1913] Gee: Behavior of Leeches 211 



frequently remains in contact with the suhstratum, and is 

 dragged along as in the case of Dina. In Dina, stronger stimu- 

 lation may produce lifting of the sucker of this region, but the 

 leech does not seem to be able again to attach this quickly enough 

 to complete the looping movement within the normal length of 

 time. This is perhaps to be explained as due to the flattened 

 shape of the body produced as the result of the contact stimu- 

 lation, this expanded condition preventing the posterior sucker 

 from readily attaching itself. Upon the attachment of the pos- 

 terior sucker, the anterior end is released and the movement as 

 described above again performed. These looping responses, fol- 

 lowing each other in rapid sequence, serve to carry the animal 

 forward with a fair rate of progression. 



4. Swimming Response 



This is provoked rather easily upon stimulating the posterior 

 end of the animal, the strength of the stimulus governing to a 

 great extent the vigor of the response. It is also secured upon 

 rather strong stimulation of the anterior end, usually under 

 these conditions, following a complete recoil and consequently a 

 complete change of the direction of the movement of the leech. 

 The reaction consists in a rhythmical undulatory muscular con- 

 traction proceeding antero-posteriorly. The body strikes up and 

 down in the water, or the lateral axis of the body may become 

 vertical in position, and the body of the animal be lashed from 

 side to side. A very characteristic feature of this "eel-fashion" 

 of swimming is the dorsi-ventral flattening of the body. This 

 serves to reduce the resistance in movement through the water, 

 and at the same time affords a greater propelling surface with 

 which to drive the animal forward. 



To a stronger stimulation of the posterior end the animal 

 responds with more rapid undulatory movements of the entire 

 body, the lateral axis of the body becoming vertical instead of 

 retaining the normal horizontal position. Greatest speed seems 

 to be secured in this way. To the average stimulus, more often, 

 the normal dorsi-ventral position is assumed; and while the 

 undulations of the wavelike course of the animal are less deep 



