i6 Evolution and Distribution of Fishes 



up the brain-masses of higher invertebrates and of verte- 

 brates. 



As will be traced in a succeeding chapter, and as the 

 writer has already shown in the above-cited work, the 

 highly complex brain-masses that characterize the nemer- 

 teans, and above them as well as derived from them, the 

 fishes, give to all of these the capacity to receive numerous 

 diverse stimuli, to pass these quickly to the correlating and 

 combining brain centres, and therefrom to proenviron or 

 project a path of action for the time that is most satisfying 

 to each organism involved. So if the sum-total of environal 

 stimuli conduces to progressive advance and improvement 

 in the adaptability of an organism to its environment, 

 evolution results; if the environal stimuli and the hereditary 

 details are in balanced relation organic equilibrium results; 

 if the summated stimuli tend to cause disintegration, sim- 

 plification, and inadaptability to an advancing environment, 

 degeneration ensues. 



Amongst Nemerteans, and every group of fishes, abun- 

 dant exhibitions of the above law are seen. Thus the lithe, 

 active and quickly adaptable movements that we associate 

 with most Teleosts represent the action of many environal 

 agents — not least of predatory enemies — through many 

 millions of years, which have acted on every hand as en- 

 vironal stimuli. These stimuli, almost instantly conveyed 

 to the great correlating centre or brain, have there been 

 combined into a single resultant response that may cause 

 each animal so to move as to escape from three or more 

 dangerous enemies on different sides; to glide rapidly from 

 noxious gases, hot waters and falling dust passed Into sur- 

 rounding waters, toward a body of water free from such 

 injurious agents; to dart suddenly from a dark position 

 to a lighted place where some food-animals are disporting, 

 and to seize accurately one or more of them. In short, 

 on slight reflection, it will be patent to every one that most 

 of the acts of fishes as well as of other animals up to man 

 himself, are truly complex or summated proenvlronal re- 

 sponses, due to a relinkage and recombination of energized 

 molecules, in definite nerve centres, where such summating 

 relinkage occurs. So while every stimulus applied to a 



