PROTOPLASM 17 



through the water and to aid in securing food. In higher organisms 

 ciliated cells line various ducts and bring about the movements of 

 fluids through them. (W. fs. 7, E ; 27.) 



Muscular Movement. In the higher animals, the power of 

 visible movement is centered in the contractile muscle tissue which 

 is differentiated for this purpose. Muscle tissue is composed of 

 highly specialized cells which act in unison when stimulated, and 

 thus bring about a movement of the muscle as a whole. In the 

 final analysis, however, it is the cytoplasmic movement in each 

 muscle cell which brings about the mass movement of the entire 

 muscle. (W. f. 7, B ; 32, E.) 



7. Summary 



In summarizing, we find that life requires the constant expendi- 

 ture of energy. This is obtained by the destructive oxidative 

 process of katabolism. To balance this and also provide an excess 

 of material for growth, there is the constructive process of anabo- 

 lism in which food formed by photosynthesis is supplied. The 

 sum total of these processes, or metabolism, involves the essential 

 life processes of nutrition, respiration, excretion, growth, repro- 

 duction, and adaptation ; all of which, in the final analysis, are 

 centered in the cell as the fundamental structural and functional 

 unit of every living organism. 



In the following pages, descriptions are given of the structure 

 and life processes of representative types of animals ranging from 

 the comparatively simple, unicellular forms through various grades 

 of multicellular complexity until the climax is attained in the 

 Vertebrate animals. In considering these examples selected from 

 the panorama of animal life, it is of primary importance for the 

 student of biology to gain a clear conception as to how each 

 organism, with its own peculiar structural and physiological 

 problems, is able to perform the metabolic processes which are 

 characteristic of, and essential to, all life. 



TEXTBOOK REFERENCES 

 Woodruff. Animal Biology (Macmillan), pp. 1-45; 461-472. 



Curtis and Guthrie. Textbook of General Zoology (Wiley), pp. 1-8; 71-76; 



130-140. 

 Guyer. Animal Biology (Harper), pp. 1-41; 111-128; 703-706. 

 Hegiver. College Zoology, 3d edition (Macmillan), pp. 7-19. 



