R. W. H. ROW—-REPORT ON THE SPONGES: NON-CALCAREA, 341 
Skeleton arrangement. 
The main skeleton consists of a large number of spicular fibres, which run 
irregularly in the sponge. In the central parts of the sponge the fibres are 
very stout and frequently contain 30 or even more rows of spicules. As they 
get nearer the surface they frequently branch, and each time the branches into 
which they divide are smaller than the parent fibre, so that at the surface the 
average number of rows of spicules in a fibre does not exceed three to five. 
The general tendency of the fibres is to run more or less toward the surface, 
but the individual fibres show very great irregularities of position. The 
various fibres never anastomose with one another, and rarely cross, and their 
frequent branching when near the surface results in a tree-like appearance, 
when seen in a section. The spicules are sometimes arranged in a slightly 
plumose fashion in the fibres, especially in the large ones. 
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Fig. 19.—Lsperella erythreana, Microscleres, x 500. 
At the surface of the sponge the fibres expand into loose brushes, about 
0°15 mm. wide on the average, and containing possibly 20 to 25 spicules. 
The dermal membrane is protected by a delicate, though irregular reticu- 
lation of spicular fibre. These fibres run without any orientation (save that 
they are necessarily longitudinal) over the surface of the sponge, and usually 
contain two or three rows of spicules, very rarely four or five. They do not 
branch or anastomose with one another. 
The dermal membrane also contains a few anisochele rosettes. 
