REPORT ON THE CRINOIDEA. 



113 



s.tc. 



Criuoids, one is not surprised to find Ludwig limiting liimself to the following statement — 

 " Die winzigeu Zellen, die sich zwischen den Nervenfasern finden, sind vielleicht aucb nur 

 die Kerne von Zellen, die in den Verlauf der Fasern eingeschaltet sind ; " ' and my own 

 observations have not enabled me to add anything to this suggestion. 



Hamann's observations on the Asterids have led him to discover that the so-called 

 ambulacral nerves are only specially developed parts of a general subepithelial plexu.3 

 containing ganglion-cells. This surrounds the whole body, and is traversed, though very 

 sparingly, by vertical fibres extending downwards from some of the "Stutzzellen"; whUe 

 sense-cells are intercalated among these at the bases of the respiratory caeca and elsewhere. 

 Hamann has found a similar ectodermic plexus, distinct from the radial nerve, in 

 Holothurians ; and the presence of a corresponding structure in Coelenterates, Nemertines, 

 Turbellarians, Chsetognatha, &c., is now thoroughly established. Thus, then, there 

 would seem to be no reasonable doubt respecting the existence of an ectodermic nerve- 

 plexus in the Crinoids. But even if the existence of this plexus be admitted, it is 

 difficult to suppose that the nervous system of a Crinoid with its innumerable pairs of 

 muscular bundles is limited to the subepithelial band in the floor of the food-grooves, its 

 tentacular branches, and the as yet undemonstrated 

 plexus. Leaving the latter out of consideration for the 

 moment. Where, I would ask, are the nerves of the pin- 

 nules of Antedon acoela and Antedon angusticalyx 

 which are shown in PI. LIV. figs. 1-3, 5 % Where is the 

 nervous system of the large number of arms on the two 

 posterior rays of the gigantic Actinometra magnijica 

 represented on PI. LVI. fig. 7, or that of the numerous 

 ungrooved arms on the three other rays 1 



It isdiflicult to conceive that these ungrooved arms and 

 pinnules (PL LXI. fig. 3), which form so large a part of 

 the entire organisation of this animal, are entirely unpro- 

 vided with a nervous system, and yet the ambulacral nerve 

 is altogether absent (fig. 4). Even when this is present, 

 Ludwig himself admits that he has seen no other branches 

 proceeding from it than those which supply the tentacles. 



Now the muscular system of a Crinoid is unusually 

 well developed. From the first radials to the ends of 

 the arms every two joints are united by a pair of 



muscular bundles (PL LXL figs. 4, 5), except in the case of the syzygies and the rare liga- 

 mentous articulations. The pinnules are always united to the arms by muscles, and in many 

 forms there are muscles between several pairs of the pinnule-joints (fig. 6 on p. 121, m). 



Fio. 4. — Diagrammatic transverse section of 

 au ungrooved ovarian pinnule of -Ic/mw- 

 tiuitra parvicirra, x 50. a, axial cord ; 

 a\ the branches proceeding from it ; c.c, 

 cceliao canal; ci.c, ciliated cup; c.s., 

 connective tissue spaces in the perisonio ; 

 g.d., genital canal; g.v., genital vessel; 

 j, skeleton of the pinnule-joint; I.e., 

 lateral canal connecting the cteliac and 

 subtentacular canals ; ov, ovary ; s.t.c, 

 subtcntacular canal ; w., radial water- 

 vessel. 



' Crinoiileen, he. cit., p. 264. 



(ZOOL. CHALL. EXP. — PAUT XXXII. 1S84.) 



li 15 



