14 SPONGES. 
VALUE OF SPONGES.—There are six species of sponges valued in 
commerce; three are found in America, in Key West and the Baha- 
mas, the others coming from the Mediterranean and Red Seas. Nearly 
all the flints are the remains of ancient sponges. 
Specimens for Study.—Sponges are difficult to keep in 
the aquarium. In our Northern fresh-water ponds, the 
Siphydora is common, and, in streams, the Spongilla, while 
various kinds can be found along the coast. In default 
of living specimens, the common toilet-sponge should be 
used, and sections made with a razor for examination 
under the microscope. 
Works on Sponges for further reference, 
“The Glass Sponges,” by Rev. Samuel Lockwood, in “ Popular 
Science Monthly,” vol. iii, p. 529 ; “ The Common Fresh-Water Sponge, 
Spongilia,” by Professor W. C. Williamson, in “ Popular Science Re- 
view,” January, 1868 ; “North American Poriferz,” by A. Hyatt, in 
“Memoirs of Boston Society of Natural History”; “ Life Histories 
of Animals,” by A. S. Packard, Jr.; “The Atlantic, and Depths of 
the Sea,” Sir Wyville Thomson, 
= —_—_--~ 
A Syrian sponger, 
