636 THE AMERICAN NATURALIST. [Vol. XXXVI II. 



cannot be considered due to local decrease in surface tension. 

 There are no superficial currents away from the re<(ion toward 

 which the animal moves, but all parts that are in motion move 

 toward the object causing the reaction. (For details, see Jen- 

 nings, :04.) The experiments do not imitate the essential 

 features of the action of Amoeba, and do not show us the 

 causes at work in its behavior. The reactions of Amoeba are 

 not simple direct results of the physical action of the agents 

 producing them, but are indirect, like those of higher ani- 

 mals. 



Many imitations have been devised for the taking of food by 

 Amoeba. Rhumbler ('98) holds that the ingestion of food by 

 Amoeba is due to physical adhesion between the liquid proto- 

 plasm and the solid food. He shows that drops of all sorts of 

 fluids take in certain solids in this manner. A drop of water 

 placed at the edge of a plate of glass draws to itself and envel- 

 opes splinters of wood and various other solids which come in 

 contact with it. Glycerine, oils, white of egg, gum arable, mas- 

 tax varnish, etc., are shown to do the same. A convenient way 

 of showing this. is to fill a capillary glass tube with the fluid, 

 then to bring a small piece of the solid in contact with the free 

 surface of the liquid at the end of the tube. The pulling of 

 the solid into the liquid is due to the adhesion of the two, in 

 connection with the surface tension of the liquid. 



These experiments of Rhumbler show that food might be 

 taken in this manner, not that it is so taken. Careful study 

 shows that there is in most species of Amoeba no adhesioa 

 between the protoplasm and the food body. Food is taken by 

 actively enclosing it along with a small quantity of water ; the 

 fact that no adhesion exists between it and the protoplasm is 

 strikingly evident, and occasions much difficulty in the ingestion 

 t>f food. (For details, see Jennings, : 04, and compare the simi- 

 lar account of food-taking by Le Dantec, '94.) Thus the 

 experiments do not really imitate the essential features of the 

 behavior m Amoeba. Only in Amoeba verrucosa and its close 

 relatives is there evidence of adhesion between the animal and 

 its food. But even here there is adhesion equally to bodies 

 which do not serve as food and are not ingested, so that for the 

 ingestion itself an additional factor is necessary. 



