294 Colour and the Struggle for Life 
(1) Mimicry may occasionally arise in one sex because the 
differences which distinguish it from the other sex happen to be such 
as to afford a starting-point for the resemblance. Here the male 
is at no disadvantage as compared with the female, and the rarity 
of mimicry in the male alone (e.g. Cethosia) is evidence that the great, 
predominance of female mimicry is not to be thus explained. 
(2) The tendency of the female to dimorphism and polymorphism 
has been of great importance in determining this predominance. 
Thus if the female appear in two different forms and the male in only 
one it will be twice as probable that she will happen to possess a 
sufficient, foundation for the evolution of mimicry. 
(3) The appearance of melanic or partially melanic forms in the 
female has been of very great service, providing as it does a change of 
ground-colour. Thus the mimicry of the black generally red-marked 
American “Aristolochia swallowtails” (Pharmacophagus) by the 
females of Papilio swallowtails was probably begun in this way. 
(4) It is probably incorrect to assume with Haase that mimicry 
always arose in the female and was later acquired by the male. Both 
sexes of the third section of swallowtails (Cosmodesmus) mimic 
Pharmacophagus in America, far more perfectly than do the females 
of Papilio. But this is not due to Cosmodesmus presenting us with 
a later stage of the history begun in Papilio; for in Africa Cosmo- 
desmus is still mimetic (of Danainae) in both sexes although the 
resemblances attained are imperfect, while many African species of 
Papilio have non-mimetic males with beautifully mimetic females. 
The explanation is probably to be sought in the fact that the females 
of Papilio are more variable and more often tend to become di- 
morphic than those of Cosmodesmus, while the latter group has more 
often happened to possess a sufficient foundation for the origin of 
the resemblance in patterns which, from the start, were common to 
male and female. 
(5) In very variable species with sexes alike, mimicry can be 
rapidly evolved in both sexes out of very small beginnings. Thus 
the reddish marks which are common in many individuals of Limenitis 
arthemis were almost certainly the starting-point for the evolution of 
the beautifully mimetic LD. archippus. Nevertheless in such cases, 
although there is no reason to suspect any greater variability, the 
female is commonly a somewhat better mimic than the male and 
often a very much better mimic. Wallace's principle seems here 
to supply the obvious interpretation. 
(6) When the difference between the patterns of the model and 
presumed ancestor of the mimic is very great, the female is often alone 
mimetic ; when the difference is comparatively small, both sexes are 
commonly mimetic. The Nymphaline genus Hypolimnas is a good 
