THE MANIFESTATIONS OF LIFE 45 



remains inactive for a short time, then again resumes its 

 movement. 



When Vorticella is touched, a sudden and powerful 

 contraction of the pedicle results, drawing the little 

 animal away from the offending agent. A whole colony 

 of Carchesium may contract when one organism is 

 irritated. 



The rotifer with its "wheels" in motion, quickly with- 

 draws the cilia if touched, is quiescent for a mo- 



FIG. 6. Vorticella [nebulifera (Entire colony magnified). C.V, Contractile 

 vacuole. A free-swimming individual with two rings of cilia is seen on the 

 right. When irritated the pedicle undergoes a spiral shortening and the organ- 

 ism is quickly drawn away from the irritant. (Masterman.') 



ment, then again expands them and continues to feed. 

 Touched again, the same effect may be produced, or 

 the animal may let go its hold and swim away to try 

 a new place where it may feed undisturbed. 



The fresh-water hydra behaves in a most interesting 

 manner according to the stimulations it receives, and we 

 soon perceive that the effects differ according to the 

 quality of the stimulus. Thus, when one of the tentacles 

 is touched by some minute swimming animal or plant, 



