92 TEXTBOOK OF ZOOLOGY 



Successive pseudopodia are formed in the moving Amoeba proteus as 

 it goes in a given direction. The pseudopodia are temporary loco- 

 motor structures. Most zoologists explain this movement as being 

 due to the contraction of the more viscous ectoplasm, particularly in 

 the "posterior" region. This brings about a forward movement in 

 the more fluid eudoplasm (plasmasol) which causes an outflow at 

 points where the ectoplasm is thinnest, or where surface tension is 

 lessened. As this plasmasol approaches the advancing tip of the 

 pseudopodium, it turns to the sides and changes to more solid endo- 

 plasm (plasmagel). This process continues, pushing the advancing 

 tip farther and farther forward. At the opposite side, the plasma- 

 gel continues to become plasmasol to provide for fluent material. 

 At the side of the animal away from the advancing pseudopodium, 

 the cell membrane (plasmalemma) moves upward and over the up- 

 per side of the body ; it continues to move forward to the tip of the 



- - Particle -"" i 



Pseudopodium 



Fig. 37. — Successive positions in the movements of an amoeba viewed from 

 the side. Notice the formation of new pseudopodia and tlae engulfing of the 

 particle on the surface. (Modified from photographs by Bellinger, 1906, Journal 

 of Experimental Zoology.) 



pseudopodium where it dips down and is laid on the substratum 

 over which the animal is moving and becomes a part of the station- 

 ary portion. If the specimen has several pseudopodia, one or more 

 may be developing while others are receding. In the latter, the 

 flow of plasmasol is back through the centers of the pseudopodia 

 toward the main mass. Temperature and other environmental fac- 

 tors affect the rate of locomotion. 



Dillinger mounted some of the animals on the edge of a slide in 

 a groove formed by the projecting edges of two cover glasses and 

 observed their movement from side view by tilting the microscope 

 to a horizontal position. He describes their movement as a sort of 

 walking on the progressively forming pseudopodia. The new 

 pseudopodia are formed at the advancing margin of the cell. 



