[LETTER XXXI.]
STATES OF INSECTS.
PUPA STATE.
We have now traced our little animals through their egg and larva states, and have arrived at the third stage of their existence, the Pupa State. This, to include all, can only be defined,—that state intervening between the larva and imago, in which the parts and organs of the perfect insect, particularly those of sex, though in few cases fully developed, are prepared and fitted for their final and complete development in the last-mentioned state; and in which the majority of these animals are incapable of locomotion, or of taking food.
Pupæ, like larvæ, may be separated into two great divisions:—
I. Those which, in general form, more or less resemble the larvæ from which they have proceeded.
II. Those which are wholly unlike the larvæ from which they have proceeded.
I. To the first division belong, with some exceptions[562], the Dermaptera, Orthoptera, Hemiptera, and most Aptera, with the neuropterous tribes of Libellulina, Ephemerina, and the genus Termes, in the class Insecta; and the majority of the Arachnida. This, like the first division of larvæ, may be subdivided into two corresponding smaller sections; the first including those pupæ which resemble the larvæ, except in the relative proportion and number of some of their parts; and the second those that resemble them, except in having the rudiments of wings, or of wings and elytra.
i. The first subdivision will include the pupæ, if they may be so called[563], of insects of the Aptera order, and of the class Arachnida: as, lice, Poduræ, Lepismidæ, centipedes, millipedes, mites, harvest-men, spiders, scorpions, &c. These mostly differ from their larvæ only in that the relative length or number of their legs, the number of the segments of the body in some, or the development of their palpi, more nearly approach the characters of the perfect insect; and in that while in their larva state they have two or more skins to cast, previously to their assumption of the imago, in their pupa state they have but one. In fact, this last circumstance is the only one which, strictly speaking, characterizes the pupæ of this subdivision; as the changes which take place in the number and proportion of the organs are partly produced with each change of the larva's skin. And hence, as it is not easy to ascertain what number of skins a spider, for example, has yet to cast, and as both the larva and pupa differ so little from the perfect insect, it is very difficult to determine in what state insects of this division are. From this difficulty has probably arisen the too great multiplication of species in some of these tribes, particularly the Arachnida, the larva and pupa having been mistaken for perfect insects. The pupæ of this subdivision were named by Linné complete, from the near resemblance which they bear to the imago.