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 as in Rhizocrinus. As in this genus too, there 

 are strongly marked interradial diverticula of the gut (PI. Vllb. fig. 7), which are 

 supported by the expanding processes attached to the inner faces of the third radials 

 (PI. VII. fig. 4a; PL Vila. fig. 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 

 (PI. VII. 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 Villa, figs. 4, 5, h) and ambulacral 

 nerve («) 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 (ty) is relatively small, being much flattened 

 from above downwards ; but the tentacles are large and bear numerous papillae. 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 x by Semper^ in A^tinometra parvicirra 

 (Actinometra armata, Semper, MS.). At the bases of the arms the subtentacular canals 

 are hardly traceable, their places being 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 Villa, figs. 4, 5, gc. It sometimes nearly fills up the small genital 

 canal in which it lies, while there is a large and triangular coeliac 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 Vc. figs. 2, 3, 8, a), they 

 take a somewhat wavy course within the radials, as is seen in PL Vllb. 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 bi'anches which are 

 usually so well defined in the Comatulse (PL LXI. fig. G) 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 Villa, figs. 4, 5, a'). This character is better shown in Bathycrinus 

 than in any other Crinoid which I have yet examined. 



1 Arleiten aus dem zool.-zootom. Instihit in Wiirzbiirg, 1874, Bd. i. p, 261. 



