32 THE PHYSICAL BASIS OF INHERITANCE 



we are led to see the force of Haeckel's definition of reproduction 

 as discontinuous growth. 



But in many unicellular elements, what is liberated to begin 

 a new life is not a half of the original nor anything like it, but a 

 minute unit often called a " spore." It also grows into a com- 

 plete reproduction of the original. In such cases, we again try 

 to make the matter more intelligible, by saying that each spore 

 is a representative fragment of the organisation of the original 

 unit, and will therefore, in appropriate surroundings, grow and 

 differentiate as the original did. Exactly the same often occurs 

 when the unicellular organism is artificially divided into several 

 parts ; and the results of these microscopic vivisection experi- 

 ments, to which no one can on any grounds object, show that, 

 if the excised fragment is to survive and develop, it must have 

 a portion of the nuclear substance as well as of the general 

 cell-substance. Without the nuclear constituent it may live 

 for a time, as in Stentor, moving and responding to stimuli, 

 but it cannot assimilate. Therefore, if we are asked what we 

 mean by " organisation," we may say, at this stage, a certain 

 protoplasmic architecture which implies essential relations 

 between nucleoplasm and cytoplasm. The protoplasmic unit 

 is like a firm with many partners of different kinds, each kind 

 having many representatives ; and the retention of vitality, the 

 possibility of regeneration on the part of the fragments, has 

 this for its essential condition, that the integrity of the firm — in 

 which lies its secret — is maintained by each fragment having 

 at least one representative of the different kinds of partners. 



The reader who is not familiar with the subject should linger 

 over the fact that a fragment or a minute spore, separated from 

 a unicellular organism, may grow into (literally, reproduce) a 

 unit, which to our senses is exactly like the original. This is 

 (within the limits of our senses) complete hereditary resemblance, 

 and we interpret it as due to the fact that the fragment or spore 

 has to start with the essential organisation of the original. This 



