134 THE BEHAVIOR OF LOWER ORGANISMS. 



point of lowered tension. Diagrams of the movement of such drops 

 are given in Fig. 34. Further, the drop may elongate in the direction 

 of the axial current, and may move bodily in that direction, just as 

 happens in Amoeba.* It is most natural, therefore, to conclude as 

 Biitschli (1892) and Rhumbler (1898) have done, that the movements 

 of Amoeba are likewise due to a lowering of the surface tension at the 

 anterior end, provided that its movements really take place in the 

 way described above. 



CURRENTS IN AMCEBA AS STUDIED FROM ABOVE ; LACK OF BACKWARD 



CURRENTS. 



At the beginning of my work I had no doubt that the movements 

 occurred exactly as above described, and, therefore, did not devote 

 special attention to this point. But I was soon struck by the fact that 

 I was unable to see any backward current at the sides, as represented 

 in Figs. 30 and 31. Further careful study of the movements of 

 Am&ba Umax, A. protcus, A. angulata, A. verrucosa, A. sphcero- 



nucleolus, and one or two 

 undetermined species 

 confirmed this fact, and I 

 may say at once that after 

 several months' continu- 



B ous study of the move- 



- 34-t 



ments and reactions of 



Amoeba I have never, except in one or two doubtful instances, seen 

 any backward movement of the substance at the sides or on the surface 

 of an Amoeba that was moving forward in a definite direction. 



It is true that in the movements of Amoeba Umax, for example, one 

 receives the impression of two sets of currents, one forward in the cen- 

 tral axis, the other backward at the sides. But if the latter is studied 

 carefully it is found that there is really no current here ; the proto- 

 plasm is at rest, and the impression of a backward current at the sides 

 is produced only by contrast with the forward axial current. Amoeba 



* All these facts are easily verified by placing a drop of clove oil on a slide in 

 a mixture of two parts glycerine to one part 95 per cent alcohol under a cover 

 supported by glass rods, as described in a previous paper by the present author 

 (Jennings, 1902). By mixing some soot or India ink with the clove oil the cur- 

 rents are made evident. 



t FIG. 34. Currents in a drop of fluid when the surface tension is decreased 

 on one side. A, the currents in a suspended drop, when the surface tension is 

 decreased at a. After Berthold (1886). B, axial and surface currents in a drop 

 of clove oil, in which the surface tension is decreased at the side a. The drop 

 elongates and moves in the direction of a, so that an anterior (a) and a posterior 

 end are distinguishable. 



