dress have developed in
their case, and of what use is it, since the species would in any case
be immune? In Eastern Brazil, for instance, there are four butterflies,
which bear a most confusing resemblance to one another in colour,
marking, and form of wing, and all four are unpalatable to birds. They
belong to four different genera and three sub-families, and we have to
inquire: Whence came this resemblance and what end does it serve? For
a long time no satisfactory answer could be found, but Fritz Muller
(In "Kosmos", 1879, page 100.), seventeen years after Bates, offered a
solution to the riddle, when he pointed out that young birds could not
have an instinctive knowledge of the unpalatableness of the Ithomiines,
but must learn by experience which species were edible and which
inedible. Thus each young bird must have tasted at least one individual
of each inedible species and discovered its unpalatability, before it
learnt to avoid, and thus to spare the species. But if the four species
resemble each other very closely the bird will regard them all as of
the same kind, and avoid them all. Thus there developed a process
of selection which resulted in the survival of the Ithomiine-like
individuals, and in so great an increase of resemblance between the four
species, that they are difficult to distinguish one from another even in
a collection. The advantage for the four species, living side by side
as they do e.g. in Bahia, lies in the fact that only one individual
from the MIMICRY-RING ("inedible association") need be tasted by a young
bird, instead of at least four individuals, as would otherwise be the
case. As the number of young birds is great, this makes a considerable
difference in the ratio of elimination.

These interesting mimicry-rings (trusts), which have much significance
for the theory, have been the subject of numerous and careful
investigations, and at least their essential features are now fully
established. Muller took for granted, without making any investigations,
that young birds only learn by experience to distinguish between
different kinds of victims. But Lloyd Morgan's ("Habit and Instinct",
London, 1896.) experiments with young birds proved that this is really
the case, and at the same time furnished an additional argument against
the LAMARCKIAN PRINCIPLE.

In addition to the mimicry-rings first observed in South America, others
have been described from Tropical India by Moore, and by Poulto