. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. CILIA. 611 In the second form (Jig. 294) the stem and Fig. Campanularia. branches are formed externally of a tough (generally horny) substance, and within this of a transparent soft tissue, which is tu- bular and contains a granular matter. The polypi resemble hydra; each is lodged in a horny cell (a, a), from which it partially protrudes itself; one orifice surrounded with tentacula serves both for receiving aliment and discharging faeces ; this leads to a stomach (6), which communicates through an opening (c) at
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. CILIA. 611 In the second form (Jig. 294) the stem and Fig. Campanularia. branches are formed externally of a tough (generally horny) substance, and within this of a transparent soft tissue, which is tu- bular and contains a granular matter. The polypi resemble hydra; each is lodged in a horny cell (a, a), from which it partially protrudes itself; one orifice surrounded with tentacula serves both for receiving aliment and discharging faeces ; this leads to a stomach (6), which communicates through an opening (c) at the bottom of the cell with the interior of the tubular stem and branches, the attached part or base of the polype being continuous with the soft internal tube, of which the po- lypes might be regarded as a prolongation. In this form of polype, which exists in most true species of Sertularia, Campanularia, and Plumularia, and in allied genera, the tentacula or arms are destitute of cilia and incapable of giving an impulsion to the water. But a very remarkable motion has been observed by Cavolini* and Mr. Listerf in the granular matter contained in the stem and branches. Although this motion has not been traced to the agency of cilia, yet as it is connected with our subject, I shall briefly notice it here. When the stem and branches of the above- named zoophytes are examined with a high magnifying power, a current of granular par- ticles is seen running along the axis of the tube. The current, which is compared to the running of sand in a sand-glass, after con- tinuing" one or two minutes in the same direc- tion, changes and sets in the opposite one, in which it continues about as long, and again resumes the first, thus alternately flowing along the stem to the extremities of the branches, and back again. The change of direction is sometimes immediate, but at other times the particles are quiet for a while, or exhibit a confused whirling motion for a few seconds before the
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