64 ECHINODERMATA. 



With a scalpel or strong scissors, cut around the equatorial 

 region of an alcoholic specimen, taking care to cut through the 

 test only. Break or cut the aboral portion away bit by bit until 

 near the genital plates, freeing the fragments from the internal 

 organs without disturbing their positions. 



Reproductive System. — How were the gonads (their appear- 

 ance is the same in both sexes) attached to the test? How 

 many are there ? Opposite what areas of the test are they placed ? 

 Where do they open to the exterior? 



Digestive System. — Remove the gonads from the three areas 

 farthest from the madreporic plate, lift the remaining aboral 

 portion of the test slightly, and examine the alimentary canal. 



1. The large and conspicuous jaws, frequently called the 

 lantern. They will be studied later. 



2. The esophagus, passing between the jaws, and bending 

 over to one side to join the intestine. 



3. The intestine. Notice its size and its shape. Do its 

 loops have any relation to the positions of the gonads? 



4. The intestinal siphon, lying along the intestine and 

 attached to It at both ends. 



5. The rectum, running from the end of the intestine to the 

 anus. 



6. The mesenteries which hold the various organs in place. 

 Make a drawing to show the reproductive and digestive organs. 

 Water-vascular System.— 1. The stone canal leads from the 



madreporite to the circular canal, which encircles the esophagus 

 at a point just above the lantern. 



2. From the circular canal radial tubes pass over the top and 

 down the sides of the lantern, to pass through the auricles and 

 up the ambulacral tract, to the ocular plates. They can be 

 easily seen along the sides of the test, but are difficult to see 

 before they leave the lantern. 



3. Along the course of each radial canal, the ampullce, which 

 supply the tube feet, are to be seen. The relations of the tube 

 feet and radial canals are practically the same as in the starfish 

 except that the removal of the radial tubes to the inner sides 



