ARISTOTLE'S ACCOUNT OF SPONGES. 127 



the present day, and, as anciently, there are 

 not wanting advocates for either view. Aristotle 

 distinguishes sponges under two heads, those 

 that might be cleaned, and those which could 

 not. Of the last he states that their substance 

 was compact, but perforated by large canals. 

 They were more viscous than other sponges, and 

 when dried remained black. The description 

 exactly applies to the common coast-line sponges 

 of the iEgean, useless for economic purposes. 

 His account of the sponges of commerce is more 

 detailed. He distinguishes three varieties : 

 those which were lax and porous; those of thick 

 and close texture; and a third kind, called sponges 

 of Achilles, finer, more compact, and stronger 

 than the others. These last were rarest and used 

 to be placed in helmets and in boots, as pro- 

 tections from pressure for the head and feet. 

 They all grow on the rock, adhering not by one 

 point only, nor by the whole surface, but by some 

 extent of their surface. The best kinds grow 

 on the coasts which become suddenly deep. He 

 attributes the superior fineness of texture in 

 these deep sea-kinds to the greater uniformity 

 of temperature of the water in such places. 

 When alive, and before they are washed, they 



