Ch. XVIII.] FRESH-WATER AXIMALS. 331 



sembled that of a sea-coast, with the waves rolling in 

 upon it, and to the south-east the water extended to the 

 horizon. Along the shore were strewn shells thrown up 

 by the surf; and on examining them, I found them 

 all to belong to well-known old-world genera Unio, 

 Planorbis, Aneylus, and Ampullaria. 



On this journey, all the beach was, as I have said, 

 covered with water, and I saw no shells ; but in the 

 pools on the road were water-beetles swimming about, 

 and these showed a surprising resemblance to the water- 

 beetles of Europe. Gynnidce swam round and round in 

 mazy circles ; Dytiscidce came up to the surface for a 

 moment, and dived down again to the depths below with 

 a globule of air glistening like a diamond. Amongst the 

 vegetation at the bottom and sides of the pools Hydro- 

 pluUclw crawled about, just as in ponds in England. 

 IS^ot only were those old-world familiars there, but they 

 were represented by species belonging to the typical 

 genera Gyrinus, Colymbetes, and Hydrophilus. Over 

 these pools flew dragon-flies, whose larval stages are 

 passed in the water, closely resembling others all over 

 the world. All the land fauna was strikingly different 

 from that of other regions ; but the water fauna was as 

 strikingly similar. 



The sameness of fresh-water productions all over the 

 world is not confined to animal life, but extends to plants 

 also. Alph. de Candolle has remarked that in large 

 groups of plants which have many terrestrial and only a 

 few aquatic species the latter have a far wider distribu- 

 tion than the former; and it is well known to botanists 

 that many fresh-water and marsh plants have an im- 

 mense range over continents, extending even to the most 



