THE MASTIGOPHORA 



169 



asymmetrical body is able to move in what is approximately a 

 straight line. 



f f I I I I 



n 



-«« 



-«¥«t 



-«« 



-«« 



-«4 



-«« 



--^^a, 



-«« 



-*a 



n 



-*<» 



< 0.03 mnir 



Fig. 92. — Euglcna sp. (?) in crawling slate, showing details in process 



of orientation. 



a-c, positions of euglena with light from n intercepted; c-m, positions after light from 

 n is turned on and that from o cut off so as to change the direction of the rays; es, eye-spot; 

 n, o, direction of light; v, contractile vacuole. (From Mast, "Light and the Behavior of 

 Organismb," John Wiley and Sons, copyright, 1910, reprinted by permission.) 



By its movements of crawling and contracting, and by its spiral 

 swimming, the euglena responds to a variety of stimuli. The 

 behavior in response to hght has been most thoroughly studied 

 since it can be easily observed. Euglenas depend upon sunlight 

 for one type of their nutrition, and hence, like green plants, they 

 respond positively to light of optimum intensity. The reactions 

 of a crawling euglena with respect to light are shown by 



