In the Edwardsiidea, Actiniaria, and Cerianthidea, that is to say in the animals popularly known as Sea-anemones, asexual reproduction does not commonly occur, but nevertheless a good many instances of it are now known in individual genera. In _Actinoloba_ (_Metridium_), for example, Parker has described a case of complete longitudinal fission, and Duerden states that it occurs in the West Indian Anemones _Actinotryx_ and _Ricordea_. A still more remarkable form of asexual reproduction known as transverse fission has been described in the genus _Gonactinia_.[397] In this case, the body of the Anemone becomes constricted in {372}the middle, a circlet of tentacles is formed below the constriction, and division takes place. The upper half floats away with the original tentacles and stomodaeum and becomes attached by the base in another place; the lower half remains behind and develops a new stomodaeum, mesenteric filaments, and sexual organs. In some of the Actiniaria another form of asexual reproduction occurs, known as "Pedal laceration." In the common British _Actinoloba_, for example, so often kept in aquaria, the pedal disc sometimes spreads on the glass or rock upon which the animal rests, in the form of a thin membrane or film of an irregular circular shape, nearly twice the diameter of the column. As the Anemone glides along, the film remains behind and breaks up into a number of hemispherical droplets, which in a few days develop tentacles, a mouth, mesenteries, and the other organs of a complete and independent Anemone. A similar method of reproduction has been observed in several species of _Sagartia_. A true process of discontinuous gemmation has also been observed in _Gonactinia_, in _Corynactis_, and in _Actinoloba_. [Illustration: FIG. 164.—Longitudinal fission of _Actinoloba_. (After Agassiz and Parker.)] In the Madreporaria, Zoanthidea and Antipathidea, the usual method of reproduction to form the colonies is continuous gemmation. The new zooids that are added to the colony as it grows arise as buds, either from the superficial canals of the coenenchym, or from the base or body-wall of the older zooids. In these cases the young zooids acquire the same number of mesenteries, and the same characters of the stomodaeum as the original parent. Some further particulars of asexual reproduction in the Madreporaria are given on p. 387.