74 
THE VOYAGE OF H.M.S. CHALLENGER. 
above into 2-4 branches, each of which is simply feathered. The anal papilla between 
the rolled-np ends of the branchia is about as high as the branchial leaves, cylindrical 
in form, and a little thicker above, and with a round-indented opening. On the right 
hand side is the wide renal pore. 
The largest specimen was carefully dissected. The pericardium was of a chocolate- 
brown colour, as also the part of the peritoneum covering the blood glands. 
The central nervous system was difficult to investigate, as it lay in a strong sheath of 
connective tissue. The cerebro-pleural ganglia were reniform, with arched surfaces ; 
the two divisions very distinct, the hindermost larger than the foremost. The pedal 
ganglia lying outside the pleural are a trifle smaller than these, and plano-convex in 
form. The common commissure is narrow, hardly longer than the diameter of the 
central nervous system ; the three commissures of which it is composed are clearly 
distinguishable, and of these the hindermost is partly free from the other. The 
proximal olfactory ganglia are sessile and bulb-shaped, the distal somewhat smaller and 
pear-shaped. The buccal ganglia (PL IY. fig. 1, aa) are a little larger than the proximal 
olfactory ganglia and plano-convex, they are united by a short commissure; the gastro- 
oesophageal ganglia are short-stalked and small, they are situated on the outer side of 
the nerve, they are not more than one-tenth of the size of the buccal ganglia (fig. 1 , bb). 
The eyes are short-stalked, the pigment is black, the lens yellow. The otocysts are 
rather smaller than the eyes, with about 200 otoconia of the usual kind. The walls 
of the cavity of the stalk and of the club of the rhinophoria are covered with greyish- 
black pigment. 
The mouth tube is strong, 3 '5 mm. long, whitish-yellow in colour; the inferior and 
median pairs of retractor muscles are very long ; its interior is as usual. The bulbus pharyn- 
geus is strong, 3 ’5 mm. long, by about 3 mm. in height, and 3 ‘5 mm. in breadth; the radula- 
sheath projects about '5 mm. below. The arched labial disk surrounds the perpendicular 
mouth slit, which is provided with a continuous dark yellowish coloured armature, which, 
especially below, but also above, passes over a portion of the labial disk. This prehensile ring 
is interrupted neither above nor below ; above it is a trifle narrower, being below about 
1 • 2 mm. broad. The ring, as usual, is formed of densely set straight or somewhat curved 
yellow rods, about '06 mm. in height, which are bifurcate (PI. III. fig. 26) at their upper 
extremities. The tongue is broad, with a deep cleft, which is covered up over its margins 
by the clear yellow-coloured radula ; in this last are forty -two series of teeth, further 
back thirty-two developed and four not fully developed series ; the total number thus 
is seventy-eight. The first eleven rows are more or less incomplete ; on the middle 
of the tongue are about fifty-eight teeth on each side, at its base sixty, and the number 
increased passing backwards to sixty-two or sixty-three. In the very narrow rhachis, 
corresponding to the hinder end of the body of the innermost teeth (fig. 27, a), there 
are small, quite colourless thickenings of the cuticle, cleft at their hinder extremities. 
