252 University of California Publications in Zoology [Vol. 11 



1. Reactions to Stimulation of the Anterior End 



The extreme sensitiveness of the body of the leech has been 

 considered in the first part of this paper. The animal is very 

 responsive even to slight stimulation of any part of its body 

 with a flexible hair bristle or a delicate capillary glass rod. In 

 the majority of cases the response is a turn or movement away 

 from the stimulus ; yet there is a decided variation in this regard. 

 Several different responses varying in character and degree can 

 be secured upon stimulation of a localized region of the anterior 

 fifteenth of the body. Some responses to stimulation of one side 



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rig. 5. — Five different responses to tiie same localized contact-stimu- 

 lation of the anterior end of Dina microstoma: (a) turn to the left, (b) 

 turn to right towards the stimulus, (c) turn to left followed by turn to 

 right, (d) turn to right followed by turn to left, and (e) a complete re- 

 versal of direction bv turn to left. 



