According to the definition which it has been found necessary to give
to this genus in general works on the lepidoptera, it includes a very
extensive range of species, and may be said to be represented in this
country by the white butterflies, which British authors generally
place in the genus _Pontia_. In this extended acceptation, however, it
comprehends individuals somewhat diversified in appearance, and which
may be assumed as the types of particular groups or sub-divisions,
perhaps of sufficient importance ultimately to become genera, if a
corresponding dissimilarity be found to characterise their different
states and metamorphoses. The antennæ are of moderate length or
slightly elongated, the articulations pretty distinct, the club obconic
and compressed; palpi thickly covered with fascicles of long hairs, the
terminal joint at least as long as the penultimate: wings of ordinary
size, the discoidal cell closed; the under pair partially embracing the
abdomen: eyes naked, head rather small.
The caterpillar is elongated, and nearly cylindrical, pubescent, and
marked with longitudinal rays; the head small and rounded. Chrysalis
terminating in a single conical point anteriorly, attached by the tail
and a medial band.
Not fewer than one hundred and sixty-six different kinds of butterflies
are referred to this genus. “They are diffused,” says Dr. Boisduval,
“nearly over the whole globe, but are particularly abundant in the
intertropical countries of the old continent. Considering the extent
of the New World, it produces comparatively few species. The most
remarkable inhabit Africa, the Indian continent and Archipelago,
and New Holland. Such of the caterpillars as are known, feed almost
exclusively on the _cruciferæ_, _residaceæ_, _tropioliæ_, and
_caparideæ_. Our _P. Cratægi_ is the only one in Europe which lives
on trees; but it is probable that many exotic kinds are of the same
habits. The prevailing colour among these lepidoptera is white, more or
less pure, with a black border, variable in width, but seldom wanting.
There are likewise species in which the ground colour is yellow or even
orange, while in others it is blackish or blue, &c. The inferior face
of the posterior wings generally differs considerably from the upper,
and is often very agreeably varied with brilliant colours. The sexual
differences, in certain species, are very conspicuous, particularly
on the surface; in others, they are much less so, the females being
distinguished from the males only by a somewhat wider border, or by
having the upper wings more rounded at the apex[32].”