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 Ciinoid. 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 Faserstriinge sind zu betrachten als unverkalkt 

 gebliebene Theile der bindegewebigen Grundlage der Kalkglieder, deren Aufgabe es ist, 

 aus dem Blutgefiissystem, genauer aixs den funf Kammern, die eruiihrende Flussigkeit 

 aufzunehmen und den Arm- und Pinuulagliedern zuzuftihreu." ^ 



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 diflerent 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 apj^licable to the Crinoids. 

 The nature of this nuclear tissue is well shown in PL Vb. fig. 1, PI. XXIV., and PI. LVIII. 

 figs. 2, 3 ; and its distinctness from the close fibrillar structure of the stem-axis is very 

 aj)parent. 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-fil )rils to be connected 

 with bipolar cells. Fig. 32 on his pi. 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 difierences 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 



' Crinoideen, loc. cit., p. 340. ^ Op. cit., pp. 433, 434. 



