Paramecium directs a current of water into its mouth by the movements of its cilia. The cilia also move the animal through the water.
Reproduction is by fission and by conjugation.
In the former case, first the smaller nucleus, then the larger, become constricted and divide into two by oblique division, and the missing organs in either part are quickly regenerated. Frequent multiplication by fission diminishes the vitality of the organism and is succeeded by conjugation, when two individuals exchange part of the substance of their nuclear apparatus. When conditions become unfavourable the animals enclose themselves in cysts. Classification Paramecium belongs to the subclass Hymenostomatia, class Oligohymenophora, phylum Ciliophora.