The Eustrongylus Gigas is a large round worm found in the pelvis of the kidney or ureter, usually in horses or cattle, but sometimes in man. The female is about one meter long and 8 to 12 mm. thick, the male about one-third as long. Is reddish in color, the anterior end is retracted, and around the mouth are six papillae. In the male the posterior end is expanded, and a spicule projects from the cloaca.