8 THE PSYCHIC LIFE 



point of the body, on a level with the anterior part; 

 but, in spite of this constant localization, the motor 

 organ has only a transitory existence; it is produced 

 at the moment it is needed, and disappears into the 

 mass of the body, when the movement has been exe- 

 cuted. In the Actinophrys there is a still greater pro- 

 gress: the numerous pseudopodia emitted by this ani- 

 mal, and which have the form of filaments, are perma- 

 nent organs with definite functions. 



The Vibratile Cilia. The vibratile cilia are short, 

 extremely thin, homogeneous filaments which are agi- 

 tated by a vibratory movement. These are distinctly 

 differentiated organs of locomotion. They have, 

 moreover, several functions: firstly, they enable the 

 animal to move about in the liquid; secondly, they 

 serve it as an organ of prehension; thirdly, they per- 

 mit a renewal of the water which furnishes the neces- 

 sary air for respiration to the animal; perhaps they 

 also serve as organs of touch. 



The vibratile cilia lend to the Infusoria their peculiar 

 character and enable them to be distinguished from 

 all the other Protozoa. Cilia are also found in 

 vegetable species when young, and in the larvae of 

 Coelenterates, of mollusks and of .worms. But 

 among the Protozoa, it is the Infusoria alone that are 

 ciliated. The cilia are distributed in various manners, 

 differing according to the species. In the holotricha, 

 they are distributed regularly over the whole surface 

 of the body, and almost all have the same length; in 

 the Heterotricha, they also cover the whole surface of 

 the body, but they are unequal in length. To this 

 group belong the Stentors which have long cilia in- 

 serted around a circular surface, extending almost to 

 the mouth. This surface is a rotatory organ, analo- 



