CHAPTER n 



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 

 continuity 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 

 germplasm. 



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 1838-1839 the "cell theory" of Schleiden and 

 Schwann, which aflBrms that all organisms, both 

 plant and animal, are made up of cellular units, 

 had its birth. 



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