DEVELOPMENT OF CUCUMARIA ECHINATA PALS 
(44, p. 45; Pl. i, fig. 52), im Holothuria floridana 
by Edwards (12, p. 214), m Cucumaria crocea and 
another antarctic Cucumaria by Mac Bride (25, pp. 7, 8 ; 
27, p. 4). The last-named author called this vesicle the axial 
sinus, 
The distal portion of the canal, which should now properly 
be called the pore-canal, runs through the. dorsal body-wall 
and opens to the exterior. The opening, or dorsal pore, is situated 
between the second and third ciliary bands, and is in most 
eases slightly on the right of the mid-dorsal line (PL. 9, fig. 22 B, 
dp; fig. 245, pe). Ludwig (22, p. 186) also found that the 
pore opens on the right. 
Closure of the Ring Canal.—From the fact that 
the rudiment of the left ventral radial canal appears on the 
ventral limb of the open hydrocoele rmg, while that of the left 
dorsal radial canal belongs to the dorsal limb of the same, it is 
clear that the closure of the rmg occurs on the left dorsal 
interradius. The Polian vesicle lies at first very near to the left 
ventral radius, but later it moves towards the middle of the 
dorsal interradius, which is its normal position as found in 
adult individuals. 
As to the time and position of the closure of the rmg no 
entirely satisfactory observations have been given. Kowalew- 
sky (17, p. 4) and Selenka (45, p. 171) were in agreement in 
the opinion that the ring closed after the formation of three 
dorsal tentacles, while the remaining two developed from the 
closed rmg. Ludwig (22, p. 607) observed in C. planei 
that the ring was complete at the end of the fourth day, and 
the closure seemed to have taken place on the right side of the 
body. From this incorrect view he concluded that the Polian 
vesicle which lay on the left dorsal interradius could not be 
an indication of the point of closure. Newth (87, p. 687) 
is quite right in concluding that in C. saxicola the ring 
closed in the left dorsal interradius on the third day, when 
the radii can be identified. He could not determine to which 
limb of the free ends of the unclosed ring the rudiment of 
the Polian vesicle belonged, being only able to say that it 
Q2 
