. The animans and man; an elementary textbook of zoology and human physiology. FIG. 206. Trichina spiralis, encysted in muscle of a pig. (Greatly en-larged.) be taken into the body of some other animal. In thecase of one of several species infesting man this second hostis the pig. In the alimentary canal of the pig the youngtapeworm develops, to bore its way later through the wallsof the canal and become imbedded in the muscles. There it ANIMAL PARASITES AND DEGENERATION 415 lies until the diseased flesh containing it is eaten (withoutbeing perfectly cooked), and thus it finds its way into the
. The animans and man; an elementary textbook of zoology and human physiology. FIG. 206. Trichina spiralis, encysted in muscle of a pig. (Greatly en-larged.) be taken into the body of some other animal. In thecase of one of several species infesting man this second hostis the pig. In the alimentary canal of the pig the youngtapeworm develops, to bore its way later through the wallsof the canal and become imbedded in the muscles. There it ANIMAL PARASITES AND DEGENERATION 415 lies until the diseased flesh containing it is eaten (withoutbeing perfectly cooked), and thus it finds its way into thealimentary canal and thence into the intestine ofman. It now continues to develop until it becomesfull grown. Many animals are infested by minute parasites belongingto the Protozoa or one-celled animals. The class Sporozoaof the Protozoa is composed almost exclusively of parasiticspecies living in the blood, liver, alimentary canal, and. FIG. 207. Tape worm; the head, magnified, at left; the whole wormmay be several yards long. (After Lenckart.) other organs and tissue of animals. Over seven hundredand fifty kinds of these Sporozoan parasites have been de-scribed. Some of them, as has already been told in Chap-ter XII are parasites of the human body causing terribleinfectious diseases among us. Parasitic insects.—Among the insects many live as para-sites during their immature or larval life, but as adults 416 THK ANIMALS AND MAN are free and independent creatures. From the chrysalidof a butterfly or moth there will often come not a butterflybut numerous tiny four-winged gnats, called ichneumonflies. This is what happened. When the butterfly cater-pillar was crawling about a female ichneumon darted downon it, and with her sharp ovipositor either laid several eggsbeneath its skin or glued them to its outer surface. Theseeggs hatched in two or three days as tiny white ichneumongrubs, which immediately burrowed deep int
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