DIGESTION A SPECIAL FUNCTION. 213 



tive material directly ; we can also conceive the digestive 

 act reduced to a sinqsle mechanical apparatus Avhich has to 

 press out certain alimentary juices capable of nourishing the 

 tissues without undergoing chemical modifications; but 

 usually the digestive act is composed of two orders of pheno- 

 mena, physical and chemical/'* This is a brief and luminous 

 classification as regards the whole animal series, and it well 

 exjiresses the ascending complexity of that series ; but inas- 

 much as special functions only make there appearance at 

 certain stages of that ascending series, inasmuch as the 

 simpler animals have not the special functions of more com- 

 plex animals, we must deny to the two first classes of M. 

 Bernard's series any such special function as Digestion, and 

 confine it to the third class. We do not, except in loose 

 latitude of phrase, speak of the legs of an animalcule, mean- 

 ing its organs of Progression; because a leg is a specific organ 

 of Progression, imiform in its elements throughout the series 

 of animals possessing legs ; nor should we, otherwise than in" 

 easy speech, talk of the Digestion of a Polype, meaning there- 

 by its Nutrition. The jmrpose of a leg, progression, is ful- 

 filled by the cilia, which move the animalcule ; the purpose 

 of Digestion, preparation of food, is performed by the cavity 

 of the Polype ; but the specific organs named legs and ali- 

 mentary canal, and the specific functions of those organs 

 (Walking and Digestion), are in both cases absent. 



If the reader has followed me thus fiir, he will have 

 understood that, when I doubted whether the Actinia? 

 digested, there was no doubt entertained of their power of 

 * Claude Bernard : Legonsde Physiol. Ex})erime7dale, ii. 490. 



