ECHINUS. ole 
length of each pore is lined by ciliated columnar cells, 
which stain deeply. Lower down, the columnar cells 
eradually give place to others of rounded form, which are 
also ciliated. Some of the pores anastomose with neigh- 
bouring ones, but the majority take a nearly straight 
course from the outer to the inner surface of the madre- 
porite. 
The madreporic ampulla communicates through its 
lower or inner wall with a tubular canal, the madreporic 
tube or sand-canal (Pl. III., figs. 28 and 24, w.t.), lined 
with ciliated columnar epithelium. This, enclosed within 
the axial sinus of the ccelom (PI. III., figs. 23 and 24, 
az.sin.), runs directly to the base of the lantern, and opens 
into the circular water vessel (Pl. III., fig. 23, c.w.v.), 
which encircles the cesophagus at that point. 
Five roughly pear-shaped and sacculated vesicular 
bodies, the Polian vesicles (fig. 23, P.v.), open inter- 
radially into the circular water vessel. From the latter, 
in each radius, there runs out a radial canal (fig. 23; PI. 
V., fig. 37, 7.w.v.) which, passing beneath the rotule, 
down the outer surface of the lantern, and through the 
arch-like auricula, traverses the whole length of the 
corresponding ambulacrum, on the inner surface of the 
test, to its apex, where it ends blindly in the pore of 
the radial plate (Pl. IV., fig. 30, 7.w.v.). Before reaching 
the auricule, each radial canal gives off a pair of lateral 
branches to the corresponding pair of buccal tube-feet 
(Pl. 1., fig. 7; PI IV., fig. 33, ¢.f’.) which, unlike the tube- 
feet to be immediately described, have no ampulle. 
From the auricular archway upwards to their blind 
extremities the radial canals give off a large number of 
alternating lateral branches (Pl. III1., fig. 23; Pl. IV., 
fig. 29, l.b.w.v.), which open into flattened, thin-walled 
vesicles, the ampulle of the tube-feet (Pl. III., fig. 23; 
