Ascaris

Ascaris, a genus of parasitic worms in the Nematode or Thread-worm (q.v.) order. Ascaris lumbricoides is one of the four thread-worms not infrequently infesting man, and especially children. It occurs in the intestine, whence it occasionally works its way into other parts of the body. The thin cylindrical body measures from 6 to 10 inches in length, is of a whitish or light-yellow colour, and is pointed at both ends. The surface of the transparent skin is somewhat wrinkled, but there are no internal segments. The sexes are separate, and the less frequent males are distinguished by their turned-up posterior extremity, and the presence of two copulatory spicules. The skin is strong and protective, and forms three lips round the mouth. The muscular system is well developed, and the name Ascaris (Gr. askarizo, 'to jump') probably refers to the lively motions of some forms. The eggs develop in water or damp earth, and it seems probable that the embryos are directly swallowed by man. This troublesome though rarely dangerous parasite is best dealt with by means of expulsive purgatives. Care as to the purity of drinking-water, and thorough cleaning of vegetables eaten raw, are evident preventive precautions. See PARASITISM, ROUND-WORMS, THREAD-WORMS.