THE STARFISH AND SOME ALLIES 



227 



branches divides to form a pair of pyloric cseca. These are 

 glands which aid in digestion. The intestine, which leads 

 from the stomach to the aboral wall of the disk, is very 

 small. It is too small to carry the undigested waste from 

 the stomach and probably serves only to remove small quan- 

 tities of waste. Any solid waste particles must pass through 

 the mouth. A pair of small branched tubes, called the in- 

 testinal cseca, are attached to the intestine. Recent studies 

 indicate that these cseca 

 pulsate in the living star- 

 fish and probably serve as 

 respiratory organs. The 

 function of the pyloric 

 cseca is digestive ; they 

 secrete a fluid analo- 

 gous to the digestive 

 fluid of the earthworm 

 and the clam. The in- 

 testine ends at the anus 

 (Figs. 122, 123), which 

 lies near the center of 

 the aboral surface. 



Aster ias feeds on oys- 

 ters, mussels, clams, and 



snails. Many fanciful theories have been proposed in the 

 effort to explain how the starfish is able to get at the soft 

 parts of animals with thick, heavy shells. By referring to 

 Fig. 124 we can see the attitude of Asterias when it has 

 captured an oyster. While crawling along the bottom the 

 hungry starfish "smells" its prey by means of the tube feet 

 at the tip of the arms. It then moves in the direction of 

 the oyster or mussel and arches itself over the shell, touch- 

 ing the bottom all around with the tips of its arms. Next 

 it turns the shell about until the hinge ligament rests on 



Fig. 124. Starfish devouring an oyster. 

 (Reduced) ■ 



Photograph by Dr. H. M. Smith ; courtesy 

 United States Bureau of Fisheries 



