CHAPTER IX 



PRIMITIVE TYPES OF INTELLIGENCE IN 

 CRUSTACEANS AND MOLLUSCS 



It is scarcely possible at present to fix, even with the 

 rudest approximation, the point where intelligence makes 

 its first appearance in the course of evolution. There is 

 little doubt that the step from instinct to intelligence has 

 been made, not once merely, but several times. The in- 

 telligence of the higher Mollusca had, in all probability, an 

 origin independent from that of the arthropods, and the in- 

 telligence of the vertebrates was probably developed in- 

 dependently of that of the other groups. Among the arthro- 

 pods themselves it is not likely that the intelligence manifested 

 by the arachnids had a common origin with that of the 

 insects, and within both of these large groups intelligence 

 may have been independently developed out of behavior of 

 the purely instinctive type. 



Intelligence grows out of the complexity and perfection 

 of the nervous mechanism, and along whatever line organiza- 

 tion reaches a certain degree of development intelligence 

 appears on the scene. From what has been said in previous 

 pages we are prepared to appreciate the fact that intelligence 

 is not an entirely new power unrelated to the other activities 

 of organic life, but a process growing out of other organic 

 functions and having the same end as these other functions; 

 it is, as Spencer has so well emphasized, but a higher phase 

 of those processes of adjustment and regulation which make 

 up the life of the animal. 



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