PROTOZOA AND II IK UTRICLES OF UTRICULARIA. 



2 4 I 



lion. The reactions of intestinal flagellates to their environment 

 within the digestive tract of their hosts represent a very inter- 

 esting phase of the subject of host-parasite relationships which 

 has occupied the attention of the writer for the past five years. 

 The studies described below were undertaken, therefore, not only 

 because of the intrinsic interest of the subject, but also because 

 they might throw some light on the factors involved in the 

 relations of intestinal flagellates to their entozoic environment. 



FIG. 3. View looking down into the vestibule of a bladder showing the two 

 pairs of bristles and various glandular hairs on the valve, and other glandular hairs 

 extending out from the sides of the vestibule. X no. 



Specimens of Utricularia vulgaris v. americana Gray live in 

 fresh-water ponds and are often present in great abundance 

 floating near the surface. A typical branch is shown in Fig. i. 

 The utricles or bladders are borne at intervals along the branches. 

 Fig. 2 represents a side view of a bladder showing the bristles 

 which extent out above and on either side of the mouth opening. 

 Within the mouth is a shallow vestibule at the bottom of which 

 is a thin, flexible valve which is attached at the top and sides 

 but free below, where it rests tightly against an inward pro- 



