MOVEMENTS, ETC., OF FRESH-WATKR TLAXAIUAN.^. 541 



as to cover nearly tlic Avliolc of the ventral surface of the 

 head. The beat is the strongest down the median line of 

 this band, and diminishes in intensity towards either edge 

 until at the mai'gins there is no ciliary movement at all. At 

 the anterior end the cilia near the side of the head beat 

 backwards and at the same tiaie inward towards the median 

 line, so that the currents take the course indicated by the 

 arrows in that region in Fig. 2. The distribution and action 

 of these cilia were made out by stirring finely powdered indigo 

 in the water, and then either directly observing the ciliary 

 action on these suspended particles as the animal glided on 

 the surface film, or by indirectly observing it in a mirror 

 placed below the bottom of the glass dish in which the 

 worms were. Both of these methods gave the same results, 



^ 



Fig. 2. — Dingrani of the ventral surface of Plaiiaria, to sliow the 

 distribution of cilia. The stijjpled area is that, which bears cilia. 

 The arrows indicate the direction of the ciliary currents. (The 

 pharynx is omitted for the sake of clearness.) 



and showed very clearly the distribution of the effective 

 cilia. 



I have found no evidence of ciliary action on the dorsal 

 surface of the body. Around the margins of the head there 

 are cilia, but in other parts of the body, either on the dorsal 

 surface or the edges, I have found no evidence of their 

 presence. Particles of indigo dropped on the dorsal surface 

 of a worm will remain in the same place for hours at a time. 

 This is in striking contrast to the conditions in the land 

 planariaus as described by Moseley ('77), Avhere the dorsal 

 surface is thickly covered Avith cilia, which serve the purpose 

 of keeping the body freed of foreign matter. 



In the gliding movement the head is raised slightly from 

 the bottom so as to form an angle with the rest of the body. 



VOL. 46, PART 4. — NEW SERIES. N N 



