244 



PH YL UM E CHI NODE RMA. 



extruded over young oysters and other bivalves. This 

 protrusible portion of the stomach is glandular and saccu- 

 lated, and bulges slightly towards the arms ; it is followed 

 by an upper portion, giving off five branches, each of which 

 divides into two large digestive caeca, a pair in each arm 

 (Fig. 1 1 6). These glands are comparable to a pancreas; 

 their secretion contains three ferments, which convert 



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 ^1 ' 



- 8 J*uiS 



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FIG. 116. Alimentary system of star-fish. After 

 Miiller and Troschel. 



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



stomach are shown. 



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" of Holothurians (Fig. 121, r.t.\ 

 Some parts of the food canal are ciliated. 



The coelom is distinct, though not much of it is left 



