284 E. A. ANDREWS. 



There remain other facts that must wait further observations 

 of elucidation. Why do individuals prevailingly lie along in 

 grooves of the wood? Why do they collect in groups near, but 

 not at the edges of leaves? Why in such cases as Fig. 4, are they 

 confined to the narrow edges of the glass and not extended over 

 the lower face of the glass as well? Why do they not settle on 

 wax or on resinous wood? 



Possible many of these facts result simply from the reversing 

 movements on receiving a stimulus; an edge to a groove or an 

 edge to the leaf, or the contact with another animal or with its 

 currents may bring about the same inability to advance over the 

 boundary. 



Possible, again, there may be some such problems here as seem 

 to exist in the earthworm in responding to angles and edges. 

 The selection of the middle of the cover glass in Fig. 3, and the 

 settlements along the top of leaves near the edges may involve 

 some resultant of spaces travelled over after stimulation at 

 edges. 



While, in a general way, the action of the motile forms toward 

 light, surfaces and in their own secretions may suggest how the 

 cases come to be placed as they are in nature, yet there is proba- 

 bility that the phenomena are much more complex than as yet 

 made out. 



SUMMARY. 



1. This protozoan occurs in the brackish waters of branches of 

 the Chesapeake Bay in temporary association with the fresh 

 water plants Elodea and Potamogeton. 



2. Its adjustment to the growth of these plants is brought 

 about by the migrations of motile forms that escape from the tubes 

 of the sessile forms. 



3. These motile forms respond to light and to solids, and these 

 actions seem to keep them ever settling upon newer parts of 

 the plants during the season. 



4. The motile forms add materially to the plankton during the 

 summer. 



5. Folliculina appears in the early summer and disappears 

 before the plants die down in the autumn, forming part of a 



