IX 



PHYLUM ECHINODERMATA 



375 



some object desired as food, and then retracted into the interior, 

 the retraction being effected by means of special retractor muscles 

 (Fig. 313, retr) which arise from the sides of the ambulacra! ridges. 

 This cardiac division of the stomach communicates aborally with 

 a much smaller chamber, the pyloric division of the stomach, and 

 this in turn opens into a 

 very short conical intest- 

 ine, which leads directly 

 upwards to open at the 

 anal aperture. The pyloric 

 division of the stomach is 

 pentagonal, each angle 

 being drawn out to form 

 a pair of large appen- 

 dages, the pyloric cceca 

 (Figs. 310, 311, 313, 315, 

 pyl. cose). Each pair 

 o f pyloric cseca com- 

 mences as a cylindrical 

 canal or duct, the lumen 

 of which is continuous 

 with the cavity of the 

 pyloric chamber. This 

 soon bifurcates to form 

 two hollow stems, ex- 

 tending to near the ex- 

 tremity of the cavity of 

 the arm, and giving off laterally two series of short branches, each 

 having connected with it a number of small bladder-like pouches. 

 The walls of the pyloric caeca are glandular : they secrete a digestive 

 fluid, and are therefore to be looked upon as digestive glands. It is 



found by experimenting with this 

 digestive fluid that it has an action 

 on food-matters similar to that 

 exerted by the secretion of the 

 pancreas in the Vertebrata, con- 

 verting starch into sugar, proteids 

 into peptones, and bringing about 

 the emulsification of fats. While 

 the pouches of the cardiac division 

 of the stomach are attached to 



FIG. 312. Transverse section through the , , ,, , , , -. , 



madreporic canal of a Starfish (Astro- the Oral Wail OI the DOdy, tne 



1100 pyloric cseca are connected with 



the aboral wall. From the short intestine are given off inter- 

 radially two hollow appendages, the intestinal cceca (Figs. 311 and 

 313, int. co?c), each with several short branches of irregular shape, 

 Ambulacral System. Running downwards from the madre- 



FlO. 311. Asterias rubens. Digestive system, an. 

 anus ; card. st. cardiac division of the stomach ; int. 

 ccec. intestinal cseca ; madr. madreporite ; pyl. crec. 

 pyloric cteca ; pyl. st. pyloric division of the stomach. 

 (From Leuckart.) 



