AND OTHER ANCIENT INSECTS
character, though nota distinctive one, since rnodern dragonflies (Fig. 58) and rnayflies (Fig. 60) likewise keep the wings extended when at test. The question of how insects "acquired wings is always one of special interest, since, while we know perfectly well that the wing of a bird or of a bat is rnerely a rnodi- fied fore lirnb, the nature of the primitive organ from which the insect wing bas been evolved is still a rnystery. The Paleodictyoptera, however, may throw light upon the subject, for sorne of thern had srnall fiat lobes on the lateral edges of the back plate of the prothorax, which in fossil specirnens look like undeveloped wings (Fig. 56). The presence of these prothoracic lobes, occurring as they do in sorne of the oldest known insects, bas suggested the
56. Examples of the earliest known fossil insects, called the Paleodic- tyoptera, having small lobes (a) projecting like wings from the prothorax 8tenodictya lobata (from Brongniart). B, EuMeptus danielsi (drawn from specimen in U. S. Nat. Mus.): TI, T,, Ta, back plates of three thoraclc segments
idea that the true wings were evolved from similar flaps of the rnesothorax and rnetathorax. If so, we rnust pic- ture the irnrnediate ancestors of the winged insects as creatures provided with a row of three flaps on each side of the body projecting stiffly outward from the edges of the thoracic segrnents. Of course, the creatures could not actually fly with wings of this sort, but probably
[9']
INSECTS
