First lesson in zoology : adapted for use in schools . 31. — Partly diagi-ammatiosketch of the anatomy_ of anActinia (Metridium) with thetentacles disproportionately en-larged, s, throat ;-m, mesen-teries, or partitions; o, egg-gland ; cr, mesenterial filaments;e, eyes; op^ orifice through thesepta. 34 FIB8T LE880N8 IN ZOOLOGY. of the digestive canal. The bones, shells, or hard covering of theanimals which may be swallowed by the Actinia are rejected fromthe mouth after the soft parts are digested. Sea-anemones have been found to have a slight sense ofsmell. ]Searly all sea-anemones, besides a
First lesson in zoology : adapted for use in schools . 31. — Partly diagi-ammatiosketch of the anatomy_ of anActinia (Metridium) with thetentacles disproportionately en-larged, s, throat ;-m, mesen-teries, or partitions; o, egg-gland ; cr, mesenterial filaments;e, eyes; op^ orifice through thesepta. 34 FIB8T LE880N8 IN ZOOLOGY. of the digestive canal. The bones, shells, or hard covering of theanimals which may be swallowed by the Actinia are rejected fromthe mouth after the soft parts are digested. Sea-anemones have been found to have a slight sense ofsmell. ]Searly all sea-anemones, besides arising from eggs,increase by budding, new individuals growing out at or nearthe base of the large one. The coral polyps only differ from the sea-anemones in. Fig. 32.—Coral polyps, some expanded and others shut up within the hollow ofthe coral-stock. secreting a limestone support or coral-stock/ Corals areeither cup-shaped and single, or are compound, formingbranching or rounded masses. The soft parts are supportedby limestone partitions secreted in the chambers of thepolyp. All polyps develop from eggs, and at first appear as littleoval, ciliated, free-swimming embryos {gastrulm), whicheventually become attached to the bottom of the sea. TEE POLYPS AND CORAL-MAKERS. 35 Before the embryo becomes fixed and the tentacles arise,the lime destined to form the partitions begins to be de-posited. Fig. 33, 0, shows the twelve rudimentary parti-tions. These, after the young polyp has become stationary,finally enlarge and become joined to the external walls ofthe coral now in course of formation (Fig. 33, C), form-ing a foundation on which the polyp rests. D representsthe young polyp resting on the limestone pedestal, withthe tentacles well develo
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1894
