ASTEROIDEA. 



257 



by sensitive and pigmented cells, containing clear fluid, and 

 covered by cuticle. The skin is diffusely sensitive. The 

 terminal 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 

 Muller and Troschel. 



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



