MOTOR RESPONSES IN INVERTEBRATES hll 



in the electric equilibrium in the molecules, which results in changes in 

 the charge they carry, or in polarization, and it is quite conceivable that 

 this could cause such an alignment of the molecules as to result in the 

 formation of gel. It is also well known that mechanical agitation facili- 

 tates the alignment of molecules in the process of crystallization. This 

 seems to indicate that it could in the same way facilitate gelation. If 

 this is true, it supports Folger's contention that stimulation by light is 

 due primarily to photophysical effects. 



McClendon (164) maintains that localized chemical stimulation of 

 one pseudopod of an amoeba results in cessation of movement in all the 

 pseudopods, i.e., that such stimulation produces impulses which are 

 transmitted to all parts of the body. Verworn (208) comes to similar 

 conclusions. Mast (154) obtained results which are in opposition to 

 these conclusions. He maintains that localized illumination causes, 

 by its gelating effect, increase in thickness and in the elastic strength of 

 the plasmagel in the region illuminated, that this effect is not transmitted 

 to other regions and that there are no impulses produced, but that the 

 effect of localized gelation and the consequent contraction is transmitted 

 and that this results in coordinated action. 



Response of Amoeba to electricity is due primarily to solation of the 

 plasmagel on the anodal side (Luce, 130; Mast, 153a). The contention of 

 Bayliss (12) that it is due to gelation has not been confirmed. Light and 

 electricity consequently appear to be opposite in action. 



Amoeba does not respond to light while it is feeding. "When the 

 food cup is being formed and the pseudopods are flowing around the prey, 

 there is no response to light, no matter how great the intensity may be" 

 (Folger, 64). This indicates that response to light in this organism is 

 closely correlated with its physiological state. The effects of mechanical 

 agitation and of chemicals in the surrounding medium support this 

 contention. 



Mast (139) and Mast and Pusch (163) maintain that the change in 

 response correlated with change in physiological state is, under some 

 conditions, analogous to what is called "learning" in higher animals. 

 They found that if a pseudopod of an amoeba, going in a definite direc- 

 tion, comes in contact with a spot of intense light, it stops and is retracted, 

 that then other pseudopods are formed in succession, come in contact 

 with the light, stop, and are retracted; that after a number have thus 

 come in contact with the light, the direction of streaming is suddenly 

 reversed and the amoeba moves away from the spot of light; and that as 

 the number of reversals in a given individual increases, the number of 

 successive contacts with the spot of light required to induce a reversal 

 decreases. This, they maintain, indicates learning. 



Mast (154, 155) observed that if a large portion of the tip of the 

 pseudopod is illuminated with very intense light, reversal occurs after a 



