194 
THE VOYAGE OF H.M.S. CHALLENGER. 
half an inch from the head, to which it gently tapers. The diminution from the same 
region to the tip of the tail is very gradual, the latter being by no means slender. 
The head has two moderate frontal lobes, and, viewed from the dorsum, it seems to 
be broader in front than behind. The ocular region on each side is elevated into 
two prominent lobes, which form two lateral bosses posteriorly, a considerable part 
of each extending behind the posterior eye. The eyes are situated in the arms of 
the usual V, the anterior being about twice the size of the posterior pair, somewhat 
ovoid, and with a trace of a “lens.” Their position is such that they look slightly 
forward as well as upward. The second pair follow after a short interval, and are 
rounded. Above the base of each frontal lobe is a tentacle (antenna of some authors) 
shorter than the median, and crenulated by the annulations. The ordinary tentacle 
springs from the centre of the head, rather in front of the first pair of eyes, and, like 
the previous processes, is somewhat narrowed at the base, while the tip is little tapered. 
The buccal segment bears two cirri in place of a foot on each side. Interiorly the 
margin of the mouth forms a disk symmetrically divided into eight lobes. The first foot 
follows, bearing dorsally a long thickish cirrus only slightly tapered at the tip, and com- 
posed of numerous segments, next a setigerous process and inferiorly a lanceolate 
ventral cirrus. 
When fully formed the foot anteriorly (PI. XXXIII. fig. 4) presents a dorsal cirrus, 
which assumes a somewhat fusiform shape, from the slight diminution at the base and 
tip. There are about twenty-five segments in the cirrus besides the basal region, which 
is formed by a prominent process of the body-wall. The setigerous region is moderately 
elongated, its prominent superior apex having two short papillae, from which its margin 
slopes downward and inward. It has about six spines, and a series of stoutish bristles 
(PI. XYa. fig. 14) with short simply hooked terminal processes. The ventral cirrus is 
a somewhat broad, tongue-shaped lobe, with its concave surface directed upward. Its 
tip projects a little beyond the setigerous region. 
Posteriorly the chief changes in the foot are the increase in the length of the dorsal 
cirrus (which also tapers slightly from base to apex), its more numerous and evident 
annulations, which amount to about forty-two. The setigerous region is smaller than in 
front and has four spines. The bristles pass out beneath the latter as anteriorly. The 
basal region of the ventral cirrus is slightly broader than in front, and its tip more tapered. 
The anus occurs as a terminal aperture posteriorly, and in the preparation no process 
remains at the sides. The last foot, which adjoins the aperture, is little differentiated. 
In transverse section (PI. XXXI Va. fig. 7) the cuticle is remarkably thick, 
especially on the ventral surface. Outside the nerve-area is the circular coat, and then 
apparently hypoderm, though the cut ends of fibres appear to be present. The oblique 
muscles pass below the cords and meet in the middle line ; moreover, a few fibres pass 
obliquely over the nerve-area from the one to the other. The longitudinal ventral 
