I2O 



CONNECTICUT GEOL. AND NAT. HIST. SURVEY. 



[Bull. 



longitudinal muscles in each of the five radii. Connected with 

 the ring canal is the madreporic canal, which, strangely enough, 

 ends in a madreporic plate situated in the midst of the coelomic 

 cavity, as shown in Plate XXX. The water of this cavity is thus 

 used for the supply of the water-vascular system. Connected 

 with the ring canal are the large Polian vesicles, which vary in 

 number in different individuals from one to two, or even three. 

 When three are present, one of them is usually quite rudimentary. 

 They contain a reserve supply of fluid. 



Scattered all over the internal surface of the body are the 

 slender ampullae connected with the tube-feet, or pedicels. 



FIG. 21. Thyone briareus. One of the 

 oral tentacles, showing the profusion of 

 branches. 



Both the very numerous pedicels, which occur in the inter- 

 radial areas as well as in the radii, and the large, branched ten- 

 tacles are connected with the radial canals of the water-vascular 



