Introduction i i 



A stage however was evidently reached in the history 

 of actively motile animals when even more rapid, corre- 

 lated and condensed perception not of one but of several 

 simultaneously acting environal stimuli, and equally rapid 

 combination of these into a single direct response, became 

 necessary in the struggle for existence. Accordingly the 

 writer has suggested the slow evolution of that still more 

 condensed exhibition of energy, the cogitic, that became 

 correlated with and conducted by a correspondingly con- 

 densed linkage of molecules to constitute the neuratin or 

 granular network substance of nerve cells. 



This stage having been reached, further evolutionary 

 progress up to the nemerteans and thence to fishes, con- 

 sisted in increasing aggregation of nerve cells to form 

 ganglionic masses, and ultimately in formation of the cen- 

 tralized brain system with its nerve fibres and its peripheral 

 sensory, motor and inhibitory nerve cells. But as is strik- 

 ingly demonstrated both by nemerteans and fishes, though 

 led up to by similar and simpler groups, a variety of periph- 

 eral sense-centers was developed to a highly perfect degree 

 for reception of varied environal stimuli. These became 

 more and more perfected as the eyes, ears, tactile skin 

 organs, taste organs, and nostrils of fishes. But, on the other 

 hand, certain sense organs, or sense centers, that were 

 originally present, may have undergone partial or complete 

 degeneration, in transition from a lower group like the 

 nemerteans to a higher one like the fishes. Thus can be 

 explained the rudimentary parietal eyes, the pituitary body, 

 and other structures of fishes. 



But in the evolution of every structural detail five fac- 

 tors of prime importance are more or less actively con- 

 cerned, and the combined action of these five, in relation to 

 the energies already noted which give potency to them, 

 we term Pentamorphogeny, or the five form-evolving fac- 

 tors. These are Heredity, Environment, Proenvironment, 

 Selection, and Reproduction. Each is discussed in the 

 author's work already cited (7:174:242), but brief con- 

 sideration of these here with special reference to the groups 

 of organisms treated in the present volume, may not be 

 inappropriate. For they form the basic evolutionary fac- 



