vii PHYLUM ECHINODERMATA 165 



of fats. From the short intestine are given off inter-radially 

 two hollow appendages, the intestinal cceca (Fig. 89, 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 madreporlc 

 or stone-canal (Fig. 88, St. c). The walls of this canal are 

 supported by a series of calcareous ossicles. The interior of 



Fig. 89. — Asterias rubens. Digestive system. an, anus; card. st. cardiac 

 division of the stomach; int. ctzc, intestinal casca; madr, madreporite; ply. 

 one, pyloric caeca; pyl. st, pyloric division of the stomach. (From Leuckart.) 



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. From the pentagonal canal are given off also a series 

 of five pairs of appendages, the Polian vesicles (Fig. 90, ap), 



