crease 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. The
four Brazilian species are _Lycorea halia_ (Danainae), _Heliconius
narcaea_ (_eucrate_) (Heliconinae), _Melinaea ethra_, and _Mechanitis
lysimnia_ (Ithomiinae).

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. Mueller 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[52]
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
Poulton and Dixey from Africa, and we may expect to learn many more
interesting facts in this connection. Here again the preliminary
postulates of the theory are satisfied. And how much more that would
lead to the same conclusion might be added!

As in the case of mimicry many species have come to resemble one
another through processes of selection, so we know whole classes of
phenomena in which plants and animals have become adapted to one
another, and have thus been modified to a considerable degree. I refer
particularly to the relation between flowers and insects. Darwin has
shown that the originally inconspicuous blossoms of the phanerogams
were transformed into flowers through the visits of insects, and that,
conversely, several large orders of insects have been gradually
modified by their association with flowers, especially as regards the
parts of their body actively concerned. Bees and butterflies in
particular have become what they are through their relation to
flowers. In this case again all that is apparently contradictory to
the theory can, on closer investigation, be beautifully