44 STRUCTURE AND PHYSIOLOGY 



that innumerable cilia or miniature lamellae clothe the surfaces 

 of their tentacula, and by their rapid vibrations drive a constant 

 equable stream of water along one side, which returns along the 

 other in an opposite direction : and by this means the purposes of 

 respiration are effected, and the nutrient fluid fitted for assimila- 

 tion with the body. The cilia, to adopt the language of Pro- 

 fessor Grant, " are disposed and moved in such a manner as 

 that the streams which they produce in the surrounding water 

 are driven along the one side of the tentaculum from the mouth 

 of the polypus, and on the other side of the tentaculum always 

 towards the mouth of the polypus. And we never find that di- 

 rection of their motion reversed, or that direction of the cur- 

 rents changed, by which their respiration is effected and their food 

 obtained. They are vibratile on the arms of most of the lower 

 zoophytes, as sertularise, plumularise, serialarise, cellarise, flustrse, 

 alcyonia, which keep their arms stiffly out in a regular cam- 

 panulate form, while the currents flow to their mouth. When 

 we watch the sides of the tentacula of these animals with atten- 

 tion, and by the aid of powerful glasses, we see the extreme ra- 

 pidity of the movements, and the remarkable regularity of the 

 form, disposition, and motions, of those singular vibratile bodies. 

 From the number of them, exceeding sometimes 400,000,000 

 in a single animal, it is not probable that their extraordinary 

 movements are the result of any spontaneous efforts of the ani- 

 mal, or are accompanied with any kind of perception or con- 

 sciousness in these animals, which have never been found to 

 present a single nerve in their bodies. The independent na- 

 ture of the motion of those minute respiratory organs is observ- 

 ed when we cut off the tentacula altogether ; and observe, that 



expiration in the Infusoria and the Molluscce. The difference, then, between the 

 density of the water expired and that of the surrounding water, proceeds from 

 a difference of temperature." P- '297 — Raspail has defended this explanation 

 of the phenomena at great length in the Mem. de la Soc. d'Hist. Nat. de 



Paris, Tome iv. p. 131 — 142 Dr Mayer also denies the existence of cilia, 



and concludes that the motion is produced by a peculiar substance named 

 by him " vibratory matter," which adheres to the surfaces on which the pheno- 

 menon shows itself. Brit, and Foreign Med. Rev. Vol. iii. p. 467. The expla- 

 nation of Raspail, and the foolish hypothesis of Mayer, are completely disproved 

 by the observations of Professor Grant on the Bcroe ; (Trans. Zool. Soc. i. 

 p. 11.) and of Dr Sharpey on numerous animals — Edin. New Phil. Journ. 

 July 1835. 



