The head of the larvæ of most species is wide and flattened. The eyes are situated at the sides, and just in front of them is a pair of short antennæ which vary with the different species. The mouth-parts too vary greatly according to the feeding habits. Some mosquito larvæ are predaceous, feeding on the young of other species or on other insects. These of course have their mouth-parts fitted for seizing and holding their prey. Most of the wrigglers, however, feed on algæ, diatoms, Protozoa and other minute plant or animal forms which are swept into the mouth by curious little brush-like organs whose movements keep a stream of water flowing toward the mouth. Another group containing the _Anopheles_ are intermediate between these two and have mouth-parts fitted for feeding on minute organisms as well as for attacking and holding other larger things. [Illustration: FIG. 55--Eggs, larvæ and pupæ of mosquitoes (_T. incidens_).] [Illustration: FIG. 56--Larva of mosquito (_T. incidens_).] [Illustration: FIG. 57--Mosquito larvæ and pupæ (_T. incidens_) with their breathing-tubes at the surface of the water.] [Illustration: FIG. 58--Anopheles larvæ (_A. maculipennis_) resting at the surface of the water.] A few kinds feed habitually some distance below the surface, others on the bottom, while still others feed always at the surface. With one or two exceptions, the larvæ must all come to the surface to breathe (Figs. 53-57). Most species have on the eighth abdominal segment a rather long breathing-tube the tip of which is thrust just above the surface of the water when they come up for air. In this tube are two large vessels or tracheæ which open just below the tip of the tube and extend forward through the whole length of the body, giving off branches here and there that divide into still smaller branches until every part of the body is reached by some of the small divisions of this tracheal system that carries the oxygen to all the tissues. The length of the breathing-tube is correlated with the feeding-habits of the larvæ. _Anopheles_ larvæ which feed at the surface have very short tubes (Fig. 58), others that feed just below the surface have breathing-tubes as long or very much longer than the ninth abdominal segment. The last segment has at its tip four thin flat plates, the tracheal gills. These too are larger or smaller according to the habits of the larvæ. Those species that feed close to the surface and have the tip of the breathing-tube above the surface most of the time have very small tracheal gills, while those that feed mostly on the bottom have them well developed.