THE MOVEMENTS AND REACTIONS OF AMCEBA. 231 



surface thus moves outward, and new parts of the surface of the body 

 continually pass on to the pseudopodium. An object adhering to the 

 surface of the pseudopodium remains at approximately the same dis- 

 tance from the tip, both when the pseudopodium is short and when it 

 has become very long (pp. 153-156, and Figs. 47-49). 



(5) In the withdrawal of a free pseudopodium (a) a process occurs 

 that is the reverse of that described in (4), the surface of the pseudo- 

 podium passing from its base on to the surface of the body (p. 156, 

 and Fig. 49) ; (b) the surface of the pseudopodium becomes wrinkled 

 and shrunken ; (c) the endosarc flows back into the body. 



(6) Any part of the protoplasm may be excluded temporarily from 

 the forward currents. In many Amoebae there is usually a region at 

 the posterior end which is thus temporarily excluded (the posterior 

 appendage, tail). In such cases the lower surface of the Amoeba 

 passes upward on each side of this appendage to become part of the 

 upper surface, then passes forward (p. 169, and Fig. 57). The sub- 

 stance of the posterior appendage is itself gradually drawn into the 

 forward current. 



(7) The anterior portion of the advancing Amoeba is attached to the 

 substratum, while the posterior portion is not (p. 165). There is a viscid 

 secretion produced on the outer surface of the Amoeba, to which the 

 attachment may be due. 



(8) The attached anterior portion of the body is spread out and 

 usually very thin. The unattached posterior portion becomes rounded 

 and thick, and is contracting, so that there is a slight forward move- 

 ment on the lower surface, as well as on the upper surface, in this part 

 (p. 166). 



(9) All the activities concerned in locomotion can be performed when 

 the animal is not attached to the substratum. (But for progression such 

 attachment is necessary, p. 215.) 



(10) The locomotion of Amoeba is similar even in details to the 

 movements of a drop of inorganic fluid which adheres strongly to the 

 substratum at one edge and spreads out upon it here, while the other 

 edge is free (pp. 209-214). It is similar in most respects (except in the 

 thinness of the anterior edge) to the movements under the influence of 

 gravity of a drop of fluid along an inclined surface to which it adheres 

 but slightly. 



(i i) The currents in a moving Amoeba are not similar to those of a 

 drop of inorganic fluid that is moving or elongating as a result of a local 

 increase or decrease in surface tension. The surface currents away 

 from the region of least tension and in the opposite direction to the 

 axial currents that are characteristic of such a drop are lacking in 

 Amoeba. Here surface and axial currents have the same direction 

 (p. 205). 



