Final answer:
The life cycle of a fluke involves multiple hosts, starting with eggs in the primary host's feces. Larval stages occur in a secondary host, typically a snail, and later the larvae encyst on grass, which is then consumed by the primary host.
Step-by-step explanation:
The life cycle of a fluke, specifically the sheep liver fluke, is an intricate process involving multiple hosts. Flukes, which are trematodes, require a vertebrate and an invertebrate host to complete their life cycle.
In the case of the sheep liver fluke, the life cycle starts when eggs laid by an adult fluke are excreted in the feces of the primary host, usually a sheep.
The eggs hatch in water, releasing larvae known as miracidia, which infect a secondary host, typically a snail. Inside the snail, the miracidia undergo several developmental stages, multiplying and eventually emerging as another larval form called cercariae. These cercariae leave the snail and attach to grass, where they encyst as metacercariae.
When the infected grass is eaten by the primary host, the metacercariae enter the host's digestive system and migrate to the liver, developing into adult flukes to repeat the cycle.
This complex life cycle ensures that flukes can spread and survive in different environments, indicating how evolution has allowed such organisms to adapt to using multiple hosts in their development.