191^] Gee: Behavior of Leeches 247 



To contact stimuli of the anterior end there is a varying 

 responsiveness and an equally varying type of response. IMueh 

 of this variation is to be attributed to different recuperative 

 capacities of the animals subsequent to decapitation. The ma- 

 jority of the reactions given to contact stimulation of the anterior 

 end are turns away from the stimulus. How'ever, all of the 

 varied combinations of responses, such as turns toward, reversal 

 followed by swimming, etc., are secured in operated specimens, 

 much as in the case of normal individuals. The manner of execu- 

 tion of these reactions is rather clumsy when compared with the 

 quick responsiveness of the normal active leech. 



In decapitated specimens, a very striking reflex is secured 

 which is not prominently expressed in the intact leech. Stimu- 

 lation of the mid-dorsal region a few millimeters posterior to the 

 wounded surface produces a vertical elevation of the anterior 

 end. The glass rod may be moved back and forth along this 

 region many times without evoking the swimming response of 

 the animal. Were one to allow one's anthropomorphic tendencies 

 sway, one might very readily imagine that the leech gains evident 

 en.joj'ment from having its back scratched. 



The decapitated leech is not altogether incapable of sponta- 

 neous movements, but certainly the removal of the anterior end 

 has a very marked effect on the degree of the animal's activity. 

 A specimen may remain for several days in a single attached 

 position, performing no more than a few undulatory movements 

 during this period. Much of this lack of internally initiated 

 responsiveness is to be attributed to the lowered vitality of the 

 decapitated animal. Some of it, I believe, is to be assigned to 

 the loss of the anterior ganglionic centers. Specimens six months 

 after operation show more decidedly this lack of movement. 



Perhaps the most significant change in the behavior as the 

 result of decapitation is the reduction of the tendency towards 

 random movements. While not restricted to the anterior region 

 of the body, the ability to perform these feeling movements seems 

 to find its chief expression in the first few anterior segments. 

 As has been stated in a previous portion of this paper, the func- 

 tion of these random movements is largely that of orienting the 

 body before the attachment of the anterior sucker. With the 



