WEISMANWS ESSAYS UPON HEREDITY. 13 



but as the vehicle of the united germ-plasms of the 

 parent plants or animals. At a certain stage in 

 the evolution of organisms, as we have already 

 noticed, a distinction arises between reproductive 

 and somatic cells the latter being perishable ; 

 the former, in the sense explained, potentially 

 immortal. The higher organisms, then, contain 

 speaking from the purely physical point of view 

 a mortal and an immortal part, what belongs to 

 the individual and what the individual merely has 

 the use of. There is no primogeniture in nature, 

 but the inheritance is strictly entailed. The 

 individual becomes the vehicle to the next genera- 

 tion of a portion of that " immortal" germ-plasm 

 out of which he himself was built up. Parent and 

 child are thus made of the same "stuff." Their 

 somatic cells grow out of the same germ-plasm, 

 and the likeness in the result is due to the identity 

 of the source. Thus heredity is traced back to 

 growth. If we compare the germ-plasm to the 

 creeping rhizome of a fern, the successive genera- 

 tions would be represented by the fronds as they 

 are successively thrown up along the line of the 

 rhizome. Coming from the same rhizome we 

 expect them to be alike, except so far as they 

 are individually modified from without. But the 

 individual modifications are individual simply, and 

 the next frond has an identical starting-point with 

 the last, and is unaffected by anything which for 



