NAVICULA. 73 



times, as if the Namcula might be extracting 

 food from it. I do not know a prettier sight 

 for the observer, than a drop of water containing 

 several of these curious little creatures of dif- 

 ferent colours and shapes, gliding in various di- 

 rections, and all actively engaged in their pur- 

 suits. Ehrenberg describes about forty species, 

 some found in salt water, some in fresh, and 

 others fossil. They are seen single, and in pairs, 

 but never in chains, or bands, like the rest of 

 this division of the family. They are generally 

 broader in the middle than at the ends : some 

 have the two ends very sharp, others are more 

 blunt, and one or two are more round than long ; 

 a few have the ends curved different ways. Some 

 are green, some brown or red, and others almost 



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