Note the large _alimentary canal_, which is divided into several regions. Note the short _oesophagus_ leading from the _mouth_ on the oral surface directly into a large membranous pouch, the _cardiac_ portion of the _stomach_. By a short constriction the cardiac portion is separated from the part which lies just above, i.e., the _pyloric_ portion of the stomach. From the pyloric portion large, pointed, paired glandular appendages extend into each ray. These are the _pyloric cæca_. Their function is digestive, and oftentimes they are spoken of as the _digestive glands_ or "livers." The pyloric cæca, as well as the cardiac portion of the stomach, are held in place by paired muscles which extend into each arm. Note two sets of these muscles, one set for thrusting the cardiac portion of the stomach out through the mouth and another for pulling it back, the _protractor muscles_ and _retractor muscles_, respectively. The starfish obtains its food by enclosing it in its everted stomach and then withdrawing stomach and food into the body. Note that the pyloric portion of the stomach opens above into a short _intestine_ terminating in the _anus_, and observe that there is attached to the intestine a convoluted many-branched tube, the _intestinal cæcum_.
Carefully remove a pair of pyloric cæca from one of the rays and note the short duct which connects them with the pyloric chamber of the stomach. Note in the angle of each two adjoining rays paired glandular masses which empty by a common duct on the aboral surface. These glands are the _reproductive organs_. Note the small bulb-like bladders extending in two double rows on the floor of each ray. These are the water-sacs or _ampullæ_, and each one is connected directly with one of the locomotor organs, the tube-feet.
Make a drawing of the organs in the dissection which have so far been studied.
TECHNICAL NOTE.--For a careful study of the locomotor organs a fresh starfish should be injected. This can usually be accomplished by cutting one ray off squarely, and inserting the needle of a hypodermic syringe (which has been previously filled with a watery solution of carmine or Berlin blue), into the end of the radial water-tube which runs along the floor of the ray. By injecting here, the whole system of vessels, tube-feet, and ampullæ are filled.