Schistosome eggs. Light micrograph of human ureter tissue containing eggs (brown, three at lower left) from the fluke Schistosoma haematobium, the cause of urinary schistosomiasis. This is a form of bilharzia. The ureter is part of the urinary system. Eggs expelled from infected humans enter lakes and rivers, hatch into larvae and infect aquatic snails, where they develop into cercariae. After leaving the snail the cercariae infect humans who enter the water. The mature adult form lives in veins around the bladder, where the females lay the many hundreds of eggs that accumulate in tissues and cause damage. Magnification unknown.