Ascaris lumbricoides, commonly known as the large roundworm, is the most prevalent intestinal nematode parasite of humans. It inhabits the small intestine and can cause complications like intestinal obstruction. The adult female worm is 20-35cm long and lays hundreds of thousands of eggs per day that are passed in feces. When ingested, the eggs hatch in the intestines releasing larvae that penetrate the intestinal wall, travel to the lungs, and are then swallowed making their way back to the small intestine where they mature into adult worms.

1. Ascaris Lumbricoides

4. Adult worm of A. lumbricoides

5. The lips of Ascaris lumbricoides The three lips are seen at the anterior end. The margin of each lip is lined with minute teeth which are not visible at this magnification.