Fig. 211—Pupa of Micropteryx (semipurpurella?). A, Dorsal aspect; B, C, D, views of head dissected off; B, profile; C, posterior, D, anterior aspects; m, mandibles. Britain.
There are no mandibles, but there is a short, imperfect proboscis. Larva (Fig. 210) without any legs, mining in leaves. The pupa (Fig. 211) is not a pupa obtecta, but has the head and appendages free, and is provided with enormous mandibles. Although these Insects in general appearance resemble Eriocephala to such an extent that both have been placed in one genus, viz. Micropteryx, yet the two forms are radically distinct. The most remarkable point in Micropteryx is the metamorphosis; the female moth is furnished with a cutting ovipositor, by the aid of which she deposits an egg between the two layers of a leaf after the manner of a saw-fly;[[342]] the larva mines the newly-opened leaves in the early spring, and feeds up with rapidity; it by some means reaches the ground, and there pupates in a firm but thin cocoon, with grains of earth fastened to it; in this it passes the greater part of its life as a larva, changing to a pupa very early in the following spring. The pupa is unlike any other Lepidopterous pupa, but is similar to those of Trichoptera; neither the head nor the appendages are glued to the body or to one another, but are free, so that the pupa can use the appendages to a considerable extent; it is furnished with enormous mandibles (Fig. 211, C, D), which are detached and shed after emergence.[[343]] In the interval between the larval period of feeding and the imaginal instar, the phenomena of life are essentially like those of Trichoptera. The larva has not been at all satisfactorily studied; the spiracles appear to be excessively minute, but have been ascertained by Dr. Chapman to be normal in number and position.
All the information we possess points to profound distinctions between Micropteryx and Eriocephala, for whereas in the former the mandibles drop off from the pupa, so that the imago has no mandibles, in the latter the mandibles exist, as they do in several other true Lepidoptera. As the history of the mandibles is not known in other Lepidoptera (where they are present in the larva but wanting in the imago), it is premature to conclude that no other Lepidoptera suffer the actual loss of the mandibles as Micropteryx does, though there is nothing to lead us to believe that in any other Lepidopterous pupa are the mandibles specially developed as they are in Micropteryx. This pupa is in fact quite unique in this Order of Insects. When the history of the pupal mandibles is known, we shall be able to decide whether they are secondary structures, like the deciduous, supplementary mandibles found in Otiorhynchides (Coleoptera, Rhynchophora).
CHAPTER VII
DIPTERA—OR FLIES; APHANIPTERA—OR FLEAS; THYSANOPTERA—OR THRIPS
Order VII. Diptera
Wings two, membranous, usually transparent and never very large; behind the wings a pair of small erect capitate bodies—halteres—frequently concealed under membranous hoods. No distinct prothorax, all the divisions of the thorax being united to form a large mass. Mouth-parts very variable, formed for suction not for biting, frequently assuming the form of a proboscis that can be retracted and concealed in a cleft of the under side of the head. The metamorphosis is very great, the larvae bearing no resemblance whatever to the perfect Insects, but being usually footless grubs or maggots; frequently the head is indistinct, small, and retracted. Pupa variable, either exposed and rather hard, with the appendages of the body more or less adherent; or enclosed in a scaly capsule looking like a seed, and when extracted, soft and delicate, with the appendages not fastened to the body incapable of movement.
This definition of the Diptera, or two-winged flies, is framed without reference to the fleas, which are wingless, or to a few other parasitic wingless Diptera, such as the sheep-tick. Although the Order is of enormous extent, these exceptional cases are remarkably few. About 40,000 species of Diptera have been discovered, but these are only a tithe of what are still unknown to science. The Order is not a favourite one with entomologists, and by the rest of the world it may be said to be detested. Flies do not display the sort of intelligence we appreciate, or the kind of beauty we admire, and as a few of the creatures somewhat annoy us, the whole Order is only too frequently included in the category of nuisances that we must submit to. Moreover, the scavenger-habits that are revealed, when we begin to study their lives, are very repugnant to many persons. It is therefore no wonder that flies are not popular, and that few are willing to study them, or to collect them for observation. Nevertheless, Diptera have considerable claims to be classed as actually the highest of Insects physiologically, for it is certainly in them that the processes of a complete life-history are carried on with the greatest rapidity and that the phenomena of metamorphosis have been most perfected. A maggot, hatching from an egg, is able to grow with such rapidity that the work of its life in this respect is completed in a few days; then forming an impenetrable skin it dissolves itself almost completely; solidifying subsequently to a sort of jelly, it in a few days reconstructs itself as a being of totally different appearance and habits, in all its structures so profoundly changed from what it was that the resources of science are severely taxed to demonstrate any identity of the organs of the two instars.
