6 THE VOYAGE OF H.M.S. CHALLENGEE. 



Thomsou^ described them as extending from end to end of the stem ; but this is not 

 strictly true. At the toj) of the stem where the young nodal joints are very close 

 together and of no great thickness (PI. XIII. fig. 1 ; PI. XV. fig. 1 ; PI. XXXI. fig. 2 ; 

 PL XXXVII. figs. 1, 2 ; PI. XXXIX. fig. 1 ; PL XLIII. fig. 2 ; PI XLIX. fig. 2), these 

 bands of ligament are, no doubt, directly continuous from their attachment to the basals 

 above, through more or fewer of the last-formed nodes and internodes. But this is 

 certainly not the case in the lower parts of the stem. For after it has been decalcified 

 the nodal and infra-nodal joints which form the syzygies are just as readily separable 

 from one another as they are after the animal matter has been x'emoved by the action of 

 hot alkalies. This would obviously be impossible if the fibrous bands passed right through 

 the joints " from one end of the stem to the other ;" while, as a matter of fact, their 

 terminations in the substance of the nodal or infra-nodal joints may be readily traced by 

 microscopic examination. They correspond to the five radiating petaloid figures which 

 are so well known on the surfaces of the stem-joints of the Pentacrinidse (PL XV. fig. 5 ; 

 PL XXVI. figs. 17, 18 ; PL XXX. figs. 28-30 ; PL XXXa. fig. 7 ; PL XXXIX. figs. 4-10; 

 PL XLL figs. 2, 3, 6, 7, 16, 17; PL XLVII. figs. 3-5, 7-9); and they are characterised 

 by a somewhat looser calcareous reticulation than exists in the remaining portions of the 

 joint (PL XXIII. fig. 3). The apposed faces are more or less cut up into ridges wdth 

 intervening furrows ; and the ridges on the lower face of the one joint correspond to the 

 furrows on the upper face of that l^elow it. (PL XV. figs. 1, 2; PL XIX. figs. 2-5 ; 

 PL XXVII. fig. 1 ; PL XXXVL ; PL XLL figs. 1,5; PL XLVIL figs. 1, 2, 6 ; PL XLIX. 

 fig. 3). Hence, while the composition of the stem out of a large number of discoidal 

 joints gives it a certain amount of motion, that motion is very limited ; and it is probably 

 only of a passive character, due to currents in the water, &c. , and independent of the will 

 of the animal. In this respect it differs from the rays and their subdivisions, the joints 

 of which are united by pairs of muscular bundles (PL Vc. fig. 2, m. ; PL Vllb. figs. 1, 5 ; 

 PL Villa, fig. 7, rm.; PL XXXIX. fig. 13; PL XLL fig. 11); and the contractions 

 of these bundles are governed by an influence proceeding outwards from the fibrillar 

 envelope round the chambered organ in the calyx (PL Vllb. figs. 1, 2 ; PL XXIV. 

 figs. 6-8 ; PL LVIII. figs. 1, 3 — ch) along the axial cords of the rays and arms 

 (PL Vc. fig. 2. PL Vllb. figs. 1, 5-8 ; PL Villa, figs. 5, 7, 8 ; PL XXIV. fig. 9—^. 

 PL LXIL). 



Although there are no true articular surfaces on the stem-joints of the Pentacrinidae 

 in the sense in which that term is employed in anatomy, yet this is by no means the 

 case in the Bourgueticrinidje. In all the members of this family there are true 

 articulations between the successive stem-joints, of the same nature as those between the 

 cirrus-joints of all Crinoids, and between the two outer radials of most Comatulas and of 

 some species of Pentacriniis. But they are efiected only through the agency of 



1 Sea Lilies, p. 3. 



