216 



MOVEMENT 



£'£& 



those which descend recede from it. Sometimes in the 



phase of upward 

 movement, the fine 

 processes on the arm 

 can be seen flattened 

 lown against it by 

 the resistance of the 

 water. In the phase 

 of downward move- 

 ment, the same pro- 

 cesses are separated 

 out, become visible, 

 and meet with re- 

 sistance from the 

 water, which thus 

 acts, as it were, as 

 a fulcrum to assist 

 the animal in its 

 locomotion. 



Locomotion by 

 means of Undulatory 

 and Lateral Move- 

 ments : Eels. — Eels, 

 and fishes of a simi- 

 lar shape, progress 

 in a horizontal 

 direction by means 

 of an undulatory 

 motion of their 

 bodies. To observe 

 this movement satis- 

 factorily, the ob- 

 server should place 

 "' himself above the 

 animal : a special 



kind of aquarium is required for taking chrono- 



photographs. 



Fir.. 151.— Cnmatula executing movement 1 

 bottom of the aquarium. The series must be read 

 from below upwards. 



