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



organs" differed from ciliated pits only in that the former were 

 differentiated into a glandular region and a sensory region. In 

 Microstoma caudatum Ldy. we find a similar differentiation into 

 glandular and sensory regions. Thus we see the affinity between 

 Turbellaria and Nemertini strengthened by the structure of the 

 ciliated pits of Microstoma caudatum Ldy. 



So much for the morphological part of the present paper. The 

 second part has to do with experiments performed upon Micro- 

 stoma. 



We have collected Microstomas by placing into an aquarium 

 sticks, leaves, and other submerged objects that have been taken 

 from the marginal bottom of the pond. It is only after the 

 filled aquarium, containing the debris from the pond, has 

 stood twelve to twenty hours that the Microstomas appear 

 at the surface of the w T ater. In making collections for histo- 

 logical material it was noticed that the animals were quite alert 

 and active when they first appeared at the surface. Under 

 laboratory conditions bacteria accumulate rapidly in the aquaria 

 so that within forty-eight hours a thin film appears at the 

 surface. After this film has appeared the Microstomas seem to 

 be less alert, and when this film has become dense the Microstomas 

 must be actually touched in order to be caused to move from 

 the place in which they were lying. This observation was made 

 only after a point brought out by some of the experiments, to 

 be described below, had indicated it. 



If specimens are collected as soon as they appear at the surface 

 and studied under supported cover-glasses by means of the 

 compound microscope they are seen to make numerous explora- 

 tory movements as they swim about by thrusting their anterior 

 ends to and fro, thus testing the water by means of their ciliated 

 pits and pharynx. These actions then may be taken to indicate 

 the nearly normal response of Microstoma to nearly normal condi- 

 tions. 



Next some specimens were placed in a .05 per cent, salt solu- 

 tion to see what their response would be to less normal conditions. 

 It was found that the exploratory movements were intensified 

 and the ciliated pits widely distended with each anterior thrust 

 of the body. Thus it was seen that a change in conduct could 

 be induced by artificial media. 



