120 THE SCIENCE OF BIOLOGY 



by the coming into existence of a host of new sciences having 

 little in common. But looking closer, these multitudinous 

 developments may all be correlated with one or the other of 

 two major hypotheses the Theory of Organic Evolution and 

 the Theory of Cells. Such sciences as Pathology, Bacteri- 

 ology, Histology, Taxonomy, Ecology, and the like, may 

 not have arisen in conscious correlation with either of the 

 major theories. But having arrived, they arrange them- 

 selves quite naturally in relation to the broader generaliza- 

 tions. Pathology is the problem of abnormalities in cells, 

 Taxonomy the problem of classifying animals and plants 

 according to their evolutionary affinities. The others can 

 be similarly aligned. Moreover, the general biological 

 problems, distinctive of recent progress, allow of the same 

 classification. Questions regarding the origin of living sub- 

 stance find their answers in the cells. The nature of vital 

 processes, whether mechanistic or vitalistic, is a cell problem. 

 The fundamental identity of vital phenomena is explained 

 by the essentially identical structure and functioning of 

 cells in all animals and plants. The nature of embryological 

 development, the mechanism of heredity, the relation of liv- 

 ing and lifeless matter, in short, the answers to "all ultimate 

 biological problems must, in the last analysis, be sought in 

 the cell." Its structures and activities give clues to the rid- 

 dles of living matter. 2 The theory of organic evolution is 

 no less inclusive. The progress of modern biology is sum- 

 marized by the story of these two greatest of biological 

 generalizations. 



THE CELL-THEORY IN ZOOLOGY 



The doctrine termed the Cell-Theory postulates that the 

 living substance exists, almost without exception, in the 

 form of microscopic units known as cells. This cellular 

 structure was discovered in plants by the microscopists of the 



2 Wilson, E. B., "The Cell in Development and Inheritance," p. 1. 



