182 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. Miiller 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 Prionidz, 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 
