124 THE VOYAGE OF H.M.S. CHALLENGER. 



I have never cut through an entire Antedon eschrichti, I 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. Bij^olar, and occasionally multipolar cells arc 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 occupied 

 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 (PI. 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 Hautnerveu bezeichnen kann " 

 in Synapta digitata} If the structures described above as forming the parambulacral net- 

 work in Antedon eschrichti, Actinometra parvicirra, Actinometra nigra, &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 filjrillar threads appear in the disk of Pentacrimis, 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 Ijlunt spines, and these " Hautnerven " extend from plate to plate, 



sending delicate fibrils up into the spines, as shown in PI. LIX. figs. 2-4, ad. I have 



many sections which contain these filires 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 PI. LXII. ; 



and a curious modification of this occurs in one of the basals of the Pentacrinus wyville- 



^/io?nson{ 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 {cii) and 



eventually enter diff"erent 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 Comatulfe. The primary trunks which proceed from the 

 angles of the chambered organ (PL XXIV. fig. 7; PL LVIII. figs. 1, 3, ai) fork within 

 the basals ; and the two secondary cords which result from the bifurcation pass out from 



> €p. cit., Zeitschr. f. wiss. Zool, Bd. sxxix. p. 322, Taf. x.xii. figs. 43-45. 



