REPORT ON THE CRINOIDEA. 13 



extremities they are well adapted to retain their hold. The stem itself passes slowly 

 from a rigid vertical attitude to a curved or even drooping position." 



The shape of the nodal joints is markedly dilfereut from that of the internodal joints 

 which separate them. They are not only somewhat higher (PI. XIX. figs. 3, 4 ; 

 PI. XXVI. fig. 12 ; PI. XXVII. fig. 1 ; Pis. XXXV., XXXVI. ; PI. XXXIX. fig. 3 ; 

 PI. XLI. figs. 1, 5, 15 ; PL XLIL; PI. XLV. fig. 6 ; PL XLVII. figs. 1, 2), but the outline 

 of the upper non-syzygial face is different from that of an internodal joint. (Compare 

 PL XXXIX. figs. 4, S ; PL XLI. figs. 2, 3, 6, 7, 16, 17 ; PL XLV. figs. 2, 4 ; PL XLVII. 

 figs. 4, 5, 8, 9 ; PL LI. figs. 9, 10 ; PL LIII. figs. 3, 4.) In the recent Pentacrinus and 

 Metacrinus every nodal joint is united by syzygy to the top joint of the next internode 

 below. I propose to give the name "infra-nodal" to this joint, which is really the 

 hypozygal of the syzygial pair (PL XXII. figs. 19-22 ; PL XXVI. figs. 12-16 ; PL XXX. 

 figs. 26-29 ; PL XXXVII. figs. 5-8, 19-22 ; PL XXXIX. figs. 3-7 ; PL XLV. figs. 3-5 ; 

 PL XLVII. figs. 3, 7 ; PL L. figs. 19-22 ; PL LIII. figs. 3, 5). The apposed faces of 

 these two joints are much more distinctly stellate than are those of the remaining stem- 

 joints, the re-entering angles of the star being the points of attachment of the cirri, 

 and the syzygial surfaces of the mature joints are almost smooth and devoid of any 

 markings whatever. 



The syzygial union of two stem-joints is efi'ected, just as it is in the rays and arms, 

 by short fibrils of connective tissue, very numerous and closely set. They form a kind 

 of " cement substance," as it was formerly called, which is connected at its ends with the 

 organic basis interpenetrating the calcareous network of the stem -joints, just as the 

 " cement-substance " of the arm-syzygies is connected with the organic basis of the 

 brachials. But these fibrils are absolutely distinct from those of the five long ligamentous 

 bundles which occupy the internodes. The latter are often spoken of as tendons, and 

 have been wi'ongly described as extending throughout the whole length of the stem. 

 Were this really the case, it is difiicult to see how the stem could break across at the 

 syzygies so easily as it does ; for there would be no reason why the five tendons should 

 be weaker at these points than at anywhere else in the internodes, while the loose ends 

 of the tendons should appear at the surfaces of fracture, just as they do where an inter- 

 node is forcibly broken across. But this is not the case : when the stem is decalcified the 

 joints separate very readily along the lines ^of syzygy, and it is then apparent that the 

 five tendons run from the lower portion of each infra-nodal joint down into the upper 

 portion of the next nodal joint below it. They end within these two joints, just as do 

 the ligaments which connect two brachials, terminating either in looped extremities or 

 else passing into the connective tissue plexus which forms the substance of all the joints 

 whether of arm or stem. 



The various internodal joints are, as it were, strung upon these tendons, which are 

 thus not continuous, but divided up into lengths, each corresponding to an internode ; 



