ASCARIS, the generic name of certain round worms, which are parasitic on various animals. A. lumbricoides is found in the human intestine, the closely allied A. suilla in the pig and A. sncgalocephala in the horse. Ascaris, which belongs to the Nema toda (q.v.), has only two chromosomes (q.v.) in the fertilized egg, and is therefore often used in the study of cytology (q.v.).