Figure 9.4 A pathogen’s life cycle through snails and ducks. Eggs of the pathogenic worm Microphallus are inadvertently consumed by snails. The eggs hatch into larvae and form cysts in the snails, causing the snails to become sterile. When the snails are consumed by ducks in the shallow waters, the worm turns into an adult and reproduces in the ducks’ intestines. When the ducks defecate, the eggs are deposited back into the water.