388 
SEXUAL SELECTION. 
Part II. 
other tropical groups, and with some of our English 
butterflies, as the purple emperor, orange-tip, &c. (Apa- 
tura Iris and Anihocharis cardamines ), the sexes differ 
either greatly or slightly in colour. No language suffices 
to describe the splendour of the males of some tropical 
species. Even within the same genus we often find spe- 
cies presenting an extraordinary difference between the 
sexes, whilst others have their sexes closely alike. Thus 
in the South American genus Epicalia, Mr. Bates, to 
whom I am much indebted for most of the following 
facts and for looking over this whole discussion, informs 
me that he knows twelve species, the two sexes of which 
haunt the same stations (and this is not always the case 
with butterflies), and therefore cannot have been dif- 
ferently affected by external conditions . 3 In nine of 
these species the males rank amongst the most brilliant 
of all butterflies, and differ so greatly from the compa- 
ratively plain females that they were formerly placed 
in distinct genera. The females of these nine species 
resemble each other in their general type of coloration, 
and likewise resemble both sexes in several allied genera, 
found in various parts of the world. Hence in accord- 
ance with the descent-theory we may infer that these 
nine species, and probably all the others of the genus, 
are descended from an ancestral form which was coloured 
in nearly the same manner. In the tenth species the 
female still retains the same general colouring, but the 
male resembles her, so that he is coloured in a much 
less gaudy and contrasted manner than the males of the 
previous species. In the eleventh and twelfth species, 
the females depart from the type of colouring which 
3 See also Mr. Bates’ paper in 4 Proc. Ent. Soe. of Philadelphia,’ 
1865, p. 206. Also Mr. Wallace on the same subject, in regard to 
Diadema, in 4 Transact. Entomolog. Soc. of London/ 1869, p. 278. 
