INSECTS
them to pursue, and which they capture by means of grasping hooks on the end of their extraordinarily long underlip (Fig. 134 A), which can be shot out in front of the head (B). The great swampy lakes of Paleozoic times must have furnished an ideal habitat for dragonflies, and it is probable that the most ancient dragonflies known had a structure and habits not very different from those of modern species.
Fig. 59. A young dragonfly, an aquatic creature that leaves the water only when ready to transform into the adult (fig. 58)
Another very common insect of the present time, which appears likewise to be a direct descendant of Paleozoic ancestors, is the mayfly (Fig. 60). The young mayflies (Fig. 61) also live in the water, and are provided with gills for aquatic breathing, having the form of flaps or filaments situated in a row along each side of the body. The adults (Fig. 60) are very delicate insects with four gauzy wings, and a pair of long threadlike tails projecting from the rear end of the body. At the time of their transformation they often issue in great swarms from the water, and they are particularly attracted to strong lights. For this reason large numbers of them come to the cities at night, and in the morning they may be seen sitting about on walls and windows, where they find themselves in a situation totally strange to their native habits and instincts. The mayflies do not fold their wings horizontally, but when at rest bring them together vertically over the back (Fig. 60). In this respect they, too, appear to preserve a character of their Paleozoic ancestors; though it must be observed that the highly evolved modern butterflies close their wings in the same fashion.
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