Page:Popular Science Monthly Volume 53.djvu/676

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IT seems an incontrovertible fact in natural history that there is not a single character which has been used to distinguish any group of considerable extent from which some one or more of the members thereof may not depart. In that great division of the animal kingdom characterized by the possession of articulated limbs, many species are met which are entirely wanting in those organs, and, similarly, the secondary division of the Annulosa, marked by the presence of wings in the final state—the Ptilota of Aristotle—contains species that, throughout life, never acquire instruments of flight. Of wingless insects, indeed, examples might be drawn from most of the orders, and in the majority of cases the females only are thus deprived. Rarely, however, both the great characteristics are absent. Yet certain moths do not possess articulated feet in the wingless state.

Consequently, if we took into consideration merely the adults of these females, this group must be regarded as among the most degraded instances of apiropodous insects. But such a conclusion can not be maintained, as shown by an examination of the early stages of the moths, for these, we find, exhibit as high an amount of organization as those of any of the other insects appertaining to the order. The truth is, these females have become degenerate—very different from the creatures they once were. Their peculiarity consists in this, that whereas, as a whole, winged insects always undergo a gradual evolution of structure, by which ultimately legs and wings are developed, these individuals gradually lose their powers of evolution, and not only this, but suffer a process of deterioration, by which the limbs which they at first possess diminish, and at length dwindle altogether away, until the animal becomes a mere short, inert vermiform bag, having not only no distinct trace of legs and wings, but also the sense-organs, the antennæ, and the organs of the mouth are almost or entirely obliterated, and even the articulated condition of the body has almost disappeared. In these extreme forms it is hardly possible for the degeneration of the female to proceed further, and in all, doubtless, the change has occupied an immense period.

Than these extraordinary moths, familiar to German entomologists under the name of Sackträgers, perhaps no more curious and interesting examples occur among the whole of the insect races; certainly in structure of the female, and in habit, they are the strangest and most abnormal of all Lepidoptera. They belong to the Psychidæ,