a beautiful shining green, but the 

 male has a red thorax. On the whole, as far as I could 

 judge, the females of those Prionidx, in which the sexes 

 differ, are colored more richly than the males, and this does 

 not accord with the common rule in regard to color, when 

 acquired through sexual selection." 



The great horns that rise from the heads of many male 

 beetles are very striking cases of sexual difference, and 



