CHAPTER X 



THE CARRIERS OF THE HERITAGE 



1. INTRODUCTION 



HEREDITY, as has been shown in the introductory 

 chapter, is essentially a matter of continuity between 

 \ succeeding generations of living organisms. This con- 

 tinuity may be direct, as when a mother protozoan 

 divides into two daughters, or it may be indirect, as 

 illustrated by the relationship of a father and son, 

 an uncle and nephew, or any other relatives of varying 

 degrees of kinship which, taken singly or collectively, 

 are somatoplasms derived from a common stream of 

 gern.plasm. 



It is the purpose of the present chapter to consider 

 this material continuity between succeeding genera- 

 tions and to discover, if possible, just what are the 

 carriers of the heritage from one generation to another. 

 To this end it will be necessary in the first place to 

 take up what is meant by the "cell theory." 



2. THE CELL THEORY 



In 1838^839 the "cell theory" of Schleiden and 

 Schwann, which affirms that all organisms, both plant 

 and animal, are made up of cellular units, had its birth. 



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