AMOEBA 23 



Diatoms, filamentous Algae, other forms of Protozoa, and organic 

 debris of many kinds. The Amoeba has only one method for secur- 

 ing all types of food material. This consists in moving towards the 

 food particle and then gradually surrounding it by means of the 

 pseudopodia. When the peripheral protoplasm comes into contact 

 with a food particle, the process of ingestion begins at once. All 

 regions of the ectoplasm of the Amoeba can perform this combined 

 process of capture and ingestion. Apparently it is the chance con- 

 tact which determines the particular region of the ectoplasm which 

 is to act as the temporary organ for capturing a particular food 

 particle or living organism, and also as the temporary mouth for 

 engulfing it. 



An Amoeba, of course, comes into contact with many particles 

 of inorganic material, such as grains of sand, which cannot be uti- 

 lized as food. It can generally be shown in such cases that the ecto- 

 plasm of the Amoeba differentiates between the materials which 

 are suitable for food and other materials which cannot be so used. 

 Thus, when an Amoeba comes into contact with a grain of sand, 

 instead of engulfing it, the flowing movement and pseudopod for- 

 mation in that direction ceases, and a movement is initiated in 

 another direction, which avoids the undesirable material. 



A food particle having been ingested by the ectoplasm next 

 passes into the endoplasm, becomes surrounded by a small amount 

 of fluid taken in with it, and constitutes a gastric vacuole in which 

 digestion takes place. The portion of endoplasm which surrounds 

 the food material apparently becomes temporarily specialized for 

 the work of digestion, and is able to secrete certain chemical sub- 

 stances, known as enzymes, which are believed to be of the same 

 nature as those secreted in higher forms of animals by the glands 

 in the walls of the alimentary canal. It is these enzymes which 

 digest the food. Digestion, in all forms of organisms, may be 

 defined as a process whereby the complex food materials are 

 chemically changed so that they can be absorbed and assimilated 

 by the cells, and thus made available for the protoplasm. This is 

 just what happens to the food in the gastric vacuoles of an Amoeba. 

 (W. f. 13.) 



The process of assimilation of the digested material in Amoeba 

 and in other unicellular forms is a comparatively simple one, for 

 the food as it is digested in the gastric vacuole passes directly into 

 the surrounding endoplasm and is at once available for energy or 



