. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. ITCH MITES —LIFE HISTORY 343 mite, but many of them can be transferred readily from one host to another. In the common human species the male is only about mm. (^ J^ of an inch) in length, while the female is about mm. {-^ of an inch) in length. A variety of this mite, S. scabiei crustosos, causing the so-called " Norwegian itch," is found in northern Europe and occasionally in the United States, but is always rare. The- disease caused by it differs in some re- spects from ordinary it
. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. ITCH MITES —LIFE HISTORY 343 mite, but many of them can be transferred readily from one host to another. In the common human species the male is only about mm. (^ J^ of an inch) in length, while the female is about mm. {-^ of an inch) in length. A variety of this mite, S. scabiei crustosos, causing the so-called " Norwegian itch," is found in northern Europe and occasionally in the United States, but is always rare. The- disease caused by it differs in some re- spects from ordinary itch. Still another species, Notoedres cati, which causes a very persistent and often fatal disease in cats, temporarily infests man, but is apparently unable to breed in human skin, since the infection dies out in the course of a week or two. The impregnated females of itch mites excavate tortuous tun- nels in the epidermis (Fig. 143) especially on such portions as. Fig. 143. Diagrammatic tunnel of itch mite in human skin, showing female depositing eggs. X about 30. (Adapted from Riley and Johannsen.) between the fingers and toes, on the groins and external genitals, and in the armpits, where the skin is delicate and thin. The tunnels are anywhere from a few millimeters to over an inch in length, and are usually gray in color from the eggs and excrement deposited by the female as she burrows. The eggs (Fig. 143) vary in number from 15 to 50. After they are all laid the female dies, having performed her duty in life. But there is no respite on account of her death, for in less than a week the eggs hatch into six-legged larvae. These live for about two weeks in the old burrow built for them by their mother, and during this time they indulge in three moults and undergo a metamorphosis which transforms them into nymphs similar in. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance o
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