20 
THE VOYAGE OF H.M.S. CHALLENGER. 
their origin from the lateral portions of the head ; the rhinophoria, which are strong and 
conical, arise from the neck behind the anterior edge of the papilla-bearing dorsal wall ; 
the stem is low, the club furnished (on either side) with about forty broad leaves (or 
laminae). Between the rhinophoria is the slender somewhat depressed comb-like organ, 
which has a length of 2 ’5 mm. and a height of 0’8 mm., and which is divided into thick 
leaves by perpendicular furrows upon its edge which seem to be again divided. The 
eyes do not appear at the base of the rhinophoria. The back is somewhat broad, 
rounded at its anterior extremity, posteriorly it narrows, and ends in a sharp point. 
Its broad marginal portion, rather prominent at the edge, is covered with a dense mass 
of papillae. In front this portion is somewhat narrower, and in the middle line that of 
either side is separated from the other by a narrow bare median space ; at the posterior 
end the same conditions are repeated, but the median space is here narrower still. The 
papillae appear to be arranged in a similar irregular fashion, as in the typical Janus. 
Only a few of the smaller papillae were left, they appear to agree with those of the 
typical Janus. The anal papilla is situated on the dorsal median line, some way 
back (6 mm. from the end of the back) ; it is cylindrical in shape and truncated, with the 
folds of the intestine prolonged to the margin ; it is directed backwards. The sides of the 
body are rather high at the middle, but diminished in height anteriorly and posteriorly. 
Rather backwards, corresponding with the anterior part of the pericardium, is the 
genital opening, surrounded by a horse-shoe shaped fold, and filled with the conically 
protruded end of the duct of the mucous gland, about 3 ‘5 mm. high. Further back still, 
corresponding to the posterior end of the pericardium, is the conspicuous renal aperture. 
The foot is very large ; in front it is straight, with a slight median notch, and with 
indications of a fine marginal furrow ; as far as its slightly prominent corner, it is fused 
with the wings of the head already-mentioned. The foot stands out from the sides of 
the body, provided as it is with an undulating lateral brim about 3 ‘5 mm. broad, 
which probably serves as an organ for swimming. The tail is broad and rounded at its 
posterior extremity ; it has no sign of any keel. 
The pericardium is the only part of the viscera that is visible through the walls of 
the body. The position of the viscera as in J anus. 
The central nervous system (PI. IX. fig. 6) is rather flattened and somewhat irregular ; 
the cerebro-pleural ganglia (fig. 6, ab.) are rather elongated ; an optic ganglion is present ; 
the pedal and gastro-oesophageal ganglia resemble those of Janus cristatus. The 
eyes (fig. 6, d,d.) also resemble those of Janus ; the outer end of the optic nerve is 
pigmented. At the base of the rhinophorion is the oval olfactory ganglion, which is 
somewhat larger than the buccal, and gives off a very stout and a thinner nerve. At the 
anterior margin of the club of the rhinophorion there are short leaves between the 
larger ; the structure of the rhinophorion was quite typical. 
The mouth-tube is about l - 3 mm. in length. The bulbus pharyngeus (PI. VIII. fig. 15) 
