Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget .. . ebladders connected with them, in different states of distentionand contraction. Fig. 96 shows the upper side of the ambu-lacra, and of the bladders connected with the feet. Dr. Grant,from some observations which he made on the structure of thecilia of the Beroe pileus, is led to suspect that the rapid vibra-tions of these singular organs in the lowest animals may dependon the undulations of water conveyed through elastic tubesalong their bases, in a manner resembling the injection of thetu
Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget .. . ebladders connected with them, in different states of distentionand contraction. Fig. 96 shows the upper side of the ambu-lacra, and of the bladders connected with the feet. Dr. Grant,from some observations which he made on the structure of thecilia of the Beroe pileus, is led to suspect that the rapid vibra-tions of these singular organs in the lowest animals may dependon the undulations of water conveyed through elastic tubesalong their bases, in a manner resembling the injection of thetubular tentacula of Actiniae and Asterise. If this conjecturewere verified, he remarks, one of the most remarkable phenomenaof animal motion, though one of the most frequent, would losemuch of its present marvellous character. t In addition to these larger tubes, there exists also a smaller set,which pierce the skin in different places, and are channels forthe absorption of the water used in respiration. These 1 shallhave occasion to notice more particularly hereafter. 204 THE MECHANICAL FUNCTIONS. I. employed in its construction, instead of formingisolated grains, is accumulated and extended into polygonal plates(Fig. 98), the edgesof which are dove-tailed into each form of eachpiece is that of alengthened hexagon;and the whole are regularly arranged in rows,like a mosaic or tesselated pavement. Ambu-lacra are also seen on the surface of the shell,passing vertically down the sides of the sphere,similar to the meridians of a globe; and con-taining, like those of the Asterias, a double rowof perforations.* On the outer spherical surface of the ex-ternal crust, there are formed a great numberof calcareous tubercles, arranged with beautifulregularity and symmetry in double lines, pass-ing, like meridian circles, from the upper to thelower pole of the sphere. Each appears, whenmagnified, to be a smooth and solid ball, pro-jecting from the surface of one of the polygonalpla
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