34 STAR-FISHES, SEA-URCHINS, ETC. 
ages called pedicellaria, 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,” #4. 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, 7 About 
the mouth extends a ring, that throws off a delicate 
nerve to the eye, ¢, at the tip of each ray; other cords 
also extend to each sucker, ¢¢, this constituting the zerv- 
ous system, 
Circulation.—There is a system of blood-vessels, but 
Fic. 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 %, flows down 
a tube, called the “stone canal,” into the circular canal, 
