110 THE BIOLOGY OF THE ANIMAL 



ampullae compare with the number of feet in the 

 same way. 



Cut all of the retractor and protractor muscles, 

 cut the stomach across just above the peristome, 

 and remove all of the digestive organs. 



Running down under the madreporic plate find 



h. The stone-canal. — What is its position? Shape? 

 Size ? Pinch it lightly between the fine forceps. 

 What is the nature of its wall ? What does the 

 canal connect? Does its end cover the entire 

 lower surface of the madreporic plate ? 



Eemove the peristome, and find lying within 

 the mouth pentagon 



c. The circum-oral water-tube.— Does it lie without 



or within the body-cavity ? What is its shape ? 

 Situated upon the circum-oral tube look for 



d. The Polian vesicles. — How many are there? What 



is their relation to the bases of the rays ? 



Extending horizontally into the cavity sur- 

 rounding the oesophagus find 



e. The racemose vesicles. — How do they compare in 



position and size with the Polian vesicles ? How 

 many are there ? How do you account for this 

 number ? 

 Make a drawing of the water-vascular system in an 

 outlined body. 



D. — The Circulatory System. 



Enclosing the stone canal find a tube, 



a. The pericardium. — To what is it attached? What 

 is the nature of its wall ? 



Lying within the pericardium look for 



