438 



ECHINODERMATA — ASTEROIDEA 



septa the axial sinus and stone-canal (see below) are embedded. 

 These septa are to be regarded as areas of lateral adhesion 

 between the arms. 



The alimentary canal consists of several distinct portions. 

 The mouth leads by a narrow neck called the " oesophagus " into 



Fig. 188. — View of upper half of a specimen of Asterias rubens, which has been 

 split horizontally into two halves, ax.c, Axial sinns ; g.d, genital duct ; oe, out end 

 of the oesophagus, the narrow neck of the stomach ; 2'y, pyloric sac ; jyy-o, pyloric 

 caeca ; r, rectum ; r.c, rectal caeca ; sept, interradial septum ; st.e, stomach lobe. 



a voluminous baggy sac termed the " stomach," which is produced 

 into ten short pouclies, two projecting into each arm. The 

 stomach leads in turn by a wide opening into a pentagonal 

 flattened sac, the " pyloric sac," which lies above it. Each angle 

 of the pyloric sac is prolonged into a tube — the so-called " pyloric 

 duct " — running out into the arm, where it immediately bifurcates 

 into two forks, each beset by a large number of small pouches 



