Although such endless diversity of colouring is observable in this class as a whole, it is, at the same time, worthy of remark, that most of the principal groups are characterized by the prevalence of particular hues, as well as considerable uniformity in their mode of distribution; that is to say, certain modifications of structure are generally accompanied with a certain pictorial design. Thus, the greater proportion of the genus _Pieris_ are white; _Colias_ and _Callidryas_ various shades of yellow, from the palest sulphur-yellow to deep reddish-ochre. _Argynnis_ is almost invariably fulvous or reddish brown, variegated with numerous undulating black lines or spots; the under side more or less ornamented with silvery streaks and spots. In the species of the European genus _Thais_, the wings are spotted or chequered with black and red. The prevailing colour in the genus _Argus_ is azure-blue. _Danais_, _Idæa_, and _Euplœa_, have this character in common, that the breast and head are always punctured with white. In _Cethosia_, hieroglyphical markings cover the under side of the wings in such a manner as is observable in no other genus. Many of the caterpillars of exotic butterflies offer peculiarities in their forms and appendages, of which we find no prototype in the kinds occurring in Britain. In the place of spines, some have the body thickly covered with long fleshy prominences, of a corneous consistency at the tip, and probably serving as a means of defence. In others, spines of singular conformation and formidable size are thickly stuck over the whole surface, making it resemble a miniature forest. A few are provided with a long anal horn, resembling that which is so conspicuous in the caterpillars of the Sphinges. If Madam Merian’s delineation of the larva of _Urania Leilus_ be correct (which there is now reason to believe is the case), it bears many slender spines, as long as the whole body, and as stiff as iron wire. Another species (that of _Papilio Protesilaus_), is likewise clothed with plumose spines, two of which at the hinder extremity are much longer than the rest, and terminate in an appendage like a star. Equally remarkable with any of these is the caterpillar of one of the Nymphalidæ (_Adoleas Aconthea_), which has a series of long filiform bodies projecting from each side, thickly clothed laterally with hairs of considerable length diminishing gradually to the extremity, which is armed with a few minute spines.