. Animal parasites and human disease. Parasites; Medical parasitology; Insects as carriers of disease. 480 OTHER BLOOD-SUCKING FLIES e/e — first segment (Fig. 222 prol.) is used for creeping, in conjunction with the posterior sucker, the larva looping along like a " meas- uring worm"; it is also of use in constructing the silken cocoon from the secretions of the salivary glands. This single little leg has a crown of tiny hooklets which make it possible for the possessor to hold its ground even in a torrent of water. The salivary glands referred to are quite unlike those of other inse
. Animal parasites and human disease. Parasites; Medical parasitology; Insects as carriers of disease. 480 OTHER BLOOD-SUCKING FLIES e/e — first segment (Fig. 222 prol.) is used for creeping, in conjunction with the posterior sucker, the larva looping along like a " meas- uring worm"; it is also of use in constructing the silken cocoon from the secretions of the salivary glands. This single little leg has a crown of tiny hooklets which make it possible for the possessor to hold its ground even in a torrent of water. The salivary glands referred to are quite unlike those of other insects, in that they extend clear back to the pos- terior end of the body (Fig. 222, sal. gl.). The fluid secreted hardens to silk at once on exposure to water, and is used not only in spinning the cocoon, but also in spinning anchoring threads and life-lines. According to Malloch, the larva when disturbed releases its holcf and floats downstream, holding by the" stumpy leg to a silken thread which is being spun out, and by means of which the insect later regains its former position. The larvae breathe by means of tiny gills which can be projected through a slit in the last segment of the abdomen (Figs. 221 and 222, an. g.). The larvae are never found solitary, as would be expected from the manner of laying eggs; the author has seen the boards dig. tr.,~ digestive tract; m. f., on the bottom of a log chute COm- rcto faa"d; ZLrtoft^Z Pletely covered with mosslike patehes posterior sucker; sal. gl., saii- of these larvae for areas of a square vary and spinning gland. yard Qr more After four or five weeks, in summer, the larvae prepare to go into the resting pupal stage, and spin for themselves a partial cocoon which is variously shaped like a jelly glass, slipper, wall pocket, etc., open at the upper end for the extrusion of the branching gill filaments which are used as breathing organs (Fig. 221C). Some species simply spin a snarl of threads, the work of a whole commun
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