112 
THE VOYAGE OE H.M.S. CHALLENGER. 
the scars left after the falling off of the papillae, which during the life of the creature, 
no doubt, cover the whole of the back. The papilla (PI. XII. figs. 14, 15 ; PL XIV. 
figs. 1-3) consist of a layer of circular muscle bundles surrounding another perpendicular 
layer ; transverse sections of the papillae showed a number of apertures, corresponding to 
the vessels and nerves (fig. 3, a), which ramify in their interior, and are occasionally accom- 
panied by a renal branch; on the surface of the papillae are a number of small unicellular 
glands. The scars left after the removal of the papillae display a somewhat yellowish 
double contour, the outer line corresponding to the circular, and the inner to the per- 
pendicular muscular coat ; the central orifice was yellowish, and contained the nerve. 
When the whole of this layer is removed, another appears which displays a branching 
network of nerves and ganglia (PL XIV. fig. 5), partly visible with a hand-lens, which gives 
off twigs to the papillae ; on the surface of this layer are a number of depressions answer- 
ing to the perforations of the upper layer; beneath the nervous “rete” is a layer of 
muscular bundles crossing each other in all directions. The deepest layer, which follows the 
last-mentioned, is also provided on its surface with a nervous ramification, beneath which 
are longitudinal and transverse muscles. Beneath this comes the peritoneum, which is 
easily separable, and is in this region of the body milky-white in colour, owing to the 
presence of an irregular mesliwork of the fine whitish renal tubules (Pl. XII. fig. 20). 
There were no spicules in the skin. 
The mouth tube is strong and thick-walled, and about 1‘5 cm. long. — The bulbus 
pharyngeus (Pl. XIII. figs. 2-6) is unusually large (5 '8 cm. long, 5 cm. in height, and 
4 ’2 cm. in breadth) ; the radula-sheath, situated on the posterior portion of its under 
surface (figs. 2, c, 6, c), is about 23 mm. long by 17 mm. broad and 7 mm. high. The 
organ is divided all around into two halves by a prominent rather sharp edge (the 
margin of the mandibles) (fig. 3) ; the anterior half is smaller and narrower, and comes 
to a point in front ; the posterior half is rounded behind in the neighbourhood of the 
large radula-sheath ; the upper surface dips downwards, in front somewhat obliquely, and 
is still more inclined posteriorly (Pl. XIII. fig. 2) ; close to the top is the origin of the 
oesophagus, and on each side of this are the openings, one on each side, of the salivary 
glands (fig. 2, cl). The anterior part of the upper side is flattened, broader upwards, 
narrower downwards (fig. 3) ; the posterior part is broad and somewhat convex behind the 
pharynx (fig. 3). The anterior part of the sides of the bulbus pharyngeus forms an 
angle with the upper surface, and in the neighbourhood of the edge is depressed; along 
the edge the posterior portion shows a deep depression, elsewhere it is convex. The 
lower surface of the bulbus pharyngeus is convex, with a slight depression at the entrance 
of the arteria lingualis ; the posterior part is broader, with a strong prominence on each 
side of the radula-sheath (fig. 2). The colour of the bulbus pharyngeus is a dirty 
yellowish-red, inclining to red on the under side and posterior extremity ; the anterior 
half of the upper side is whitish, and has a nacreous appearance. Several strong adductor 
