68 



FIRST LESSONS IN ZOOLOGY 



whiplasli-like. In some the cilia seem to be in constant 

 rhythmic motion, in others they seem to move only when 

 the animal wills it. Motion by the contraction of a fiber is 

 seen in the peculiar Protozoan called Vorticella (fig. 37). 



Fig. 36. — rarainQ:fiiiiii ^p. ; 

 buccal groove at right. 

 (Greatly magnified; from 

 life. ) 



Fk;. 37. — l'oiiiit-//a sp. ; one 

 individual with stalk coiled, 

 and one with stalk extended. 

 (Greatly magnified; from life.) 



This animal has a tiny bell-like body on the end of a 

 slender stalk. The stalk is made up of an outer rather 

 firm elastic substance with a contractile fiber in the core. 

 When the fiber contracts the stalk is drawn up into a spiral 

 and tlius becomes sliortened. 



Muscles and skeleton. — The livin.i,^ elements in the 

 Vjody of the hiyher animals are small parts called cells, 



