232 THE BEHAVIOR OF LOWER ORGANISMS. 



(12) Similarly, the movements of material in a forming pseudo- 

 podium are not like those in a projection which is produced in a drop 

 of inorganic fluid as a result of a local decrease in surface tension. The 

 surface currents away from the tip in the inorganic projection are lack- 

 ing in Amoeba, the surface here moving in the same direction as the 

 tip (p. 206). 



(13) The body of Amoeba shows under some conditions elasticity 

 of form, such as is characteristic of solids (pp. 175 *77)- 



(14) Besides the movements directly concerned in the usual loco- 

 motion, limited local contractions may occur, resulting in swinging or 

 vibratory motions of the pseudopodia (p. 177), or in sudden, jerky 

 movements of the body as a whole (p. 179), or in the constricting oft' 

 of parts of the body (p. 180). 



(15) The roughness of surface in a retracting pseudopodium, the 

 retention of irregular forms by Amoeba, and the movements mentioned 

 in the foregoing paragraph, are similar to certain phenomena to be 

 observed in mixtures of solids and fluids, as a result of the interaction 

 of surface tension and the friction of the solid particles (p. 215). 



REACTIONS TO STIMULI. 



(16) The following reactions are described : Positive and negative 

 reactions to mechanical stimuli (pp. 181-187) ; negative reactions to 

 chemical stimuli (pp. 187-190); negative reaction to heat (pp. 190-191); 

 reaction to the constant electric current (pp. 191-192); complex reac- 

 tions connected with food-taking (pp. 193-202); reactions to injuries 

 (pp. 202-204). 



(17) In most reactions modifying the direction of motion a new 

 advancing wave of protoplasm is sent out from some part of that por- 

 tion of the body which is already attached to the substratum. The 

 internal and surface currents then flow in that direction, thus changing 

 the course of the animal. Thus, when the animal changes its course in 

 a reaction, the surface currents change their course in a corresponding 

 way, as shown by the movements of particles on the surface (pp. 143, 

 185, 192). 



(18) Sometimes the course is squarely reversed as a result of a 

 stimulus. In this case the original anterior region becomes detached 

 from the bottom, while a new pseudopodium projects freely into the 

 water from the former posterior (unattached) region, settles down, and 

 becomes attached ; the internal and surface currents then follow it. 

 This process requires usually a considerable interval of time (pp. 183, 

 184). 



(19.) Both surface currents and internal currents are toward the 

 source of stimulation in a positive reaction, away from the source of 

 stimulation in a negative reaction. 



