The Mind of the Simplest Animals 39 



in consequence of the diminished tension there, rolls. Such 

 movements, Rhumbler shows, can be reproduced by placing, 

 say, a drop of clove oil under the proper conditions of surface 

 tension (361, 362). Jennings, on the other hand, has ob- 

 served, at least in certain species of Amoeba, that the proto- 

 plasmic currents are all forward in direction, the movement 

 being really one of rolling, complicated by the attachment of 

 the lower part of the body to the solid object on which the 

 animal crawls. Mechanical conditions of surface tension 

 would not account for such currents (204, 206, 211). Del- 

 linger, finally, rejects both the surface tension and the "rolling" 

 theories, and from a study of side views of the moving Amoeba 

 concludes that progression occurs through the advancement 

 of the front end freely through the water and its subsequent 

 attachment, the rest of the body following through active con- 

 traction brought about by a contractile substance (98). The 

 problem is of great interest to the student of vital phenomena, 

 but its bearing on the question of mind in the Amceba is so 

 obscure that we need not consider it further, but may pass at 

 once to the study of the animal's reactions to special stimula- 

 tion. 



These are, according to Jennings (206, 211), the foremost 

 authority on the behavior of the lowest organisms, three in 

 number; namely, the negative, the positive, and the food- 

 taking reactions. First, if an Amceba comes into strong con- 

 tact with a solid obstacle in its movements, or if a solution of 

 different composition from the water in which it lives strikes 

 against it, or if one side of it is heated, the animal responds 

 by contracting the part stimulated, releasing it from the sub- 

 stratum, and moving in another direction, usually one form- 

 ing only a small angle with the preceding one. If the whole 

 of one side or end receives a strong stimulus, if light falls on 

 one side, or an electric current is passed through the water, the 



