7 8 



THE BEHAVIOR OF LOWER ORGANISMS. 



We have dealt thus far specifically only with reactions to simple 

 mechanical stimuli, such as are presented by an obstacle in the path of 



FIG. 26.* 



the rotifer or by a simple mechanical jar. This type of reaction under 

 such conditions I have observed for Diurella tigris Miiller, D. por- 



* FIG. 26 is a diagram of the reaction of the rotifer Anuraea to a strong stimulus, 

 as when it reaches a source of mechanical stimulus or a region where some 

 chemical is dissolved in the water. From a to b the animal is unstimulated, 

 hence it follows the usual spiral course. At b it reaches the stimulating region, 

 whereupon it turns strongly toward the dorsal side, following the arc of a circle, 

 from b to d. Here it resumes the usual spiral course (d to <?). The large arrow 

 x shows the general direction of progression before the stimulus was received; 

 the arrow y shows the direction of progression after the reaction has taken place. 



