124 THE VOYAGE OF H.M.S. CHALLENGER. 
I have never cut through an entire Antedon eschrichti, 1 am unable to say positively that 
this is the case, though it certainly is so in Pentacrinus decorus. 
This parambulacral network extends right down along the food-grooves, being especially 
developed among the sacculi (woodcut, fig. 8, a.d.); and it forms an annular plexus in 
the connective tissue of the lip, but of course farther from the mouth than the ambulacral 
nerve-ring. Bipolar, and occasionally multipolar cells are in connection with its finer 
fibrils, which can be followed very close to the superficial epithelium. Hardly any traces 
of it are visible in the interpalmar areas between the ambulacra, which are chiefly oecupied 
by the water-pores, though it is extensive enough at their sides. I have seen it more or 
less satisfactorily in various other disks of Antedon eschrichti, in Antedon rosacea, and 
in Antedon carinata (Pl. LX. fig. 2, ad); and I have no doubt that the action of suitable 
reagents upon fresh material would give very valuable results. [See Appendix, Note G.] 
In the mean time I would draw attention to Hamann’s figures of the “zu der 
Epidermis abgehenden Nervenziige, die man kurzweg als Hautnerven bezeichnen kann” 
in Synapta digitata.’ If the structures described above as forming the parambulacral net- 
work in Antedon eschrichti, Actinometra parvicirra, Actinometra mgra, &c. (Pl. LIX. 
figs. 6, 7; woodcuts, figs. 4, 5, 7, 8), be not “ Hautnerven,” I am entirely at a loss to 
understand their nature. 
The same fibrillar threads appear in the disk of Pentacrinus, not only in the plates of 
its ventral surface, but also in those which are developed on the perisome uniting the rays 
and support it below. Many of these plates, including those on the anal tube, are 
produced into small blunt spines, and these ‘‘ Hautnerven” extend from plate to plate, 
sending delicate fibrils up into the spines, as shown in Pl. LIX. figs. 2-4, ad. I have 
many sections which contain these fibres in the plates on the sides of the disk, and they 
are evidently derived from the axial cords of the rays and arms, which give off numerous 
branches. Even in the basal plates I have found branches extending from the axial cords 
towards the surface of the skeleton, as shown in the diagrammatic figure on Pl. LXIL.; 
and a curious modification of this occurs in one of the basals of the Pentacrinus wyville- 
thomsoni which was devoted to anatomical research. The two secondary cords (Pl. XXIV. 
fig. 7, ar) which result from the bifurcation of the primary interradial trunk (a7) and 
eventually enter different radials, are united to one another within the substance of the 
basal plate by a commissure. This reminds one at once of the horizontal commissure 
discovered by Ludwig in the radial axillary, by which the individual cords of the two 
arms borne by the axillary are united immediately beyond their point of separation. 
The arrangement of the axial cords within the radials of Pentacrinus or Metacrinus 
is exactly the same as in the Comatule. The primary trunks which proceed from the 
angles of the chambered organ (Pl. XXIV. fig. 7; Pl. LVIIT. figs. 1, 3, az) fork within 
the basals ; and the two secondary cords which result from the bifurcation pass out from 
1 Op. cit., Zeitschr. f. wiss, Zool. Bd. xxxix. p. 322, Taf. xxii. figs. 43-45. 
