viz PHYLUM ECHINODERMATA 165 



intestine are given off inter-radially two hollow appendages, 

 the intestinal caca (Figs. 82 and 83, int. cac.\ each with 

 several short branches of irregular shape. 



Running downwards from the madreporite to near the 

 border of the mouth, is an S shaped cylinder, the madreporic 

 or stone-canal (Fig. 82, St. c.). The walls of this canal are 



coec 



FIG. 83. Asteiias rubens. Digestive system. an. anus ; card. st. cardiac 

 division of the stomach ; int. ca>c. intestinal csca ; madr. madreporite ; pyl. ca;c. 

 pyloric caeca ; pyl. st. pyloric division of the stomach. (From Leuckart. after 

 Muller and Troschel.) 



supported by a series of calcareous ossicles. The interior of 

 the madreporic canal communicates above with the exterior 

 through the grooves of the madreporite. Below, the canal 

 opens into a wide five-sided, ring-like canal, the ring-vessel 

 of the ambulacral system. From this are given off the five 

 radial ambulacral vessels, passing to the extremities of the 

 arms. 



