420 
THE VOYAGE OF H.M.S. CHALLENGER. 
the fragments of shells can be observed through it. Externally the tube is on the whole 
pale. 
The minute anatomy of the anterior region of the body corresponds generally with 
that in the foregoing form. The same intricate muscular central region occurs, and it is 
even more regular and beautiful, especially in connection with the two median and two 
lateral channels in the dorsal region, after the body-wall has been comj^letely formed, i.e., 
behind the mouth. The nerve-cords in this j)art are internal, abutting on the perivisceral 
chamber. In the anterior third of the body the cuticle is very indistinct. The dark 
hypoderm is thicker dorsally than ventrally, and in the preparation it assumes a series of 
regular frills along the dorsum. A thick hyaline basement-layer occurs beneath the 
hypoderm in the latter region. The circular muscular coat is well developed. The 
longitudinal dorsal muscles are much more massive than the ventral, and are continuous 
in the median line dorsally over the vascular channel. The separate nerve-cord lies on 
each side of the median line amidst a series of interlaced muscular fibres within the circular 
coat. The sections of their bases show that the great thoracic bristles alternate with a 
smaller series, probably the roots of the second row. The oesophageal region of the 
alimentary canal is slung by muscular fibres below^ the dorsal vascular canal. Externally 
it presents a thick layer of longitudinal fibres, then a firm circular coat on wdiich the 
frilled inner lining rests. Strong muscular bands connect it with the ventral wall a little 
within the nerve-cord on each side. 
The posterior region differs considerably from that in Sabellaria (Pcdlasia) johnstoni, 
in the jmoportions of the dorsal and ventral muscles, both of which are comparatively 
small. The former have a slight bulbous enlargement at the external region of the 
dorsal arch, and then form a thin layer inward to the central line. The latter muscles 
appear in section as a small elliptical mass between the bristles and the nerve-cord on 
each side. The neural canal lies at the inner and inferior region of the nerve-cord. The 
circular muscular layer’ is well developed, but the preparation is not in a condition to show 
the su|)erficial parts. The great central area of the body in this region is occupied by the 
distended alimentary canal, while the reproductive elements occur at the sides. A band of 
muscular fibres and connective tissue from the lower surface of the alimentary canal slings 
the ventral blood-vessel and then spreads outward to be attached between the nerve-cords. 
The long caudal appendix has the cuticular and the thin hypodermic layer externally, 
then a delicate band of circular fibres and a more or less continuous though thin longitu- 
dinal layer. Some longitudinal fibres also appear to exist externally to the circular, 
indeed, the impression from the sections is that there are two thin circular and two 
longitudinal layers, but the state of the preparations does not warrant a decided state- 
ment. The glandular lining is firm. This part of the alimentary canal contained sand- 
grains and sponge-spicules. 
Schmarda procured his examples at Table Bay, Cape of Good Hope. 
