Large, multinucleated trophozoites live in the rectum of frogs, and reproduce by fission for most of the year. During the breeding season of the frog, smaller trophozoites are formed that secrete a cyst and pass in the feces. When these cysts are eaten by the new generation of tadpoles, they excyst and begin dividing to produce uninuclear gametes. The gametes fuse, become new large trophozoites, and continue multiplication.