COMMERCIAL SPONGES. 19 



to disintegrate. For example, Cliona sidphurea, a j'el- 

 lovvish sponge, has been found by VerriU 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 tuhdifera) corresponds 

 to Spongia Adrmtica, which is the Turkey cup-sponge and 

 Levant toilet sjionge of the Mediterranean. Spongia gos- 

 sypina, the wool sponge of Florida and the Bahamas, is 

 used as a horse or bath sponge. 



CHAPTER III. 

 Branch III. — Ccelenterata {Hydroidft, Poly27S,efc.).* 



Geneeal Chaeactees OF CCELENTEEATES. — We nowcome 



to animals of more definite shape tlian sponges, while their 

 structure is moi-e 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 month 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 tlie digestive cavity or stomach is 

 simple, being hollowed out of the bodv, there being no 

 genuine separate digestive canal, as in the higher animals, 

 all the species of this branch are called Calenterata (Greek, 

 KO?Ao?, hollow; and evtep ov, digestive track). 



"T^^be works of Darwiu on Cuial Reefs, Dana's Corals and 

 Coral Islands, A. Agassiz's Seaside Studies in Natural History, 1871. 



