18 THE NEWEST THEORIES CONCERNING EVOLUTION SEC. 



his germ-plasm, pack it away in the cell-nucleus alone, but 

 conceives it as a network or framework which permeates the 

 whole body from cell to cell. It is the idioplasm which 

 changes from generation to generation from internal causes, 

 and thus, without being essentially influenced by accidental 

 variation and selection, produces quite new forms. 



Nageli thus fundamentally takes us back to the concep- 

 tion of the vital force, applying it to the modification of forms, 

 to the doctrine of evolution, and attempts to divest the 

 principle of utility of any considerable importance. 



His principle of improvement therefore effects greater 

 complexity and greater division of labour in organisms in 

 definite directions. When this metamorphosis is once in 

 progress " it continues by mechanical necessity in the direc- 

 tion in which it started. For when, in virtue of the begin- 

 ning made, one generation produces offspring which in one 

 respect are in advance of the parents, then by the law of per- 

 sistence of motion the offspring of these offspring must be 

 altered to a farther degree, and the evolution must go on as 

 far as the nature of the conditions allows." Thereupon 

 adaptation comes into action. 



We have thus, according to Nageli, as the mechanical 

 causes of the evolution of the organic kingdoms "the 

 persistent advance towards perfection from the simpler to the 

 more complex, and further, the definite action of the external 

 conditions in adaptation." 



"Competition, with its consequent crowding out among 

 living beings, has, within the definitely directed changes 

 towards perfection and adaptation, its effect in separating and 

 in defining, but not in forming, the strains : not a single 

 phylogenetic pedigree owes to competition its existence, but 

 the several pedigrees through the extermination of inter- 

 mediate forms stand forth more clearly and more char- 

 acteristically. 



