ZOOPHYTES. 227 free or fixed, the transverse section is usually round, as the Tur- binolia. The second mode is by buds which results in the ag gregation of individuals, but each individual is perfectly distinct from the others; the calice is generally circular, as in fig. 79, the Favastrae rugosa. The last mode, by division or fissiparity, the individual is divided and forms two individuals, this form also results in the aggregation of individuals; the calice is irre gular, or oval, the elongation being the first step towards a division of the individual. The form therefore, of the calice, to gether with its mode of aggre gation are important generic characters. The Polypiers are divided by M. Milne Edwards into three orders, the Zoantharia, the Alcyonaria and the Hydraria; the two former only, are represented in a fossilized state. The general characteristics of the subkingdom Zoophita are, animals formed for a sedentary mode of life, being provided with a circle of retractile tentaculae around the mouth, and a central gastric cavity with only a single orifice, and in which are lodged the reproductive organs. The Cokallaria which forms a subclass under Zoophyta, em brace the calcareous corals which in form may be tubular, cyathoid or discoidal, but exclude all the cylindrical, tubular or horny sprigs, which bear bell shaped cells for the reception of contracted tentaculae. The Zoantheria embrace most of the known fossil stony corals. They have either a conical, tubular, simple or arbo rescent forms, and an internal gastric cavity divided vertically by a circle of septa, radiating from the internal wall of the corallum.