CILIA. 



[ 1-G ] 



CILIA. 



overcome by the feeble power of the cilia, 

 tbey produce motion iu the surrounding 

 medium, as on the giUs of fishes, of young 

 reptiles, and of the Mollusca, tlie gill-tufls 

 of the Annulata, and the various mucous 

 surfaces of the Vertebrata upon whicli they 

 exist, in which they favour respiration and 

 excretion. liy the same agency they also 

 bring particles of food suspended iu the 

 medium towards the mouth. It need 

 scarcely be remarked, that the motion of 

 cilia must be stronger in one direction than 

 the other, otherwise there could be no 

 current. 



The cause of the motion of cilia has long 

 formed a subject for discussion ; but it is 

 still unknown. In some instances, as in the 

 Infusoria, it appears to be voluntary. In 

 certain cases it might be attributed to the 

 action of a contractile amorphous tissue, 

 such as that composing the Amwb(e. It 

 would naturally be attributed to muscular 

 agency ; but no muscular tissue can be de- 

 tected : in fact, cilia are quite structureless ; 

 moreover they are often of less breadth than 

 the ultimate hbrillfe of muscle. Neither 

 the most powerful poisons, as strychnine, 

 prussic acid, opium and belladonna, nor 

 electricity, produce any elfect upon ciliary 

 motion, provided the structure upon which 

 the cilia are situated be not injured. It 

 also lasts a long time after death, having 

 been observed iu the lower aniirials nineteen 

 days after this occurrence, and when putre- 

 faction was far advanced. The question has 

 however, lost its interest in regard to its ne- 

 cessary dependence upon muscular action, 

 because cilia are common among the lower 

 plants, where this is out of the question. 



The cilia and their motion may readily be 

 observed in the common Rotatoria and Infu- 

 soria, or iu a thin piece cut from the margin 

 of the gills of the oyster; or still better, the 

 sea-mussel ; in the latter they form a most 

 beautiful and interesting object. Fresh 

 water almost innnediately arrests the motion 

 of the cilia in marine animals. In some cases, 

 solution of potash excites the movement of 

 animal-cilia after it has become languid. 



The detection of the cilia is fi-equently of 

 great importance, as the characters of Infu- 

 soria, &c. are often based upon their num- 

 ber and arrangement. The means are either 

 indirect — as by the addition of moistened 

 particles of colouring-matters, as indigo &c., 

 to the living organisms, and watching for 

 the movements of the particles — or dircct,by 

 examining the structures after the addition 



of solution of iodine, bichloride of mercury, 

 or of osmic acid, or drying them at a gentle 

 heat. Both methods should be adopted to 

 check each other: for molecular movement 

 has some resemblance to ciliary motion 

 when feeble, although there is absence of a 

 definite current ; and fine hair-like Algpe 

 or Fungi attached to aquatic organisms 

 often resemble cilia, but are deficient in the 

 motion. 



See Infusoria ; Membranes, undu- 

 lating ; and Molecular motion. 



BiBL. Purkiiije & \'alentin, Comm. Phys, 

 ^•c. ; Sharpey, Todcfs Ci/cL of An. i^- Phi/s. 

 i. 606; Valentin, Wagner's Handto. Phys. 

 Si'c. i. 481 ; Yirchow, Archiv, vi. 133 ; Fn- 

 gelmann, Jen. Zeitschr. iv. 321 ; Roth, 

 Virchoiv's Arch, xxxvii. 184 ; Ilackel's 

 Biol. Stud. 147 ; Frey, Hist. 1876, 173. 



CILIA of Vegetables. — These minute 

 vibratile threads, apparently of the same 

 (unknown) nature as those of animals, are 

 in all cases met Avith in connexion with the 

 protoplasmic or nitrogenous structures of 

 plants, the structure bearing the closest re- 

 lation to animal organizatiuu. Cilia have as 

 yet been found only in Flowerless Plants, 

 viz. in all the higher or stem - forming 

 Cryptogams, and in the Alga3 among the 

 Thallophytes. In the Marsileaceaj, Lyco- 

 podiacese. Ferns, Equisetaceae, Mosses, Ile- 

 paticae, and Characese, they are found upon 

 the active filaments (spermatozoids) dio- 

 charged from the antheridia. In the Algjfc 

 they occur upon the zoospores and some- 

 times upon the spermatozoids, and on the 

 fully-developed plants of the family Vol- 

 vocineas. They have been stated to occur 

 in certain other complete organisms, as iu 

 Closteriwn ; but this statement we believe ' 

 to be erroneous. Rigid filaments bearing 

 some resemblance to cilia occur occasionally 

 upon Diatomacpte and Osciliatoriefe ; but 

 these are not vibratile organs. The mode 

 of arrangement, &c. varies considerably 

 among the cases above cited. In the sper- 

 matozoids of the Marsileacefe, Lycopodi- 

 acete, I'erns, and Equisetacei^, they are set 

 in considerable number along a filament 

 spirally or heliacally coiled (1*1. 40. tig. 34). 

 In the Muscacea), Ilepaticfe, and Characeoe, 

 a pair of very long cilia is attached at one 

 end of the filament (fig. 123, p. 162). In 

 zoospores, either they occur in a pair at 

 the apex, as in Prvtococcus, Conferva, Cla- 

 dophora, Cvdiuin, &c., or there are four iu 

 the same situation, as in Ulothrix, (Jhceto- 

 phora^ Ulva, &c. ; while the large zoospores 

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