x COLOURS AND ORNAMENTS CHARACTERISTIC OF SEX 271 
difference of colour, in many cases so remarkable that the two 
sexes of the same species remained for many years under 
different names and were thought to be quite distinct species. 
We find, however, every gradation from perfect identity to 
complete diversity, and in some cases we are able to see a 
reason for this difference. Beginning with the most extra¬ 
ordinary cases of diversity—as in Diadema misippus, where the 
male is black, ornamented with a large white spot on each 
wing margined with rich changeable blue, while the female is 
orange-brown with black spots and stripes—we find the 
explanation in the fact that the female mimics an uneatable 
Danais, and thus gains protection while laying its eggs on low 
plants in company with that insect. In the allied species, 
Diadema bolina, the females are also very different from the 
males, but are of dusky brown tints, evidently protective and 
very variable, some specimens having a general resemblance 
to the uneatable Eupkeas; so that Ave see here some of the 
earlier stages of both forms of protection. The, remarkable 
differences in some South American Pieridse are similarly 
explained. The males of Pieris pyrrha, P. lorena, and 
several others, are white with a feAv black bands and marginal 
spots like so many of their allies, Avhile the females are 
gaily coloured with yelloAv and brown, and exactly resemble 
some species of the uneatable Heliconidse of the same 
district. Similarly, in the Malay Archipelago, the female 
of Diadema anomala is glossy metallic blue, while the 
male is brown; the reason for this reversal of the usual 
rule being, that the female exactly mimics the brilliant 
colouring of the common and uneatable Eupkea midamus, 
and thus secures protection. In the fine Adolias dirtea, the 
male is black with a feAv specks of ochre-yelloAv and a broad 
marginal band of rich metallic greenish-blue, Avhile the female 
is brownish-black entirely covered Avith rows of ochre-yelloAv 
spots. This latter coloration does not appear to be protective 
when the insect is seen in the cabinet, but it really is so. 
I have observed the female of this butterfly in Sumatra, where 
it settles on the ground in the forest, and its yellow spots 
so harmonise Avith the flickering gleams of sunlight on the 
dead leaves that it can only be detected Avith the greatest 
difficulty. 
