Fresh-Water Animals 253 
up by the surf; and on examining them, I found them all to 
belong to well-known old-world genera—Unio, Planorbis, 
Ancylus, and Ampullart. 
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. 
Gyrinidé swam round and round in mazy circles; Dytiscide 
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 Hydrophilide crawled about, just as in ponds in 
England. Not only were those 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 globe 
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 distribution than the former. It 
is well known to botanists that many fresh-water and marsh 
plants have an immense range over continents, extending 
even to the most remote islands. The close affinities of 
fresh-water animals and plants have been noticed by many 
naturalists. Darwin saw with surprise, in Brazil, the simi- 
larity of the fresh-water insects, shells, etc., and the dis- 
similarity of the surrounding terrestrial beings compared 
with those of Britain.2, Dr. D. Sharp informs me that water- 
beetles undoubtedly present the same types all over the world. 
He believes there is no family of Coleoptera in which tropical 
or extra-tropical species so closely resemble one another as in 
the Dytiscide. Cybister is found in Europe, Asia, Africa, 
Australia, New Zealand, Brazil, and North America; and 
the species have a very wide range. Dr. Sharp remarks that 
this wide distribution and great similarity of the Dytiscide 
is of special interest when we recollect that they are nothing 
+ Darwin, Osigin of Species, p. 417. 2 [btd., p. 414. 
