404 S. y. Holmes 



If a stimulus is applied to the posterior end of the body, or a 

 short distance in front of this on either side, the usual motor reflex 

 is not produced. The animal swims directly forward. With 

 repeated stimulation of the posterior end it may be kept swimming 

 forward for a long time. If the stimulus is applied during the 

 progress of the animal the rate ot movement is accelerated. Essen- 

 tially the same behavior has been found by Jennings to occur in 

 Paramecium in response to weak stimuli, and I have often ob- 

 served the same phenomenon in this and several other infusoria. 

 It indicates the first step toward reacting in a specific manner to 

 the localization of a stimulus. 



The reactions of Loxophyllum are quickly modified by suc- 

 cessive responses to stimulation. This, I believe, is in large part 

 due to the dulling of the sensitiveness of the organism through 

 the repetition of stimuli. A very slight stimulus to the anterior 

 end of the body suffices at first to produce a reaction. With 

 repeated poking the anterior end becomes so dulled that the organ- 

 ism may continue to swim forward in spite of frequent stimulation 

 at this point. Recovery, however, is quick, for in a few minutes 

 the responsiveness is as great as ever. 



A similar result is more quickly reached by the application of 

 stimuli to the sides. The motor reflex may be elicited very readilv 

 for a few times, but it soon requires much stronger stimuli to bring 

 it about. If the stimuli are applied quite far back it requires 

 fewer stimulations before the animal refuses to respond at all. 



There seems to be a tendency for the organism to resume its 

 usual activity which asserts itself when its sensitiveness becomes 

 dulled so that it does not react so readily to stimuli. It may be 

 kept from going forward, for instance, by repeatedly stimulating 

 the anterior end of the bodv. But sooner or later the tendency 

 to normal activity predominates and the animal may go forward 

 in spite of considerable stimulation. 



Notwithstanding its rapid habituation to stimulation Loxo- 

 phyllum exhibits certain features of behavior that seem referable 

 to the summation of stimuli. Repeated stimulation may induce 

 a condition of unusual excitement which may be manifested in con- 

 tinual and quite rapid swimming, increased writhing movements. 



