X COLOURS AND ORNAMENTS CHARACTERISTIC OF SEX 271 



difference of colour, in many cases so remarkaljle 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 Avith 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 

 exjDlanation 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 Euplteas ; so that we see here some of the 

 earlier stages of both forms of protection. The remarkable 

 differences in some South American Pieridoe are similarly 

 explained. The males of Pieris pyrrha, P. lorena, and 

 several others, are white with a few 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 uneatal)le Heliconidae of the same 

 district. Similarly, in the Malay Archipelago, the female 

 of Diadema anomala is glossy metallic blue, Avhile 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 Euplsea midamus, 

 and thus secures protection. In the fine Adolias dirtea, the 

 male is black with a few sj^ecks of ochre-yellow and a broad 

 marginal band of rich metallic greenish-blue, while the female 

 is lirownish-l^lack entirely covered Avith roAvs of ochre-yelloAV 

 spots. This latter coloration does not appear to be protective 

 Avhen 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 yelloAV spots 

 so harmonise Avith the flickering gleams of sunlight on the 

 dead leaves that it can only be detected Avith the greatest 

 difficulty. 



