4 BEHAVIOR OF THE LOWER ORGANISMS 



obtained in the following way: Pin two edges of a handkerchief to- 

 gether, so as to make a flat cylinder. Within this place some heavy 

 objects that will fill part of the cylinder, and lay the whole on a flat sur- 

 face. Now pull forward the upper surface of the cloth near the anterior 

 edge, a little at a time, bringing it in contact with the substratum. If 

 this process is continued, the handkerchief rolls slowly forward with thin 

 anterior edge and high posterior portion, — the weight within dragging 

 behind. The lower surface is at rest while the upper surface moves 

 forward. In all these respects the movement is like the locomotion of 

 Amoeba. A diagram of the movement of Amceba as it would appear 

 in side view is given in Fig. 6. 



While typically all the currents are forward in a progressing Amoeba, 

 any portion of the protoplasm may be excluded temporarily from the 

 currents. This is especially common at the posterior end or tail, which 

 is often composed of quiet protoplasm, covered with wrinkles or papillae 

 But the substance of the tail is in the course of time drawn into the cur- 

 rents and passes forward. 



In the formation of pseudopodia the movement is much like that at 

 the anterior end of the body. If the pseudopodium is in contact with the 

 substratum, the upper surface moves forward while the lower surface is 

 at rest. If the pseudopodium is sent forth freely into the water, its 

 entire surface moves outward, in the same direction as the tip. These 

 movements have been determined by observing the motion of particles 

 attached to the outer surface of extending pseudopodia. 



In some Amoebae, according to Rhumbler (1898, 1905), the external 

 protoplasmic currents turn backward at the sides of the anterior end, 

 so that there is produced a fountainlike arrangement, an internal 

 current forward, external currents backward. Such currents resemble 

 those due to local decrease of surface tension in a drop of inorganic fluid. 



Through such a local 

 decrease the tension 



/^_ „ - * — -^~ ■« — *j\ p or pulling along the 



surface is lessened 

 in a given region, 

 so that the remain- 



FiG. 7. — Currents in a drop of fluid when the surface tension . - . . 



is decreased on one side. A, the currents in a suspended drop, OCT OI tne SUTiace 



when the surface tension is decreased at a. After Berthold. B, fllni is Dulling more 

 axial and surface currents in a drop of clove oh in which the , . ' , 



surface tension is decreased at the side a. The drop elongates Strong!) , It tnere- 



and moves in the direction of a, so that an anterior (a) and a fore dl'a^S the SUT- 



posterior (p) end are distinguishable. { ] ( +1 



drop away from the point of lowered tension. The result is that cur- 

 rents pass on the surface in all directions away from this point (Fig. 7). 



