CHAPTER I 



THE RESOLVING OF INDIVIDUALS INTO THE PEDI- 

 GREES OF THEIR CELLS 



i. Purpose and Method 



Since the founding of the cell-theory by Schleiden and 

 Schwann, cells have come more and more to the fore- 

 ground of anatomical and physiological consideration. 

 The theory of heredity, also, which about two decades 

 ago was hardly at all in touch with the cell-theory, has 

 given up this isolated position, and sees in the more re- 

 cent investigations on cell-division and the process of 

 fertilization an important furtherance of its problems. 



Oninis cellula e cellula. Not only does this saying 

 dominate microscopic science, but it is steadily rising into 

 supreme command over all Biology. That every cell has 

 originated from a material part of its mother-cell, and 

 that it owes its specific characters to this origin, is now 

 accepted in the theory of heredity as the basis of all 

 thorough considerations. Whether or not this source is 

 sufficient for the explanation of all phenomena was the 

 question which induced Darwin to formulate his pan- 

 genesis. And this question remains the first to be an- 

 swered with reference to every new group of facts ap- 

 pearing within the domain of heredity. 



The phenomena known at present, at least in so far 

 as they have been sufficiently thoroughly investigated, 

 demand an affirmative answer to that question. This 

 was conclusively demonstrated by Weismann, as has been 



