. Outlines of zoology. Zoology. 150 CGELENTERA. SYSTEMATIC SURVEY. A. Class Hydrozoa. There are two types, polypoid and medusoid, which may be com- bined in one life history. The mouth leads directly into the gastric cavity. The mesoglcea is simple, and without migrant cells. The reproductive cells seem to be usually ectodermic. I. Order Hydromedus;e. —Simple or colonial forms in which the sex- ually reproductive persons are either liberated as free-swimming medusoids or are sessile gonophores. (a) Hydrophora.—Two types are included here. The first includes the Tubularians, Hydractinia, and ot
. Outlines of zoology. Zoology. 150 CGELENTERA. SYSTEMATIC SURVEY. A. Class Hydrozoa. There are two types, polypoid and medusoid, which may be com- bined in one life history. The mouth leads directly into the gastric cavity. The mesoglcea is simple, and without migrant cells. The reproductive cells seem to be usually ectodermic. I. Order Hydromedus;e. —Simple or colonial forms in which the sex- ually reproductive persons are either liberated as free-swimming medusoids or are sessile gonophores. (a) Hydrophora.—Two types are included here. The first includes the Tubularians, Hydractinia, and other forms in which the polypes are not enclosed in the protective sheath which often surrounds the colony (gymnoblastic), and in which the free medusoid forms, when present, have their genital organs placed in the wall of the manubrium (Anthomeduste), and are furnished with ocelli placed at the base of the tentacles. Hydra and its allies may be included here. Examples :— Syncoryite sarsii, the free medu- soid of which is called Sarsia tubulosa. Bougainvillea ramosa liberates the medusoid Margelis ramosa. Cordylophora lacustris and Tubularia larynx have sessile gonophores. The second type includes Campanu- larians, Sertularians, Plumularians, and others, in which the protective modified hydranth (blastostyle) sheath surrounding the colony is bearing sporosacs ; /., medusoid continued into little cups enclosing "; the polypes (calyptoblastic). The free medusoids have their gonads placed in the course of the radial canals (Leptomeduspe), and are either "ocellate" or "; Examples :— Plunmlaria and Sertularia have sessile gonophores. Campanularia geniculata liberates the medusoid Obelia geniailata. (b) Hydrocorallinas.—Colonial forms which suggest the Hydractinice in their polymorphism and division of labour, but are distinguished by. KlG. 67.—Diagram of a gymno- blastic Hydromedusa. —After Allman. a., Stem ; £., root; c,
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Keywords: ., bookauthorth, bookcentury1800, bookdecade1890, booksubjectzoology
