570 



RAYMOND PEARL. 



The behavionr is not of auy evident benefit to the organisms, 

 as it is in the case of infusoria, where it is apparently closely 

 connected with the obtaining of food. On the contraiy, it 

 seems to be, at least potentially, a harmful thing, because 

 any accident or enemy would affect a number of individuals 

 rather than a single one when they were so collected. 



d. The Effect of Operations on Movement. — It 

 may be well to put together in one place the results which 

 were obtained with reference to the movements from animals 

 which had been cut in various ways. From these we can 

 form some idea of the relation of the nervous system of the 

 planarian to its movements.^ 



The immediate effect of any operation is that of a very 

 strong mechanical stimulus applied to the same part of the 



Fig. 9. — Operation diaj^rani. Tlie heavy str.night, line indicates tlie cut 

 made. For results see text. 



body, and the sort of movement resulting in each piece 

 depends on the position of the cut. The details of this im- 

 mediate effect will be described in connection with other 

 mechanical stimuli. What concerns us here is the permanent 

 after-effect of operations on the movements. We can best 

 get at this matter by taking up some specific cases. 



^ All the operations were performed with a sharp scalpel, in most cases 

 with the specimen in a dish of water. In some cases the worm was transferred 

 to a drop of water on a soft board for the cuttins', but in all cases where 

 immediate observations were wanted, the operations were performed in tlie 

 dishes used for t,lie experiments. The only difficulty in performing operations 

 on planarians arises from tiie fact that if the edge of the knife is allowed to 

 rest on the surface of the body for even a very short time before the cut is 

 made, it will become covered with the sticky slime from the aninuil, and tiien 

 any clean cut is impossible. The edge will slip off the back of the worm 

 without iicnct rating. 



