The study following the first study, and using the same snails. Each snail was put in a 5.0 × 1.5 cm diatom culture dish half-filled with conditioned tap water. All snails were left in a shaded area near a window to expose them to natural light for the shedding of cercariae throughout the experiment. Each Petri dish culture was changed daily at 8:00 AM and the cercariae from each snail were counted and recorded. Room and water temperatures, and intensity of light (Lux meter DIGICOM LX-150) were also recorded daily.