EUGLENA, AMOEBA, AND PARAMECIUM 287 



These are known as pseudopodia, and they are constantly changing 

 in shape in the active animal by the flowing of the protoplasm. 



Under favorable conditions the protoplasm can be differentiated 

 into two portions. The firmer, somewhat tougher outer portion, the 

 ectosarc (ectoplasm), is nearly homogeneous and includes the plasma 

 membrane (or plasmalemma) : the more fluid inner portion, endosarc 

 (endoplasm), is much more granular and contains the cyiosome, cell 

 inclusions as well as the nucleus. The larger bodies in the cytosome 

 are food vacuoles, single, shiny, contractile vacuoles containing watery 

 fluid and varying in size ; water vacuoles ; various granules ; mitochon- 

 dria; fat globules; and crystals. Some authors distinguish two types 

 of protoplasm in the endosarc; the inner more fluid, plasmasol, in 

 which the streaming movements take place and, surrounding this a 

 more viscous, passive portion, the plasmogel. The nucleus usually 

 appears somewhat dense and granular, and is located in the portion 

 away from the end which is advancing in a moving specimen. 



Metabolism 



This refers to the constant building up (anabolism) of living pro- 

 toplasm and its concurrent oxidation (catabolism). It includes all 

 activities necessary for maintenance of itself and its race. These 

 phenomena are the same as those found in the highest forms of life 

 but reduced to very simple terms. Here we may study the entire 

 metabolic cycle in progress within the conflnes of a single cell. Its 

 phases are as follows: 



Food. — Its prey consists chiefly of smaller Protozoa, small single- 

 celled plants, such as diatoms and desmids, and portions of filamen- 

 tous algae. Bacteria may be used to some extent and rotifers (small 

 Metazoa) are sometimes devoured. 



Ingestion. — ^Amoeba has no definite mouth but the food is taken 

 into the body by engulfing it at any point that comes in contact 

 with it. A pseudopodium is formed at this point, and the end of it 

 flows around the food particle until the particle is entirely enclosed. 

 A droplet of water is included with the food to form what is called a 

 food vacuole. These vacuoles move about in the endoplasm. 



Digestion. — The food gradually disintegrates and much of it goes 

 into solution in the fluid of the vacuole. The function of digestion is 

 to convert complex materials into a soluble, absorbable form. It 

 is assumed that the surrounding cytoplasm secretes enzymes into the 



