AND FLIES
mosquito to lay her eggs upon the surface of the water, and that the larvae come from the eggs. There are many species of mosquitoes, but, from the .standpoint of human interest, most of them are included in three groups. First there are the "ordinary" mos- quitoes, species of the genus Culex or of related genera; second, the yellow-fever mosquito, dëdes aegypti; and third, the malaria-carrying mosquitoes, which belong to the genus dnopheles. The common Culex mosquitoes (Fig. I74 A) lay .their eggs in small, fiat masses (C) that float on the surface of the water. Each egg stands on end and is stuck close to its neighbors in such a manner that the entire egg mass has the form of a miniature raft. Sometimes the eggs toward the margin of the raft stand a little higher, giving the mass a hollowed surface that perhaps decreases the chance of accidental submergence, though the raft is buoved up from below by a film of air beneath the eggs. A]most any body of quiet water is acceptable to the Culex mosquito as a receptacle for her eggs, whether it be a natural pond, a pool of rainwater, or ?vater standing in a barrel, a bucket, or a neglected tin can. Each egg raft contains two or three hundred eggs and sometimes more, but the largest raft seldom exceeds a fourth of an inch in longest diameter. The eggs hatch in a very short time, usually in less than twenty-four hours, though the in- cubation period may be prolonged in cool weather. The young mosquito larvae come out of the lower ends of the eggs, and at once begin an active lire in the water. The body of the young mosquito larva is slender and the head proportionately large (Fig. 174 D). As the creature becomes older, however, the thoracic region of the body swells out until it becomes as large as the head, or finally a little larger (E). The head bears a pair of lateral eyes iFig. 175, b), a pair of short antennae (dnt), and, on the ventral surface in front of the mouth, a pair of large brushes of hairs curved inward (a). From the sides of
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INSECTS
