1877.] ~ The Colors of Animals and Plants. 661 
been brought about. The most difficult case, which may be taken 
as a type of the whole, is that of the genus Leptalis (a group of 
South American butterflies allied to our common white and yel- 
low kinds), many of the larger species of which are still white or 
yellow, and which are all eatable by birds and other insectivorous 
creatures. But there are also a number of species of Leptalis 
which are brilliantly red, yellow, and black, and which, band for 
band and spot for spot, resemble some one of the Danaide or 
Heliconidæ which inhabit the same district, and which are nause- 
ous and uneatable. Now, the common objection is that a slight 
approach to one of these protected butterflies would be of no use, 
while a greater sudden variation is not admissible on the theory 
of gradual change by indefinite slight variations. This objection 
depends almost wholly on the supposition that when the first 
steps toward mimicry occurred, the South American Danaide _ 
Were what they are now, while the ancestors of the Leptalides were 
like the ordinary white or yellow Pieridz to which they are allied. 
But the danaioid butterflies of South America are so immensely 
numerous and so greatly varied, not only in color but in struct- - 
ure, that we may be sure they are of vast antiquity and have un- 
dergone great modification. A large number of them, however, 
are still of comparatively plain colors, often rendered extremely 
elegant by the delicate transparency of the wing membrane, but 
Otherwise not at all conspicuous. Many have only dusky or 
purplish bands or spots, others have patches of reddish or yel- 
lowish brown, — perhaps the commonest color among butterflies, 
—while a considerable number are tinged or spotted with yellow, 
also a very common color, and one especially characteristic of the 
Pieridze, the family to which Leptalis belongs. We may there- 
fore reasonably suppose that in the early stages of the develop- 
ment of the Danaidæ, when they first began to acquire those 
_ Rauseous secretions which are now their protection, their colors 
were somewhat plain, either dusky with paler bands and spots, 
or yellowish with dark borders, and sometimes with reddish: 
. bands or spots. At this time they had probably shorter wings 
_ anda more rapid flight, just like the other unprotected families 
_ Of butterflies. But as soon as they became decidedly unpala- 
table to any of their enemies, it would be an advantage to them to 
be readily distinguished from all the eatable kinds; and as but- 
erflies were no doubt already very varied in color, while all 
: Probably *had wings adapted for pretty rapid or jerking flight, 
the best distinction might have been found in outline and habits ; 
. 
