SUS CEN eae 
- C ) ‘ : 
12 THE VOYAGE OF H.M.S. CHALLENGER. 
I].—THE STEM AND ITS APPENDAGES. 
We have already seen that three types of stem occur in the recent Crinoids, which 
are characteristic respectively of the families Pentacrinide, Bourgueticrinide, and 
Hyocrinide. Broadly speaking, it may be said that these embrace all the varieties of 
stem which are met with in the Neocrinoidea. For the mode of union of the joints in 
Apwcrinus, Millericrinus, and Eugeniacrinus must have been very much what it is in 
Hyocrinus; though the “root” of the first-named genus is somewhat peculiar in its 
nature. 
A. PENTACRINID2. 
In all the genera of this family the stem consists of discoidal joints which are never 
(in the adult) higher than wide, and have the characteristic petaloid markings on their 
terminal faces (Pls. XI, XIV.; Pls. XV. fies. 4, 5; Pls. XD, X XI” Pixie 
figs. 12-18; Pls, XXVIII, XXIX; Pl. XXX. figs. 25-30; Pl. XXXa. figs. 1-7; 
Pl. XXXVII. figs. 10-22; Pl. XXXIX. figs. 3-11; Pl XLI. figs. 1-5, 6-8, 15-17; 
Pl. XLVI. figs. 1-9). Certain of these joints, separated from each other by intervals of 
variable length, bear whorls of cirri, and they have consequently received from Sir 
Wyville Thomson’ the very appropriate name of “nodal joints.” There are usually five 
cirri at each node, situated in the direction of the rays (Pls. XI, XVIII, XIX., XXXIV.— 
NK eS OX TL XL VL XLVIII.—LIL). Sometimes, however, one cirrus is 
deficient, as shown in the left hand figure on Pl. XXXVI; while in Pentacrinus 
alternicirrus there are only three cirri at one node, and two at each of those above and 
below it, the positions of these two corresponding to the two gaps at the node of three 
curi (PL XXV.; Pl. XXVI. figs. 13, 14; Pl XXVII. figs. 1-3). The cirri of two 
successive nodes therefore alternate in position as the leaves do in the stem of a Labiate 
plant, the two faces of the stem which bear no cirri at one node being the only ones which 
have cirri at the nodes above and below it. 
The function of the cirri, which vary considerably both in length and in stoutness, is 
described by A. Agassiz’ as follows :—“ These they move more rapidly than the arms, and 
use them as hooks to catch hold of neighbouring objects, and on account of their sharp 
1 Sea Lilies, p. 7. 
* Letter No. 3, on the dredging operations of the U. S. Coast Survey, Sr. “Blake,” from December 1878 to March 
10, 1879, Bull. Mus. Comp. Zodl. vol. vy. No. 14, p. 296. 
