DEVELOPMENT OF MIND IN ANIMALS I23 



to reject the paper. The learning process here apparently 

 involved central as well as local modifications. 



Above the level of the lowly coelenterates, evolution be- 

 gins to organize a much more centralized and efficient nerv- 

 ous system by gradually introducing central ganglia and by 

 suppressing the diffuse nerve networks (as in the coelenter- 

 ates) in favor of definite nerves which run like telephone 

 wire directly from point to point. Extensive network nerv- 

 ous systems still survive, however, in some primitive organ- 

 isms and even in man, as in the mechanism which controls 

 intestinal wave-like rhythms known as peristalsis. Nature 

 also found ways gradually to speed up nerve transmission 

 from the very slow two or three seconds per inch in a fresh 

 water mussel to the four hundred feet per second transmis- 

 sion in man. In the echinoderms (starfish), which may be 

 close to the line from which the vertebrates were derived, 

 the nervous system is still decentralized, and the same may 

 be said to some extent of their behavior. There is a circle of 

 nervous tissue around the mouth, and from this nerve, 

 trunks are derived which run out in the Rve arms. There is 

 great independence in these Rvc arms, almost as though they 

 were five individuals springing from a common center. A 

 single arm can act independently if cut off, even to righting 

 itself if turned over. If the whole animal is turned over on 

 its back, it rights itself as soon as one of the arms, by twist- 

 ing about, gets a hold on the substratum; at that moment the 

 other arms are inhibited in their motions by a message from 

 the successful arm via the nerve ring around the mouth. 

 Also on these animals there are pincer-like structures stick- 

 ing up all over the outer surface to keep it free of ectopara- 

 sites. These pincers are triggered through their own individ- 

 ual reflex systems. 



In spite of the rather justifiable assumption that the echi- 

 noderms are near the remote ancestral origins of man, they 

 do not seem to show any precocious talents. Psychologists 

 have not been successful in demonstrating learning ability in 



