Elementary text-book of zoology, tr Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote elementarytextbo01clau Year: 1892-1893 HYDROZOA. 233 Septa but slightly developjd. Midi'/'porn ci-rvicornls Lam., Dcndroplnjllia ramca Edw., Mediterranean. Astroides calycularis Pall. CLASS II.—POLYPOMEDUSJE.* [HYDEOZOA.] Polyps without cesophageal tube, ivith simple gastrovascular cavity. The generative elements are developed in medusoid forms ivhich may be either free-swimming, or permanently attached to hi/droid forms. This class includes the small polyp
Elementary text-book of zoology, tr Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote elementarytextbo01clau Year: 1892-1893 HYDROZOA. 233 Septa but slightly developjd. Midi'/'porn ci-rvicornls Lam., Dcndroplnjllia ramca Edw., Mediterranean. Astroides calycularis Pall. CLASS II.—POLYPOMEDUSJE.* [HYDEOZOA.] Polyps without cesophageal tube, ivith simple gastrovascular cavity. The generative elements are developed in medusoid forms ivhich may be either free-swimming, or permanently attached to hi/droid forms. This class includes the small polyps and polyp stocks, and the Medusce which form the sexual generation. The Polypomeduscs have always a simpler structure than the Anthozoa to which they are also usually infe- rior in size. They lack oesophagus, septa, and gastrovas- cular pouches. Only the polyps of the a- sexual generation of the Scyphomedusse [Acraspeda], known as ScypMstoma, pos- sess a remnant of the gastric folds as four gastric from which filaments are developed. The polyp stocks develop in rare cases (Mille~ poridce) a compact calcareous framework comparable to the polypaiium. When skeletal formations ai'e present they con- sist as a rule of more or horny secre- tions of the ectoderm, which as delicate tubes surround the stem and its ramifications, and sometimes form small cup-like structures surrounding the jo'yp, and known as FIG. ISO a.—Brarch of an Obelia-stock (0, ge'atinofa). O, llnuth of a nutritive polyp wi h extended tentacles. JLT, Medusa buds on the body of a proliferous polyp (blastu- style) ; Th, bell-shaped iup (theca) of a nutritive polyp. * Escholtz, 'System cler Acnlephen,' Berlin, 1S20. Th. Huxley, 'Memoir on the Anatomy and Affinities of the Medusas,' Phil. Trans., London, 184U.
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