tes) has never yet been found in localities to which the male
(Pammon) does not extend. In this case, as in the last, distinct
species, local forms, and dimorphic specimens, have been confounded
under the common appellation of varieties.

But, besides the true P. Polytes, there are several allied forms of
females to be considered, namely, P. Theseus (Cramer), P. Molanides (De
Haan), P. Elyros (G. R. Gray), and P. Romulus (Linnaeus). The dark female
figured by Cramer as P. Theseus seems to be the common and perhaps the
only form in Sumatra, whereas in Java, Borneo, and Timor, along with
males quite identical with those of Sumatra, occur females of the
Polytes form, although a single specimen of the true P. Theseus taken at
Lombock would seem to show that the two forms do occur together. In the
allied species found in the Philippine Islands (P. Alphenor, Cramer = P.
Ledebouria, Eschscholtz, the female of which is P. Elyros, G. R. Gray,)
forms corresponding to these extremes occur, along with a number of
intermediate varieties, as shown by a fine series in the British Museum.
We have here an indication of how dimorphism may be produced; for let
the extreme Philippine forms be better suited to their conditions of
existence than the intermediate connecting links, and the latter will
gradually die out, leaving two distinct forms of the same insect, each
adapted to some special conditions. As these conditions are sure to vary
in different districts, it will often happen, as in Sumatra and Java,
that the one form will predominate in the one island, the other in the
adjacent one. In the island of Borneo there seems to be a third form;
for P. Melanides (De Haan) evidently belongs to this group, and has all
the chief characteristics of P. Theseus, with a modified colouration of
the hind wings. I now come to an insect which, if I am correct, offers
one of the most interesting cases of variation yet adduced. Papilio
Romulus, a butterfly found over a large part of India and Ceylon, and
not uncommon in collections, has always been considered a true and
independent species, and no suspicions have been expressed regarding it.
But a male of this form does not, I believe, exist. I have examined the
fine series in the British Museum, in the East India Company's Museum,
in the Hope Museum at Oxford, in Mr. Hewitson's and several other
private collections, and can find nothing but females; and for this
common butterfly no male partner can be