n8 



BEHAVIOR OF THE LOWER ORGANISMS 



with the solid object and remains against it. It may now continue quiet, 

 while the oral cilia bring a current of water containing food to the mouth. 



But sometimes the animal 

 runs over the surface of the 

 solid, using its cilia as if they 

 were legs. This, as we have 



Fig. 81. — Side view of Stylonychia creeping along Seen, is the Common method 

 a surface. After Putter (i 9 oo). of l ocomot i on i n t h e Hypo- 



tricha. A side view of one of the Hypotricha while creeping along a 



surface is shown in Fig. 81. In other cases the animal secretes a layer 



or thread of mucus and thereby attaches 



itself to the solid. Attached in this way 



by a long thread (Fig. 82), Spirostomum 



and Urocentrum often remain in a certain 



position, revolving on the long axis. The 



thread is usually quite invisible, but by 



passing a needle between the solid object 



and the animal, the latter may often be 



pulled backward by the thread of mucus. 



In still other cases the infusorian reacts 



to solid objects by fixing its posterior end 



firmly, remaining in this place for long 



periods, like a plant. How this occurs in 



Stentor is described in Chapter X. 



The contact reaction is often directed 

 toward very minute objects, as we have 

 set forth in detail in the case of Parame- 

 cium. It then serves the purpose of help- 

 ing to obtain food. In some of the fixed 

 infusoria such behavior is especially strik- 

 ing. Thus, if a small object touches gen- 

 tly one side of the disk of Stentor, the 

 animal may bend over toward it. This 

 reaction may be seen when a small or- 

 ganism in swimming about comes against 

 the disk of the animal, then attempts to 

 swim away. The Stentor bends in that 



... . . . Fig. 82. — Spirostomum attached 



direction, so as to keep in contact with to the bottom by a threa d of mucus 



the Organism as long as possible. At and remaining stationary with anterior 



the same time, of course, the ciliary vor- c 



tex tends to draw the prey to the Stentor's mouth. This reaction 



may be produced experimentally by attaching a bit of soft, flocculent 



