HAIRIVOR1VI. Any of the long, thread-like nematode worms of the parasitic order Gordi oidea. (See Goanius.) In these, nematodes the body-cavity is lined by a distinct epithelium; there is a simple large ventral nerve-trunk, and the reproductive organs are arranged metameri cally and are separate from the gonoducts. The group includes a small number of species, which are parasitic in locusts and other insects in the asexual, but free and mobile in the sexual stage. They inhabit moist situations, are sometimes found on the leaves of plants, but more fre quently in stagnant pools, and in mud, through which they work their way with great ease. They often twist themselves into complex knots, whence their name Gordius, from the celebrated Gordian knot, and many of them are sometimes found thus twisted together; but they are also often to be found extended in the water. The eggs are laid in long chains in the water, and the young which hatch from them swim about until they reach some aquatic larvae into which they bore and encyst. When this insect is eaten by some minnow or other small fish the cyst is dis solved and the young Gordius lives parasitically in the intestine of its new host, until it reaches sexual maturity, when it bores its way out of the cyst, passes into the intestinal cavity of the fish, and from thence is carried out with the into the water. When fully grown a large
hairworm may be nearly three feet long. One popular name is `hair-eel'; and a notion still prevails even among educated people that it is nothing else than a horsehair, which has some how acquired life by long immersion in water, and which is destined in time to become an eel, or, as some say, a snake. They are often seen in fresh-water pools or horse-troughs, whence they are supposed by the ignorant to be transformed horsehairs. A.popular notion prevails in Swe den that the bite of the Gordius causes whitlow. Most hairworms in their last stage live in ground-beetles and locusts, turning in the intes tines of their host, and finally passing out of the anus. Consult Villot, "Monographie des Dragon neaux," in Archives de zoologie experimentale, vol. iii. (Paris, 1874).