even though it does not offer better distinguishing characters
than do the extreme forms of the variable species. Cases of this kind
are the Ornithoptera Priamus, which is confined to the islands of Ceram
and Amboyna, and is very constant in both sexes, while the allied
species inhabiting New Guinea and the Papuan Islands is exceedingly
variable; and in the island of Celebes is a species closely allied to
the variable P. Severus, but which, being exceedingly constant, I have
described as a distinct species under the name of Papilio Pertinax.

2. _Polymorphism or dimorphism._--By this term I understand the
co-existence in the same locality of two or more distinct forms, not
connected by intermediate gradations, and all of which are occasionally
produced from common parents. These distinct forms generally occur in
the female sex only, and their offspring, instead of being hybrids, or
like the two parents, appear to reproduce all the distinct forms in
varying proportions. I believe it will be found that a considerable
number of what have been classed as _varieties_ are really cases of
polymorphism. Albinoism and melanism are of this character, as well as
most of those cases in which well-marked varieties occur in company with
the parent species, but without any intermediate forms. If these
distinct forms breed independently, and are never reproduced from a
common parent, they must be considered as separate species, contact
without intermixture being a good test of specific difference. On the
other hand, intercrossing without producing an intermediate race is a
test of dimorphism. I consider, therefore, that under any circumstances
the term "variety" is wrongly applied to such cases.

The Malayan Papilionidae exhibit some very curious instances of
polymorphism, some of which have been recorded as varieties, others as
distinct species; and they all occur in the female sex. Papilio Memnon
is one of the most striking, as it exhibits the mixture of simple
variability, local and polymorphic forms, all hitherto classed under the
common title of varieties. The polymorphism is strikingly exhibited by
the females, one set of which resemble the males in form, with a
variable paler colouring; the others have a large spatulate tail to the
hinder wings and a distinct style of colouring, which causes them
closely to resemble P. Coon, a species having the two sexes alike and
inhabiting the same countries, but with which they have no dire