CHAPTER IX. 



WHAT IS AN ORGANISM ? THE CHARACTERISTICS OF 

 THE INDIVIDUAL AND ITS MODE OF DEVELOPMENT. 



Mutability of Organisms a Foundation Principle of all Evolu- 

 tion. In an analysis of the meaning of evolution, it is essen- 

 tial to remember, at the outset, that the evolution takes place 

 only in respect of mutable things. The species is said to be 

 mutable, but it is the organic species as contrasted with 

 everything else. The mutability, therefore, is respecting 

 organisms only. I have shown how the organic " species," 

 which one school of naturalists calls ''mutable," is in one 

 sense a mere abstract idea but in another it stands for an 

 aggregate of real existing individual organisms. Such an 

 earnest advocate of mutability of species as Oskar Schmidt 

 says, " The retention of species is, moreover, scientifically 

 justifiable and necessary, if only the determining impulses be 

 taken into account and the definition reduced to harmony 

 with reality;" and the definition he gives is, "While we re- 

 gard species as absolutely mutable, and only relatively stable, 

 we will term it, with Haeckel, ' the sum of all cycles of repro- 

 duction which, under similar conditions of existence, exJiibit 

 similar forms? "* 



Morphological Similarity the Characteristic of Species. The 

 essential notion in species is similarity of form. The fact 

 recorded in the term species is the occurrence in nature of 

 numerous organisms of almost identical form and structure 

 individuals which seem, in general, to live and grow sepa- 

 rately, but are also organically associated together. In order 

 to explain this community of form among the individuals of 

 the same species, we must examine into the laws by which 



* "The Doctrine of Descent and Darwinism," p. 103, New York, 1878. 



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