STARFISH 81 



sect similar parts? All inter- radii? Are radii or inter-radii 

 marked in any way on the aboral surface of animal? Notes re- 

 quired. 



11. Make an outline drawing of the aboral surface show- 

 ing details on the disc and a portion of one ray only. 



12. With the oral surface uppermost notice: 



The mouth. Position? Size? Is its margin smooth or 

 rough? Note the clusters of spines projecting over it. Are they 

 radial or inter-radial? 



The pcristome or membrane surrounding the mouth. 



The ambulacral grooves. One runs outward along the ven- 

 tral surface of each ray. They contain : 



The ambulacral feet or tube feet. Note their terminal 

 suckers. 



Draw the oral surface showing details of the disc and one 

 ray. In determining the arrangement of the tube feet pull off the 

 feet from a portion of one groove and note the openings from 

 which the feet protruded. 



II. INTERNAL ORGANS 



Remove, under direction, the aboral wall of the anterior ray 

 and the disc, being very careful to leave undisturbed those por- 

 tions directly beneath the wall of the disc and in the vicinity of 

 the madreporic plate. 



THE DIGESTIVE SYSTEM 



Note how the pyloric ceca are attached to the aboral walls of 

 the arms and how the stomach is attached to the aboral wall of 

 the disc. Note further: 



1. Intestine, a very short tube, extending from pyloric sac 

 to anus. 



2. Intestinal ceca opening into the intestine. How many 

 lobes ? 



