Copulation

Copulation (from Latin copulatio—union), the sexual process of protozoa, in which the complete fusion of both the plasma and the nuclei of the two copulating individuals occurs. It is found among flagellates (Flagellata) and sporozoans (Sporozoa). In flagellates, copulation takes the form of hologamy, when two vegetative individuals, which are thus gametes, join and, fusing, form a zygote or copula. The latter is usually encysted, and the contents of the cyst divide, as a result of which small individuals are developed again from the formed cysts, which again develop into the original vegetative form. If the copulating individuals are differently differentiated in a sexual sense, they are called anisogametes; otherwise, they are called isogametes. In sporozoans, copulation proceeds in the form of merogamy, when it is not the vegetative individuals themselves that copulate, but the small sexual individuals, the gametes, formed from them by schizogony. Copulation of gametes—see Fertilization.