COMMERCIAL SP0KQE8. 19 



to disintegrate. For example, Cliona svlphurea, a yel 

 lowish sponge, has been found by Verrill boring into 

 various .-lulls, such aa the oyster, mussel, and scallop; it, 

 also spreads oul 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 - s, with nu- 

 merous varieties. Thcv are available for our use from being 

 simply horny or fibrous, having no flinty or silicions spi- 

 cules. The Mediterranean sponges arc t lie best, being the 

 softesi ; those of the Red Sea are next in quality, while our 

 Wi -i Indian species are coarser and less durable. Our 

 \\ est Indian glove-sponge (Spongia iubulifera) corresponds 

 to Spongia .\<lri<ilirit, which is the Turkey cup-sponge and 

 Levanl toilel sponge of the Mediterranean. Spongia g08~ 

 8ypina, the wool sponge of Florida and the Bahamas, is 

 used as a horse or bath sponge. 



OHAPTEB III. 

 Branch III. — C<i:u:n ti:kata (Hydroids, Polyps, etc.).* 

 General Characters of Ccelenterates,— We now come 



to animals of more definite shape than sponges, while their 

 structure is more easily understood. A common typi 

 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 

 int. From the fact that the digestive cavityor 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 Cmlenterata ((ireek. 

 koiXoS, hollow; and errepiw, digestive track). 



* See the work- of Darwin on Coral Reefs, Dana's Corals and 

 Cond Islands, A. A.gassiz's S< Studies in Natural History, 1871. 



