. Animal life as affected by the natural conditions of existence. Animal ecology. A CORAL AND A WORM. 341 a cylindrical cavity lying parallel to the main stem of the Antipathes. Among the numerous specimens found by Pourtales not one occurred that had not a tube, and thus the same thing has happened here as in the other instances adduced. An abnormal peculiarity caused by a modification in the mode of growth has, by the constant recurrence of the exciting cause, become a distinguishing mark of the species. In conclusion I cannot refrain from mentioning one more very singular and hitherto littl
. Animal life as affected by the natural conditions of existence. Animal ecology. A CORAL AND A WORM. 341 a cylindrical cavity lying parallel to the main stem of the Antipathes. Among the numerous specimens found by Pourtales not one occurred that had not a tube, and thus the same thing has happened here as in the other instances adduced. An abnormal peculiarity caused by a modification in the mode of growth has, by the constant recurrence of the exciting cause, become a distinguishing mark of the species. In conclusion I cannot refrain from mentioning one more very singular and hitherto little-noticed case of the association of two organisms which seems closely allied to the well-known case of Lichens among plants. These, according to Schwen- dener's researches, are to be regarded as colonies of true one- celled Algae and Fungi, and though individual botanists still raise their protest against this view, the latest investigations on. Fig. 00.—Antipathes filix, Pourtales, a horny coral of tlie West Indian seas, which by constant association with an Annelid has been forced to form a tube for the worm. Deep-sea corals. the subject seem to prove that they are no longer justified in doing so. The Sponges are now universally classed with animals; their soft parts consist exclusively of cells which are scarcely ever co-ordinated to form special otgans such as occur among the higher animals. These soft portions are usually strength- ened and supported by a network of fibres secreted from the cells and extremely variable in structure. In the forms which are genei'ally regarded as the simplest and most typical, all the parts unite to form a funnel attached by the pointed end, and of which the free end has a large opening leading into a central cavity ; this, for brevity, we will call the mouth of the sponge. But, besides this, the internal cavity communicates with the sur- rounding water by a system of fine canals which penetrate the lateral portions of the sponge funnel i
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