BRANCH ECHINODERMATA : STARFISHES, ETC. in 



in the anus, and observe that there is attached to the in- 

 testine a convoluted many-branched tube, the intestinal 

 ccecum. 



Carefully remove a pair of pyloric caeca 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 ampulla, 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 accom- 

 plished 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 ampullae 

 are filled. 



Note a ring-shaped canal which passes around the 

 alimentary canal near the mouth from which radial vessels 

 run out beneath the floor of each ray and from which a 

 hard tube extends to the madreporite. This hard tube is 

 the stone canal, so called because its walls contain a series 

 of calcareous rings, while the circular tube is the ring 

 canal or circum-oral water-ring from which radiate the 

 radial canals. In some species of starfish there are 

 bladder-like reservoirs, Polian vesicles, which extend 

 interradially from the ring canal. 



Note that the ampullae and tube-feet are all connected 

 with the radial canals. By a contraction of the delicate 



