THE IMPENETRABLE SEA 



and also their families and family customs, their dress, 

 language and dances, and their passionate love of colour 

 and music, and of the sea itself More than three thousand 

 Greeks are now living in Key West, gathering great crops 

 of sponges from the nine thousand square miles over 

 which the industry now extends, and using boats which 

 are little changed in shape — but equipped with Diesel 

 engines — from those employed in sponge fishing for 

 centuries in the Mediterranean. 



Aristotle mentions the sponge as a ''zoophyte" — an 

 animal-plant akin to corals and sea-anemones — but it is 

 now known to form a very distinct phylum or sub- 

 kingdom, the Porifera, because of the water-pores with 

 which it is provided in abundance. 



All the sponges are aquatic, and most of them thrive 

 in the sea. They vary widely in size from tiny sponges 

 scarcely visible to the naked eye to great compound 

 masses several feet in circumference. They also differ 

 considerably in shape, because of their power of bud- 

 ding. They are many-celled, but the individuals in a 

 colony (like the man-of-war, each sponge is a com- 

 munity) retain a considerable independence in their duties. 



It is important to distinguish sponges from the Coelen- 

 terates — comprising jelly-fish, sea- anemones, corals, etc. 

 The Coelenterates consist essentially of two main cell 

 layers, although these may be elaborately folded, and the 

 nervous system of one is always a net — never a central 

 nervous system. The nerve net, however, may be especi- 

 ally well-developed around the mouth. 



The sponge has no nervous system. Some authorities 

 believe it has evolved from the Protozoa, along a 

 separate line of descent from that of the other Metazoa 

 (many-celled animals) but there is no evidence of any 

 change in the sponge throughout its known history. It 

 has always been as distinct, so far as human knowledge 

 goes, as it is today. 



But although the sponges must be sharply distin- 



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