THE ROCK STAR-FISH. 43 
pass the ducts that connect the ampullee with the 
pedicells. 
13. Make a tolerably thin transverse section through one 
of the rays in which the ampulle have not been 
scraped away. It should contain two or three sets 
of ambulacral ossicles. Examine with the inch 
objective. Notice the ambulacral canal for supply- 
ing the pedicells and ampulle with fluid. It lies 
just below the angle formed by the ambulacral 
ossicles. Below it notice the ambulacral nerve pro- 
jecting downward between the pedicells. | 
14. Turn the animal over in the saucer so that it lies with 
its oral side upward. Examine the pedicells. Re- 
move one with the forceps, and examine with the 
microscope. Notice that the fluid it contains is 
corpusculated, and that the pedicell itself is composed 
of two muscular layers, longitudinal and circular. 
15. Carefully remove the pedicells of one of the rays, and 
observe the ambulacral nerve. Trace it inwards to 
its bifurcation to join the nerve of the rays right 
and left of it. Then trace it outwards to the red 
eye-spot, at the tip of the ray. Observe the pedicell- 
like ocular tentacle above the eye (probably a tactile 
organ). Cut both out, and examine with the micro- 
scope. 
