256 THE OCEAN WORLD. 
Another species, Asterias aurantiaca, 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 
“yos.—Asterias aurantiaca (Lamarck). 
colour—hence its name. When 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 
