I 



CHAPTER VIII 



CRUSTACEA OF FRESH WATERS 



'THHE Crustacean fauna of fresh water is much 

 ^ less rich and varied than that of the sea. 

 Although the number of individuals in a pond or 

 lake may be enormous, they will be found to belong 

 to a comparatively small number of species. All the 

 subclasses of Crustacea with the exception of the 

 Cirripedia have representatives in fresh water, but 

 in most of them only a very few of the families and 

 genera comprise truly fresh-water species. In spite 

 of the comparative poverty of the fauna, however, it 

 is of very great interest, more especially with regard 

 to the problems of geographical distribution ; and 

 the ease with which specimens may be collected 

 everywhere, and kept in small aquaria, renders it 

 a particularly attractive subject of study for the 

 amateur naturalist. 



The general uniformity of the fresh-water fauna 

 throughout the world has often been remarked. 

 Darwin says : " When first collecting in the fresh 

 waters of Brazil, I well remember feeling much 



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