20 



PSYCHOBIOLOGY 



Fig. 7' Diagram showing an amoeba in three stages of locomotion. (Jennings, 

 'Contributions to the Study of the Behavior of Lower Organisms.) In a the amoeba, 

 with its pseudopodia fully extended so that its body is reduced to little more than a 

 pseudopodial conjuncture, is floating in the water, but one pseudopod has come in 

 contact with the surface of a solid. In b the protoplasm has begun to flow out of the 

 other pseudopodia into the one attached to the solid. In c the amoeba is reduced to a 

 more compact mass, creeping along the surface. In thus creeping the protoplasm flows 

 from the larger portion into the smaller, and the upper surface moves forward, so 

 that the motion is somewhat like that of rolling a bag partly filled with a semi-fluid, 

 i by pulling on the front edge. 



Fig. 8. Pigment cell from skin of frog, showing four stages, from A, complete 

 extension, to D, complete retraction of the pigment. (Verworn, Allgemeine Physi- 

 Mogie.") It is a question whether the cell-branches are retracted and extended (and 

 are therefore to be considered as pseudopodia) or the branches are fixed in form, and 

 only the pigment moves. 



Certain unicellular organisms are able to throw out pseudopodia, or 

 leg-like projections of the protoplasm, and retract them, thus assuming 

 various irregular shapes [Fig. 8]. By means of these pseudopodia cer- 

 tain cells are enabled to move about; according to one theory, using 





