326 
THE VOYAGE OF H.M.S. CHALLENGER. 
It is about 50 mm. in length, but being bent in the form of a shepherd’s crook, its 
tunnel is much longer. The diameter is about 6 mm. It is firm and rounded, coated 
externally with greyish sandy mud, and internally liy a tough whitish secretion. The 
ventral curve of the tube is comparatively smooth externally, but the rest of the surface, 
and especially the posterior curve, is furnished with a series of long, slightly bent elastic 
spines, in length three or four times the diameter of the tube, or about 25 mm. These 
stiff elastic spines (PI. XLI. figs. 5, 6) are composed of layer upon layer of a hyaline 
secretion, probably the same forming the lining of the tube, a well-marked central cavity, 
moreover, giving the process a resemblance to a large s]Donge-spicule. 
The central region, indeed, appears to be plaited or folded in some parts towards the 
tip, the distal region being veined like a piece of finely marked pitch-pine. It is filled 
with an opaque mass of granules towards the base, which is greatly enlarged at the 
point of attachment to the tube, and is there coated by the sandy rnucl of the general 
investment. When a spine is torn out a deep pit remains in the wall of the tube, for the 
bulbous base of the spine forms a hard solid mass. In their complete state the tips of 
the spines are acutely pointed. 
An examination of the sections of the body-wall of Nothria willemoesii (PI. XXXVa. 
fig. 1) shows that the comparative size and disposition of the great longitudinal muscles 
is a feature of some value, and not altagether dependent on the degree of distention of 
the perivisceral chamber. In proportion to its size the body is sujDplied with powerful 
muscles. The dorsal longitudinal are massive and characteristically reniform, the 
internal hilum being occupied by a large blood-vessel. The ventral are ovoid, and two 
or three fasciculi of vertical fibres branch from their upper margins obliquely downward 
and inward. The nerve-area is well marked, and the cords attain considerable size. Their 
investment lies on the circular coat, and the powerful vertical muscles from the middle 
line of the dorsal wall bound them at each side. A neural canal occurs rather below 
the middle of the united cords. The vertical fibres pass from the mid-dorsal region 
between the longitudinal muscles, support the wall of the intestine on each side, and are 
attached ventrally as before mentioned. The conspicuous strength of thesebands must exer- 
cise an important influence on the canal. Fibres of attachment, moreover, occur between 
their inner surface and the digestive tract. Other vertical fibres proceed from the dorsal 
wall outside each longitudinal muscle, and are directed slightly inward inferiorly, so as to 
send fasciculi into the ventral longitudinal. The circular muscular layer is equally developed 
dorsallyand ventrally, and the narrow hypoderm is densely granular dorsally, and thickened 
in the median line ventrally. A cavity dorsally at the base of each foot contains the 
large glandular mass, probably connected with the special function of tube-secretion. 
A fragment of the tube of this species occurs in the British Museum, from the collec- 
tion made by H.M.S. “Alert,”Mat. 34° 11' N., long. 136° 33' E.; depth, 71 fathoms. 
1 I may here hear testimony to the extent and value of the Annelida collectedly the “ Alert.” 
