Text-book of comparative anatomy . rm and ectoderm there is a struc-tureless supporting membrane (si). A more highly developed form, «the Ci-aspcdote Medusa (Fig. 64, B) \may proceed from the Hydropolypby adaptation to a free-swimming ,manner of life. The aboral portionof the Hydropolyp body (from the attached pole to the tentacles) (longitudinal section); B, of a Craspedote spreads out like an umbrella or bell, f^^\ si,s^o^Lgi^^, /jeuybe- and becomes the exumbrella of the tween ectoderm and endoderm ; rk, radial Mitlt/xtt. The Oral portion of the canal 3l vascular Amelia or cathammalif plate
Text-book of comparative anatomy . rm and ectoderm there is a struc-tureless supporting membrane (si). A more highly developed form, «the Ci-aspcdote Medusa (Fig. 64, B) \may proceed from the Hydropolypby adaptation to a free-swimming ,manner of life. The aboral portionof the Hydropolyp body (from the attached pole to the tentacles) (longitudinal section); B, of a Craspedote spreads out like an umbrella or bell, f^^\ si,s^o^Lgi^^, /jeuybe- and becomes the exumbrella of the tween ectoderm and endoderm ; rk, radial Mitlt/xtt. The Oral portion of the canal 3l vascular Amelia or cathammalif plate ; v, velum; rik, circumferential canal. body (from the tentacles to the mouth) also widens out, deepens, and becomes the subumbrella. Wethus have a convexo-concave body, on whose circular margin thetentacles are radially arranged (Fig. 65, A). The mouth lies in themiddle of the concave side, and generally on the summit of a pro-jection (gastric peduncle, gastric tube). The supporting membrane of the Hydropolyp thickens very much,. FIG. 64.—A, Diagram of a Hydropolyp COMPARATIVE ANATOMY CHAP. and becomes the gelatinous disc of the Medusa, an elastic passiveorgan for locomotion and support. The partial fusing of the innerwall of the oral portion of the body with that of the aboral portionconsiderably reduces the gastric cavity lying between them, whichoriginally spread throughout the whole extent of the disc. Thereremain only : 1. the cavity of the gastric peduncle into which the mouth leads. 2. A central stomach above the oral peduncle. These two partsform the main intestine. 3. A peripheral canal at the edge of the disc (the circumferentialcanal) which is continued into the tentacles. 4. Kadially arranged connecting canals between the central stomach and the circumferentialcanal. These canals becomenutritive gastro-canals, whichalso serve the purpose of blood-vessels (which are wanting) andconvey food from the centralstomach to the organs at thediscs edge. These two portions
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
