THE CONSERVATION OF LIFE 



213 



that it does not retain the same shape for Jong. Now it rolls 

 itself up into a ball, the next moment extends the body longi- 

 tudinally, or thrusts out sac-like processes. Only sudden stimuli 

 or unfavourable external conditions render the animalcule tem- 

 porarily motionless (fig 51). 



Like all other typical cells, the Amoeba consists of protoplasm 

 and a nucleus. Specific organs have not yet been evolved, but 

 the protoplasm has become separated into a granulated endo- 

 plasm and a more trans- 

 parent hyaline ecto- 

 plasm which surrounds 

 the whole body of the 

 animalcule as with a 

 thin mantle. In the 

 endoplasm take place 

 the digestive functions, 

 while the light-coloured 

 protoplasm - mantle 

 serves the purposes of 

 locomotion. Apart from 

 this the cell-body ap- 

 pears uniform, except 

 that in the interior we 

 observe a little vesicle, 

 filled with a clear liquid, 

 which expands at rhyth- 

 mic intervals, then col- 

 lapses suddenly, and ejects its contents into the surrounding 

 water, when the process commences anew. This is the l pulsat- 

 ing vacuole.' Its task is the removal of the water which has 

 been taken in and used up in respiration, and the ejection of 

 liquid excreta. 



If we let the Amceba remain undisturbed we shall see that 

 the ectoplasm begins to protrude in a certain spot, and forms a 

 pseudopodion. The rest of the body-substance flows lazily after 

 the protrusion, and by repeating this process the Amceba floats 

 slowly along the surface of the rock or plant. If any particle of 

 food, such as a bacterium or alga or any other similar protozoon, 

 is encountered by the Amceba it is engulfed by the pseudopodia. 



FIG. 51. Amoeba proteus IN VARIOUS STAGES OF 



MOTION. BELOW, DIVISION OF THE PABENT-AMCEBA 

 INTO TWO DAUGHTER-AMCEBJE. 



