4 8 



WM. A. KEPNER AND W. H. TALIAFERRO. 



acid they ceased to show any exploratory movements. Perhaps 

 this loss of the exploratory movements may be accounted for 

 by injury of the ciliated pits. Usually the specimens would be 

 unable to free themselves from the acid and would die. A 1/50 

 per cent, acetic acid solution was tried with similar results. 



Thus it is seen that both 1/25 per cent, or 1/50 per cent, acetic 

 acid are dangerous even fatal media to Microstoma. Therefore 

 .1 per cent, and .05 per cent, common salt solutions were tried. 

 The first experiment was made upon an animal seventeen hours 

 after removal from the pond. The animal was placed in a .1 

 per cent, salt solution and left to find the drop of fresh water 

 which was placed in the center. The animal's course is indicated 

 in text-figure 4. When the animal entered the fresh water it 

 continued straight across it until it came to the far side of the 

 drop, then it would turn away from the ciliated pit lying nearest 

 the salt solution. By repeating this reaction to contacts with 

 the salt solution the specimen would rotate in the drop of fresh 

 water. 



FIG. 5. Diagram indicating the path of a specimen when placed in .1 per cent, 

 salt solution and encountering a drop of fresh water. The dotted line indicates 

 the contour of the enclosed drop of fresh water surrounded by .1 per cent, salt 

 solution. 



We made only one experiment within twenty-four hours after 

 the specimens w r ere removed from the pond. Five days later 

 specimens were taken from the same aquarium which furnished 

 the last one. These specimens showed no definite reaction to 

 the fresh water when they were treated like the specimen referred 

 to in text-figure 4. The course of one of these is shown in text- 



