Page:Insects - Their Ways and Means of Living.djvu/390



the body segments project laterally groups of long hairs, some of which are branched in certain species. The rear end of the body appears to be forked, being divided into an upper and a ]ower branch. The

Fm. 7- Structure of a Culex mosquito larva a, mouth brushes; abdomen; Ant, antenna; b» eye; c, respiratory tube; d, terminal lobes; H, head; " P8p, posterior spiracle; TA, thorax; Tra, dorsa tracheal trunks

upper branch (c), however, is really a long tube projecting dor- sally and backward from the next to he last segment. The lower branch is the true terminal seg- ment of the body and bears the anal opening of the alimentary canal at its extremitv. On the end of this segment ur long, trans- parent flaps project laterally (d), tso groups of long hairs are situ- ated dorsally, and a fan of hairs ventrally (.Fig. 174 E. The principal characteristic of the mosquito larva is the speciali- zation of its respiratory system. The larva breathes through a single large aperture situated on the end of the dorsal tube that projects from the next to the last segment of the body (Fig. 175, PSp). This orifice opens by two mner spiracles into two wide tracheal trunks (Tra) that extend forward in the body and give off branches to all the internal organs.

The mosquito larva, therefore, can breathe only when the tip of its respiratory tube projects above the surface of the water, and, though an aquatic creature, it can be drowned by long submergence. Yet the provision for breathing at the surface has a distinct advantage: it renders the mosquito larva independent of the aeration of the water it inhabits, and allows a large number of larvae to thrive

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MOSQUITOES