142 



THE EVOLUTION OF MAN. 



nucleus. This unicellular body now begins to move, and 

 crawls about in various directions on the glass, on which we 

 are observing it. The shapeless body accomplishes these 



Fig. 13.— A creeping Amoeba (much en. 

 larged). The form-value of the whole or- 

 ganism is that of a simple naked cell, which 

 moves about by means of variable processes, 

 sometimes extended from the protoplasm of 

 its body, sometimes drawn in. In the centre 

 is the round kernel, or nucleus, with its nu- 

 cleolus. 



movements by extending finger-like 

 processes from various points of its 

 surface, which are moved in slow but 

 constant alternations, and draw the rest of the body after 

 them. After a time something new is seen ; the Amoeba 

 suddenly stands still, draws in its processes, and assumes 

 a spherical form. But soon the little slimy ball begins to 

 spread out again, and stretches its processes in different 

 directions, and moves forward again. These variable pro- 

 cesses are called false-feet (Pseudopodia), because they 

 perform the office of feet, and yet are no special organs, in a 

 morphological sense; for they vanish as quickly as they 

 appear, and are only variable extensions of the semi-fluid, 

 homogeneous, and structureless substance of the body. 



If one of these creeping Amoebae is touched with a 

 needle, or if a drop of acid is added to the water, the whole 

 body at once contracts in consequence of this mechanical or 

 chemical irritation. Usually it reassumes its spherical 

 form. Under certain circumstances, for example, if the 

 impurity is retained in the water, the Amoeba begins to 

 encase itself. It exudes a homogeneous envelope, or cap- 



