ii. The second subdivision will include the pupæ of the Dermaptera, Orthoptera and Hemiptera orders, with few exceptions; as likewise the Libellulina, Ephemerina, and Termitina? amongst the Neuroptera: including the well-known tribes of earwigs, cockroaches, crickets, grasshoppers, locusts, lanthorn-flies, froghoppers (Cicada L.), bugs, plant-lice, dragon-flies, day-flies, white ants, &c. Of these, as in the former subdivision, the pupæ are equally capable of eating and moving with the larvæ, which they resemble, except in having the rudiments of wings, or of wings and elytra. The pupæ of the three orders first enumerated differ from those of the Neuroptera in resembling the perfect insect in most instances, both as to shape and the organs for taking their food; and in all other respects, except in not having their wings and elytra fully developed[564]. The resemblance of the pupæ of the Libellulina and Ephemerina to the perfect insects is more distant, and the above organs in the two states are very dissimilar; for the pupæ of the former are furnished with a prehensory mask similar to that of the larvæ before described[565], which the perfect insect has not; and those of the latter with the usual oral organs of masticating insects, of which the imago has scarcely the rudiments.
I have applied the term rudiments to the wings and elytra in this state, not in a strict sense, but merely to denote their appearance; for in fact the wings, &c. are complete, but only folded up longitudinally and transversely, and inclosed in membranous cases, which when the last change takes place remain attached to the puparium or pupa-case. The tegmina or hemelytra in this state usually cover the wings, and the upper wings the under; but in the Libellulina both are usually visible. Though commonly very small compared with the instruments of flight in the perfect insect, some of these rudiments, contrasted with the majority, are of considerable magnitude. This is the case with those of some species of Chermes, as we learn from De Geer[566].
II. The second grand division comprises by far the largest number of pupæ: those of all coleopterous, strepsipterous, lepidopterous, hymenopterous, dipterous, and aphanipterous, and by far the majority of neuropterous insects, as well as the hemipterous genus Aleyrodes, and one sex of Coccus of the same order. These pupæ, however, though agreeing in the circumstance of being unlike the larvæ from which they proceed, differ from each other in several respects, and require to be divided into three great sections, as under:—
i. Those pupæ in which the parts of the future insect, being folded up under a membranous skin closely applying to each, are distinctly visible. To this head belong generally, the pupæ of coleopterous[567] and hymenopterous insects; those of the neuropterous genera Myrmeleon and Hemerobius, &c.; the Trichoptera; amongst the Diptera, Culex, Tipula L., Tabanus, Bombylius, &c.; and that of the flea (Pulex). These were the incomplete pupæ of Linné.
ii. Those pupæ in which the parts of the future insect, being folded up under a harder skin, are less distinctly discoverable. To this subdivision belong the pupæ of all Lepidoptera, and of them alone. These are what Linné termed obtected pupæ.
iii. Those pupæ which are inclosed in the thick and opaque skin of the larva, through which no trace of the perfect insect can be discovered. These, which Linné termed coarctate pupæ, include a large proportion of the dipterous genera; as Œstrus L., Musca L., Empis L., Conops L., &c. &c.[568]
I shall next advert, chiefly to the pupæ of the grand division last described, under the distinct heads of substance, figure, and parts; colour, age, sex, motions, and extrication of the perfect insect.
i. As to their substance—at first interiorly all pupæ consist of a milky fluid, in which the unformed members of the future perfect insect may be said to float, and in which they may be discerned, and separated with the point of a pin[569]. In proportion as these acquire consistency, and are more and more developed by the absorption of the surrounding fluid, they occupy its place, and fill up the cavity of the puparium. The rest of this fluid passes off by transpiration[570]. Reaumur is of opinion that it is from the epiploon, or corps graisseux, that this matter is prepared, which he regards as analogous to the white of an egg[571]. In coarctate pupæ the included animal, or the pulp that contains its germes (in which the limbs and body at first are not discernible), fills at this period the whole skin-cocoon; but in proportion as the above evaporation takes place, and the consolidation of the body and parts proceeds, it shrinks at each end, so that when near assuming the imago, a considerable cavity appears both at the head and tail of the cocoon[572]. At this period of its existence, from the quantity of fluid included in the puparium, the animal weighs usually considerably more than it does when become a perfect insect[573].