Elementary text-book of zoology, general part and special part: protozoa to insecta . elementarytextbo00clau Year: 1892 234 C(ELENTEIIATA. hydrothecae (fig. ISO a). A more or less stiff mesoderm lamella is also developed in the interior of the body wall, between the ectoderm and the endoderm. This serves to support the soft parts of the animal, and, in the Mediisce, is in part represented by the gelatinous connective tissue of the disc. The Medusa (fig. 180 b) is without doubt morphologically higher than the Polyp, since it represents the mature sexual individual, while the Polyp performs the
Elementary text-book of zoology, general part and special part: protozoa to insecta . elementarytextbo00clau Year: 1892 234 C(ELENTEIIATA. hydrothecae (fig. ISO a). A more or less stiff mesoderm lamella is also developed in the interior of the body wall, between the ectoderm and the endoderm. This serves to support the soft parts of the animal, and, in the Mediisce, is in part represented by the gelatinous connective tissue of the disc. The Medusa (fig. 180 b) is without doubt morphologically higher than the Polyp, since it represents the mature sexual individual, while the Polyp performs the nutritive and vegetative functions. The Medusa, in correspondence with its power of free locomotion, possesses an ectodermal nervous system and sense organs. The nervous system consists of nerve fibres and ganglion cells, and is usually specially concentrated round the edge of the disc, where it forms ring of fibres running parallel to the circular vessel. The sense organs are the so-called marginal bodies. The generative pro- ducts of the Medusae cither have their origin in the ectoderm, in which case they may be developed on the under surface of the disc (sub- umbrella) in the ecto- derm immediately un- derlying the radial canals (Eucopicke), or in the ectoderm of the manubrium (Oceanidce); or they may arise from the endoderm of the under surface of the umbrella (>Sc)/2}homedus(je). Both Polyps and Medusae frequently remain at a lower grade of morphological differeatiation, the former becoming polypoid appen- dages, the latter medusoid buds enclosing the generative products. In either case they are situated on the stem or on some part of the Polyp. The individuality of such appendages appears limited; the medusoid or polypoid animal sinks, physiologically speaking, to the value of a portion of the body or of an organ, while the entire stock L. Agassiz, ' Coutribntion to the Natural History of the United States, Aca- lephae,' vol. iii., 1S60, vol. iv., 1S62. E. Ha
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