Chapter 1 

 Introduction 



PROTOZOA are unicellular animals. The body of a protozoan 

 is morphologically a single cell and manifests all character- 

 istics common to the Hving thing. The various activities which 

 make up the phenomena of life are carried on by parts within the 

 body or cell. These parts are comparable with the organs of a 

 metazoan which are composed of a large number of cells grouped 

 into tissues and are called organellae or cell-organs. Thus one 

 sees that the one-celled protozoan is a complete organism some- 

 what unhke the cell of a metazoan, each of which is dependent 

 upon other cells and cannot live independently. From this view- 

 point, certain students of protozoology maintain that the Proto- 

 zoa are non-cellular, and not unicellular, organisms. Dobell (1911) 

 for example, points out that the "cell" is employed to designate 

 1) the whole protozoan body, 2) a part of an organism and, 3) a 

 potential whole organism (a fertilized egg) which consequently re- 

 sulted in a confused state of knowledge regarding living things, 

 and, therefore, proposed to define a cell as a mass of protoplasm 

 composing part of an organism, and further considered that the 

 protozoan is a non-cellular but complete organism, differently 

 organized as compared with cellular organisms, the Metazoa and 

 Metaphyta. The great majority of protozoologists, however, con- 

 tinue to consider the Protozoa as unicellular animals. Through 

 the processes of organic evolution, they have undergone cyto- 

 logical differentiation and the Metazoa histological differentia- 

 tion. 



In being unicellular, the Protozoa and the Protophyta are 

 alike. The majority of the Protozoa are quite clearly distinguish- 

 able from the majority of the Protophyta on the basis of nuclear 

 condition, method of nutrition, direction of division-plane, etc. 

 While numerous Protophyta appear to possess scattered nuclear 

 material or none at all, the Protozoa contain at least one nu- 

 cleus. It is generally considered that the binary fission of the 

 Protozoa and the Protophyta is longitudinal and transverse, re- 

 spectively. A great majority of CiUata, however, multiply by 

 transverse division. In general the nutrition of Protozoa is holo- 



