120 THE VOYAGE OF H.M.S. CHALLENGER. 
between the surrounding pigment bodies, and ramify in the small spaces left between 
the petaloid areas that are occupied by the five mterradial ligaments (Pl. XXIV. fig. 1; 
fig. 2, ca’). These extensions towards the surface of the stem eventually become so fine 
that I have been unable to trace them in the somewhat thick sections with which I have 
been obliged to content myself, owing to the large size and the toughness of the stem 
ligaments. But from what I have seen in the arms, and more especially in the pinnules, 
I have very little doubt that the ultimate subdivisions of these branches are in connection 
with a subepidermic plexus. I have found similar branches in the cirri. 
The occurrence of this tissue around the axial vessels of the stem and cirri has been 
employed by Ludwig as an argument against its nervous nature on account of the 
absence of muscles in these organs.’ “ Wozu also ein dieselben im ihrer ganzen Liinge 
durchziehender (motorischer) Nervenstrang?” The same ‘argument might be employed 
with respect to the extension of branches from the axial cords within the calyx up into 
the anambulacral plates on the sides and ventral surface of the disk of Pentacrinus 
decorus (PI). LIX. figs. 2-4, ad). But their presence is readily understood if we consider 
them as sensory nerves establishing a communication between an ectodermic plexus and 
the axial cords of the rays, which all commence in the envelope of the chambered organ 
situated within the calyx. It is however in the arms and pinnules that the lateral 
extensions of the axial cords are most evident (Pl. LXI. fig. 6), and the inadequacy of 
Ludwig’s theory as to their nature is strikingly manifest. 
The species in which I have found these branches best developed are Bathycrinus 
aldrichianus, Pentacrinus decorus, Antedon eschrichti, Actinometra parvicirra, and 
Actinometra nigra. But they may also be met with in less abundance in the small 
arms and pinnules of Antedon rosacea, and I cannet understand how they escaped the 
notice of Greeff, Teuscher, and Ludwig. 
The lateral branches from the central fibrillar axis in the stem of Bathycrinus 
aldrichianus have been already mentioned (Pl. VIIa. fig. 1, ca’). The axial cords within 
the rays and arms have a similar extensive distribution. Numerous branches proceed 
outwards from them into the calcareous substance of the successive joints, as is shown in 
the second and axilliary radials, which form an important part of the cup enclosing the 
visceral mass (Pl. VIIb. figs. 6,7, a’). The arms become free higher up, however, and 
the deep median groove in the ventral surface of the skeleton receives the ambulacrum 
with its armature of covering plates (Pl. VII. fig. 8). The axial cord gives off a large 
branch on each side which proceeds upwards, subdividing freely as it goes. The ultimate 
branches, many of which have bipolar cells intercalated in their course, extend right up 
to near the top of the side-walls of the arm-groove, where they become so small that I 
have been unable to trace them further (Pl. VIIIa. figs. 4, 5, a’). I have occasionally 
seen a cell with three processes instead of two, but these are rare. The ambulacral nerve 
1 Crinoideen, loc. cit., p. 335. 
