272 E. A. ANDREWS. 



Failure to collect such motile forms in the open by dragging 

 nets over and through the Elodea was in part due to the lateness 

 of the season, August 19-20, and in part to the difficulty of re- 

 taining ciliated cylinders one tenth to one twentieth of a milli- 

 meter in diameter in a bolting cloth of one tenth millimeter mesh. 



The motile forms must be very abundant at times in all these 

 waters and through the summer floating branches of Potamogeton 

 and of Elodea taken in the middle of the river are more thickly 

 covered with tubes than those growing along shore, as if they had 

 been colonized while floating. Far swimming motile forms 

 carried by the currents may be the first settlers in the spring 

 that so rapidly take possession of all the Elodea zones. Such 

 motile forms must be a considerable addition to the plankton 

 and may fall a prey to the schools of young menhaden that 

 frequent the river and its branches, feeding over and near the 

 Elodea zone as well as farther from shore. 



That the sessile forms have some enemies is seen in the utiliz- 

 ation of their cases by the larvae of aquatic insects that bite 

 them off and from them construct sinuous tubes in which they lie 

 stretched out over the surface of the leaves, with green contents 

 in their digestive tracts strongly suggesting that they not only 

 destroy the cases of Folliculina but eat the contained animals; 

 and one larva was seen to bite off and chew up a Folliculina 

 recently settled on filter paper. 



The distribution of the Folliculina cases over the leaves being 

 due to the behavior of the motile forms, two questions call for 

 answer; why are the upper leaves selected and why are the cases 

 placed in groups or aggregates? The following observations on 

 the actions of the motile forms aid in answering these questions. 



BEHAVIOR OF MOTILE FORMS. 



The motile forms seen emerging from tubes, Fig. 2, are long 

 cylinders abruptly truncated at the anterior end and bluntly 

 pointed at the posterior end. They change form by local con- 

 tractions, bending the part outside the tube in various directions 

 and swelling and contracting in diameter in some regions at 

 expense of others. The figure represents one in successive poses 

 from left to right, finally leaving the tube. After some minutes, 



