ASTER IAS SKELETON 



435 



spines then form a trail is- work covering and protecting the 

 delicate tube- feet; the numerous pedicellariae are then in a 

 position to make it unpleasant for any intruder. The closure of 

 the groove is effected by means of powerful muscles connecting 

 each ambulacral ossicle with its fellow. There are also feebler 





m 





c^er- 





Fig. 187. — A, Asterias rubens, seen from the oral surface, drawn from a living specimen. 

 X 1. B, an adambulacral spine, showing three straight pedicellariae ; C, a tube- 

 foot expanded and contracted. 



muscles connecting these plates with their successors and pre- 

 decessors, which enable the 'arm to be bent downwards in a 

 vertical plane. It is raised by a muscular band running along 

 the dorsal wall of the coelom to the point of the arm. 



When the series of ambulacral and adambulacral ossicles is 

 followed inwards towards the mouth it is seen that the first 

 ambulacral ossicle is closely fixed to the second, but is widely 



