REACTIONS OF OPALINA RANARUM 



325 



flattened dorsoventrally and somewhat asymmetrical at the 

 more pointed anterior end of the " adult " animal, (Fig. 1). 

 From the anterior end to the notch, in the middle of the right 

 side, the surface of the body is concave, and below the notch, 

 this side is markedly drawn in. The left side shows no such 

 irregularity. Cilia are distributed abundantly over the entire 

 pellicle; on the dorsal and ventral surfaces. They are arranged 



Fig. 1. — Opalina ranarum. Ventral view (after Dolflein) 



in diagonal rows across the body. Small Opalinas or those 

 formed by recent divisions usually have the posterior end more 

 pointed than the anterior. 



The object of the present paper is to present a general ac- 

 count of the behavior of Opalina and to compare its reactions 

 with those of free-living protozoans which are well known through 

 the work of Jennings, Mast, and others. 



The experiments discussed in this paper were performed in 

 the Zoological Laboratories of the University of Wisconsin dur- 

 ing the months of January, February, March and April, 1915. 

 My thanks are due to Professor A. S. Pearse, under whose direc- 



