148 MODIFICATIONS OF BEHAVIOR 



which has been ' stirred up ' from what are seen in the case 

 of one which is in the normal condition." 



In the earthworm repeated stimuli give rise to a great 

 variety of reactions which have been classified by Jennings 

 as follows: 



" (a) The state of rest, in which the worm does not 

 react readily to slight stimuli, such as a touch with the tip 

 of a glass rod. 



" (b) A state of moderate activity, in which a touch at the 

 anterior end causes movement backward; at the posterior 

 end movement forward, while lateral stimuli (in the anterior 

 region) cause turning away from the side stimulated. 



" (c) A state of excitement, after repeated stimuli, in 

 which the animal persists in the direction of movement once 

 begun, merely stopping for a few seconds when stimulated 

 at the end which is advancing. 



" (d) A state of greater excitement, in which stimuli merely 

 cause the animal to hasten its movements in the direction in 

 which it has started, without regard to the localization of 

 the stimulus. 



" (e) A state of still greater excitement, after long-con- 

 tinued and intense stimulation. Now the worm responds 

 to a stimulus at the anterior end, that would in a resting 

 worm cause only a comparatively slight reaction, by a rapid 

 'right-about-face.' The body is suddenly doubled at its 

 middle, so that the anterior and posterior halves become 

 parallel, with the two ends pointing in the same direction, 

 then the posterior half is quickly whipped about, so that 

 the whole worm is again straight, but is facing the opposite 

 direction from that in which it was pointed before the 

 reaction. . . . 



" (f) A state of still more intense excitement, after repeated 

 strong stimulation that is of such a character as to actually 



