ASTEROIDEA. 



227 



The star-fish may be found with part of its stomach 

 extruded over young oysters and other bivalves. This 

 protrusible or cardiac portion of the stomach is glandular 

 and sacculated, and bulges slightly towards the arms ; it is 

 followed by an upper or pyloric portion, giving off five 

 branches, each of which divides into two large digestive 



Fig. 99.- 



-Alimentary system of star-fish.- 

 Muller and Troschel. 



-After 



The dorsal surface has been removed ; the digestive ceeca and the 

 stomach are shown. To the left lies the intestine ending in 

 the anus. 



caeca, — a pair in each arm (Fig. 99). These glands are 

 comparable to a pancreas ; their secretion contains three 

 ferments, which convert proteids into peptones, starch into 

 sugar, and break up fats into fatty acids and glycerine. 

 From the short tubular intestine between the stomach and 

 the almost central dorsal anus two little outgrowths are 

 given off, perhaps homologous with the " respiratory trees " 



