288 S. O. MAST AND K. S. LASHLEY 



ing reaction which is not accompanied with the production of a 

 feeding cone. Under these conditions the cone, how^ever, is 

 sometimes produced as the animals enter the cloud, although 

 there is no apparent turning aside as in the typical weak avoid- 

 ing reaction. The cone in such cases is usually small and the 

 animals frequently seem to pause just before it is produced. 

 The reaction is relatively infrequent and it could not be studied 

 under a magnification great enough to reveal the ciliary move- 

 ments, but in some cases the pause in the animal's progress just 



Fig. 3 Illustrating the production of the feeding-cone during the weak 

 avoiding reaction. 1, 2, 3, successive positions of the Paramecium; 1', 2', 3', 

 corresponding positions of the edge of the cloud of ink. The Paramecium, weakly 

 stimulated by the edge of the cloud of ink, reacts by reversing the cilia of the 

 body, but not those of the oral groove. Currents of water are drawn in from 

 both anterior and posterior directions but most strongly along the oral groove 

 where the currents are visible as a cone in the movements of the edge of the 

 cloud of ink. Note that the feeding-cone is not produced until after the Para- 

 mecium begins to turn. 



before the formation of the cone was unmistakable and indi- 

 cated that the formation of the cone was due to an avoiding 

 reaction so weak that there was no deflection in the course of 

 the animal. 



The absence of feeding cones in strong avoiding reactions is 

 especially striking in responses to alkalies. If, for example, 

 strong potassium hydrate is added to the cloud of ink the ani- 

 mals, without producing a cone, swim forward until the anterior 

 end penetrates the edge of the cloud, then they reverse all their 

 cilia and swim backward violently, leaving a deep depression in 



