fluke cercaria and metacercaria

The cercaria hatches out of the ova in the feces, swims to a snail where it attaches, then it produces redia for several generations. Some of the redia form metacerceria which swim and fina a plant and attach. The host, maybe a cow, eats the encysted metacerceria and it grows to maturity in the body. In humans sometimes the ova hatch in the body and produce the cercaria which then attach to a snail substitute, often burrowing thru the intestinal wall into the body. The longer the ova stay in the body the more likely it will be that they hatch and attach or invade. The cercaria are relative large, the metacercaria are small. Tweet