Text-book of comparative anatomy . FIG. S3.—Diagrammatic representationof the organisation of a Siphonanth , Pneumatophore ; sg, swimming-bell; •.bract; t, tentacles ; goi, go*, 903, gonophores ;hy, oral or gastric peduncle (siphou); p,feeler or taster (palpon); A • II, variousgroups of appendages which are never foundin this way together in any single Siphou-anth. Black portion = gastric system. 110 COMPARATIVE ANATOMY CHAP. these three parts—umbrella, tentacle, and gastric peduncle. Thismedusoid larva is bilaterally symmetrical. Its umbrella has a deepcleft, it possesses only one ten
Text-book of comparative anatomy . FIG. S3.—Diagrammatic representationof the organisation of a Siphonanth , Pneumatophore ; sg, swimming-bell; •.bract; t, tentacles ; goi, go*, 903, gonophores ;hy, oral or gastric peduncle (siphou); p,feeler or taster (palpon); A • II, variousgroups of appendages which are never foundin this way together in any single Siphou-anth. Black portion = gastric system. 110 COMPARATIVE ANATOMY CHAP. these three parts—umbrella, tentacle, and gastric peduncle. Thismedusoid larva is bilaterally symmetrical. Its umbrella has a deepcleft, it possesses only one tentacle, its gastric peduncle is filled withyolk. The Siphonophora colony arises on the gastric peduncle bygemmation. Let us now consider the polymorphic appendages of the Siphonanthstem, which we compared with the daughter Medusce budding on thegastric peduncle of Sarsia siphonophora. All these appendages arearranged on the stem in a line whose position is called ventral. The. FIG. 84.—Stephalia corona, after Haeckel. A, Halved longitudinally. B, From life, sb, Swim-bladder ; au, aurophore ; sg, swimming-bells; fca, canal system of the stem (chief stomach, st); go,gonophore clusters ; o, aperture (mouth) of the peduncle (chief gastric tube, st); hy, gastric tubes(siphons); /, tentacles. line generally becomes a spiral, because of the spiral twisting of thestem. Highest up on the stem under the pneumatophore (when oneis present) the so-called swimming-bells or neetophores are inserted ;these are wanting only in the Cystonecta. The swimming-bells exclu-sively and alone provide for the locomotion of the whole stock. Theyhave lost all those Medusa organs which were of no use to or evenhindered the fulfilment of this function, first of all therefore, mouth,gastric peduncle, and tentacles. The locomotory organ of the Medusa,the disc or umbrella, however, is all the more strongly developed ; itis much vaulted with a strong circular muscular layer in the sub-umbr
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
