DE. WYVILLE THOMSON ON HOLTENIA. 
703 
large oscular opening about 30 mm in diameter, whence a cylindrical cavity passes vertically 
into the substance of the sponge to a depth of 55. This oscular cavity is cupped 
beneath, and lined by a network with the same general character as the external net- 
work of the sponge. The osculum is fringed by a close range of siliceous spicules placed 
vertically. The sponge-body between the oscular and external walls is composed of a 
loose spongy mass of consistent sarcode containing a multitude of minute brownish or 
greyish granules which make it semiopaque, supported by an irregular framework of 
stellate siliceous spicules, and containing numerous minute feathered spicules and 
amphidisci. Close beneath the outer wall the sponge-substance is hollowed into wide 
anastomosing sinuses, which surround and separate perpendicular spongy columns 
which support the external stellate wall. From the surface of the upper third of the 
sponge, bunches of rigid spicules project outwards and upwards from the substance of 
the sponge through the outer wall ; and from the surface of the lower third of the 
sponge, bundles of enormously long siliceous threads, coated with glairy sarcode, pass 
out to be diffused to a great distance through the chalk-mud, in which the sponge is 
buried nearly to the lip. 
Four specimens only of this species have as yet been found, at a depth of 530 fathoms 
in lat. 59° 36' N., long. 7° 20' W. One of these, figured in Plate LXVII-. of the present 
Memoir, has the body about a decimeter in length by 8 centimeters in width ; the outline 
is elliptical. A second specimen, figured in section, Plate LXIX. fig. 1, is nearly spherical, 
about 9 centimeters in diameter ; a third, in the British Museum, is more cylindrical in 
form, about a decimeter in length by 7 centimeters in width ; and the fourth, in the 
possession of Dr. Carpenter, is rather smaller and nearly globular. These four speci- 
mens were all procured at one haul of the dredge. They were brought up alive, and with 
higher organisms, clams and starfishes, also living, attached to them. Unfortunately, from 
the state of the weather, we were unable to observe them in a living state ; we were 
obliged to put them at once into spirit. 
The Structure of the Sponge. 
The siliceous spicules. — The spicules which enter into the composition of the sponge 
may be conveniently divided into three groups, the spicules of the sponge-body, the 
spicules of the beard, and the spicules of the sarcode. 
1. The Spicules of the Sponge-body. — The spicule which enters almost exclusively 
into the structure of the framework of the sponge-body, forming the stellate trellis of 
the outer wall and of the wall of the inner exhalent cavity, and supporting and defining 
the trabeculae of the areolated sponge-substance, is formed on the hexradiate-stellate 
type ; usually, however, only five rays are developed, so that the spicule is quinque- 
radiate. There are two well-marked sizes of this spicule. The larger form by the 
symmetrical distribution of their rays, the siliceous framework of the large stars of the 
outer and inner walls ; while the smaller, which are altogether much more delicate in 
their proportions, support the small secondary stars of the walls, and the meshes of the 
sponge-substance. 
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