. Fresh-water biology. Freshwater biology. AQUATIC INSECTS 913 ceridae) live in rapid streams, and are peculiar in the very strongly depressed form of both larva and pupa, and in the row of ventral sucking discs which the larva has developed for hanging fast. The black-flies (Simuliidae) also live in running water. The larvae adhere to stones and timbers by a single sucking disc at the hinder end of the flask-shaped body, which thus hangs sway- ing in the current with head downstream. Above the mouth on the front of the head there are two processes which bear the name of "; Thes
. Fresh-water biology. Freshwater biology. AQUATIC INSECTS 913 ceridae) live in rapid streams, and are peculiar in the very strongly depressed form of both larva and pupa, and in the row of ventral sucking discs which the larva has developed for hanging fast. The black-flies (Simuliidae) also live in running water. The larvae adhere to stones and timbers by a single sucking disc at the hinder end of the flask-shaped body, which thus hangs sway- ing in the current with head downstream. Above the mouth on the front of the head there are two processes which bear the name of "; These are composed of a very large number of scythe-shaped rays fringed along the side. Set at an angle upon the pedicel, hke the fingers of a reaper's cradle upon the handle, together these constitute - —.^ a net for retaining small organisms adrift ''fory'disc It'Vsrie-flyTa™; in the water, and for holding them up to setedon. the mouth. This is an aboriginal plankton apparatus. Simulium larvae play in the rapids, spinning silken threads in the water, and swinging on them from place to place. Occasionally the threads thus spun in the troughs of fish hatcheries have been sufficiently numerous to entangle and kill newly hatched trout. These threads are spun from the saUvary glands; a final use for the secretion of these glands is the making of the open-meshed half-cornucopia- shaped cocoon in which, attached to the sides of the rocks or tim- bers, the pupal stage is passed; a branched prolongation of the tracheal lining of the prothoracic spiracles constitutes the so-called "tube gills," by means of which the black-fly pupa is able to get its air supply while wholly submerged. The soldier flies (Stratiomyiidae) live as larvae on the surface of still water. They float stiff and rigid and stick-like, with a circlet of water-repellent bristles surrounding the terminal spiracles, keep- ing open the way to the air. The pupa is formed within the larval skin, without further
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectfreshwa, bookyear1918
