26 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



completely digested, the stomach is again drawn back into the 

 body cavity by means of five pairs of long retractor muscles, 

 which are attached to the upper side of the ambulacral ossicles 

 in tlie rays, as shown in Plate V. 



At its aboral end the cardiac stomach is constricted and 

 leads into a narrower cavity, the pylorus, from which five pairs 

 of large, profusely branched pyloric, or hepatic, caeca (Plate V) 

 extend outward into the cavities of the rays. These caeca form 

 the digestive fluids, which are able to act on fats, proteids, and 

 carbohydrates. From the pylorus a short and narrow intestine 

 (Plate V) leads to a minute anal opening on the aboral sur- 

 face near the center of the disk, and on a line between the bases 

 of the left and middle rays of the trivium* Connected with 

 the intestine are two small glands, the rectal cseca (Plate V), 

 which doubtless excrete waste products, to be discharged from 

 the body through the anus. 



As stated on page 32, whenever any considerable amount 

 of refuse remains after digestion such substances are thrown out 

 of the mouth. Consequently the intestine has little use except 

 as an excretory organ. 



Water-vascular System. — The complex system of vessels 

 constituting the water-vascular, or ambulacral, system are of 

 great importance in the locomotion of the body, as described 

 above under the heading, " Tube-feet." 



The madreporic plate serves as a sieve (m, Fig. 2) through 

 which the external sea water enters the water-vascular system. 

 This plate connects with the madreporic canal (the so-called 

 stone canal), which leads into a large circular vessel surround- 

 ing the mouth. From this vessel a large radial vessel runs along 

 the roof of the ambulacral groove to the tip of each arm. The 

 radial vessel gives off paired lateral branches to the tube-feet 

 (Fig. 2). The latter are all arranged in two rows on each side, 

 and those of the two rows alternate. Consequently longer and 

 shorter lateral branches alternate. The action of these tube-feet 

 in locomotion is explained on page 23. Connected with the in- 

 ternal border of the circular vessel is a series of nine glandular sacs 

 known as Tiedemann's bodies, shown in the diagram (Fig. 2). 

 These sacs give rise to amoebocytes, or cells which float about 

 in the fluid of the water-vascular system. They probably serve 



