4 THE PSYCHIC LIFE 



have not a trace of an anatomically differentiated 

 visual organ; it is the entire protoplasm of the ele- 

 mentary organism that is excitable by light, as it is 

 also by heat or by electricity. In other Micro-organ- 

 isms somewhat higher in the scale, a beginning of 

 differentiation may be seen to make its appearance, 

 giving birth either to some organ of sense or to some 

 organ of locomotion. 



We shall give a general description of these organs. 

 The study of this first move in the work of differentia- 

 tion is of great interest to comparative anatomy and 

 physiology; no less interesting is it to psychology. 

 Besides dwelling on these preliminaries of our work, 

 we shall have occasion to note new and interesting 



facts. 



I. 



THE MOTORY ORGANS AND THE ORGANS OF SENSE. 



Motility. From the schedule of the groups of ani- 

 mal micro-organisms which we have given, it will 

 be seen that they are subdivided into four classes, 

 the Infusoria, the Mastigophores, the Sarcodines and 

 the Sporozoa. The distinction between these classes 

 depends on the existence and the nature of the motor 

 organs. 



The Infusoria comprise the protozoa that move by 

 the aid of vibratile cilia distributed in greater or less 

 number over their body. 



The second class, the Mastigophores, comprises 

 those animals which move by the aid of flagella, that 

 is to say by the help of long filaments. 



The third class, the Sarcodines, comprises those 

 animals which move by the aid of pseudopodia; which 

 are projections of the substance of their bodies. 



The fourth class, the Sporozoa, is characterized by 



