28 STUDIES OF ANIMAL TYPES 



B. INTERNAL FEATURES. Turn the animal on the oral 

 side and cut off the tip of one ray. Note that the space in- 

 side is taken up by two soft brown organs. With a pair 

 of scissors, cut carefully along each side of the arm to the 

 disk. Lift up the aboral wall, and gently cut the membrane 

 which holds the soft brown organs to the wall. They will 

 then fall down and lie in the arm . , Serve each-ray - in-the 

 same way. Then carefully cut away the aboral wall of the 

 central disk. igttre-44--(text) shows- a starfish treated~4n 

 this manner. Note that there are two branches of the 

 soft brown organs in each arm. These organs are the 

 pyloric cceca, or " .livers/ ' as they are often called. Note that 

 each pair of branches is connected by a small tube with 

 a large membranous pouch over the mouth. This pouch 

 is the stomach. The stomach is often found protruding 

 from the mouth. Turn to the text and find out how the 

 starfish procures-its food. Note the short gullet leading 

 from the mouth to the stomach. There is also a short 

 intestine leading from the stomach to an opening through 

 the aboral wall. Ta the intestine is attached a small con- 

 voluted, branched tube, the intestinal ccecum. Trace .the 

 intestine to its outlet and find the intestinal ca3cum. 



Remove the pyloric caeca. Note on the floor of tharay 

 two double rows of white globular sacs. These are the 

 ampullce. * They are connected with the tube feet and are 

 filled with a watery fluid which, when the ampullae are con- 

 tracted, is forced into the tube feet, thus lengthening and 

 expanding these organs of locomotion. There are two 

 glandular, reproductive organs in each arm. They lie at 

 the very base of the arm where the latter joins the disk. 

 In some specimens, depending upon the maturity of the 

 animal, these organs reach almost to the tip of the ray, 



