210 THE BEHAVIOR OF LOWER ORGANISMS. 



By inclining the vessel the drop may be made to roll away from the 

 attractive spot ; then when the level is restored it moves back again. 

 By repeating this process the movements may be studied in detail. 

 P"br studying the movements in all parts except at the anterior edge 

 another more convenient method may be employed. A small piece of 

 wood may be brought against one side of the drop ; toward this it 

 moves in the manner just described. If the piece of wood is moved 

 continually in a certain direction, the drop follows, and its movements 

 may be examined with ease. In this case the anterior edge, of course, 

 is not thin and pressed against the surface, but otherwise the move- 

 ments are the same. 



By proper modifications further details of the movement of Amoeba 

 are exactly imitated. Thus a quantity of sand grains or other heavy 

 objects may be added to the drop. In the movement these collect at 

 the posterior end, as happens with the coarse internal contents in 

 Amoeba. A large, spherical bubble of oil may be introduced into the 

 drop, in imitation of the contractile vacuole ; this likewise stays near 

 the posterior end. When a considerable quantity of heavy material is 

 collected at the posterior end, the latter becomes drawn out into a sort 

 of pouch, which is dragged along, its substance not partaking of the 

 currents shown by the remainder of the drop. It thus plays the same 

 part as the well-known posterior appendage of Amoeba. Material 

 passes up from the bottom to the upper surface on each side of this 

 posterior pouch, just as happens in Amoeba (see p. 168). Particles 

 clinging to the outer surface at the posterior end are often dragged 

 along for a considerable time, then finally pass upward to the upper 

 surface and so forward, exactly as described for Amoeba (p. 169).* 



In another detail the movements of the drop of water or glycerine 

 are strikingly like those of Amoeba. As we have seen, the current is 

 most rapid at the anterior end in both cases, becoming as a rule slow 

 toward the rear. But I have pointed out that in Amoeba the move- 

 ments at the posterior end are not uniform. Sometimes the under sur- 

 face remains attached to the bottom longer than usual, then, when it 

 becomes detached over a considerable area at once, there is a sudden 

 rush of the fluid forward from the posterior region (p. 168). Exactly 

 the same thing is to be observed in the inorganic drop. The bottom 

 is not uniform, so that sometimes the posterior end clings to it longer 

 than usual ; this end is then drawn out, and when it is finally released 



*It may be worth while to state that these experiments on inorganic fluids 

 were performed after the work on the movements of Amoeba had been completed 

 and the description entirely written in the form given in the preceding pages. 

 No details of the movements of Amoeba were added after the behavior of the 

 inorganic drops had been studied; 



