. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. CILIA. 609 Gleichen,* in , described the currents produced by the vorticellse. In an earlier work be ascribed an agitation of small bodies, which he had observed in the neighbour- hood of one of the Infusoria, to an electric or magnetic force, not having perceived the FontanaJ described the rotatory apparatus of the Rotifer and its use ; he conceived that its apparent rotation was produced by the succes- sive elevation and depression of the cilia which encircle it. Of the more recent writers who have inves-
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. CILIA. 609 Gleichen,* in , described the currents produced by the vorticellse. In an earlier work be ascribed an agitation of small bodies, which he had observed in the neighbour- hood of one of the Infusoria, to an electric or magnetic force, not having perceived the FontanaJ described the rotatory apparatus of the Rotifer and its use ; he conceived that its apparent rotation was produced by the succes- sive elevation and depression of the cilia which encircle it. Of the more recent writers who have inves- tigated or described these phenomena in the Infusoria, I may mention Dutrochet,§ Gruit- huisen,|| Agardh,H llaspail,** and Ehren- Raspail denies the existence of cilia, attributing their appearance to an optical de- ception, an opinion which is undoubtedly erroneous. Ehrenberg, who, of all recent ob- servers, has contributed most to the knowledge of the economy and natural history of the Infusoria, has particularly investigated the structure and mode of action of their cilia. The substance of his observations has been already given. The ciliary motion has been recently ob- served in the embryoof Infusoria while enclosed in the 2. Poli/pi and Sponges. — a. Fresh-water poli/pi. The phenomena in question have not been discovered in the Hydra, which is the largest and best known of the Fresh-water Polypi; but they have been seen and described by many observers in another sort, viz. that known by the names of the Polype a panache, or Plumed Polype of Trembley, the Bell- flower animal of Baker, and Plumatella, Cris- tatella, Alcyonella, &c. of other naturalists. The Polypes of this kind are connected in groups on a common stock or stem, (a, a, Jig. 291, which represents the animal magnified,) and each is furnished with a tube (b, b ), into which it can wholly withdraw itself. From time to time they advance a little way out of the tubes and display a double row
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