in zoology, a genus of insects belonging to the order of vermes intestina. The body of the ascaris is cylindrical, filiform, and tapers at both ends. The species are two, viz. 1. The vermicularis is about a quarter of an inch long, and is found in lakes, in the roots of putrid plants, and very frequently in the rectum of children and horses. 2. The lumbricoides is about the same length with the lumbricus terrestris, or common earth-worm, but it wants the protuberant ring towards the middle of the body, the only mark by which they can properly be distinguished. The body of the lumbricoides is cylindrical, and subulated at each extremity; but the tail is somewhat triangular. The lumbricoides is the worm which is most commonly found in the human intestines. For the method of expelling these two kinds of insects, see Medicine, Of worms.