Krull (1934) and Hunter and Hunter (1934 and 1935a) determined that the cercaria of Clinostonmun marginatunz is a fork-tailed form that develops in rediae. The cercariae penetrate various species of fish and develop into large metacercariae, popularly known as "yellow grubs," which attain almost adult size. When infected fish are eaten by certain species of water birds, the "yellow" grubs are freed and migrate to the oral cavity of the host where they become sexually mature in a few days. The eggs escape into the water and the miracidia develop and hatch, penetrating into certain species of planorbid snails. Although Hunter and Hunter (1935a) carried through infection experiments, they did not give an accurate account of the structure of the mother sporocyst and the early development of the rediae. However, they (Hunter and Hunter, 1935b) described the miracidium in detail and found that it had four flame cells.