244 
DARWINISM 
CHAP. 
the former and reject the latter. The Pierkhe would, however, 
usually be less numerous, because their larvae are often pro¬ 
tectively coloured and therefore edible, while the larvae of the 
Heliconidae are adorned with warning colours, spines, or 
tubercles, and are uneatable. It seems probable that the 
larvas and pupae of the Heliconidae were the first to acquire 
the protective distastefulness, both because in this stage they 
are more defenceless and more liable to fatal injury, and also 
because we now find many instances in which the larvae are 
distasteful while the perfect insects are eatable, but I believe 
none in which the reverse is the case. The larvae of the 
Pieridae are now beginning to acquire offensive juices, but 
have not yet obtained the corresponding conspicuous colours ; 
while the perfect insects remain eatable, except perhaps in 
some Eastern groups, the under sides of whose wings are 
brilliantly coloured although this is the part which is exposed 
when at rest. 
It is clear that if a large majority of the larvae of Lepido- 
ptera, as well as the perfect insects, acquired these distaste¬ 
ful properties, so as seriously to diminish the food supply of 
insectivorous and nestling birds, these latter would be forced 
by necessity to acquire corresponding tastes, and to eat with 
pleasure what some of them now eat only under pressure of 
hunger ; and variation and natural selection would soon bring 
about this change. 
Many writers have denied the possibility of such wonderful 
resemblances being produced by the accumulation of fortuitous 
variations, but if the reader will call to mind the large amount 
of variability that has been shown to exist in all organisms, 
the exceptional power of rapid increase possessed by insects, and 
the tremendous struggle for existence always going on, the 
difficulty will vanish, especially when we remember that 
nature has the same fundamental groundwork to act upon in 
the two groups, general similarity of forms, wings of similar 
texture and outline, and probably some original similarity of 
colour and marking. Yet there is evidently considerable 
difficulty in the process, or with these great resources at her 
command nature would have produced more of these mimicking 
forms than she has done. One reason of this deficiency prob¬ 
ably is, that the imitators, being always fewer in number, have 
