NEMATEL'MIA (derived from the Gr. words News a thread, and lielmins, an intes tmalworin), is the term given by recent zoologists to a large and important class of the subdivision vermes of the artkuluta. The worms belonging to this class arc of a more or less elongated cylindrical form. - Their skin is thick and strong, and is usually wrinkled in such a manlier as to give the body an annulated appearance, which, however, disap pears if the animal is placed in water. The nervous system in the higher forms (as the aseareda) consists of two lateral ganglia at the anterior extremity, which are united by a slender nervous ring. and from which two lateral nervous trunks proceed to the posterior part of the body; while in the lower forms no distinct nervous system can be recognized. No special organs of the senses are met with; but a general sense of touch is probably present. The digestive organs are extremely simple. In one order (the neasithoeephala: no trace of an intestinal canal can be detected; in another order (the fiordieseea), there is a mouth, but no anus; while the higher forms are provided, with. mouth; intestinal canal, and anus In the higher forms, a kind of va,ettlar systemIS developed in the skin, la the shape of canals, in which the nutrient fluid is propelled by the movements of the body. No distinct respiratory organs can be detected; but in some genera there are glands whose object is not clearly known. These worms are uniusexual; but the males are comparatively rarely found, and are always smaller than the females. With the exception of two families—the urolabeu and anguillulidie, or paste and vinegar eels—ail the animals of this class are parasitic; indeed, Carus, in his Thindbuch der Zoologie (1863), vol. ii. p. 458, goes so far as to say that " probably all the nematelmia live as parasites, either during their whole lives or during certain stages of their existence."
T11:3 nematelmia are sometimes termed round-worms, just as the platyelmia (tape worms, flukes, etc.) are called flat-worms. Most commonly, however, the term round worm is restricted to the ascaris lumbricoldes, the most common of the human entozoa.
This class is divisible into three very distinct orders—viz., the acantkocephala, which are destitute of an intestinal canal; the gordiacea, which possess an intestinal canal, but no anus; and the nenuitt4lea, which possess a perfect intestinal canal, provided with two orifices.
NEMATOrDEA constitute the highest order of the nematelmia, and indeed of intes tinal worms generally, inasmuch as they present a distinct nervous system, a complete intestine provided with mouth and anus, and distinct sexual organs. The history of their development is not fully known; but there is no reason to believe that these animals undergo any remarkable metamorphoses, although some perforate the intestinal walls, and become encysted in parenchymatous organs. The great majority of the nematoidea are parasitic. The nematoidea are divided by Carus into twelve families, all the members of which are known only in a parasitic state of existence, excepting certain genera of the first and second family.
Although the intestinal canal is the most common residence of these worms, some, as trichina spirals, are found chiefly in the muscles; others, as filar& medinensis, in the subcutaneous cellular tissue, and others in the kidneys, lungs, etc. See ENTOZOA. For further information regarding these worms, the reader is referred to Eberth's Untersueh Millen liter Neniatoden (4to, 1863).