METABOLISM OF ORGANISMS 



35 



to the destructive agents; from the collectors of energy to the 

 energy dissipators ; from the green plants to animals and then to 

 'colorless' plants. 



B. Animals 



There is probably no better introduction to the study of the 

 biology of an animal than that afforded by an Amoeba such as 

 Amoeba proteus, a common organism of ponds, ditches, and de- 

 caying vegetable infusions. Amoebae, frequently referred to as 

 the simplest animals, are representatives of the great group of 

 single-celled animals, or Protozoa. Members of this group are 

 found in almost every niche in nature and, like the Protophyta, 

 as the unicellular plants are sometimes called, are important be- 

 cause, although small in size, the number of individuals is incon- 

 ceivably large. Collectively they produce profound changes in 

 their environment. 



1. Amoeba 



In order to study Amoeba it is necessary to magnify it several 

 hundred times. This done, it appears as a more or less irregular 



Pseudopodium 

 Ectoplasm 

 Endoplasm 



Gastric vacuole 



Nucleus 



mass of granular jelly-like ma- 

 terial, rather slowly changing its 

 shape and thereby moving along. 

 As a matter of fact it is essen- 

 tially a naked bit of protoplasm, 

 without obviously specialized 

 parts. However, careful study 

 reveals that the organism really 

 consists of a single protoplasmic 

 unit differentiated into cyto- 

 plasm and nucleus — it is a 

 cell: an animal. (Fig. 11.) 



But there are no specialized Contractile^ 

 locomotor organs — merely now 

 and again the clear outer layer of 

 protoplasm, or ectoplasm, flows 

 out, followed by the internal granular endoplasm, so that a pro- 

 jection, or pseudopodium, is formed. There is no permanent 

 mouth, food being engulfed by the protoplasm flowing about it 

 as opportunity offers. There is no permanent digestive or excre- 

 tory apparatus. (Figs. 6, 13.) 



vacuole 



Fig. 13. — Amoeba proteus. 



