actively about, but as the arms coins to rest Tor the 

 backward movement, the tentacles are thrust down a- 

 gainst the substratum and cease to move. The tenta- 

 cles ten t acles thus fit themselves into the inequal — 



ities of the surface and fe4**s afford fixed points 

 to pull against. THe tentacles or the posterior arms 

 act in the same way and are efficient in preventing 

 the force of the stroke being lost in side motion. 



In ophiurans with long arm spines these latter 

 structures may perform the function just described 

 for the foot tentacles , but in the genus Ophiura the 

 arm cpir.es are very minute and closely applied to 

 the sides of the arms. 



It is interesting to note. the wonderfull coor- 

 dination of locomotor movements immediately follow- 

 ing the amputation of throe of the arms .In this 

 case if the nerve ring has been uninjured one of the 

 remaining arms takes up the part of guiding and bal- 

 ancing while other strokes first on one side then on 

 the other. F/<J$ 3.a**L¥, 



When the central nerve ring is cut at any point 

 coordination in movement is impaired and when cut in 

 five places , between the arms, it is lost entirely. 



Bhen placed en its aboral surface an ophiuran 

 quickly turns over. The method used is quits definite 



