356 
THE VOYAGE OF H.M.S. CHALLENGER. 
nine of these segments, which are characterised hy having a dorsal and a ventral cirrus, 
of nearly equal size. The tenth shows the large ventral process characteristic of the 
subsecjuent segments, though it is more ventral in position, and has not attained the 
development it afterwards assumes. Minute branchise of the usual form appear on the 
twelfth bristled segment, and slowly increase in size from before backward. 
The anterior feet present a dense tuft dorsally and ventrally of the same kind of 
bristles as in Scoloplos armiger, viz., transversely barred forms (PI. XXIIa. fig. 19 ), only 
they are much longer, and it is to be noted that the appearance of such Ijristlcs varies 
considerably according to the adjustment of the focus. Toward the termination of the 
region [i.e., about the twelfth and thirteenth somites) these bristles have increased 
considerably in length, though they are much less numerous. A few of the dorsal are 
extremely elongated, with the transverse markings distinct and wide apart. The latter 
kind only remain in the ventral tuft of the twentieth foot, and, so far as the examples 
show, a similar arrangement exists posteriorly. 
After the transition of the feet anteriorly is fairly accomplished, we have from above 
downward, first the tongue-shaped branchia, then the filiform dorsal papilla (which at 
the twentieth foot is only a little longer than in front), and lastly the doul)le ventral 
process on the pedicle. In contrast with the foot of Scoloplos armiger, there are in the 
Challenger form much longer bristles, a filiform dorsal cirrus, instead of one dilated above 
the basal pedicle, and the ventral (double) process is shorter and thicker than in the 
('ommon species. 
The intestine contained a quantity of dark sand. 
The body of this species presents in section a decided difference from that of Scoloplos 
armiger, in which the greater part of the area is filled up Ijy muscles. Externally is a 
thin but firm cuticle, which exactly in the centre ventrally has a linear thickening. The 
hypoderm has the same j^roportional depth as in the British form just mentioned, and is 
also increased in the subneural region. The circular muscular coat is less developed than 
in the latter species. The longitudinal ventral muscles form in section long flat bands on 
each side of the nerve-area, and stretch far upward laterally. The dorsal are somewhat less. 
Both are distinguished from the condition in Scoloplos armiger by the absence of the 
densely interwoven vertical muscles which occupy the entire area with the exception of the 
limited central alimentary region. The nerve-area is proportionally large and rounded, 
has the circular layer externally, and is clasped internally l)etween the longitudinal 
ventral muscles. The region thus contrasts strongly with that in Scoloplos armiger, 
which lies beneath the powerful and nearly horizontal oblique muscles, Avith the vertical 
fibres bounding it laterally, and the massive circular layer externally. In the new form, 
therefore, the muscular environment is less striking. The central space of the body is 
occupied by large folds of the alimentary canal. 
