Mr. Wallace, for instance, describes a certain butterfly which
presents in the same island a great range of varieties connected by
intermediate links, and the extreme links of the chain closely resemble the
two forms of an allied dimorphic species inhabiting another part of the
Malay Archipelago. Thus also with ants, the several worker-castes are
generally quite distinct; but in some cases, as we shall hereafter see, the
castes are connected together by finely graduated varieties. So it is, as
I have myself observed, with some dimorphic plants. It certainly at first
appears a highly remarkable fact that the same female butterfly should have
the power of producing at the same time three distinct female forms and a
male; and that an hermaphrodite plant should produce from the same seed-
capsule three distinct hermaphrodite forms, bearing three different kinds
of females and three or even six different kinds of males. Nevertheless
these cases are only exaggerations of the common fact that the female
produces offspring of two sexes which sometimes differ from each other in a
wonderful manner.
DOUBTFUL SPECIES.
The forms which possess in some considerable degree the character of
species, but which are so closely similar to other forms, or are so closely
linked to them by intermediate gradations, that naturalists do not like to
rank them as distinct species, are in several respects the most important
for us.
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