ECHINODERMATA. 
755 
of tlie larva, wliicli lins contracted uniformly over the body and stem of the 
crinoid, its surface retaining, with the exception of the absence of the bands 
of cilia, the same character as the surface of the pseudembryo, with the same 
pyriform oil-cells arranged in the same way, and leaving the same interstices 
of nearly transparent delicately vacuolated sarcode. The head of the crinoid 
now becomes more regularly pyriform, and the stem rapiclly lengthens. The 
posterior disk becomes firmly and permanently fixed to its point of attachment. 
The cup of the crinoid gradually expands and increases in size. The five 
basal plates enlarge and become more definite in form. Their upper edges arc 
still irregular in outline, somewhat crescentic, arching upwards towards the 
bases of the orals ; but the lateral edges are now bounded by smooth straight 
calcareous bands, the sides of each plate applied, with the intervention of a 
narrow band of sarcode, to the similar edges of the two contiguous plates. The 
narrow lower edges of the basals are rough and irregular, resting on the upper 
surface of the irregular ring-like rudiment of the centrodorsal plate. The 
oral plates likewise undergo a change in form. They become wider inferiorly^ 
and the sides of the plates towards the lower margin curve outwards, the 
lower borders thus becoming concave, the convexity turned inwards towards 
the centre of the body. At the same time the upper edges, which remain 
narrow and rounded, curve slightly forwards and inwards towards the open- 
ing of the cup. If the animal remain undisturbed in well aerated water, 
when the development of the skeleton has reached this stage, the five lobes 
(the ‘‘ oral lobes ”) forming the edge of the calyx gradually expand, till the 
cup assumes the form of an open bell. Immediately on opening, at least five, 
and more usually fifteen, delicate, extremely extensile tentacles are protruded 
from the cup. The mouth, with the organs immediately surrounding it, is 
formed even before the separation of the oral lobes. It may be seen occu- 
pying the centre of the cup immediately after its expansion, as a large patent 
aperture. When the ciip is fully expanded, the transparent tissue continuous 
with the five oral lobes, and forming the margin of the disk, seems to curve 
over uniformly into the wide funnel-shaped central opening. The mouth, 
however, frequently contracts, though it never appears to close completely ; 
and when contracted it is bordered by a slightly thickened very contractile 
rim, which projects over the cavity of the oesophagus and forms an imperfect 
sphincter. W^lien this sphincter is relaxed and the mouth fully open, it is 
easy to see down to the very bottom of the digestive cavity, a sac-like space 
apparently simply hollowed out in the general sarcode-body. 
Commencing immediately within the mouth, a series of irregularly lobed 
glandular masses, of a pale yellowish-brown colour, project into the cavity 
of the stomach, curving in an irregular spiral down to the bottom of the cup. 
These glandular folds are richly clothed with long vibratile cilia. The merest 
film of sarcode separates their secretion from the stomach-cavity. The 
slightest touch, even of a hair, ruptures them and causes the effusion of a 
multitude of minute granules, some colourless and transparent, and others of 
a yellow or brownish hue. There can be little doubt, from their position and 
colour, that these lobes form a rudimentary liver. They appear very early in 
the pentacrinoid, colouring the lower portions of its body in the earlier stages 
of its growth within the pseudembryo. They increase steadily in bulk during 
its later stages, and with but little change of character make up a large por- 
tion of the visceral mass in the adult Antedon. 
3 c3 
