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sized but regularly disposed calcareous plates. In the Sea-ur- 

 chin (Echinus) these plates are joined so that the whole body 

 seems to be in one piece. In the Starfish (Asteridae), on the 

 contrary, they are more loosely connected and permit motion, 

 and the Starfish can move its arms up and down as well as 

 sideways. This fact is seen best when the animal is on its 

 back and wants to turn over. ( The keeper will induce this 

 movement at the visitor's request). 



The Brittle-stars (Ophiuridae) are so made that their single 

 arm constantly moves like a snake, and the Feather-stars (Com- 

 atulae) can even swim by lashing their long arms. But the 

 skin or shell of the Sea-cucumbers Holothuridae) has no such 

 calcareous mosaic; it is like a piece of leather dotted at intervals 

 with strangely formed calcareous bits, like anchors , stars and 

 rosettes, so that the skin is very elastic, allowing the animal to 

 stretch and bend its body in all directions. This construction 

 of the skin, however, can scarcely be seen, so covered is it with 

 spines and other appendages. The tiny calcareous plates of the 

 starfish are also not easy to be distinguished, but in dead 

 examples, which the keeper has at hand, we perceive their enor- 

 mous number, amounting, in some of the large individuals, to 

 a hundred thousand! 



You will ask how the Sea-urchins and Starfish move in the 

 water, since they have no legs, and cannot, like worms, and 

 eels, creep or swim by the undulating movements of the whole 

 body ? Before we answer this question we beg the reader to 

 examine carefully one of these animals, which he will certainly 

 find either sticking to the glass of the tank, lying on the sand, 

 or climbing on the rocks. 



On the side turned to the glass (in the first case) he will 

 see a great number of small transparent tubes, provided at the 

 end with a sucking- disk. These tubes or tentacles are extremely 

 flexible, can stretch and contract like worms, and adhere to 

 any object. They are called sucking- feet , and are connected 

 with a system of water pipes, consisting of a circular channel 

 with branching arms, lying in the central disk of the animal. 

 Each arm has two canals, which are studded with sucking-feet 

 like the leaves on a stalk, and through these canals the sucking- 

 feet are filled with water. The water is received through a 

 sieve-like calcareous plate on the animal' s back fmadrepore- 

 plate) and is pressed by the contraction of the canals into the 

 sucking-feet. By this alternate expansion, contraction and adhe- 

 sion the animal pushes itself along on its base. 



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