6 THE VOYAGE OF H.M.S. CHALLENGER. 
Thomson! described them as extending from end to end of the stem; but this is not 
strictly true. At the top of the stem where the young nodal joints are very close 
together and of no great thickness (Pl. XIII. fig. 1; Pl. XV. fig. 1; Pl. XXXI_ fig. 2; 
PL XXXVIL figs. 1,2; Pl. XXXIX. fig. 1; Pl. XLII. fig. 2; Pl 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 anima] matter has been removed 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 jomts 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 Pentacrinide (Pl. XV. fig. 5; 
Pl. XXVI. figs. 17,18; Pl. XXX. figs. 28-30; Pl. XXXa. fig. 7; Pl. XX XIX. figs. 4-10; 
Pl. XLI. 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 (PI. XXIII. fig. 3). The apposed faces are more or less cut up into ridges with 
intervening furrows ; and the ridges on the lower face of the one joint correspond to the 
furrows on the upper face of that below it. (Pl. XV. figs. 1, 2; Pl. XIX. figs, 2-5; 
Pl. XXVIL fig. 1; Pl. XXXVI; Pl. XLI. figs. 1,5; Pl. XLVII. 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. Ve. fig, 2, m.; Pl. VIIb. figs. 1, 5; 
Pl. Villa. fig. 7, rm.; Pl. XXXIX. fig. 18; Pl. XLI. 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. VIIb. figs. 1, 2; Pl. XXIV. 
fios. 6-8; Pl. LVI. figs. 1, 3—ch) along the axial cords of the rays and arms 
(BI Velie: 2. Pl: VIIb: figs. 1,05=85: Pho Villlandigs<h) 7,180; EIRGhY he — 40 
Pl. LXIT.). 
Although there are no true articular surfaces on the stem-joints of the Pentacrinidee 
in the sense in which that term is employed in anatomy, yet this is by no means the 
case in the Bourgueticrinide. 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 Comatulee and of 
some species of Pentacrinus. But they are effected only through the agency of 
1 Sea Lilies, p. 3. 
