MENTAL EVOLUTION OF MAN 205 



they conduct impulses from one part of the animal 

 to another, and thus serve as coordinating members of 

 the community. For the first time, then, a nervous 

 system as such is set apart and specialized to devote 

 itself to the two tasks of sensation and coordination 

 that are performed by nervous systems throughout the 

 entire range of organisms higher in the scale. But the 

 activities of Hydra, like those of Amoeba, are reflex 

 and mechanical, that is to say, given similar stimuli 

 and similar physiological states of the animal, the reac- 

 tions will be the same. A little water-crustacean like 

 Daphnia may swim against the tentacles of Hydra; 

 it is stung to death by the minute cell-batteries which 

 the animal possesses, and then in a mechanical way 

 the tentacles transport the food to the mouth, through 

 which it is passed inward to the digestive cavity. 

 There is nothing that can be called " mentality " 

 throughout these processes, but the series of activities 

 is much more complex than in Amoeba because the 

 whole organism is constructed more elaborately, and 

 because the special and peculiar mechanism directing 

 the activities has advanced to a far higher condition. 



Passing to the jointed animals like worms and in- 

 sects, we find nervous mechanisms that are still more 

 intricate, and with their advance in structural respects 

 there is a corresponding and correlated progress in 

 their functions. Because the whole organism has de- 

 veloped more highly differentiated groups of organs 

 to perform the several biological tasks, such as eating 

 and respiring and moving, it is necessary for the nervous 

 structures concerned with the direction of these actions 

 to become more efficient. An earthworm avoids the 



