. Fresh-water biology. Freshwater biology. 902 FRESH-WATER BIOLOGY lakes into deep water. The gills of the caddisfly larvae are always of the filamentous type, never lamelhform. They are wanting in members of several famiUes, and are variously disposed about the body, singly or in clusters, in many others; their number, form, and arrangement furnish group recognition characters. The more typical caddisworms, having their gill filaments along the sides of the abdomen completely inclosed within the case, keep water flow- ing through by means of continual undulating motion of the abdo- men; three
. Fresh-water biology. Freshwater biology. 902 FRESH-WATER BIOLOGY lakes into deep water. The gills of the caddisfly larvae are always of the filamentous type, never lamelhform. They are wanting in members of several famiUes, and are variously disposed about the body, singly or in clusters, in many others; their number, form, and arrangement furnish group recognition characters. The more typical caddisworms, having their gill filaments along the sides of the abdomen completely inclosed within the case, keep water flow- ing through by means of continual undulating motion of the abdo- men; three tubercles at the base of the abdomen and a pair of stout prolegs at its apex serve to keep the walls properly spaced for the admission and the flow of the water. The case is always large enough so the larva can entirely withdraw itself inside. By this means it doubtless escapes from many enemies. But some of the larger fishes, as, for example, brook trout, eat case and all. The pupa of caddisflies is peculiar in that it also is aquatic. It is formed within the larval case or tube, the larva closing the apertures with a perforate web of silk before its final moulting; this web admits water for respiration, but keeps out enemies. True tracheal gills, of the same type as those possessed by the larvae, are present on the pupae of many caddisflies. All the pupae are more or less active; some maintain constant undulating move- ments of the abdomen to keep the water circulating, and at the close of the pupal stage all work their way out of the larval case, and swim to the surface of the water to imdergo their final trans- formation. In the case of species that inhabit swift waters and transform in the current, this takes place very quickly, the adidt emerging instantly on reaching the sur- face and fljdng away at once. Although the adults have Jaws of the most rudi- mentary sort, the mandibles of the pupa are often large and conspicuous; they are supposed to be of use in cutting a wa
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectfreshwa, bookyear1918
