THE STARFISH. 158 



different regions of the body wall. Along the middle 

 of the oral surface of each ray may be seen the 

 shrivelled remains of the tube feet, or ambulacra. 

 The region in which they lie is the ambulacral area. 

 The plates along this tract are the ambulacral plates. 

 One row of plates on each side of these ambulacral 

 plates are known as the inter-ambulacral plates. Ex- 

 amine these closely for comparison with the sea-urchin. 



6. The wart-like elevation on the aboral surface is the 

 madreporic body. Note that it is situated opposite 

 one of the inter-radial angles. Examine it with a lens. 



7. Make drawings of the oral and aboral surfaces of the 

 starfish. 



ALCOHOLIC SPECIMEN. 



1. Briefly review the points noticed in examining the 

 dried specimen. Bend the rays; their flexibility is 

 now much less than in life. 



2. Compare the spines of different areas as to their shape, 

 size, and degree of mobility. 



3. Between the spines are soft, tapering projections, the 

 aboral tentacles. 



4. Observe a circle of projections surrounding the spines ; 

 delicately pinch them with the forceps to determine 

 their consistence ; remove some of these bodies to 

 strong alcohol; mount temporarily in turpentine on a 

 slide, cover, and examine with a low power. There 

 should be distinguished a short stalk bearing a pair of 

 pinchers; these bodies are the pedicellariae. In the 

 live starfish these pinchers may be seen continually 

 snapping; they are supposed to serve in removing 

 foreign matter from the body. 



