256 



THE OCEAN WORLD. 



Another species, Asterias aiiratitiaca, will give a good idea of the 

 general type of the animals in this order. This Echinoderm, which 

 is represented in Fig. 105, is common in the northern seas ; it has 

 five rather long arms, furnished with spines, which are of an orange 



105. — Asterias aurantiaca (Lamarck). 



colour — hence its name, \^^len we see one of these animals stranded 

 upon the shore, it appears to be entirely destitute of all power of 

 progression. But it is by no means immovable ; it is provided with 

 a special apparatus for locomotion, consisting of membranous tubes 

 usually termed feet, or ambulacra, which issue from the ambulacral aper- 

 tures ; but besides these, the rays themselves are movable, and, in 

 animals which are free to move from place to place, these are perhaps 

 used for the purpose. Thus, in the common star-fish the rays may be 

 bent towards the upper or lower surface of the disc, so as to facilitate its 



