12 ECONOMIC ZOOLOGY 



remove waste. Between the outer layer of cells, the ectoderm, and the 

 inner layer, the entoderm, is a more or less gelatinous layer, the meso- 

 derm, in which are found the skeletal elements that give the sponge 

 its definite form. In the commercial sponges, of particular interest 

 here, the skeleton consists mainly of a complicated network of horny 

 fibres of a substance called spongin, which is stiff and hard when dry, 

 but is more or less flexible when wet. 



In other sponges the skeletal elements are tiny structures of various 

 shapes, called spicules, which may be either calcareous or silicious. 



Sponges multiply asexually by budding and by means of asexual 

 spores or gemmules; and sexually by means of ova and sperm. The fer- 

 tilized ovum develops into a ciliated, free-swimming larva that later 

 becomes attached and develops into the plant-like adult sponge. 



In the ordinary commercial sponges the process of budding and 

 branching has gone so far that it is difficult to recognize the primary 

 vase-shaped individual in the complicated mass with dozens or hundreds 

 of oscula and thousands of pores. 



In some of the older texts the sponges were classified under the 

 phylum ccelenterata, but they are now generally placed in a separate 

 phylum. Fossil sponges are found in all geological formations from 

 the Cambrian upward. Although found in all seas and at almost 

 all depths, it is in tropical and subtropical waters they especially 

 abound. 



"The sponges of commerce come from the eastern Mediterranean Sea, 

 the West Indies, and the coasts of Florida and Central America. In the 

 Grecian Archipeligo, Crete, Cyprus, on the coasts of Asia Minor, Syria, 

 Barbary, and the Bahama Islands, sponge fisheries constitute a very im- 

 portant industry. The finest sponges are obtained in Turkish waters. The 

 fishing season commences in May and closes in September or October. 

 Diving is practised, and is carried on in a rude, primitive manner. The 

 diver, who has no dress, siezes hold of a large stone, to which a line is attached, 

 and sinks by means of it to a depth varying from 30 to 180 (?) feet. Keep- 

 ing hold of the rope, he tears the sponges off the rocks within his reach, and 

 places them in a net; when he secures a netful he signals by means of the rope 

 to be drawn up. 



"Modern diving dresses have been successfully introduced in some 

 places. The West Indian trade is annually increasing, and the fishing in- 

 dustry gives employment to 500 boats and 2000 persons. The Bahamas 

 and the coast of Florida are the best fishing grounds. 



