NEMATHELMINTHES (Neo-Lat. nom. pl.. from Gk. vijpa, nilna, thread + nws. hr/min-c, worm). A large and important phylum of the unsegmented worms, of a more or less elon gated cylindrical form and known as 'round worms.' Their skin is thick and strong, and is usually wrinkled. giving the body a slightly annulated appearance, which. how ever, disappears if the animal is placed in water. Thr• nervous system in the higher forms consists of two lateral ganglia at the anterior extremity, which are united by a nervous ring. and from which two nervous trunks, one dorsal and one ventral, proceed to the posterior part of the holly. In the lower forms the dorsal cord is wanting. or else the ventral cord is wanting and there are two lateral cords. Special organs of sense are rarely met with lint a general sense of touch exists, and a few of the free-living spe cies have two simple eye-spots. The digestive organs are extremely simple. No blood system
our distinct respiratory or excretory organs can be detected. These worms are unisexual; but the males are comparatively rarely found, and are always smaller than the females. With the ex ception of the two families—the Enoplida., which are mostly marine forms, and the Anguillulhhe, or paste and vinegar eels—all the animals of this class are parasitic.
This phylum is divisible into three very distinct classes, namely, Acanthecephala, which have a protrusible proboscis armed with continuous hooks, and are destitute of an intestinal canal; the Gordiaeca, which possess an intestinal canal, but no anus; and the Nenzatoda, which usually possess a perfect intestinal canal, provided with two orifices. See A SCA RI s ; ENTOZOA ; EILARIA ; GUINEA-WORM; PINWORM; ROUNDWORM; T HREAD WOR MS ; TRI('It INA.