13 THE PSYCHIC LIFE 



axis on the one spot, during which movement the cili- 

 ated belts beat the water in opposite directions, the 

 anterior ones being turned forwards, while the posterior 

 are turned backwards (fig. 3). The result of this is 

 that the effects of these small locomotive apparatuses 

 neutralize each other in the same manner as two heli- 

 ces acting in opposite directions, and that the animal 

 remains stationary, while all the time turning rapidly 

 about itself, sometimes horizontally, sometimes verti- 

 cally on its conical appendage, just as on a pivot." 



Certain Infusoria, for example the Condylostoma 

 patens, which has been thoroughly studied by M. 

 Maupas, possess at the same time the two kinds of 

 appendages, the cilia and the cirri. The former, which 

 cover the dorsal surface of the animal, are fine, very 

 dense and animated by a rapid and unceasing vibra- 

 tile movement. The cirri, which cover the ventral 

 surface are placed apart; furthermore they do not vi- 

 brate rapidly; their movements are slow, and when 

 the infusory moves, one can see them move success- 

 ively on the plate of glass and support themselves 

 there, in the manner of a foot, to make the body ad- 

 vance. When the animal stands still, the cirri are ab- 

 solutely immobile, while the cilia continue their vibra- 

 tile movement. This observation which* can equally 

 well be made of the Oxytrichid, shows that the vibra- 

 tile cilia are the organs of involuntary movement, and 

 that the cirri are more directly subject to the will. 

 The fact is demonstrated by the experiments of Ross- 

 bach, who observed that, under the influence of the 

 falling of the temperature (from + 15 to 4- 4) or of 

 the rising of the temperature (from + 35 to 4- 40) or 

 under the influence of various chemical substances, 

 the large cilia, the organs of voluntary movement, are 



