34 



STAR-FISHES, SEA-URCHINS, ETC. 



ages called pedicellaricB^ c, having two calcareous jaws. 

 Between the arms, on the upper surface, is a hard, flat, 

 pinkish body, perforated with holes, called " the madre- 

 poric plate," h. The under surface of the rays is chan- 

 neled, the plates being pierced with four rows of minute 

 holes. 



Internal Organs. The mouth, m, is on the under sur- 

 face, and leads into the stomach, s, which is seen ex- 

 tending into the rays, ending in a short intestine, to 

 which is attached the green, branching liver, /. About 

 the mouth extends a ring, that throws off a delicate 

 nerve to the eye, e, at the tip of each ray ; other cords 

 also extend to each sucker, / /, this constituting the nerv- 

 ous system. 



Circulation. There is a system of blood-vessels, but 



FIG. 31. Pentacrinus caput medusa. 



what is called the water-vascular system is most impor- 

 tant, aiding in both locomotion and respiration. Water is 

 taken in at the sieve-like madreporic plate h, flows down 

 a tube, called the "stone canal," into the circular canal, 



