20 OUTLINES OF NATURAL HISTORY. 



as well as tlie "feet" proceeding from them, may be 

 called " water-vessels," because they are filled with water 

 from without. The sea-water, in fact, is admitted to 

 them by means of a little grooved, rounded tubercle 

 which is seen on the back of the animal (fig. 6) placed 

 at the angle where two of the arms unite. 



The mouth of the Star-fish is not provided with teeth, 

 and opens into a very thin and membranous stomach, 

 w'hich can be thrust forth or "pouted out" through the 

 mouth. From the stomach proceed ten much-branched 

 membranous saci?; two of which are prolonged into each 

 of the arms. The stomach terminates in an intestine, 

 which opens by a minute vent upon the back of the 

 animal. 



The nervous system has the form of a circular cord 

 surrounding the mouth, and sending a branch along the 

 groove in each of the arms. At the tip of each arm there 

 is also seen a small reddish spot, surrounded by a circle 

 of spines, and these are of the nature of rudimentary eyes. 



There are no distinct breathing-organs, and the process 

 of respiration appears to be chiefly carried on by the absorp- 

 tion of the sea- water through the skin of the back, the 

 delicate membrane which lines the interior of the animal 

 being protruded for this purpose in the form of small 

 tubes which project through interspaces in the integument. 



The common Star-fish usually measures from three to 

 six inches across, and is generally of a reddish, yeUowish, 

 or orange colour. During life its skin, though very rough 

 and prickly, is comparatively soft; but it contains so 

 much lime that it can be excellently preserved simply by 

 drying it in the sun. It is entirely a native of the sea, 

 and is found from low water to depths of twenty or thirty 

 fathoms. It is very voracious, and feeds upon oysters 

 and other shell-fish, seeming to suck the animal out of 

 the shell by means of the protrusible stomach. Lastly, 

 the Star-fish has the power of reproducing its arms when 

 broken off or injured. 



Recapitulation of Essential Characters — The 

 body exhibits more or less clearly a star-like arrangement 



