Till! DISTRIBUTION OF ANIMALS 4 5r 



The fresh-water fauna does not present such a variety of 

 types as the marine. It may he divided into lacustrine or lake 

 fauna, and fluviatile or river fauna. The lacustrine fauna has 

 not as yet been studied very extensively; in it we recognize, as 

 in the ocean, a plankton of floating animals, mostly transparent, 

 a nekton of swimming- individuals, and a benthos of bottom 

 types; the most abundant animals are certain Protozoa, the 

 Rotifera, and small Crustacea. The fluviatile fauna contains 

 large numbers of Protozoa, one family of sponges, a very few 

 Cnidaria, the Hydridae, and no Echinodermata ; the worms are 

 represented by Turbellaria, a few Nemertina, many Nematoda, 

 some Bryozoa, many Rotifera, and Oligochaeta and Hirudinea. 

 Of the Crustacea all the Entomostraca are represented except 

 the barnacles; of the Malacostraca are found Isopoda and Am- 

 phipoda and a few Decapoda, crabs and crayfishes. Some 

 insects live in fresh water and some Mollusca, such as some of 

 the Gastropoda and the Lam ellib ranch ia. Fishes are numerous, 

 representing the Cyclostomata, Ganoidei, Teleostei, and Dipnoi. 

 All aquatic Amphibia inhabit fresh water. A few reptiles, such 

 as the Crocodilia and some Chelonia, some birds, and a few 

 mammals, such as the hippopotamus and some dolphins, belong 

 essentially to the fresh-water fauna. In addition we find many 

 larvae in streams and ponds, such as the larvae of the Trematoda, 

 of many insects and of the terrestrial Amphibia. Animals liv- 

 ing in subterranean streams and lakes are often blind and pale 

 in color. 



In the terrestrial fauna we have animals which live in the 

 ground or on its surface or in trees. The lowest type of strictly 

 terrestrial animals, not taking parasites into account, is the 

 worms, of which we find representatives of the Turbellaria, 

 Nemertina, Nematoda and Oligochaeta. Of the Crustacea the 

 wood lice (Isopoda) and some crabs (Decapoda) are more or less 

 adapted to life on land. All of the Arachnida, Protracheata, 

 and Mvriapoda are terrestrial, and also many of the insects. 

 Of the Mollusca we find only the majority of the Pulmonata, 

 Some fishes can live for a time on land, notable a few Teleostei 

 and the Dipnoi. The Gymnophiona and Anura are essentially 

 terrestrial, and of the reptiles, the Lacertilia, most of the Ophidia, 

 the Rhynchocephalia, and some Chelonia. Of the birds all 



