Reactions of /Eolosoj?ia to Chemical Stinndi 59 



On the following day, when the new prostomium seemed tolerably 

 well developed, there was still no response. About two days later, 

 when the sensory hairs could be distinguished, the great majority 

 of the animals reacted as normal. 



The next experiment was made by tapping gently with a fine 

 bristle that part of the epidermis in which the cerebral ganglia lie 

 buried. The animal wriggles energetically at first, but upon repe- 

 tition the nervous system suffers paralysis or fatigue, and the 

 animal soon curls up and refuses further movement. After the 

 ^Eolosoma had begun to relax, the threshold experiments were 

 tried and received no response. In many cases it was nearly an 

 hour before the exploring reactions could thus be stimulated. In 

 all of these cases, very soon after the introduction of the mechani- 

 cal inhibitions^ the stronger solutions, here called " normal stimuli" 

 would develop their characteristic reactions. 



These data suggest that any interference with the integrity of 

 the nervous system of. ^olosoma, will raise the threshold of chemi- 

 cal stimulation. 



Effect of Changes in the Ambient Medium on the Reactions 



Changes in temperature were made by placing the culture dish 

 in a water bath which is warmed or cooled to the requiredtempera- 

 ture and so maintained for several hours. The experimental 

 media were also correspondingly treated. For very bright day- 

 light the animals were subjected to the light coming from above 

 and also reflected upward from beneath. For much of the time 

 direct daylight was used. 



1 If the temperature of the water is lowered to about 10° C. 

 no characteristic response can be developed by means of these 

 threshold solutions. 



2 If the temperature of the water is raised to 20° C. the reac- 

 tions to the above threshold solutions are very similar to those 

 recorded later under the so-called "normal stimuli." The thresh- 

 hold of chemical discrimination is raised to solutions more than 

 twice as dilute as the above. 



3 If the animals are subjected to bright light for several hours 



