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) Astate of still more intense excitement, after repeated 
strong stimulation that is of such a character as to actually 
