ON THE LOCOMOTOR SYSTEM OE ECHINODERMA.TA. 
883 
f Aperture between sinuses wliich leads into space around oesophagus. 
This space communicates with circumoral sinus (Plate 79, fig. 2, a). 
g. Ampulla. 
h. Circle indicating constriction between oval sinus and retracted tentacle. 
i. Madreporic plate. 
k. Radial canal giving oft’ two lateral branches, each branch gives rise to 
an ampulla (g) and a pedicel (a). 
/. Longitudinal muscular band. 
m. Retractor muscle. 
Fig. 2. Section through anterior portion of Holotliuvia. 
a. Circumoral sinus. 
b. Circular ambulacral canal. 
c. Sinus of circular canal. 
d. Sinus of tentacle. 
e. Aperture through which circumoral sinus communicates with space 
around oesophagus. 
f Csecal prolongation from sinus of circular canal. 
h. Fibres stretching inwards from sinuses and circular canal to oesophagus. 
m. Retractor muscle. 
Fig. 3. Holothuria with tentacles fully distended. 
c. Circumoral sinus. 
b. Aperture through which sinus communicates with space around 
oesophagus. 
a. Csecal end of prolongation from sinus of circular canal. 
d. Aperture of cloacal chamber. 
Fig. 4. Section of cloaca in Holothuria; valve open and retracted. 
Fig. 5. Section of cloaca in Holothuria; valve closed and projected. 
Fig. 6. Partially retracted pedicel of Echinus showing sucking disc. 
Fig. 7. Section of partially retracted pedicel of Astropecten. 
Fig. 8. Section of pedicel of Astropecten slightly retracted at one side (a) so as to act 
as a sucker. 
Fig. 9. Section of pedicel of Ophiura. 
Fig. 10. Section through lantern of Eclunus. 
a. Sinus under madreporic plate (6). 
c. Madreporic canal. 
d. “ Heart.” 
f. Radius. 
g. Rotula. 
h. Circular muscle. 
i. Radial canal. 
j One of the inner series of pedicels with a tubular ampulla (k). 
5 x 2 
