INTRODUCTION 5 



Relationship of protozoology to other fields of 

 biological science 



A brief consideration of the relationship of Protozoology to 

 other fields of biology and its possible applications may not be 

 out of place here. Since the Protozoa are single-celled animals 

 manifesting the characteristics common to all living things, they 

 have been studied by numerous investigators with a view to dis- 

 covering the nature and mechanism of various phenomena, the 

 sum-total of which is known collectively as life. Though the in- 

 vestigators generally have been disappointed in the results, in- 

 asmuch as the assumed simphcity of unicellular organisms has 

 proved to be offset by the complexity of their cell-structure, 

 nevertheless any discussion of biological principles today must 

 take into account the information obtained from studies of Pro- 

 tozoa. It is now commonly recognized that adequate information 

 on various types of Protozoa is a prerequisite to a thorough com- 

 prehension of biology and to proper application of biological prin- 

 ciples. 



Practically all students agree in holding that the higher types 

 of animals have been derived from organisms which existed in the 

 remote past and which probably were somewhat similar to the 

 Protozoa of the present day. Since there is no sharp distinction 

 between the Protozoa and the Protophyta or between the Pro- 

 tozoa and the Metazoa, and since there are intermediate forms 

 between the major classes of the Protozoa themselves, progress 

 in protozoology contributes toward the advancement of our 

 knowledge of the steps by which living things in general evolved. 



Geneticists have undertaken studies on heredity and variation 

 among Protozoa. "Unicellular animals," wrote Jennings (1909), 

 "present all the problems of heredity and variation in miniature. 

 The struggle for existence in a fauna of untold thousands showing 

 as much variety of form and function as any higher group, works 

 itself out, with ultimate survival of the fittest, in a few days 

 under our eyes, in a finger bowl. For studying heredity and varia- 

 tion we get a generation a day, and we may keep unlimited num- 

 bers of pedigreed stock in a watch glass that can be placed under 

 the microscope." Morphological variations are encountered com- 

 monly in all forms. Whether variation is due to germinal or en- 

 vironmental conditions, is often difficult to determine. The recent 

 discovery of the sex reaction types in Paramecium aurelia (Son- 



