Elementary text-book of zoology, general part and special part: protozoa to insecta . elementarytextbo00clau Year: 1892 HTDROZOA. Septa but slightly developed. Midrcpora ccrvicornls Lam. ratnoa Edw., Mediterranean, Astroides ealycularis Pall. 233 Dandroj^ihijllla CLASS IL—* [HYDEOZOA.] PoIi/2)s loithout oesophageal tube, with simple gastrovascular cavity. The generative elements are developed in medusoid forms which may he either free-swimming, or permanently attached to hydroid forms. This class includes the small polyps and polyp stocks, and the Medusce which form the sexual g
Elementary text-book of zoology, general part and special part: protozoa to insecta . elementarytextbo00clau Year: 1892 HTDROZOA. Septa but slightly developed. Midrcpora ccrvicornls Lam. ratnoa Edw., Mediterranean, Astroides ealycularis Pall. 233 Dandroj^ihijllla CLASS IL—* [HYDEOZOA.] PoIi/2)s loithout oesophageal tube, with simple gastrovascular cavity. The generative elements are developed in medusoid forms which may he either free-swimming, or permanently attached to hydroid forms. This class includes the small polyps and polyp stocks, and the Medusce which form the sexual generation. The Folyjwmedusce have always a simpler structure than the Anthozoa to which they are also usually infe- rior in size. They lack cusophagus, septa, and gastrovas- cular pouches. Only the polyps of the a- sexual generation of the Scyphomedu^ie [Acra?peda], known as S'cyj^histoma, pos- sess a remniint of the gastric folds as four gastric ridges from which filaments are developed. The polyp stocks develop in rare cases (Jlille- poridce) a compact calcareous framework comparable to the poly par ium. When skeletal formations are present they con- sist as a rule of more or horny secre- tions of the ectoderm, which as dehcate tubes svirround the stem and its ramifications, and sometimes form small cup-like structures surrounding the fo'yp, and known as * Escholtz, 'System der Acalephen,' Berlin, 1820. Th. Huxley, 'Memoir on the Anatomy and Affinities of the Medusae,' I^Iiil. Tranx., London, 1849. Fig. 180 o.—Branch of an Obelia-stock (0, ge'athwaa). O, Mouth of a nutritive polyp wi h extended tentacles. M, Medusa buds on the body of a proliferous polyp (blasto- style) ; Th, bell-shaped tup (thcca) of a nutritive polyp.
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