An egg of the liver fluke (Fasciola hepatica), a parasitic flatworm. The egg contains a miracidium, a tiny ciliated larva. After hatching, the free-living miracidium infects certain species of freshwater snail, the liver fluke's secondary host. It penetrates the snail's tissues, and after further stages of development, larvae called cercaria emerge. These form cysts on nearby vegetation, which are ingested by ruminants, or sometimes by humans. Immature flukes emerge from the cysts and migrate into the bile ducts. Here they reach maturity and pass thousands of eggs into the host's faeces, which can contaminate water, thus continuing the fluke's life cycle. Liver flukes cause fascioliasis, a liver disease with symptoms including digestive problems, fever, pain, anaemia and jaundice. Footage filmed at Ridgeway Research, Gloucestershire, United Kingdom.