STARFISH, SEA URCHIN, BRITTLE STARS 



91 



Through these openings, very small, soft, fringelike pro- 

 jections of the inner body-Uning protrude. These are 

 the hranchke. 



The digestive system of the starfish. —The mouth opens 

 into a short gullet that leads to a five-lobed sac, the stomach. 

 The stomach is large, thin-walled, and very extensible. 

 It is divided into two portions by a constriction in the 

 middle. The lower part is called the cardiac jmiion, and 

 the upper part is 

 called the 'pyloric por- ^,' j| 



tio7i. The pyloric di- 

 vision opens into a 

 short intestine that 

 leads to a very small 

 anal aperture on the 

 dorsal side of the 

 body. 



Nearly filling the 

 cavity of each arm is 

 a pair of long, brown- 

 ish appendages, the 

 pyloric cceca (Fig. 44) . 

 The pyloric caeca have 

 glandular walls, and 

 as they secrete a digestive fluid are to be looked upon 

 as digestive glands. Each pair is connected by a single 

 tube with the pyloric division of the stomach and empties 

 its secretions into this part of the stomach. 



The food of the starfish and how eaten. — The starfish 

 lives upon crustaceans and moUusks, especially oysters. 

 When a starfish attacks an oyster, its body is arched over 

 the latter, and the stomach is extruded through the moutl 



Fig. 44. — Upper walls of a starfish cut away 

 to show the pyloric cseca, or hepatic lobes. 



