COMMERCIAL 8P0NQE8. 
19 
to disintegrate. For example, Cliona sulphurea, a yel- 
lowish sponge, has been found by Verrill boring into 
various shells, such as the oyster, mussel, and scallop; it 
also spreads out on all sides, enveloping and dissolving the 
entire shell. It has even been known to penetrate one or 
two inches into hard statuary marble. 
Of the marketable sponges there are six species, with nu- 
merous varieties. They are available for our use from being 
simply horny or fibrous, having no flinty or silicious spi- 
cules. The Mediterranean sponges are the best, being the 
softest; those of the Red Sea are next in quality, while our 
West Indian species are coarser and less durable. Our 
West Indian glove-sponge {Spongia tuhtdifera) corresponds 
to Spongia Adriatica, which is the Turkey cup-sponge and 
Levant toilet sponge of the Mediterranean. Spongia gos- 
sypina, the wool sponge of Florida and the Bahamas, is 
used as a horse or bath sponge. 
CHAPTER III. 
Brakch hi. — CcELEi^TERATA {HydvoidSy Polyps, etc.) * 
Geneeal Characters of C(Elenterates.— We now come 
to animals of more definite ^hape than sponges, while their 
structure is more easily understood. A common type or 
representative of the group is the fresh-water Hydra. Its 
body is like a slender cylindrical sack, with a mouth in the 
middle surrounded by a circle of feelers or tentacles. The 
mouth leads into a simple stomach-like cavity; whatever is 
not digested, such as pieces of shell, etc., is rejected from 
the mouth. The walls of this very simple body consist 
of two cell-layers, the ectoderm and endoderm; the middle 
layer (mesoderm), found in higher animals, not being pres- 
ent. From the fact that the digestive cavity or stomach is 
simple, being hollowed out of the body, there being no 
genuine separate digestive canal, as in the higher animals, 
all the species of this branch are called Coelenterata (Greek, 
Koiko^y hollow; and errepov^ digestive track). 
* See the works of Darwin on Coral Reefs, Dana's Corals and 
Coral Islands, A. Agassiz's Seaside Studies in Natural History, 1871. 
