2 14 THfe BEHAVIOR OF LOWER ORGANISMS. 



the substratum in Amoeba, may also be induced in the oil drops. For 

 this purpose it is necessary to produce a greater adhesion on a small 

 area at one side. A projection is at once sent out here. The move- 

 ment in sending out such a projection is the same as that to be observed 

 in the formation of a pseudopodium under such circumstances. The 

 projection is thinnest at the tip ; its upper surface moves forward and 

 rolls over at the point, while the lower surface is at rest. 



FORMATION OF FREE PSEUDOPODIA. 



On the other hand, the projection of free pseudopodia into the water 

 cannot be imitated under these conditions. As we have seen, the move- 

 ment in the formation of a free pseudopodium differs from that in form- 

 ing a pseudopodium along a surface merely in the fact that in the latter 

 case the contact surface is at rest, while in the free pseudopodium all 

 surfaces move equally, a given point on the surface remaining approx- 

 imately at the same distance from the 'tip. In the inorganic drop pro- 

 jections can indeed be formed in which the surface moves in exactly 

 the same manner as in the free pseudopodia of Amoeba, but under con- 

 ditions that are essentially different. If some small object to which the 

 fluid adheres, such as a sliver of wood, is brought into contact with one 

 side of the drop, the fluid flows out over it, and may form thus a long, 

 slender projection. The surface of -this projection moves in the same 

 manner as the surface of a pseudopodium in Amoeba (p. 153). Thus 

 the surface of a free pseudopodium shows such movements as it would 

 if drawn out by an object to which it adheres at its tip. Since no such 

 object is present, it is clear that the formation of free pseudopodia is not 

 explicable in this manner. 



As we have seen above, the locomotion and the formation of pseudo- 

 podia in contact with the substratum could, if they stood alone, be con- 

 sidered due to the adherence and spreading out of a fluid on a solid, as 

 maintained by Berthold (1886). But they do not stand alone ; we have 

 the additional fact that pseudopodia may be sent out which are not in 

 contact with the substratum. The anterior edge of an Amoeba, further, 

 may be pushed out freely into the water as a single pseudopodium. 

 This may frequently be seen in Amoeba Umax. As a reaction to a 

 stimulus the protoplasm may push upward freely as a thick lobe, till 

 the greater part of the substance is transferred upward and the Amoeba 

 topples over (p. 184) . In the formation of such a lobe, the protoplasm 

 may flow from both ends toward the middle, producing the " heaping 

 up" from which the thick upward projection results (see p. 183). 

 Currents flowing in this manner could not possibly be produced by 

 adherence to the substratum. Again, in an advancing Amceba ang'u- 

 lata, short triangular pseudopodia are constantly pushed forward, some 

 in contact with the substratum, others not thus in contact, but raised a 



