CHAPTER I 



INTRODUCTION 



PROTOZOA are considered as single-celled organisms; that is 

 to say, the body of a protozoan, no matter how small or 

 large it may be, is morphologically a single cell. Yet Protozoa 

 possess all the characteristics common to living things. The 

 various functions which make up the phenomenon known as 

 life are performed by differentiated parts within the body. 

 These parts, being comparable to the organs of a metazoan 

 which are composed of a large number of cells grouped into 

 tissues, are called organelles, or cell-organs. Thus one sees the 

 one-celled protozoan is a complete organism somewhat unlike 

 the cells making up a metazoan, each of which is dependent on 

 other cells and cannot live independently. From this view- 

 point, certain students maintain that the Protozoa are non- 

 cellular, and not unicellular, organisms. Through the process 

 of organic evolution, the Protozoa have undergone cytological 

 differentiation and the Metazoa histological differentiation. It 

 is beyond the scope of the present work to discuss these view- 

 points in detail. It may, however, be added here that certain 

 cells which compose the body of a metazoan, as for example 

 the leucocyte, spermatozoon, etc., behave as if they were inde- 

 pendent organisms. 



In being unicellular, the Protozoa and the Protophyta are 

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

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

 condition, method of division, nutrition, etc. While the major- 

 ity of the Protophyta appear to possess scattered nuclear ma- 

 terial or none at all, the Protozoa contain at least one nucleus. 

 It is generally considered that the binary fission of the Protozoa 

 and 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 Pro- 



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