ASTEROIDEA. 257 
by sensitive and pigmented cells, containing clear fluid, and 
covered by cuticle. The skin is diffusely sensitive. The 
term#nal tube-foot of each ray seems to be olfactory. 
The starfish may be found with part of its stomach 
extruded over young oysters and other bivalves. This 
protrusible portion of the stomach is glandular and saccu- 
FIG. 133.—Alimentary system of starfish. —After 
Miiller and Troschel. 
The dorsal surface has been removed ; the digestive czeca and the 
stomach are shown. 
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 ceeca,—a pair in each arm 
(Fig. 133). 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 
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