. An introduction to zoology [microform] : for the use of high schools. Zoology; Zoologie. which, in some cases, differ very much from the ordinary polyp in shape, and may even be detached and swim off as Medusiv, (Fig. 170). There is then an alternation between the Hydra- form, multiplying by buds, and the Medusa-form multiplying by eggs. Some Medusae, however, the larger jelly-fishes (Fig. 180), do not come from Hydroid colonies, but their eggs give rise to tube-like larvae, which undergo multiplication by division into young Medusae, related to each other like a pile of saucers. In such hig
. An introduction to zoology [microform] : for the use of high schools. Zoology; Zoologie. which, in some cases, differ very much from the ordinary polyp in shape, and may even be detached and swim off as Medusiv, (Fig. 170). There is then an alternation between the Hydra- form, multiplying by buds, and the Medusa-form multiplying by eggs. Some Medusae, however, the larger jelly-fishes (Fig. 180), do not come from Hydroid colonies, but their eggs give rise to tube-like larvae, which undergo multiplication by division into young Medusae, related to each other like a pile of saucers. In such higher forms of Hydroids an abundant layer of gelatinous connective tissue (mesoderm) separates the endoderm from the ectoderm, 6. The class Actinozoa (exclu- sively marine) derives its name from the Sea-anemone—A ctinia — ( Fig. 1?1), These creatures attain a considerable size, and are often very brilliantly coloured. They differ from the Hydroids by having the mouth-end of the tubular body turned in as a siomach-sac, which is connected by mesenteries or septa to the outer tube (Fig. 182), The chambers between the septa open above into the tentacles, which are separated from the mouth by an intervening disc. The Sea-anemonies have no skeleton, and do not form colonies, but allied forms give rise by budding, or division, to colonies, which may be arborescent or massive, and in which a skeleton or coraUuni is a marked feature. The corallum may be confined to the axis of the common flesh (ccenosarc), which unites the indi- vidual polyps, as in the Fan-corals and the Red Coral of commerce (Fig. 183), or it may invade the polyps them- F!g. 180.—Higher Jelly-fish. (AtirelicL aurita).. Fig. 181.—A Sea anemone (Acti- nia), a,the mouth; h, the disc ; c, the tentacles ; d, margin of the disc ; e, the wall; i, the base. ,11 1,. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of the
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Keywords: ., bookcentury1800, bookdecade1880, bookpublishe, booksubjectzoology
