116 ' THE VOYAGE OF H.M.S. CHALLENGER. 
found no difficulty in this, but despite the physiological improbability of the want of 
innervation to the muscular bundles, he declines to accept the fibrillar envelope of the 
chambered organ and its extensions into the stem and arms as belonging to the nervous 
system of a Crinoid. One ground for his objection lies in the presence of this fibrillar 
tissue in the axis of the stem and of the cirri that it bears, which contain no muscular 
tissue. This point, which supports Dr. Carpenter’s view rather than opposing it, will be 
considered later. 
The only explanation of the presence of this fibrillar tissue within the skeleton which 
Ludwig can suggest is as follows :—‘“ Die Faserstringe sind zu betrachten als unverkalkt 
gebliebene Theile der bindegewebigen Grundlage der Kalkglieder, deren Aufgabe es ist, 
aus dem Blutgefiissystem, genauer aus den funf Kammern, die erniihrende Flussigkeit 
aufzunehmen und den Arm- und Pinnulagliedern zuzufiihren.” ? 
I have no doubt whatever that the axial cords are permeated by a nutritive fluid, 
which finds its way from the chambered organ into the substance of the organic basis of 
the skeleton. For I have frequently found coagulum, both in this last and in the axial 
cords themselves ; but I should hesitate to speak of either of these as connective tissue. 
The closely set fibrils forming the axial cords are quite distinct from the nuclear network 
which interpenetrated the calcareous substance; and both are as different as possible 
from the connective tissue fibres of the articular ligaments, or the general connective 
tissue of the ventral perisome (see fig. 6 on p. 121). Simroth has given an excellent 
description and figures of the nucleated reticulum forming the organic basis of the skeleton 
in Ophiurids,’ and nearly everything which he says is equally applicable to the Crinoids. 
The nature of this nuclear tissue is well shown in Pl. Vb. fig. 1, Pl XXIV., and Pl. LVIII. 
figs. 2, 3; and its distinctness from the close fibrillar structure of the stem-axis is very 
apparent. The general aspect of the axial cords in thin sections is identical with that of the 
Ophiurid nerves as represented by Simroth, who finds the nerve-fibrils to be connected 
with bipolar cells. Fig. 32 on his pl. xxxiv., which shows the relation of the radial nerve 
to the organic substance of the under arm-plates beneath it, would serve, with very little 
alteration, for a part of a longitudinal section of the arm or pinnule of a Crinoid. The 
fibrillation of the axial cords and their marked differences from the organic basis of the 
skeletal plates is well seen in sections through the calyx of the Pentacrinoid. At this 
early stage the cords lie on the ventral surface of the flat calyx plates outside the organic 
basis of the skeleton altogether ; and it is by an endogenous thickening of the calcareous 
substance of these plates that the cords come to lie in grooves which are subsequently 
closed into canals ; while by a further continuance of the same process these canals are 
eventually so surrounded by calcareous tissue that they come to occupy the centre of the 
successive joints of the skeleton. 
Ludwig’s view of the nature of the axial cords is therefore not altogether in accordance 
1 Crinoideen, loc. cit., p. 340. 2 Op. cit., pp. 433, 434. 
