236 THE VOYAGE OF H.M.S. CHALLENGER. 
the imperfect condition of the top of the disk in the specimens which were cut, I have 
been quite unable to make out many details of structure. One point, however, is of 
interest, and that is that there are more than five water-tubes; for there seem to be 
three in each interradius, and not one only asin Rhizocrinus. As in this genus too, there 
are strongly marked interradial diverticula of the gut (Pl. VIIb. fig. 7), which are 
supported by the expanding processes attached to the inner faces of the third radials 
(ELA VEL, fie: 4a; Pl Vilage 17): . 
The arms of Bathycrinus present no essential anatomical differences from those of 
other Crinoids. The food-groove which is sunk within the ventral furrow of the skeleton 
(Pl. VIL. fig. 8; Pl. Villa. figs. 4, 5), instead of being some distance above it (Pl. LXI. 
figs. 4-6), is narrow relatively to the width of the arm, and protected by covering plates, 
as already described. The radial blood-vessel (Pl. VIIIa. figs. 4, 5, b) and ambulacral 
nerve (7) could be clearly distinguished in sections, the latter being exceedingly thin, or 
apparently sometimes even absent beneath the middle line of the ambulacrum. 
Except at the arm-bases the water-vessel (w) is relatively small, being much flattened 
from above downwards ; but the tentacles are large and bear numerous papille. Beneath 
the water-vessel, and projecting into the subtentacular canal, so as almost to divide it 
into two parts, is a more or less continuous band of closely nucleated connective tissue, 
which perhaps represents the structure marked « by Semper! in Actinometra parvicirra 
(Actinometra armata, Semper, MS.). At the bases of the arms the subtentacular canals 
are hardly traceable, their places bemg occupied by a complicated network of genital 
vessels, which are doubtless connected in the disk with the upper end of the plexiform 
gland, as in other Crinoids. But this plexus soon passes into a simple genital cord, as 
represented in Pl. VIIIa. figs. 4, 5, gc. It sometimes nearly fills up the small genital 
canal in which it lies, while there is a large and triangular cceliac canal beneath it (cc). 
The axial cords of the rays and arms of Bathycrinus, like that within the stem, are 
remarkable for the extensive subdivisions of the branches which proceed from them. 
Like those within the pinnules of Holopus and Hyocrinus (Pl. Ve. figs. 2, 3, 8, a), they 
take a somewhat wavy course within the radials, as is seen in Pl. VIIb. fig. 1, A; while 
the branches which come off from them in the second and third radials are shown in 
figs. 6,7, a’. Owing to the small height of these joints, the two dorsal branches which are 
usually so well defined in the Comatule (Pl. LXI. fig. 6) extend themselves laterally in 
the plane of the transverse articular ridge, while they are scarcely visible at all in the 
arms. On the other hand, the branches which extend upwards towards the ventral 
surface of the arm subdivide again and again, giving rise to a number of exceedingly 
fine fibrils, in the course of which bipolar, and occasionally multipolar, cells are clearly to 
be distinguished (Pl. VIIa. figs. 4,5, a’). This character is better shown in Bathyerinus 
than in any other Crinoid which I have yet examined. 
1 Arbeiten aus dem zool.-zootom. Institut in Wiirzburg, 1874, Bd. i. p. 261. 
