20 



AMEBOID MOVEMENT 



Figure 3. Formation of longitudinal ridges and grooves in the ecto- 

 plasm of Amoeba proteus. A, B, C, D, showing stages in the development 

 of a single pseudopod. a, b, c, d, d 1 , cross sections of pseudopods at the 

 levels indicated. The arrows show the direction of endoplasmic stream- 

 ing with special reference to the formation of ridges. The numerals I 

 to 7 indicate the order in which the ridges were formed. Note the tongues 

 of ectoplasm which extend into the endoplasm, in the cross sections. 



thetically-minded naturalist, that of the large number of subse- 

 quent writers on ameboid movement only one (Penard, '02, p. 

 63) seems to have noticed these folds. Leidy says that "... the 

 main trunk and larger pseudopods of the same ameba (proteus} 

 assumed more or less the appearance of being longitudinally 

 folded. The endosarc axially flowed as if in the interior of thick 

 walled canals, of which the walls appeared to be composed of 

 finer granular matter with scattered imbedded crystals. In the 

 flow, all the contents did not move with the same rapidity, and 

 usually the smaller particles were swept quickly by the larger 

 ones. Other matter, including some of the largest elements ap- 

 peared to stick to the inner surface of the extemporaneous tubes, 

 but successively became detached to be carried along with the 

 rest of the contents (p. 46)." "The endosarc appeared to flow 

 within thick walls of ectosarc which often seemed to be longi- 

 tudinally folded (p. 326)." Penard ('02) confirms Leidy's obser- 

 vation as to the existence of these folds: "The current (of endo- 

 plasm) indeed is not unified, but there exist many currents at the 

 same time because of the fact that the endosarc is divided into a 



