140 



ELEMENTARY ZOOLOGY 



ducks, geese and chickens, for instance, are also infested 

 by tapeworms, and the intermediate hosts in these cases 

 are usually insects or small aquatic crustaceans like the 

 familiar Cyclops. 



Roundworms (Nemathelminthes) . TECHNICAL NOTE. 



Vinegar-eels from mouldy vinegar, and hair-worms from fresh- 

 water pools, can usually be readily obtained. They should be 

 examined, and drawings should be made of them, showing their 

 shape and simple external structural character. If a specimen of 

 trichinosed pork be obtained, the encysted stage of 

 the Trichina, described in the following account, can 

 be shown. 



The roundworms are slender, smooth, 

 cylindrical worms pointed at both ends. 

 They are all very long in proportion to their 

 diameter, although their actual length may 

 be short. Some species are of microscopic 

 size; as the Trichina worm, which is about 

 ^ in. long; while the guinea-worm, one of 

 the worst parasites of man, may reach a 

 length of six feet. Many of the round- 

 worms are parasites living in the various 

 organs of other animals. Some, however, 

 lead an independent free life in water or in 

 damp earth. 



Familiar examples of roundworms are the 

 so-called vinegar-eels (Anguilluld) (fig. 32) 

 to be found in weak vinegar, and other 

 species of this same genus which live in water 

 or moist ground or in the tissues of plants, 

 doing much injury. The hair-worms (Gor- 

 dius) or horse-hair snakes, which are believed 

 by some people, to be horse-hairs dropped 

 into water and turned into these animals, are 

 also familiar examples of roundworms. They 

 are often found abundantly in little pools after a rain, and 



FIG. 32. A 

 vinegar eel, 

 Anguiilula 

 sp. (From 

 a living 

 specimen.) 



