HABITS AND REACTIONS OF LACRYMARIA 233 



that when the side of the' head strikes an object the cilia on that 

 side become more active and force it in the opposite direction. 



(b) If the anterior end comes in contact with an object more 

 directly the animal usually stops and either contracts the neck 

 sharply, turns it toward one side and proceeds in a different 

 direction or reverses and swims backward, frequently for a 

 considerable time, especially if the stimulus is the result of an 

 injury. If the posterior end strikes an object in swimming back- 

 ward the creature immediately reverses again and swims forward. 



By means of a very fine glass rod I was able to stimulate 

 specimens which were at rest or swimming slowly at any desired 

 point and it was also possible by this means to vary the strength 

 of the stimulus. In this way numerous attempts were made to 

 ascertain more precisely the relation between the reaction and 

 the location of the stimulus. The results of these observations 

 together with those described above show very clearly that tha 

 response in Lacrymaria is somewhat dependent upon the part 

 of the body stimulated. When the anterior portion of the animal 

 is touched it frequently swims backward, whereas I was never 

 able to induce this reaction by stimulating the posterior portion 

 either in animals that were at rest or in those that were swimming 

 slowly. There is consequently in this creature a differential 

 response to a localised stimulus in a restricted sense. A given 

 stimulus applied to the anterior end causes a response different 

 from that caused by the same stimulus applied to the posterior 

 end. Further than this I was however unable to demonstrate that 

 the response depends upon the location of the stimulus. If the head 

 is stimulated the neck usually contracts, then turns toward one side 

 and extends in a different direction as already stated, but the 

 direction in which it turns bears no observable relation to the 

 location of the stimulus on the head. After being stimulated at 

 a given point the head may turn either toward or from this point 

 or in any other direction. The direction of turning under such 

 conditions seems to be regulated entirely by internal factors. 

 The same is true with reference to Paramecium, Euglena and 

 many other similar organisms. In these organisms, however, 

 the direction of turning is restricted by a structural or physio- 

 logical differentiation of the body. They always turn toward a 

 given side. Paramecium, e. g., as Jennings has clearly shown, 

 always turns toward the abiral side and Euglena toward the 



