CILIA. 



609 



Gleichen,* in 1778, described the currents 

 produced by the vorticellae. In an earlier 

 work he 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 

 cilia.f 



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 Raspail,** and Ehren- 

 berg.f -f 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 ovum.JJ 



2. Polypi and Sponges. a. Fresh-water 

 polypi. 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, o, 

 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 

 of arms or tentacula (c) ranged round the 

 mouth in the figure of a horse-shoe. When 

 the arms are spread out in this manner, cur- 

 rents appear in the surrounding water, which 

 are made evident by the motion of any small 

 particles that may accidentally or intentionally 

 be suspended in it. The currents pass along 

 the tentacula, the water being drawn towards 



* Abhandlung ueber -die Saamen -und Infusions 

 Thierchen, 1778. 



t See Miiller, Infus. p. 87. 



j Traite sur le venin de la Vipere, etc. 1781, 

 torn. i. p. 87. 



Sur les Rotiferes, Ann. du Musee d'Hist. 

 Nat. 1812, torn. xix. et 1813, torn. xx. 



II Salzburg. Med. Chir. Zeitung, 1818, iv. p. 

 222. 



H Ueber die Zauberkraft der Infusorien, Nov. 

 Act. Acad. Caes. Leop. torn. x. p. 127. 



** Hist. Nat. de 1'Alcyonella Fluviatile, etc. 

 Mem. de la Soc. d'Hist. Nat. torn. iv. and Chimie 

 Organique, 1833. 



ft Abhandl. d. Akad. der Wiss. zu Berlin fur 

 1831. 



it Wagner, Isis, 1832, p. 383. 



i. 291. 



them from every side, and the main stream at 

 last issues from the midst of them, appearing 

 as if it came out of the mouth, from which, 

 however, it really is not derived. The arms 

 are fringed on their two borders with a mul- 

 titude of cilia, (see A, a single arm mag- 

 nified,) set close together, which vibrate in 

 regular succession, their motion appearing 

 like progressive undulations along the ten- 

 tacula. When one of the arms is cut off, it 

 affects the water in the same way as when con- 

 nected with the animal, its cilia impelling the 

 fluid in a current, or carrying the separated 

 arm through it, according as it is fixed or free. 



As to the use of these motions, it may be 

 stated that they serve undoubtedly for renew- 

 ing the water in respiration, and probably also 

 to convey food to the animal. Steinbuch, 

 however, remarked that the currents were most 

 lively in pure water, and that the extraneous 

 matters which they conveyed seemed rather to 

 incommode the animal, which endeavoured 

 to avoid them ; and from this he inferred that 

 the currents served chiefly if not solely for 

 respiration. 



Trembley* and Bakerf observed the currents 

 produced by this polype, but both erroneously 

 conceived them to be caused by agitation of 

 the tentacula. Roesel} correctly remarked 

 that, during the production of the currents, the 

 tentacula were motionless, but not perceiving 

 the cilia, nor being aware that the arms when 

 detached still produced motion in the water, 

 he supposed that the currents were occasioned 

 by a stream issuing from the mouth. At 

 length Steinbuch discovered that separated 

 tentacula retained the power of impelling the 

 water; he distinguished the cilia and their 

 motion as the cause of the impulsion, and 



* Mem. pour servir a 1'Hist. d'un genre de 

 Polype d'eau douce, 1744, p. 212. 



t Of Microscopes, ii. p. 309. 



j Insecten Belustigungen, torn. iii. 1755, p. 

 458. 



$ Analccten neuer Beobachtungcn und Unter- 

 suchungen fur die Naturkunde, 1802, p. 89. 



