STARFISHES 159 



animal can fill its ' water system ' direct from the sea, and, by the 

 contraction of muscles that surround the main canals, force this 

 water into the little ' tube-feet,' causing them to protrude and 

 present their sucking-discs to any solid object over which it desires 

 to creep. We may observe, however, that some of the little 

 protrusible tubes have no sucking-discs, and probably serve the 

 purpose of feelers only; also, that while these tube-feet are the 

 principal means of locomotion in certain species, in others the 

 movements of the body are performed almost exclusively by the 

 five or more rays that extend from the centre of the animal, and 

 which are readily curved into any desired position by the action 

 of well-developed muscles. 



All the echinoderms come within the domain of the marine 

 naturalist, for no members of the sub-kingdom are inhabitants 

 of fresh water ; and it is interesting to observe that, unlike the 

 animals previously described, none of them live in colonies. 



A general examination of the various starfishes to be found 

 in our seas will show that they may be divided into three distinct 

 groups. One of these contains the pretty Feather Stars, which are 

 distinguished by their long and slender ' arms,' usually ten or more 

 in number, each of which bears a number of pinnules that give it 

 quite a feathered appearance. The second includes the Brittle 

 Stars, possessing five slender arms that are jointed to the small, 

 flattened, central disc, and which are so named on account of the 

 readiness with which the animal falls to pieces when alarmed or 

 disturbed ; and the third is formed by the remaining five-rayed 

 stars, the arms of which, instead of being jointed to, are continuous 

 with, the centre of the body. 



All these starfishes have a leathery skin, supported and 

 hardened by a framework of calcareous plates, and presenting a 

 number of hard ridges or spines. In addition to the system of 

 water tubes already mentioned as characteristic of the echinoderms, 

 they also possess a second circular vessel round the mouth, from 

 which a number of vessels are distributed to the walls of the diges- 

 tive tube. These, however, are bloodvessels, and are directly 

 concerned with the nutrition of the body. Some, also, have imper- 

 fectly developed eyes at the ends of the arms or rays. 



Contrary to what one would expect after watching the some- 

 what sluggish movements of starfishes, they are really very 

 voracious creatures, attacking and devouring molluscs and small 

 crustaceans, sometimes even protruding their stomachs to surround 



