290 



THE STARFISH. PHYLUM ECH INODERM ATA 



madreporite, and a spongy, brown organ, the axial organ, to 

 which also we shall return. 



ALIMENTARY CANAL, FEEDING, AND EXCRETION 



The mouth opens through a short oesophagus into a great sac, 



Fig. 2i6. — Parts of the aboral half of a starfish {Asterias rubens), removed, with 

 the alimentary canal, from the rest of the body, and viewed from within. 

 One lobe of the stomach has been cut away, and another partly turned back. 

 The detached figure represents an enlarged view of the axial sinus and 

 adjoining structures. 



ab.musc, Aboral muscle; ax.o.. axial organ; ax.s., axial sinus; l.st. .one of the lobes of the stomach; 

 oes., oesophagus ; Py.c, pyloric caecum ; py.d., pyloric duct ; Py.s., pyloric sac ; r.c, rectal caecum ; 

 Sep., septum ; st.c, stone canal. 



the stomach (Figs. 215, 216), which has in each interradius a 

 wide pouch, attached to the ambulacral ridge by two retractor 

 muscles. Above, the stomach communicates by a wide opening 

 with a five-sided pyloric sac, each angle of which is prolonged 

 into a tube or pyloric duct, that runs into an arm, and there forks 

 into two branches, the pyloric caeca, each beset with numerous 



