220 THE VOYAGE OF H.M.S. CHALLENGER. 
examined there are two pores in the oral plate of the anal interradius, and there are no 
others in any of the anambulacral plates which lie between it and the edges of the radials. 
The remaining oral plates, however, are not invariably pierced by the water-pores, as 
pointed out in Chapter VI. (ante, p. 95). 
The five ambulacra which radiate outwards from the mouth are protected as soon as 
they have passed through the angles of the oral pyramid by a very complete armour of 
caleareous plates (Pl. VI. fig. 3). This seems, as in most recent Crinoids, to be less 
completely differentiated on the arms than on the pinnules. In the wider, basal and 
middle portions of the pinnules which contain the fusiform genital glands, every 
pinnule-joint supports two or three quadrate side plates upon each side (Pl. Ve. 
figs. 9, 10, sp). Upon each of the side plates rests one of the covering plates (ep), which 
overlap one another alternately from opposite sides. There are no large side plates, 
however, in the narrow, proximal portion of the pinnule before the genital cord swells 
out into the fusiform genital gland; but the covering plates are separated from the 
pinnule-joints by a number of small irregular plates which belong to the anambulacral 
system (Pl. Ve. fig. 10). ‘Towards the distal end of the pinnule, on the other hand, the 
covering plates rest directly upon the edges of the pinnule-joints (Pl. Ve. figs. 8, 9; 
Pl. VI. fig. 6), as is the case throughout the entire length of the ambulacrum in 
Bathycrinus and Rhizocrinus (Pl. VI. fig. 7; Pl. VIIL figs. 4,5; Pl IX. figs. 2, 4). 
They are of a slightly oval shape, and may be as much as 0°6 mm. in diameter. 
The genital glands are long and fusiform, and give a swollen appearance to the lower 
portions of the pinnules (Pl. VI. fig. 1). This lasts for about six or seven of the 
elongated joints, after which the pinnules taper away slowly to their extremities, while 
the glands themselves are continued onwards for some little distance as delicate cords 
which often have a somewhat undulating course, and gradually diminish in size until 
they are no longer traceable (PI. Ve. fig. 8, t). The axial cord of the skeleton (a) is also 
thrown more or less into curves. The specimen obtained was a male, and the testes have 
lost all trace of histological structure, as seems to be not unfrequently the case with these 
glands in other species of Crinoids. They fill up the cavity of the pinnule almost entirely 
(Pl. Ve. fig. 7, t). A reduced cceliac canal (cc) with its ciliated cups (cic) being visible 
below the gland in transverse section ; while a small subtentacular canal (stc) intervenes 
between it and the water-vessel. The ambulacral nerve and blood-vessel, however, could 
not be detected, though there can of course be no possible doubt as to their presence. 
In one of the fragments’ which was obtained, the interior of the oral pyramid is 
exposed (Pl. VI. fig. 5). There is a ring of tentacles around the mouth, and, so far as can 
be judged from the condition of the specimen, there seem to be four of these on either 
side of the strong median keel of each oral plate, so that there would be forty in all. 
1 Mr. Black did not see the original of this figure, but simply copied the woodcut, drawn in the first instance by Mr. 
Wild, which appeared in the Journ. Linn. Soc. Lond. Zool.) vol. xiii. p. 54, and subsequently in The Atlantic vol. ii. p. 96. 
