224 RADIATES: ECHINODEEMS. 



their hold. Their covering is not solid as in the Sea- 

 Urchins, but is composed of movable plates, so that 

 these animals are able to bend themselves in every di- 

 rection, and thus work their way into holes and fis- 

 sures in rocks where we should hardly expect to find 

 them. Star-Pishes feed upon moUusks and other ma- 

 rine animals, and when they feed they turn the stom- 

 ach out of the mouth and over the food to be devoured. 

 A curious spot is seen on the back near the junction 

 of two of the arms. This is the madreporic body de- 

 scribed in speaking of the Sea-Urchins. It is a sort of 

 minute sieve, and forms an entrance to a series of in- 

 ternal water-tubes, some of them connecting with the 

 locomotive suckers and supplying them with water. 

 Water is also admitted into the body through minute 

 pores which cover the whole surface of the animal. 

 Star-Fishes often lose one or more of their arms, or 

 rays, by being dashed against the rocks by the waves, 

 or the arm is bitten off by a fish. In all such cases a 

 new one sprouts out in the place of the old one, and 

 specimens may be found showing such new rays in all 

 stages, from those that have just begun to sprout to 

 those that have nearly reached their full growth. 



OPHIUEANS, OR SERPENT-STARS. 



The Serpent-Stars, or Ophiurans, are so called from 

 the resemblance of their long slender rays to a snake's 

 tail. They are found on nearly all coasts, and are at 

 once distinguished by a small disk or central portion 

 from which the rays start off very abruptly, instead of 

 the gradual passage of the central part into the arms, 

 as seen in the true Star-Fishes. They move about 

 mainly by means of their spines. Nearly all have the 



