DIFFERENT KINDS OF RESPONSE 147 
If the mass is nearer one edge of the disk this edge usually 
begins to sink, while at the same time the tentacles between 
the edge and the waste object collapse and practically 
efface themselves. Thus a smooth, sloping surface is pro- 
duced and the waste mass slides off the disk. If this does 
not occur at once, after a little time the region lying behind 
the mass (between it and the center of the disk) begins to 
swell, producing a high, rounded elevation, with tentacles 
plump and swollen. The waste mass is now on a steep 
slope, and is bound soon to slide down and over the edge. 
Sometimes by a continuation of this process the entire disk 
comes to take a strongly inclined position, with the side 
bearing the débris below. Often one portion of the edge of 
the disk after another is lowered in this way, till all the waste 
matter has been removed. The disk then resumes its 
horizontal position, with nearly flat or slightly concave 
surface.” If the edge near which the foreign body is placed 
cannot be lowered the part external to the body may be 
raised while the surface toward the opposite edge is depressed 
so that the object may be rolled off the disk in another 
direction. 
In Planaria, according to Pearl, repeated mechanical 
stimulation of the anterior end causes the worm to turn 
farther away at each succeeding stimulus, without at first 
causing any movements of locomotion. After a time the 
worm jerks back vigorously, bends the body strongly to one 
side and then extends usually toward the source of stimulus. 
Stronger stimuli soon alter the general physiological condi- 
tion of the organism; “the animal becomes ‘stirred up’ 
generally, moves about with increased rapidity, its sensitive- 
ness to stimuli becomes diminished, and it will give only the 
negative response to stimulation of the anterior end... . 
One may get totally different appearances from an individual 
