172 
THE VOYAGE OF H.M.S. CHALLENGEE. 
of the shaft are rounded off, and the spines reduced to short stumpy rods or elongated 
tubercles ; the middle of the shaft is usually smooth and free from spines, but sometimes 
spines are produced from it at a great number of points ; the whorls then disappear and a 
generally tuberculated irregular mass results. The commonest dimensions are 0'0158 by 
O'OllS mm. (including the spines); these are sometimes however exceeded, the length 
sometimes reaching 0‘0198 mm. 
Colour. — A deep puce-black externally, grey within. 
Habitat. — Off Port Jackson, June 3, 1874 ; depth, 30 to 35 fathoms. 
Remarhs. — There is a single large specimen of this sponge overgrown by a large 
Gelliodes {Gelliodes poculum, Eidley and Dendy). The irregularly winding flattened 
base is about 150 mm. in length by 80 mm. in width ; the wall-like mass of the sponge 
is about 18 mm. in thickness and 122 mm. in height; the oscules attain a diameter of 
3 mm. 
Ectosome. — This varies in thickness from 175 to 3'0 mm. (PI. XIX. fig. 10). Beneath 
the outer epithelium (PL XIX. fig. 11) is a very thin deeply stained layer, about 
0'02 mm. in thickness, crowded with amphiasters and containing numerous fusiform cells 
tangentially arranged. This passes into the main ectosomal tissue, which consists of 
collenchyma containing large thin-walled cells in such numbers as to constitute by far 
the larger part of the tissue. These cells (PI. XIX. figs. 16-19) are round or oval in 
outline, and usually about 0‘044 by 0'036 mm. in length and breadth; within the thin 
membranous wall is a finely meshed network of thin protoplasmic films and threads, 
surrounding a small, more or less central, nucleus, about 0’005 mm. in diameter, which 
contains a small, deeply stained, spherical nucleolus. The nucleus is supported by 
protoplasmic threads which radiate from it and extend into the general network (fig. 17). 
The network varies in character in different cells ; sometimes small accumulations of 
deeply stained protoplasm occur at the nodes, and the w^hole terminates in a thin 
peripheral film lining the outer wall. Sometimes the network is contracted into a small 
central mass surrounding the nucleus at some distance from the outer wall (fig. 18); 
sometimes, again, small, pale, scarcely visible bodies, of circular outline and about 0'004 
mm. in diameter, are thickly scattered through the network. 
Associated with these cells are others (PI. XIX. figs. 11, 20) on which the dark colour 
of the sponge depends. They are of the same size and shape as the foregoing, and are 
similarly provided with a thin membranous outer wall, but in place of a protoplasmic 
network they contain a number of spherical, sepia-coloured bodies, about 0’003 to 
0‘005 mm. in diameter, which are frequently closely packed together so as to completely 
fill the cellular envelope. By careful focussing these spherical bodies are resolved into 
a dark coloured external wall enclosing a clear central space, "within which again a small 
dark, almost black, spherule occurs. In the process of cutting thin slices of the sponge 
