ILLUSTRATED AMONG PROTOZOA. Ill 



repeated. At any rate, there would be almost 

 constant variation in the chemical changes of the 

 protoplasm. Thus after each movement of the 

 protoplasm, the stimulus remains to start a new 

 movement. By constant repetition of the reaction, 

 nervous co-ordinations would be formed and per- 

 fected, so that movements at first slow would 

 become more and more rapid, until they finally 

 resemble a tetanus, or else the quick movements of 

 the cilia or flagella of the infusoria. Some of the 

 shell-amoebae make movements intermediate in form 

 and rapidity between the ordinary slow amoeboid 

 motion and the quick motion of the flagellum of 

 an infusorian. Any movements of the body would 

 thus constantly tend to become a means of loco- 

 motion. 



The periodical and occasional stimuli acting on 

 an organism so primitive would necessarily be of 

 few kinds. The same stimuli and series of stimuli 

 would be frequently repeated. Those which were 

 repeated most frequently would of course have the 

 greatest effect, while those that occurred very rarely 

 would have little or practically no effect. In the 

 course of time, therefore, as this process of repeti- 

 tion goes on, the organism would acquire a facility 

 of reaction due to nervous co-ordinations. In these 

 nervous co-ordinations we see a development caused 



