mod sa 
previous year, passing in that year its larval and great part of 
its pupal life, while what is commonly called the second brood 
passes its whole life in the spring or first part of the summer of one 
and the same year. As to their life-habits, I sum them up as 
follows: winter phase — egg and larva in summer and early autumn, 
pupa in winter, imago in spring, period of life eight to nine months; 
summer phase — whole life (egg, larva, pupa and imago) in spring 
and first part of summer, period of life three to four months. 
Let me here shortly describe the difference in aspect of the two 
phases. In A. /evana the winter phase (/evana proper) is orange 
brown chequered with blackish brown spots, the summer phase 
(prorsa) is uniform black with a conspicuous white oblique fascia 
extending across both pairs of wings, usually with a few small 
orange-brown spots, or traces of them; this phase is generally 
larger, sometimes considerably so, than the winter phase; I have 
not found that it is usually greater in weight. In S. bilunaria the 
imago of the winter phase is dull brown with a strongly marked 
pattern of darker hue, that of the summer phase is bright chestnut, 
verging, especially on the under side, on orange, the pattern 
somewhat different from that of the other phase, and not so 
strongly marked. But the great difference in what I have called 
aspect, is in size or mass; from a large number of weighings made 
of several broods, it may be taken as about the difference between 
13 Or 14 grammes and 18 grammes, i. e. the winter phase is some- 
thing over 30 °/. heavier than the summer phase. 
TEMPERATURE THE CAUSE OF THE DIFFERENT PHASES. 
We come now to the question of the causation of these two 
different phases. Without by any means doubting that other 
influences than temperature, such as moisture, are, under some 
circumstances, more particularly in tropical and semitropical 
countries (1), the determining cause, I do assert that in the species 
operated on by me, and, as I am convinced, in many other 
species, the appropriate temperature, and nothing more, applied 
in the right stage, is sufficient in itself to cause the Insect to belong 
(1) In Southern Africa, for example, as shown by the experiments of 
Mr, Guy MARSHALL. 
