OF MICRO-ORGANISMS. 31 



formed of a vesicle, the centre of which is occupied by 

 a refracting globule; they are called the vesicles of 

 Miiller, after Johannes JMuUer, who discovered them. 

 The auditory organs which have been observed in 

 Worms and the Ccelenterata are apparentl}' composed 

 of a vesiculiform capsule enclosing a solid concretion, 

 called otolith. Thus it is possible that the vesicles of 

 Miiller may be auditory vesicles. Up to the present 

 time this organ has not been met with in any other 

 species of Protozoa. 



NUTRITION. 



After studj'ing the organs, let us pass to a study 

 of their functions. 



It is not our intention to devote special chapters to 

 irritability, instinct, memory, reasoning, and thepowers 

 of volition in Micro-organisms. This would lead to 

 diffuseness of treatment. Our method will be quite 

 different. We shall describe as a whole all the dif- 

 ferent manifestations of psychical activit}' attendant 

 upon the actions of Micro-organisms in the exercise 

 of the important functions of their existence. The 

 present chapter will be devoted to psychical phe- 

 nomena connected with the act of nutrition. 



All living matter possesses the power of continu- 

 ally increasing its mass b}' the inward reception of 

 materials, and of simultaneously decreasing the same 

 through the combustion of its substance with the 

 oxygen of the atmosphere. The first of these pro- 

 cesses is called nutrition, and the second, respiration. 



We shall first examine the psychical phenomena 

 which precede and determine the act of respiration. 

 These phenomena are often very simple and of little 



