88 THE EVOLUTION OF MAN 



tions to the animal as a whole can be kept clearly in mind, the 

 tentacle will still be found to respond to food brought in con- 

 tact with it and will eventually turn toward that side which 

 was originally toward the mouth. Thus the tentacle has within 

 itself a complete neuromuscular mechanism for its own re- 

 sponses and it is unnecessary that it should be connected with 

 any general nervous center in order to carry out its char- 

 acteristic movements. Its share of the diffuse nervous system 

 is sufficient for its own needs. How different this type of 

 organization is as compared with the centralized type is seen 

 when we contrast the activity of the tentacle with that of the 

 leg of a dog or the claw of a lobster when severed from the 

 animal's body. These parts when thus cut off are quite in- 

 capable of coordinated movement and show no evidence what- 

 ever of the type of response that characterizes them as a part 

 of the whole organism. 



Another activity of the sea-anemone that illustrates the na- 

 ture of the diffuse nervous system is creeping. This operation 

 is accomplished by the so-called pedal disc, that portion of the 

 animal by which it attaches itself to the substrate. By means 

 of muscular waves that pass across this disc the sea-anemone 

 may creep slowly like a snail from spot to spot. If a sea- 

 anemone is cut crosswise in two and the upper half of the 

 animal carrying the mouth and tentacles is thus removed, the 

 lower half with the pedal disc intact will pucker up the 

 wounded surface and soon creep about with as much success 

 as the whole animal did. Here again the part concerned 

 carries within its own bounds a neuromuscular mechanism 

 complete for its needs. 



Again if a sea-anemone is fed from one side of its mouth, 

 it will take in by means of the tentacles on that side one frag- 

 ment of food after another. If, now, bits of meat be alter- 

 nated with bits of filter paper soaked in meat juice, the two 

 materials will be accepted indiscriminately for some eight or 



