58 AMEBOID MOVEMENT 



Figure 24. Showing the effect of a narrow anterior end on the rate of 

 movement of the surface. Length of the ameba, about 320 microns. 



narrowed down very considerably. These changes in the width 

 of the anterior end are reflected, as in Figure 17 by a decrease in 

 the relative speed of the moving particle. Thus the particle moved 

 1.75 times as fast as the ameba from I to 2 while from 2 to 4 

 the particle moved only 1.27 times as fast as the ameba. 



The movement of the third layer in proteus is difficult to study 

 owing to the formation continually of ridges, as explained on page 

 20. Even in clavate shaped amebas, waves of protoplasm are 

 pushed out on the sides and on the tip with consequent formation 

 of ectoplasm, so that the ameba grows in width slowly at the same 

 time that it grows in length. A typical shape of a proteus in 

 clavate form is slightly tapering toward the anterior end. This 

 shape is maintained by gradual extension of the sides of the 

 anterior half or two-thirds of the ameba as it moves along. These 

 conditions are just the reverse of what was seen to be the case 

 in sphaeronucleosus and verrucosa, where the anterior edge was 

 wider than any other part of the body. But discoides, although 

 free from the ridges and grooves characteristic of proteus, fre- 

 quently has an anterior edge that is narrower than any part of 

 the body, thus necessitating extension of the sides as the ameba 

 moves forward. 



Let us now see what is the effect of ridge formation upon the 

 movement of the surface layer. Figure 25 shows a proteus and 

 a narrow anterior end in proteus with two pseudopods and a 

 particle attached to the side of the ameba at i. Both pseudopods 

 advanced until stage 4 was reached, but the particle was not 

 appreciably deflected from an approximately straight path by 

 the small pseudopod at the other side of the ameba. Reference 

 to the figure shows that the particle travelled much faster while 

 the pseudopod on the side was extending than after it began to 



