Title: Elements of biology; a practical text-book correlating botany, zoology, and human physiology
Identifier: elementsofbiolog00hunt (find matches)
Year: (c1907) ((c10s)
Authors: Hunter, George William, 1873-1948
Subjects: Biology
Publisher: New York, American book company
Contributing Library: NCSU Libraries
Digitizing Sponsor: NCSU Libraries

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WORMS 213
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to the shore of the pond, and encyst themselves in the grass near its border. If this grass is eaten by sheep, the encysted larvje (called cercarice) are taken into the digestive tract and then develop into adult hukes. Cestodes or Tapeworms.— These parasites infest man and many other vertebrate animals. The tapeworm (Tcenia solium) passes through two stages in its life history, the first within a pig, the second within the intestine of man. The eggs of the worm are taken in with the pig's food. The worm develops within the intestine of the pig, but soon makes its way into the muscles. If man eats pork containing these worms, he may become a host for the tapeworm. The animal, which at this stage consists of a round headlike part provided with hooks, fastens itself to the wall of the intestine. This head now buds off a series of segmentlike structures, which are practically bags full of eggs. These structures, called proglottids, break off from time to time, thus allowing the eggs to escape. The proglottids have no separate digestive systems, but the whole body surface, bathed in digested food, absorbs it and is thus enabled to grow rapidly. Roundworms. — Still other wormlike creatures called round- worms are of importance to man. Some, as the vinegar eel found in vinegar, or the pinworms parasitic in the lower intestine of man, do little or no harm. The pork worm or Trichina, however, is a parasite which may cause serious injury. It passes through the first part of its existence as a parasite in a pig or other verte- brate (dog, cat, ox, or horse), where it encysts itself in the muscles Development of the liver fluke; A, ciliated larva; B, sporocyst, containing new sporocyst (r), and redia(m.); C, redia, containing daughter rediaand tadpolelike cercaria; D, fully developed cercaria.

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