362 STUDIES IN GENERAL PHYSIOLOGY 
known, any regeneration occurring. Both pieces can execute 
swimming motions: in the case of the posterior piece the oral 
end leads. Both pieces attach themselves by means of their 
suction disks. At times I also saw the posterior piece exe- 
cute lively progressive movements, without however being 
able to discover an external stimulus for this movement. 
Both pieces returned to the ventral position when they were 
laid upon their backs. For the rest however the two pieces 
behaved differently. While I frequently found the anterior 
piece attached to the vertical glass sides of the aquarium, I 
found the posterior piece attached to the bottom. I sus- 
pected that the attachment of the suction disk came to pass 
reflexively, in consequence of the pressure or the friction to 
which the skin of the suction disk is exposed when it is allowed 
to come in contact with the bottom. It was therefore to be 
expected that it should be possible to compel the animal to 
attach itself to any desired point by pressing the suction 
disk against it. The experiment succeeds very readily with 
the posterior piece of a transversely divided animal, when it 
is gently pressed against the desired spot by means of a 
brush. The anterior piece however behaves entirely differ- 
ently when the same experiment is made with it. It turns 
itself in an apparently aggressive manner against the brush 
so that it is impossibe to press the suction disk against the 
wall. 
If the posterior piece is laid upon its back, it begins to 
execute swimming motions by means of which it brings itself 
back into the ventral position. The anterior piece returns 
to the ventral position by turning over. The tendency to 
execute swimming motions is much more marked in the 
posterior than in the anterior piece. If the leech is divided 
in such a way that the two pieces are still connected by a 
small piece of skin, they at times cxecute co-ordinated pro- 
gressive movements, as in Friedlinder’s experiment. More 
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