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THE COMMERCIAL SPONGES AND THE SPONGE FISHERIES. 409 
the openness of the canal system. Sponges with comparatively slender fibers, 
with the microscopic meshes rather open, with a small amount of foreign mat- 
ter included in the spongin, and with an open canal system, are the softest. 
Those in which the fibers are heavily laden with sand are invariably harsh. 
Fineness.—Fineness depends upon the macroscopic rather than on the 
microscopic arrangement of the skeleton, though the slenderness of the fibers 
is a factor. The Matecumbe sheepswool is one of the softest of sponges, but 
its open structure makes it appear coarse when compared with Mediterranean 
kinds. Fineness in the same species varies more or less with the environment 
under which the individual is produced. 
Toughness and durability —These qualities depend upon both the micro- 
scopic and the macroscopic characters of the sponge skeleton, and also appar- 
ently to some extent upon its chemical properties. These factors vary with the 
sort or species and in the same sort are subject to environmental differences. In 
any given species the looser the general structure and the larger and more numer- 
ous its canals and subdermal spaces, the more easily it is torn and the sooner 
it breaks down in use. The loose, open-textured sheepswool sponge of Bis- 
cayne Bay is much more quickly destroyed in a given service than is the denser 
Rock Island variety. That chemical factors also enter into the matter is appar- 
ently indicated by the greater tenderness of the red-rooted Key sheepswool as 
compared with equally open selected specimens from the Bay grounds not 
exhibiting this peculiar color. 
Restliency.—Upon this quality depends very largely the value of a sponge 
for economic purposes. Sponges are generally more elastic when dry and more 
compressible when wet, and if under the latter condition they return promptly 
to their original shape when the compression is removed they are more useful 
than if sluggish or “soggy” in their reaction. Resiliency depends upon the 
size of the fibers and the arrangement of the microscopic mesh work, and also 
upon the thoroughness and manner of cleaning. Specimens poorly cleaned and 
containing much “gurry” are sluggish in returning to shape after compression. 
Absorptiveness.—This quality depends upon a combination of softness, fine- 
ness, and resiliency, and is the fundamental property upon which the usefulness 
of a sponge depends. A sponge that takes up little water or that absorbs it 
slowly or that drains quickly after it is removed from water is inferior for all 
purposes to one having the converse properties. 
Water is absorbed by the capillarity of the mesh work, and the finer and 
closer this is the more water taken up and retained. The fibers themselves 
absorb a small amount of moisture, but this is not available for mechanical 
purposes, as it is released by evaporation only. Resiliency assists in absorp- 
tion by promptly opening the meshes after compression, so that they act mechan- 
ically like so many minute pumps. The most copiously and quickly absorbent 
