456 
THE YOYAGE OF H.M.S. CHALLENGER. 
spinous processes pale. The most perfect spines occur amongst the masses of sponge 
encrusting certain tubes, and are fully 16 mm. in length, of a pale straw colour, and 
almost entirely composed of secretion and sponge-spicules. It is interesting to notice 
how neatly the sponge-spicules are ranged longitudinally in these processes, a consider- 
able amount of design being apparent in every instance. From the great number as well 
as the length of the spines amongst the encrusting sponge, it would appear that a special 
advantage had been gained, other than is observable in the protective function of the 
sponge, or that special efforts had been made under the circumstances. The spines have 
a broad base of attachment, and then are slightly tapered upward to the point, the 
spicules at the tip being drawn together to form a termination. Besides the spicules, 
numerous twigs of Polyzoa are attached to the tubes. 
The tubes are all simple, the only apparent branching being due to the attachment of 
a tube belonging to another species, or a smaller one of the same form. The length 
varies, the longer examples reaching 150 to 160 mm., with a diameter of about 4 mm. 
Some present a soft flexible prolongation at the posterior extremity. 
Microscopically the wall of the tube shows a vast series of sponge-spicules, often laid 
in close parallel rows, numerous sand-grains, and fine particles of mud. A few Diatoms, 
bristles of Annelids, and small Foraminifera also are present. 
In the interior of one of the tubes are many ova, arranged in a somewhat linear 
manner, but such may have been due to rupture of the body of the parent and not to 
any special nidamental disposition. The Annelid was distended with ova in various 
stages of development. 
The sections of the anterior third of the body-wall of this species present a 
characteristic appearance, since they are more definite and firm than usual in the group 
(PL XXXVIIa. fig. 2). The hypoderm forms a thin coat dorsally, but assumes greater 
bulk toward the infero-lateral regions. In the ventral median line it constitutes a thick 
external envelope to the nerve-area. Moreover, in the preparations it seems to have 
an intimate relation to a large mass of similar structure and of a somewhat foliate 
aspect, extending between the oblique and ventral muscles, and superiorly almost 
touching the alimentary canal. This constitutes a great glandular mass, with whitish 
opaque regions here and there, which must have a special function, probably of 
secretion. The large and rounded nerve-cords are situated in the outer portion of the 
median hypoderm, their inner (upper) boundary being the circular muscular coat, 
while a belt of hypodermic fibres is placed externally. A small neural canal lies 
between them. The circular muscular coat is of more than average strength. A 
thin band of longitudinal fibres lies on the inner surface of the latter coat over the 
nerve-area. Moreover, in what appear to be the interganglionic regions, the same 
changes in the relationship of the nerve-cords to the circular coat occur as in Pista 
abyssicola. The hiatus between the ventral longitudinal muscles is lessened, the cords 
