SENSORY EPITHELIUM OF MICROSTOMA CAUDATUM. 49 



figure 5. It can be seen that the animal passed through the 

 fresh water twice and did not react to it at all. 



These experiments suggested to us that a change may have 

 taken place in the physiological condition of Microstomas which 

 were kept in the laboratory for a certain length of time. 



Collections were then made of Microstomas and 150 additional 

 experiments performed during five months in order to test the 

 suggestion made by these two sets of experiments. 



These experiments must be divided into two groups and each 

 of these groups into two sub-groups: 



1. Reactions of Microstomas kept in the laboratory for less 

 than twenty-four hours. 



(a) When they were placed in fresh water and left to come 

 in contact with an undisturbed drop of .05 per cent, common salt 

 solution which was placed in the center. 



(&) When they were placed in .05 per cent, salt solution and 

 left to come in contact with an undisturbed drop of fresh water 

 which was placed in the center. 



2. Reactions of Microstomas kept in the laboratory for more 

 than twenty-four hours. 



(a) When they were placed in fresh water and left to come 

 in contact with an undisturbed drop of .05 per cent, common salt 

 solution which was placed in the center. 



() When they were placed in .05 per cent, salt solution and 

 left to come in contact with an undisturbed drop of fresh water 

 which was placed in the center. 



The following are three experiments of each of the above 

 groups picked at random from our notebooks: 



Group I -a (specimens placed in fresh water and allowed to 

 encounter a drop of .05 per cent, salt solution). 



January 13, 1912. A specimen that had been in the laboratory 

 twenty hours came in contact with the drop of .05 per cent, salt 

 solution and each time reacted by turning away from the margin 

 of the salt solution (text-figure 6-a). 



February 3, 1912. A specimen that had been in the laboratory 

 eighteen hours came in contact with the drop of .05 per cent, salt 

 solution five times and each time it reacted by turning away from 

 the margin of the salt solution (text-figure 6-b). 



