RESPONSIVE LIFE OF ORGANISMS 437 



I. ANIMAL ACTIVITIES. 

 I. Some typical sensory phenomena of the Protozoa. 



In such an organism as an amoeba, which lacks as we have 

 seen, permanent organs of either of the classes just men- 

 tioned, we may observe activities of the same sorts as those 

 above cited for the slime-mold plasmodium. An amoeba 

 creeps about freely, manifesting like movements of contact 

 and avoidance. It adjusts the form of its body to getting 

 through narrow passageways, it changes its course of loco- 

 motion in avoidance of an obstruction. Now and then it 

 makes a more special response to things in its environment. 

 Coming in contact with a diatom, or other small organism 

 suitable for food, the amoeba moves toward it, extends its 

 pseudopodia and flows about it, and finally completely 

 engulfs it. This is a definite food 

 taking reaction. On the other hand, 

 it withdraws itself promptly from a 

 sharp mechanical stimulus, such as 

 the prick of a glass stylus (fig. 256), 

 a wave of movement in the proto- 

 plasm of its body away from the 

 point stimulated, being immediately 

 discernible. 



FIG. 256. Diagram of the q> n -u/hat cnrf rvf 

 avoiding reaction in Amoeba. iO Wiiat SOrt OI 



?aVeV h b e y P a Si g?a n ss w st e ;iu s s im 6" * hese simple external acts may corre- 

 &*fcrfS5?arn>cd we cannot say. What the 

 protoplasm. (After Jen- world and the things therein may be 



like to an animal of this sort we could 



only know by being amcebas awhile. Indeed, we cannot 

 conceive what it would be like to ourselves if we had never 

 seen or handled things, and if we had no means of knowing 

 objects as such, but only as the obtruding parts of a general 

 environment. Perhaps, there may be some sort of vague 



