53 THE VOYAGE OF H.M.S. CHALLENGER. 
B. Tae PINNULEs. 
The pinnules are repetitions of the arms on asmall scale, and are especially adapted for 
the protection of the genital glands (PI. Ve. figs. 7, 8,10, ¢; Pl. VII. fig.7; Pl. X. fig. 20). 
In no ease is a pinnule developed earlier than the second joint above the first radials 
of the calyx. This condition occurs in the two five-armed genera Thawmatocrinus 
(Pl. LVI. figs. 1, 2) and Eudioerinus. One species of the latter (Hudiocrinus varians) 
has this second brachial free and capable of lateral movement, while im another 
(Ludiocrinus indivisus) it is the epizygal of a syzygy. The corresponding radial joint 
of Metacrinus is of the same character, and there are pinnules on each of the following 
radials as far as the axillary (Pl. XXXVIIL; Pl. XXXIX. fig. 1; Pl XLIL; Pl. XLII 
fier kl SUuEW.s (Pi, kV, oat PL VIL PY ek VEE ines ole Lee ke tess 
Pls. L.—LII. fig. 1). But in the majority of Neocrinoids which have the third radial 
an axillary, the preceding joint bears no pinnule, while it sometimes contributes to the 
enlargement of the cup. 
Pinnules are always absent from every axillary joint, from the hypozygal of every 
syzygy (Pl. XXXa. fig. 106; Pl. XXXII. figs. 4, 6, 13, 14; Pl. L. figs. 11, 12), and 
also from the lower one of every pair of joints which are united by a ligamentous articu- 
lation; so that in the great majority of Comatule, as in some species of Pentacrinus, 
the first joint after each axillary bears no pinnule. In the former group too the pinnules 
on the third and the four or five following brachials which form the arm-bases, do not 
appear till after those of the eighth and following joints, though the pinnule of the 
second brachial is developed comparatively early ; while in Atelecrinus, Rhizocrinus, and 
Bathycrinus more or fewer of the lowest brachials are permanently devoid of pinnules. 
The lowest pinnules of the Comatule, and in a less degree those of the Pentacrinidze 
also, usually differ somewhat from their successors; and they may present a variety of 
characters, which are of considerable value in the discrimination of species, owing to 
the comparative constancy of their occurrence. They are frequently distinguished by 
the presence of spurs or keels upon their basal joints, as in Actinometra solaris; or they 
may be long, slender, flexible, and flagelliform, as in Antedon rosacea; or they may be 
stiff, straight, and spine-like, as in Antedon protecta; or they may have large prismatic 
basal joints, as in Metacrinus (Pl. XXXVIIL; Pl. XXXIX. fig: 1; Pl. XLIIT. figs. 2, 4 ; 
PL SEI. “fie, 2;PE XLVI: Pl XIX. fies, 15/2 PE os ear ey eA siren 
or the dorsal surfaces of their joints may have forward projecting keels, as in Pentacrinus 
asterius (Pl. XIII. figs. 1, 14). 
Dr. Carpenter’ has observed that the first pinnules of the ten-armed Antedon rosacea, 
which habitually arch over the disk and are much longer than their successors, are 
1 On the Structure, Physiology, and Development of Antedon (Comatula) rosaceus, Proc. Roy. Soc., vol. xxiv., 1876, 
p. 226. 
