REPORT ON THE CRINOIDEA. 4138 
and probably form a subepidermic plexus (Pl. VIIa. fig. 1; Pl XXIV. fig. 2—cq’). 
Extensions of it also proceed into the cirri round the cirrus-vessels (Pl. LXIL., ev), and 
give off similar radiating branches. Jickeli’s observations on Antedon rosacea show that 
the movements of the cirri, like those of the arms, are dependent upon an influence pro- 
ceeding from their axial cords ;* and it is clear that if the central capsule and axial cords 
of Comatula constitute its principal nervous system (as few will now deny), this must be 
regarded as also extending throughout the whole stem of a Stalked Crinoid, even though 
it reach 70 feet in length, as in the fossil Hxtracrinus subangularis. 
It may also be assumed with tolerable certainty that there was a similar neuro- 
vascular axis in the stem of all the fossil Pelmatozoa, including the Blastoids. These had 
no arms attached to the radials, as a Crinoid has. 
ment of axial cords in the basals and radials as prevail in a Crinoid, which [ see no reason 
to doubt, it is unlikely that the radial cords, starting from the circular commissure 
(fig. 20, A) should have ended in the forks of the radials which receive the distal ends of - 
the ambulacra. In the Mesozoic Phyllocrinus the radials have almost exactly the same 
forked shape as those of a Pentremites; but the point where the limbs of each fork 
separate is marked by an articular facet to which the arm was attached. 
In a Blastoid, however, the sinus between the two limbs of the radial is filled wp by 
the ambulacrum, which terminates in a more or less prominent lip at the same point in 
the body of the radial as is occupied by the articular facet in 
Phyllocrinus. That the axial cord in.the radial of a Pentremites 
(fic. 20, A) ended in this lip seems to me improbable; and I 
cannot help suspecting that it may here have become continuous 
with the nerve of the ambulacrum. From what we know of the 
But if they had the same arrange- 
\\ 
( 
MN 
Pa 
f 
il 
ambulacral nerves of recent Crinoids, this is not likely per se to 
have been related to any other movements but those of the 
tentacles, even if these organs were present ; while it may ar 
perhaps have been removed from the superficial epithelium, as 
Fic. 20.—Diagram showing the 
in an Urchin, and lodged within one of the canals in the lancet 
plate. This would have brought it deep enough to be continuous 
with the axial cord of the radial at the termination of the 
ambulacrum. The movements of the so called pinnules of the 
Blastoid would thus have been controlled by the central capsule, 
instead of by the oral ring, which is not likely to have had 
anything to do with them; for the oral ring of a recent Crinoid 
has absolutely no control over the movements of any part of the 
arrangement of the axial cords 
in the calyx of a Pentremites, 
supposing it to be the same as 
in the calyx of a Crinoid. The 
pinnules are represented as 
preserved on one ambulacrum, 
Bat not on the other. A, axial 
cord of the ray; a, primary 
interradial cord ; a7, one of the 
converging radial cords which 
result from its bifurcation; 
B, basal; cco, circular com- 
missure; J, interradial plate 
(deltoid of Roemer) ; 2, radial. 
calcareous skeleton; and the jointed pinnules of a Blastoid cannot have remained 
permanently closed over the ambulacra, as they are found in the fossils (fig. 20). 
1 See the quotation from Agassiz, ante, p. 333. 
