THK MOVEMENTS AND REACTIONS OF AMCEBA. 219 



the restoration of the original length in a given side after liquefaction 

 and consequent contraction had occurred. This could, perhaps, be 

 brought about by an elastic rod in the axis of the structure, such as 

 many cilia and flagella are known to possess. 



The above is merely a suggestion made tentatively ; its justification 

 as a suggestion lies in the following facts: (i) The swinging move- 

 ment of pseudopodia in Amoeba in some cases strikingly resembles 

 movements of the character above set forth in inorganic fluids, and 

 precisely the conditions for such movements are present in Amoeba ; 

 (2) Swinging movements of pseudopodia seem to grade almost insen- 

 sibly into the vibratory movements of flagella. 



DIRECT OR INDIRECT ACTION OF EXTERNAL AGENTS IN 

 MODIFYING THE MOVEMENTS. 



Is the effect of external agents in modifying the movements of Amoeba 

 due to the direct physical action of the agent on that part of the fluid 

 substance with which it comes in contact? Or is its action indirect, 

 in that it serves merely as a stimulus to certain internal changes, the 

 latter bringing about the modifications in the behavior? Both views 

 find adherents. The difference between them is fundamental, for they 

 lead to essentially different conceptions as to the nature of behavior in 

 these lower organisms. 



In higher animals we know that the movements and changes of 



o o 



movement are not produced in a direct way, but the effect of external 

 agents is to cause internal alterations which result in changes of move- 

 ment. It is not, therefore, possible to predict the movements of the 

 organism from a knowledge of the direct physical changes produced in 

 its substance by the agent in question. If the theory of direct action is 

 correct for Amoeba, we have in these animals a condition of affairs incom- 

 parably simpler, for here we can resolve the behavior directly into its 

 physical factors. If, on the other hand, the theory of indirect action is 

 correct, then there appears to be nothing fundamentally different in 

 principle between the behavior of Amoeba and that of higher organisms. 

 How the form and movement of a fluid mass might be determined 

 by the direct action of external agents on its surface may be simplv 

 illustrated by certain experiments which I have described elsewhere 

 (Jennings, 1902). A mixture of 2 parts glycerine and i part 95 per 

 cent alcohol is placed on a slide and covered with a cover glass sup- 

 ported by glass rods. Into this is introduced with a capillary pipette 

 a drop of clove oil. The clove-oil drop, at first circular in form, soon 

 changes shape, shows internal currents, sends out projections in various 

 directions, moves about from place to place, and may divide into two 

 drops. The alcohol, not being uniformly distributed throughout the 

 glycerine, acts more strongly on some parts of the clove-oil drop than 



