WEISMANWS ESSA YS UPON HEREDITY. 9 



have provided a sufficient number of successors, they them- 

 selves, as consumers of nourishment in a constantly increas- 

 ing degree, are an injury to those successors. Natural 

 selection, therefore, weeds them out, and in many cases 

 favours such races as die almost immediately after they have 

 left successors." 



Here we have Weismann's theory of the origin 

 of death, not indeed worked out as it is in his 

 Essays on the " Duration of Life " and " Life and 

 Death," but thrown out as a suggestion, which 

 seems to have lain dormant and been forgotten 

 even by the author till the essays of Professor 

 Weismann were submitted to him in proof. 



2. The other point in Professor Weismann's 

 philosophy is his theory of heredity, which follows 

 as a consequence from his theory of the origin of 

 death and the separation of somatic and reproduc- 

 tive cells in the heteroplastids. 



It is clear that in those organisms which increase 

 by simple division the likeness which exists between 

 the divided parts is simply the likeness of identity. 

 The offspring is " a chip of the old block " in a 

 literal sense, except that the question of age does 

 not come in, each part being as old, or as young, as 

 that of which it is a part. There is, as yet, no 

 question of heredity. After the separation, any 

 of the separated parts might by direct action of 

 environment be modified, and so become different 

 from the others, but when they in turn increased 

 by fission their divided parts would, to start with, 



