VARIATIONS IN THE COLOUR OF LEPIDOPTERA. 175 
edusa and C. hyale are both dimorphic in the female sex. Some 
of the females of the former are red and some yellow; and of the 
latter some are yellow and others white, or nearly so. 
TrimorPHisM.—Trimorphism in butterflies is not found in 
England, but attention has been drawn to it by Mr. A. Russel 
Wallace in the case of certain species of Papilio inhabiting 
the Austro- and Indo-Malayan Archipelago. Papilio pammon, 
P. theseus, and P. ormenus, are all trimorphic in the female sex. 
HorromorpPHisM.—In this class I place all those Lepidoptera 
which appear twice a year, and with such a difference in their 
coloration that in many cases they have been held to be distinct 
species. The best illustration of this, found in Great Britain, is 
Pieris napi: this insect appears in May and June, and again in 
July and August. The males of the spring emergence are almost 
white on the upper side, and the under sides of the secondary 
wings have their venations densely irrorated with dark grey. The 
females on the upper side have the venations of the wings densely 
irrorated with grey on a whitish ground, and the under sides 
strongly suffused with the same colour, denser at the sides of each 
venation. The males of the summer emergence have well-defined 
larger or smaller subapical black spots on the upper wings on a 
pure white ground, the sprinkling of grey near each venation on 
the under side being much less than in those of the spring 
emergence. ‘The females have a pure white ground colour to all 
the wings on the upper side, and the venations are well defined 
with black edgings; on the under side the irrorations on the 
edges of the venations are very much less pronounced. It 
appears, from the researches of Dr. Weisman, that whether the 
insect presents the coloration of the spring or summer emergence 
depends entirely on the time it remains in the chrysalis. The 
butterflies which appear in spring have spent the winter in the 
chrysalis state; these lay eggs in June, which pass through all 
the stages of egg, caterpillar, and chrysalis states in a few weeks, 
appearing as perfect insects in the summer, but in the form of the 
summer emergence. Now Dr. Weisman has found that if the 
chrysalis, which in ordinary course would produce the summer 
emergence form, are prevented from developing by being placed 
for a sufficient time in the cold, say in an ice-safe, they appear 
with the coloration of those of the usual spring emergence, or, 
in other words, in nature, A produces B, B A, and so on; but 
