84 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



calcareous ossicles, forming the wall of the centre of the 

 flattened oral surface. 



1. In the centre of the peristome is the mouth, sur- 

 rounded by a thickened lip-like fold of the peristome. 



2. The white tips of the five calcareous teeth project 

 from the mouth, and meet at the centre of the oral surface. 



3. Examine the peristome with a hand-lens, and notice 

 the pedicell arise, each consisting of three movable jaws 

 mounted upon a long slender movable calcareous stem. 



4. Notice five clusters of mushroom-like ambulacra, 

 or feet, projecting from among the spines around the mar- 

 gin of the peristome. Each foot is made up of : — 



(i.) A long cylindrical shaft, which during life could be 

 so lengthened as to reach beyond the tips of the longest 

 spines. 



(ii.) A terminal sucker or flattened disc, which contains 

 a flat circular calcareous plate. 



5. Five pairs of much larger ambulacra project from 

 the peristome, close to the edge of the mouth. 



h. In most dried specimens the ambulacra may be seen 

 to run in five double lines around the spheroidal body, 

 like the meridians upon a globe. They lie among the 

 bases of the spines, and the lines converge towards, but do 

 not reach, a point directly opposite the mouth. 



c. Notice that the whole surface of the body except the 

 peristome and a small region opposite it, is studded with 

 long, movable spines. 



1 . The spines are arranged in ten sets : five double rows 

 between the halves of each double row of ambulacra, and 

 five pyramidal groups between the five double rows. 



2. Remove a spine, and after cleaning off the remains 

 of the muscles by ^vhich it was moved, examine it with a 

 hand-lens, and notice : — 



