124 



IRRITABILITY 



within a wide limit according to the strength of the stimulus 

 and the distance from the point of stimulation, it is self-evident 

 that no constant figure can be stated. To give a general idea of 

 the rapidity, they might be estimated according to observations 

 I have made with second watch and ocular-micrometer as from 



Fig. 16. 



Difflugia urceolata. A In non-stimulated condition. B The same individual 

 locally stimulated in the middle of a long extended pseudopod. The excita- 

 tion spreads in both directions, centripetal as well as centrifugal. 



within a slight fraction to that of a millimeter in the second. 

 When a very long extended pseudopod is locally stimulated in 

 the middle, the response spreads from the point affected in both 

 directions diminishing in intensity and rapidity. The excitation 

 extends equally in all directions. (Figure 16.) These facts 



