CHAPTEK XXI. 



WHAT IS A SPONGE? 



Before entering upon the great subject of 

 water and ice two of the most tremendous 

 factors in world-building let us consider a 

 small matter, so far as its permanent effects 

 are concerned, yet one which enters largely 

 into the comfort and health of mankind, and 

 which, though an animal, may be discussed 

 where it belongs under "Water." 



There are few things more familiar about 

 the ordinary household than a piece of sponge, 

 and yet, perhaps, there are but few things 

 about which there is so little known. The 

 sponge had been in use many, many years be- 

 fore it was given a place in either the animal 

 or vegetable kingdom. The casual observer, 

 because he saw it attached to a rock, jumped 

 to the conclusion that it was of vegetable 

 origin. But after being kicked back and 

 forth, so to speak, from one kingdom to the 

 other, even by what are called well-educated 

 people, it has finally been received into the 

 family of animals; a dignity in which the 

 sponge itself seems to take but little interest. 



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