Sponge
Spongida, a horny substance valued for its ready imbibition of water, and consisting of the keratode skeleton of certain Protozoa or lowest animals.
A sponge is thus a colony of living animals. Such a colony communicates with the outer world by means of certain openings (capable of being closed at wil will), traceable in an ordinary sponge, and of which the larger are named oscula and the smaller pores. By the latter, currents of water are continually drawn into the sponge, while through the oscula currents are as continually discharged. These currents are kept up through the action of the minute vibratile processes named cilia, which are limited usually to certain spaces of the canals named ciliated chambers. The main use of this circulation in the sponge is evidently nutritive. Particles of food are thereby swept into the organisms, while oxygen is also inhaled and effete matters exhaled.
Sponge reproduction is effected by means of specially developed masses of SPONGE protoplasm named spores, which are formed in autumn, and which on liberation in spring are found to contain small reproductive particles, which after a free existence develop into sponges.
Sexual reproduction is represented by the union of certain cells representing ova or eggs, and other cells representing spermatozoa. After fecundation a sponge-egg undergoes the stages of segmentation common to the developing eggs of all animals, till the morula or mulberry stage is reached. Thereafter the egg becomes elongated and swims freely about in the water. An internal cavity is next formed, this cavity communicating by a mouth externally, and being bounded by two layers (ectodern and endoderm). In this stage the young sponge is a gastrula. Latterly the outer cilia disappear, internal cilia are developed, and the sponge ultimately fixes itself, and circulation is established.
Sponges are classified either as the keratosa (horny), silicea (flinty, e. g., "Venus's flower basket," or euplectella), and calcarea (e. g., sycon). A more philosophical arrangement divides the sponge class into families: (1) Fibrospongiæ (fibrous, including silicea); (2) Myxospongia (Halisarca); Calcispongiæ (e. g., sycon and calcareous generally). Fossil sponges are of frequent occurrence. e. g., The sponges of commerce come from the Eastern Mediterranean Sea, the West Indies, and the coasts of Florida.
In the Archipelago, Crete, Cyprus, on the coasts of Asia Minor, Syria, Barbary, and the Bahama Islands, sponge fisheries constitute a very important industry. The finest sponges are obtained in Turkish waters.
Sponges of a coarse texture and large honey-combing are found all along the coast of Tripoli and Tunis. The West Indian trade is of importance. The Bahamas and the coast of Florida are the best fishing grounds. The qualities most in commercial demand are "wool," "reef," and "velvet"; the other kinds go by the names of "boat," "silk" or "glove," "grass," "hardhead," "mixed," "yellow," and "refuse." West Indian sponge is harsher, coarser, and less durable than its Mediterranean congener.
About 2,250 men are engaged in Florida sponge fishery, and 156 vessels are employed. The fishing is generally confined to the S. W. part of the coast and reefs and shoals between St. Mark's and Anclote Keys.
The methods employed in the fishery differ greatly from those employed in the Mediterranean, where divers go down and bring up the sponges. Small