. Animal parasites and human disease. Insects as carriers of disease; Medical parasitology. 408 FLEAS The exact identification of fleas, especially if the host is un- known, is difficult, being based largely on such minute charac- teristics as relative lengths of different segments of the legs, number and distribution of spines, etc. Most species of fleas, however, are quite closely confined to their respective hosts, only a few species being able to thrive on a number of different hosts. Some of the commoner species of the fleas which are of most im- portance to man can be fairly closely iden
. Animal parasites and human disease. Insects as carriers of disease; Medical parasitology. 408 FLEAS The exact identification of fleas, especially if the host is un- known, is difficult, being based largely on such minute charac- teristics as relative lengths of different segments of the legs, number and distribution of spines, etc. Most species of fleas, however, are quite closely confined to their respective hosts, only a few species being able to thrive on a number of different hosts. Some of the commoner species of the fleas which are of most im- portance to man can be fairly closely identified, if the host and geographic locality is known, by the presence or absence of the " combs " on the head and thorax. The common human flea, Pulex irritans (Fig. 179A), and the Indian rat flea, Xenopsylla cheopis (Fig. 177), have no combs, the common rat and squirrel fleas of temperate climates (Figs. 179C and 178) have only the thoracic comb, while the cat and dog fleas (Fig. 179B) have both facial and thoracic combs. Life History and Habits. — The life history of all fleas is quite similar. Like the Diptera, or flies, they pass through a complete metamorphosis, , undergo a complete reorganization from larval to adult form during a resting pupal stage. The eggs are oval, whitish in color and relatively large, often one-third the length of the parent flea, and are laid singly, except in the chiggers, being dropped at random in the fur of the host or in the lairs or habitations of the hosts. The human flea, for instance, lays its eggs in the dust and debris in cracks in floors, under carpets, etc., whereas the fleas of most mammals lay their eggs loosely in the fur of the host, whence they drop off when the animal shakes himself or prepares to sleep. The time required for the eggs to reach the hatching stage varies with the species and with climatic conditions from two or three days to over two weeks. The larvae (Fig. 180) are tiny cylindrical maggot-like cre
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmedical, bookyear1918
