MOVEMENTS, ETC., OF FRESH-WATER PLANARIANS. 599 



mains quiet and contracted. This short anterior region, 

 including hardly more than the head, goes through the 

 crawling movements, but on account of its small size is very 

 ineffective so far as pulling the body away from the needle 

 is concerned. In my experiments I have never seen any 

 worm succeed in getting free from a needle put through the 

 body in this position. 



This general behaviour of the animal in response to restraint 

 of movement is very interesting, especially in the cases where 

 the restraint is at the posterior end, as showing the relation 

 between the behaviour and the capability of regenerating. 

 The organism tears itself loose from a restraining body with 

 entire nonchalance, as it were, and its confidence is well 

 founded because no permanent harm comes from the action. 

 The lost and wounded parts are regenerated and healed in a 

 short time. The behaviour takes advantage of the ability to 

 regenerate. Whether the form of behaviour (pulling away 

 from restraining objects) or the power of regeneration and 

 reparation appear in the organism first Ave cannot say, for 

 either might very well follow, in a more or less remote causal 

 connection, the other. What we do know is that at present 

 there is a very nice condition of mutual adaptation between 

 the two things. 



The effect of the hindrance of a rather light weight at the 

 posterior end of a worm is to induce the craAvling movement. 

 This can be seen in case the animal is feeding on a small 

 piece of food material, and, as frequently happens, starts into 

 movement before the pharynx is withdrawn. The piece of 

 food attached to the end of the pharynx is dragged along 

 behind, and the movement is the crawling. Frequently, also, 

 in feeding experiments pieces of food will get stuck to the 

 posterior end of the worm by means of the mucous secretion 

 of the body, and these have the same effect in inducing the 

 crawling movement. 



Having now obtained a descriptive basis we nuiy pass to a 

 discussion of some general features of these reactions. We 

 may first take up — 



