Chapter 1 

 Introduction 



PROTOZOA are unicellular animals. The body of a protozoan 

 is morphologically a single cell and manifests all characteristics 

 common to the living 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 somewhat unlike the cell of a 

 metazoan, each of which is dependent upon other cells and cannot 

 live independently. From this viewpoint, certain students of proto- 

 zoology maintain that the Protozoa are non-cellular, and not uni- 

 cellular, organisms. Dobell (1911) for example, pointed out that the 

 term "cell" is employed to designate (1) the whole protozoan body, 

 (2) a part of a metazoan organism, and (3) a potential whole organ- 

 ism (a fertilized egg) which consequently resulted 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 organ- 

 ism, 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, continue to consider the Protozoa as uni- 

 cellular animals. Through the processes of organic evolution, they 

 have undergone cytological differentiation and the Metazoa histo- 

 logical differentiation. 



In being unicellular, the Protozoa and the Protophyta are alike. 

 The majority of the Protozoa are quite clearly distinguishable 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 nucleus. It is generally con- 

 sidered that the binary fission of the Protozoa and of the Protophyta 

 is longitudinal and transverse, respectively. A great majority of 

 Ciliata, however, multiply by transverse division. In general the 

 nutrition of Protozoa is holozoic and of Protophyta, holophytic; 

 but there are large numbers of Protozoa which nourish themselves 

 by holophytic method. Thus an absolute and clean-cut separation 

 of the two groups of unicellular organisms is not possible. Haeckel 



