72 THE GERM-PLASM THEORY 



is to pass from the unicellular to the multicellular 

 condition. A differentiation in function then takes 

 place, certain cells being capable of one duty but 

 incapable of another, until we come to the con- 

 dition of complexity met with in the mammal, 

 for example, where we have nerve cells, muscle 

 cells, liver cells and the like, all derived from the 

 single-celled fertilized ovum, and all capable of 

 performing their own functions and no others. 

 Now, according to Weismann, the first stage in 

 this process of differentiation is the cutting off of 

 some of the original germ-substance to form the 

 germ-substance of future generations. This sub- 

 stance, thus cut off, is as much derived from the 

 first germ as the two unicellular organisms were 

 developed from one. It is consequently, like these 

 organisms, potentially immortal. The rert of the 

 germ, which goes to make the body or soma, is 

 mortal ; it is the home, the protector and the 

 nourish er of the immortal germ-plasm. The soma 

 is the visible part ; the germ-plasm is invisible 

 except under the microscope ; but it is the in- 

 visible part which is handed on, not the visible. 

 Hence, according to this view of things, the germ- 

 plasm in an individual is the same as that which 

 was in his progenitors, and in theirs back to the 

 nth generation. Consequently the individual really 

 is his ancestors, and, therefore, naturally would 

 resemble them. 



This is the first and most fundamental point in 

 Weismann's theory. Now for the next. Is this 

 germinal substance (which he considers to be the 

 chromatin filaments of the nucleus of the germinal 



