i8 



OUTLINES OF NATURAL HISTORY. 



bases of tlie arms united together. The body of the Star- 

 fish is therefore said to have a " radiate " structure 

 (Latin, radius, a ray). 









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< -. --v-:VA, -^v. ■:;.-'.. -,.';;^- 



Fig 6.— The Common Star-fish [Uraster rubem), natiu-al size, vievv'ed 



from above. 



The entire upper surface of the body in the Star-fish is 

 covered with a leathery skin, from which project nume- 

 rous bhmt conical spines or prickles composed of lime. 

 Along the middle of the back of each arm, these spines 

 form a well-marked zigzag line, more conspicuous in some 

 examples than in others. Between the spines also are 

 much smaller, stalked prickles, which can be seen when 

 magnified to terminate in little pincers. 



In the centre of the under surface of the body is placed 



