FEATHER-STARS, RECENT AND FOSSIL. 
197 
PL YI. figs. 7, 9, cd.) This forms the dorsal or lower pole of 
the body and bears on its exterior a number of jointed appen- 
dages, the cirri (ci.) by which the animal anchors itself. Each 
cirrus is pierced by a central canal lodging a blood-vessel (c. v.) 
which is continuous through the wall of the centrodorsal with 
one of the chambers of the chambered organ, or with one of the 
vessels in its central axis. 
Soldered on to the centrodorsal are the five first radials 
(PL Y. fig. 1, Pl. YI. figs. 7, 9, r r ) forming the lower part of 
the cup in which the disc rests. Jointed on to them and 
attached to them by muscles are the five second radials (r 2 .). 
Each of these in its turn bears a third or axillary radial (r 3 .), 
the outer face of which is not flat but roof-shaped, and usually 
bears the lowest joints (br-J of two arms working on it by 
means of muscles, as the second radials work on the first. 
These arms, which are thus primarily ten in number, consist 
of a series of joints that may be all like the first. But in other 
cases some of the joints may be axillary, so that the primary 
arms fork as the rays do. In the deep-sea Comatulce , in the 
two British species, and in those from cold climates, the ten 
primary arms rarely divide, but in the tropical species the 
forking of the rays may be so often repeated that the number 
of arms becomes very great, sometimes reaching nearly two 
hundred. Each arm- joint (with a few exceptions) bears a 
similarly jointed appendage, the pinnule (Pl. YI. figs. 1, 2, pi), 
which is merely a small edition of the arm, containing pro- 
longations of the water-vessel, the blood-vessel, the body- 
cavity, and in the case of the lower pinnules of the arm, the 
genital glands also (Pl. Y. fig. 2). 
Each joint of the rays, arms, and pinnules, is pierced by a 
central canal lodging a fibrillar cord (Pl. YI. figs. 1, 2, a. c.), 
that proceeds through the first radials from a yellowish fibrillar 
envelope (sh.) around the chambered organ. A sheath of the 
same substance surrounds each of the cirrus vessels (c. v.) that 
proceed downwards and outwards from the chambered organ. 
From each of the interradial angles of the chambered organ 
five large cords pass upwards and outwards, and fork almost 
immediately. (Pl. Y. figs. 1, 3.) The right branch of one fork 
and the left branch of its neighbour enter two adjacent openings 
on the inner face of each first radial. They run side by side 
through its central canal and on into the third radial where 
each of them forks. The two right branches enter the central 
canal of the skeleton of the right arm, while the left branches 
enter that of the left arm to form their respective axial cords. 
Before leaving the third radial, however, these two cords are 
imited by a transverse commissure. There are also commissures 
in the first radials. The two cords which each contains are 
united with one another and with those of adjacent radials by 
