Ascaris in infective eggs are ingested with contaminated food and water. The eggs hatch into larvae in the small intestine and penetrate the gut wall. It reaches the liver through portal system and then migrates to the lungs via herat through blood. After about 10 days they swallowed down the oesophagus. This migratory phase lasts for about two weeks during which the larvae undergo two additional moults. On arrival at the small intestine, the fourth moult occurs and the larvae form immature adult worms.