Chapter IX Molluscs 



MOLLUSCS abound in all latitudes, save 

 in the Arctic and Antarctic circles, in- 

 vading the land, and all waters, fresh 

 and salt. They are soft-bodied inverte- 

 brate creatures, provided with gills and, 

 in most cases, an external shell. The 

 shell is secreted by a soft fold of the body 

 called the mantle and consists largely of 

 carbonate of lime taken from the soil or 

 water. The richer the supply of lime, 

 the stronger the shell. Fresh-water 

 molluscs have much weaker shells than 

 those of marine species, and the reason 

 for this is that in fresh water there are 

 usually no great waves or other disturb- 

 ances liable to break the shell. 



Though of lowly status in the scale of 

 life the Mollusca are of great economic 



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