. Civic biology; textbook of problems, local and national, that can be solved only by civic coöperation. Biology. 266 Ci\ iC JUOLOGY forms may be direct (that is, worm, egg, worm in the same host) or it may require two or even three hosts for its com- pletion. The sexes axe usually distinct. Typical nematode parasites are Roundworm—Ascaris lumbricoides. This is the most coninion para- site of iiiau; it is reddish-yellow, resembles the earthworm in general shape, and may attain a length of from 12 to 15 inches. It lives in the small in- testine, and, being unattached, is easily dislodyed. The l
. Civic biology; textbook of problems, local and national, that can be solved only by civic coöperation. Biology. 266 Ci\ iC JUOLOGY forms may be direct (that is, worm, egg, worm in the same host) or it may require two or even three hosts for its com- pletion. The sexes axe usually distinct. Typical nematode parasites are Roundworm—Ascaris lumbricoides. This is the most coninion para- site of iiiau; it is reddish-yellow, resembles the earthworm in general shape, and may attain a length of from 12 to 15 inches. It lives in the small in- testine, and, being unattached, is easily dislodyed. The life cycle is direct, the eggs being taken in with polluted water or dirty foods. Since they have been found to pass through flies uninjured, these insects are thought to be one of the active means of distributing the euus to human foods. Pinworm — Oxyuris vermicularis. This is a minute nematode, from 4 to 12 mil- limeters long, that affects children the world over. Its life cycle is direct. Gape worm — Syngamus trachealis. The habitat of this parasite is tlie trachea or bronchi of birds. The male is smaller than and permanently attached to the female, and the eggs are not laid, but are set free by the disintegration of the mother in the soil. Here they hatch in about a week, in warm weather, the eml>ryos are picked up by the l)irds, and the direct life cycle is repeated. Trichina worm — Trichinella spiralis. The presence of this parasite in man causes the well-known disease trichinosis', and our constantly re- curring epidemics prove that, with all the publicity given to the matter, we have not reached a solution of the problem. Has proper attention been directed to extermination of rats from premises where swine are raised? The course of infection is indicated in Fig. 119. The adult worm, the size of a very fine hair 2-4 millimeters long, lives in the wall of the small intestine, where the female gives birth to from 1000 to 1500 ^. Fig. 118. Gapeworms, female with
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