62 H. G. Kribs 



head is first turned toward the pipette before expressing these 

 movements. There is a large increase in the amount of mucus 

 secreted. When stimulated at the posterior papillae, the caudal 

 segments are slowly contracted and swing toward either side. 

 Some seconds after stimulation the head segment shows a marked 

 increase in the exploring reaction. When applied to the lateral 

 segments the animal first curls as usual, then twists about with 

 increasing energy but with no locomotor results. The reactions 

 to CUSO4 were similar to those with the mineral acids. In the case 

 of ZnSO^ the great majority moved away from the stimulus with a 

 spiral twisting reaction, alternating this reaction every few seconds 

 by curling up and vigorously rubbing the prostomium on the sub- 

 stratum. When put back into a culture dish they immediately 

 burrowed into the ooze at the bottom of the jar. 



In all of the above reactions, which were followed by locomotion 

 there was noticeable a marked increase in the vigor of the charac- 

 teristic "exploring movements." The end result was that the 

 animal followed a decidedly zig-zag course. 



Reactions Under Changing Conditions 



a. The head is severed from the body by a cut through the 

 region of the oesophagus. Within a few hours the anterior seg- 

 ment of the body will respond to the above stimuli of normal 

 strength m a way characteristic of the normal explormg reaction. 

 Lateral applications may cause the dorso-ventral contractions but 

 they are not followed by the reverse movements that are noted 

 under normal conditions. 



b. The animal is physiologically depressed by tapping the cere- 

 bral ganglia as described under threshold stimuli. The reactions 

 to the various chemicals under these conditions do not exhibit the 

 usually distinctly negative quality but resemble more closely those 

 given above under FeS04. 



c. The temperature is gradually lowered to about 10° C. It is 

 difficult to get any characteristic reactions except at the prosto- 

 mium, and these correspond closely to the threshold reactions at 

 15° C. The lack of any marked reaction when the body segments 



