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 bo 

 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 execute co-ordinated pro- 

 gressive movements^ as la x riediander's experiment. More 



