SENSORY EPITHELIUM OF MICROSTOMA CAUDATUM. 



47 



In casting about for reagents with which to further experiment 

 we decided to try dilute acetic acid because these specimens were 

 found among decaying vegetable matter in which we inferred 

 acetic acid might be present. Specimens were placed in eosin 

 water. 1 One of these in eosin water was placed under a sup- 

 ported rectangular cover-glass and by means of a capillary 

 pipette, mechanically controlled, a drop of 1/25 pei cent, acetic 

 acid added. The specimen swam about until it came in contact 

 with the colorless margin of the drop of acetic acid solution 

 when it reacted by turning directly away from the acid as 

 indicated by text-figure 3. This experiment, was repeated 



FIG. 3. FIG. 4. 



FIG. 3. Diagram indicating the path of a specimen when placed in eosin water 

 and encountering a drop of 1/25 per cent, acetic acid solution. The dotted line 

 indicates the contour of the enclosed drop of 1/25 per cent, acetic acid surrounded 

 by eosin water. 



FIG. 4. Diagram indicating the path of a specimen when placed in . i 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- 



eighteen times with practically the same results. When the 

 animals came' near the zone of acetic acid their anterior ends 

 would be expanded to such a great extent as to make them dis- 

 tinctly three-lobed. When the acid was reached the anterior end 

 would be greatly distorted while the posterior end would show 

 no change^of shape. Occasionally a specimen would strike the 

 acid with such'momentum that it would be carried into it. When 

 they had thus entered the acid, globules would appear about 

 the sides of the anterior end as if the ciliated pits were discharging 

 droplets of mucus. When such specimens escaped from the 



1 Fresh water in which just enough eosin was dissolved to make it distinguishable 

 from the acid solution. 



