94 Jennings, The Movements and Reactions of Amoeba. 



movements due to this cause there is a surface current away from 

 the region of lower tension, with a central current toward this 

 region, while in Amoeba surface and central currents are congruent; 

 they are indeed one and the same. Such movements as are shown 

 by Amoeba cannot be produced through local changes in the sur- 

 face tension of a drop of fluid. The commonly accepted expla- 

 nation of the movements of Amoeba, to the effect that they are 

 due to a decrease in surface tension at the anterior end, must 

 then be given up. Such a local decrease of surface tension would 

 produce movements of a character totally different from those 

 which actually occur 1 ). The actual movements of Amoeba resemble 

 even in details the movements of a drop of fluid which adheres 

 on only one side to the substratum. But all the movements con- 

 cerned in the locomotion of Amoeba can take place without such 

 adherence, so that this does not furnish an explanation for the 

 movements of the animal. 



All the movements, and the reactions to stimuli, were studied 

 carefully and are described in the original paper in much detail. 

 Special attention was paid to the various physical explanations 

 that have been proposed for the reactions, and it w T as found that 

 most of these will not stand the test of a comparison with what 

 actually occurs in the organism. Under some conditions the be- 

 havior was found to be very complex; this was notably true of 

 the process of food taking. Illustrated descriptions are given of 

 Amoebae following a spherical cyst of Euglena, which is pushed 

 forward by the efforts of the animal to ingest it; in some cases 

 a single Amoeba follows the same rolling cyst for fifteen minutes 

 over an irregular path. The pursuit of one Amoeba by another 

 is described in a number of cases. A twenty minute drama is 

 illustrated in detail, with sketches made while it was in progress. 

 One Amoeba pursued another for a long time, finally capturing 

 and ingesting it. After carrying it away for a short distance, the 

 prey partly escaped, and was recaptured. It again escaped com- 

 pletely, but was pursued, overtaken, recaptured, and again carried 

 away. After five minutes it escaped again, and this time comple- 

 tely, so that the hunter Amoeba went on its way without its meal. 



University of Pennsylvania, Philadelphia, Penn., U. S. A.. 

 Nov. 7, 1904. [80] 



Explanation of Figures. 



Fig. J. Paths of two particles attached to the outer surface of Amoeba 

 sphaeronucleolus. The animal is moving toward the end marked a; no attempt is 

 made to represent this movement in the figure. That portion of the paths that is 

 on the lower surface is represented by broken lines. These two particles were seen 

 to make five complete revolutions about the animal, in the paths shown. 



Fig. 2. Diagram of the locomotion of Amoeba, in side view. A, anterior 

 end; P, posterior end. The arrows show the direction of the currents of proto- 



1) There remains of course the' same possibility as for ciliary and muscular 

 movement, - that the phenomena result in some way from changes in the sur- 

 I'ace tension of the ultimate protoplasmic elements. This hypothesis is not open to 

 experimental test. 



