THE STARFISH. 155 



4. Along each side of the ridge in the floor of the ray, 

 observe rows of thin-walled sacs, sometimes distended, 

 but more often collapsed in alcoholic specimens. 

 These are the ampullae, or ambulacral vesicles. 

 Watch the ampullae while pressing on the tube feet, 

 and vice versa. If a specimen injected with coloring 

 matter be at hand it should now be examined. 



5. Near the base of the ray find, on each side, an elon- 

 gated body resembling a bunch of grapes, and of a 

 lighter color than the caeca; these are the reproduc- 

 tive bodies and are very much alike in appearance in 

 the two sexes, and only distinguishable by color or by 

 microscopic examination in the living specimens. Find 

 the point of attachment of one of them. The open- 

 ings in the inter-radial angle are not very evident. 



6. Cut along the sides of the two rays lying on the right 

 and left of the anterior ra}% connect the cuts at the 

 inter-radial angles, and turn back the cover of the 

 three rays and disk. Within the disk is the large, 

 thin-walled stomach. Examine this organ carefully. 

 Pass a blunt probe through the mouth and explore 

 its interior. 



7. Observe the large lobes of the stomach extending a 

 short distance into the rays ; lift one of these lobes 

 and trace the thin retractor muscles of the stomach 

 to the sides of the ridge in the ray. 



In the live starfish the stomach is often found pro- 

 truded and surrounding a mussel or an oyster; after 

 digesting and absorbing its soft parts the stomach is 

 retracted. 



8. Turning to the caeca of the anterior ray, trace them 

 toward the stomach: find the union of their tubes 



