140 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
INTERNAL CAVITY OF THE CALYX. 
A. The Chambered Organ and the Axial Canals. 
A striking feature in the organization of the Comatule is the quinquelo- 
cular organ, situated in the cavity of the centrodorsal, and placed at right 
angles with the central axis. This organ was first noticed by Heusinger, 
who in 1828 described it as the central organ of the blood vascular system. 
Miiller also took it to be a heart-like organ in connection with a system 
of membranous tubes. Dr. W. B. Carpenter regarded the membranous 
tubes of Miiller as solid fibrillar cords, proceeding from a similarly con- 
stituted envelope around the chambered organ, and he came to the con- 
clusion that this fibrillar sheath, and the cords proceeding from it, constitute 
the central nervous system of the Comatule. This was afterwards confirmed 
by experimental evidence, and is now generally admitted by zodlogists. 
The organ in question is a sac, divided into five radial compartments, 
enclosed by a thick envelope in connection with the axial cords. From the 
dorsal surface of this envelope processes are given off to the cirri, and from 
its margin arise interradially five short primary cords, which, passing up- 
wards and outwards, bifureate into right and left branches between the 
centrodorsal and radials. The ten secondary cords diverging from one 
another, enter the substance of the radials, and either unite in pairs, the 
right branch from one interradial meeting the left branch from the adjoining 
one (Figs. 3 and 4), or the two branches, as in Hnerinus liliiformis (Fig. 5), 
without touching each other, proceed on separately to the costals. On 
reaching the first axillaries the two cords open out into two branches, right 
and left, and after traversing the plates, enter the right and left arms, 
respectively. In addition to the above connections, there is a circular or 
pentangular commissure, which, immediately after entering the radials, con- 
nects the various branches among themselves, and additional connections 
between the branches within the axillaries supply the arms (Figs. 3 to 4). 
The axial cords along the arms lie in tubular channels piercing the calcareous 
part of the various arm joints, each cord giving off alternately right and 
left branches, which enter the pinnules. 
Chambered organs have been observed also in Stalked Crinoids, but the 
position is not quite the same as in the Comatule. While in the latter the 
