92 



STAIiFISlI, SEA U1U!H1N, BKriTLK STARS 



and wrapped ;ii()und the Adetiiii, which is tlien dissolved 

 and digested, after which the stomach is withdi-awn into 

 the body. 



The water vascular system. — The niadreporite, of wliich 

 we liave ah'eady spoken, is the cover to a sh(^rt canal, the 

 stone vdiKtl. that runs downward and <ii>ens into a ringlike 

 canal that encircles tlie mouth. Fi\'e long canals, one for 



each arm, radiate 

 from the ring canal 

 about the mouth. 

 Each of these long 

 H radiating canals is 

 provided with many 

 sliort side branches 

 to which are at- 

 tached the tube feet 

 (Fig. 45). Each tube 

 foot is connected, by 



Fig. 45. — Diagram tif tin- water vascular svs- , , , , ,i , 



temofastarfisli: ,S, .s,,,,,. .anal ; C, circular ^ slendcr tubc that 



canal ; R, radial canal ; T, tube feet ; A, am- paSSCS through a 

 pullie. After Broolcs. • j i , 



^ nunute pore between 



the ossicles, witli a water bulb in the body cavity. The 

 bull) and the tnljc foot ai-e both contractile. 



This whole system of tuljes is called the water vascular 

 system (Fig-. 45). The tubes are filled with a watery fluid 

 composed largely of sea water that flows in through the 

 madrcpoi-i(c. 



Locomotion of tire starfish. — ^^^u■n the starfish <lesires 

 to move, it c()in|)i'esses the water bulb comiected with each 

 tube foot and foices the \\'ater out into the lattei- oi'gan. 

 This gi-eatly cdoiigates each tube foot which is then dii'ccted 

 forward in the ilii-ection tlie animal wishes to go. .\fter 



