Passing from the Ornithoptera, which may be esteemed the chiefs and
princes of their race, we now come to the Papilios, properly so called,
some of which are scarcely inferior in their dimensions and imposing
aspect. Such, at least, is the case with _P. Antimachus_ and _P.
Antenor_, which besides their large size, partake of some of the other
characters of the group just referred to, and thus form the passage
from it to Papilio. But the great majority are of very inferior size,
and many of them so dissimilar in aspect that they might be thought to
afford sufficient distinctions for arranging them in numerous different
genera. On a close examination, however, the species are found to
be so intimately allied in all essential parts of structure, that
the most judicious systematists have not attempted to separate them.
Such authors as have followed an opposite course, Hubner for example,
have proved by no means successful in establishing sub-divisions;
and the only effect of such a proceeding is to encumber the subject
with a number of generic names without eliciting a more philosophical
arrangement, or one better adapted to aid the student. As at present
constituted, the genus is compact and natural; and if it were broken
up by attaching undue importance to very subordinate characters, no
partial change would suffice; for any principle that might be thought
to justify the establishment of one genus, would render it necessary,
if consistently acted upon, to create not fewer than thirty or forty.
One of the most obvious differences among the species is the presence
or absence of a tail; but an arrangement founded on this circumstance,
separates, by a wide interval, kinds which are in other respects most
closely allied. Nay, the tail itself is often more or less developed
in the same species, being sometimes distinct in the one sex while it
is inconspicuous or wanting in the other; its value as a diagnosis of
genera is thus in a great measure destroyed.
Considerable differences likewise prevail in the appearance of the
caterpillars, but these are too imperfectly known to be made the
groundwork of an arrangement, even if they were likely to be available
for such a purpose by indicating natural groups or affording additional
means of characterising them. “Some of them,” says Dr. Boisduval,
“such as those of _Machaon_, _Alexanor_, _Asterias_, are cylindrical
and smooth; others (_Crassus_, _Philenor_), are protected with rather
long fleshy prominences; in a very great number (_Pammon_, _Memnon_,
_Chalchas_, &c.) the two first segments are attenuated, and capable
of being retracted under the third and fourth, which are dilated and
often ornamented with ocular spots analogous to those presented by
many of the _Sphingides_; others are short and thick, and furnished
with numerous rather short fleshy points; finally, there are some
(_Podalirius_, _Ajax_, _Antiphates_) which somewhat resemble snails
in shape. The caterpillars of _Papilio_ may be distinguished from
those of other genera belonging to the same tribe by the following
characters:--They differ from those of _Ornithoptera_ in their
retractile tentaculum not being enclosed in two exterior cases; from
those of _Thais_, in the projections which they sometimes present being
never hispid at the extremity; and from those of _Parnassius_, in the
body being always free from pubescence; but it is more particularly
from the characters drawn from the chrysalis and perfect insect that
this last genus is distinguished from _Papilio_[29].”
The perfect insects are characterised by very short palpi not passing
beyond the eyes, all the joints very indistinct, the third quite
invisible; antennæ pretty long, the club slightly curved upwards;
abdomen pretty large, the anal valves in the male of moderate size;
wings rather strong, the inferior pair having the abdominal margin
folded upwards and leaving the abdomen free, their exterior border more
or less dentated, and often prolonged posteriorly into a tail.
According to the above definition, the genus comprehends rather upwards
of 220 species. They are distributed over almost every quarter of the
globe, but are by far most abundant in intertropical countries. They
are more numerous in the new continent than the old, but the difference
is by no means considerable. In the former, Brazil alone produces
between forty and fifty species; in the latter, the greatest number
occur in the islands of the Indian Archipelago, already referred to as
the native country of the magnificent Ornithoptera. The continental
parts of India, China, Java, &c. likewise possess many fine species,
and a few are found in New Holland. Europe is exceedingly poor in
insects belonging to this group, there being only four indigenous
kinds. These are _P. Xuthus_, _P. Alexanor_, _P. Machaon_, and _P.
Podalirius_; the two latter, which are the most common, are well known
to extend to Britain.
The first species selected to exemplify one of the prevailing forms of
this important genus, is
[Illustration: