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140 suspended by cold and accelerated by warmth. In some species the eggs remain dormant throughout the winter or through a long term of dry weather, but in ordinary circumstances the larvæ hatch out in from two to three days, and at once proceed to feed voraciously on the organic materials suspended in the water. Being air-breathers, a great part of their time is passed at the surface of the water, where they lie in such a position which varies with species that the respiratory opening placed near the tail can function readily (Figs. 27, 28). After the several moultings the larva, now very much increased in size, passes to the nymph or pupa phase (Fig. 29), during which the little animal ceases to

feed, and for the most part floats just awash at the surface of the water. In from one to two days the pupa-case bursts and the insect, emerging, stands on the empty case till its wings have dried, when it flies away. From first to last, from egg to imago, the process of development takes about a month in the temperature of the Italian summer; but a much shorter time (seven to ten days) may suffice in a tropical climate. As each female mosquito may lay eggs many times in a season, and many hundreds of eggs each time, and as the young female can produce eggs within a week or ten days after her emergence from the pupa-case, it follows that one pair of insects can give rise to a large progeny in the course of a summer.

During cold weather the development of the larva is temporarily suspended, and the surviving adults,