LOCOMOTION IN WATER 



215 



a flower by its stern, and there it executes movements 

 which are so slow that they almost escape observation. 

 But if separated from its attachment, and irritated by 

 means of a rod, it soon begins to throw its arms about 

 in a rapid manner — movements which result in its 

 removal from the unwelcome object. As in the case 

 of the jelly-fish, the direction of movement corresponds 

 to the long axis of the body ; by inclining its cup 



Fig. 150.— Movements of the bell of a medu«a. The first position is the first of the 

 upper series on the right ; the last position is the one on the extreme left of the 

 lower series. 



obliquely, it can alter the direction of progress. In 

 the case here represented (Fig. 151), the animal was 

 trying to rise from the bottom of the aquarium. 



The following is the method of propulsion. The 

 arms of a comatula are ten in number, five invariably 

 move upwards, and five downwards ; two neighbour- 

 ing arms never move in the same direction. Those 

 which rise upwards approach the axis of the body, 



