sway from a strong stimulus, the arm which precedes 



may also take part in the stroke, fts contractions 



fep&*made simultaneously with those of the side arms. 



This added force if produced repeatedly on one side 



would soon chans-:- the cours^of progression but this 



difficulty is overcome by an alternation of the 



stroke of the preceding arm, first on one side then 



on the other. T><J. 1. 



In s third method of normal locomotion the arms 



are arranged as in Fig. 5 . in which only one arm 



follows acting cs the rudder .This leaves twc pairs 



of arms for the stroke but the anterior pair Is 



usually meet vigorous in Hi contractions. 



Since no physiological differentiation into 



anterior, posterior or lateral parts is to be found 

 in ophiurids the creatures are under no necessity 

 of turning fche body when a change in the direction 

 of progression is to be made; the arm which finds it- 

 self pointing in the new direction to be traveled 

 takes the lead although it may have been either lat- 

 eral or posterior in position in the previous movements. 

 As has been mentioned before- the foot tentacles 



aid in making the strokes of the arms efficient in 

 propelling the body. After a stroke has been made , 

 while the arms are being drawn forward and extended 



