94 S. (). MAST 



through an angle of nearly 180 degrees, Fig. i. Then the body 

 gradually straightens again, the anterior end turning back 

 somewhat toward its former position, the flagellum straightens, 

 the tip becomes active and the creature proceeds on its new- 

 course, having changed its direction of locomotion approxi- 

 mately 90 degrees. In this way objects are avoided which 

 frequently have been only slightly touched by the very tip of 

 the flagellum. This bending reaction is not dependent upon 

 the activity of the flagellum as maintained by Verworn (All- 

 gemeine Physiologie, 1909, p. 451). It is entirely due to con- 

 traction of one side of the body. Moreover, I was unable to 

 obtain any evidence indicating that the direction of motion in 

 crawling specimens is changed in any other way. Neither the 

 beating of the flagellum nor any thing connected with the wave- 

 like contractions of the body functions in changing the course 

 of this animal. 



The fact that Peranema responds when only the tip of the 

 flagellum is touched indicates that this structure is sensitive 

 to contact. It does not, however, prove that it is, for it may 

 be that the response is due to change in pressure on the anterior 

 end of the body owing to the contact of the flagellum or to 

 mechanical waves transmitted through it to the body. How- 

 ever this may be, the animal responds precisely the same when 

 the body is touched with a glass rod, as was repeatedly done. 

 Moreover, this response bears no relation to the location of 

 the stimulus on the body; it is precisely the same no matter 

 whether the posterior or the anterior end is touched, or any 

 other point on the surface. There is no indication whatever 

 of a differential response to localised stimulation. Peranema 

 differs in this respect from most of the other unicellular forms 

 that have been tested. When Lacrymaria or Stentor e. g., is 

 stimulated on the posterior end it ordinarily does not respond 

 the same as when it is stimulated on the anterior end. Thus 

 the character of the response in these creatures depends in 

 some measure upon the location of the stimulus, while in Pera- 

 nema this is not true. But in this animal there may be local 

 response to local stimulation. One often sees contraction of 

 the tissue in the immediate region to which the stimulus is 

 applied, and these contractions may spread over the body in 

 wave-like form. Whether or not the direction and the char- 



