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forms, such as the Sturgeons, migrate to the sea at certain seasons. 

 The Dipnoi are exclusively fluviatile, or live in swamps caused by 

 river overflow, and the perennibranchiate Amphibia, as well as the 

 larvae of the caducibranchiate forms, are characteristic members of 

 the fresh-water fauna. Many Chelonia and Crocodiles, such 

 Birds as Ducks and Grebes, and such Mammals as Otters, the 

 Hippopotamus, and Ornithorhynchus, may also be included in the 

 fresh-water fauna, and some Dolphins are purely fluviatile. 



The animal inhabitants of large lakes, like those of the sea, are 

 divisible into littoral, pelagic, and deep-water, and the pelagic 

 forms are, in this case also, characterised by their extreme 

 transparency. Mention must also be made of animals dwelling in 

 deep subterranean caves, shut off from sunlight, such as ProUus, 

 the blind Urodele of the caves of Carniola, the blind Fish 

 {AmUyopsis spclceus) of the Mammoth caves of Kentucky, numerous 

 Insects, &c. These, like abyssal species, are blind, and usually 

 colourless, and are obviously specialised derivatives of the ordinary 

 fresh -water or land-fauna. 



In the Terrestrial Fauna, also, we find certain groups pre- 

 ponderant, others absent or nearly so. A terrestrial Amoeba has 

 been described, and the Mycetozoa are all terrestrial, but no other 

 Protozoa, nor any Sponges, Coelentrates, or Echinoderms. Among 

 Platyhelminthes we have the numerous species of Land-Planarians 

 and the Land-Nemer tines, and among Chstopods nearly the 

 whole of the Earthworms. Several Crustacea are more or less 

 completely adapted to terrestrial life, such as the Woodlice, Land- 

 crabs, Cocoa-nut Crab, and Burrowing Crayfish. The Onychophora 

 and Myriapoda are characteristic land-animals, so also are most 

 Arachnida and many Insects^ Among the Mollusca the only 

 terrestrial forms are the majority of pulmonate Gastropoda. Among 

 Fishes the Climbing Perch, Periophthalmus, and some others are 

 imperfectly adapted to life on land, and the Caducibranch Urodeles, 

 the Anura, and the Gymnophiona are all terrestrial or semi- 

 terrestrial. The Lacertilia, Sphenodon, the majority of Snakes, and 

 the Tortoises are land-animals, and so also are many Birds, 

 including all the Ratitae, the Crypturi, Gallinse, &c., and the vast 

 majority of Mammals. 



Among terrestrial animals, those which habitually live on the 

 open ground must be distinguished from arboreal forms, such 

 as Tree-Kangaroos, Sloths, and Monkeys, which pass their lives 

 among the branches of trees, and from cryptozoic forms, which 

 Uve under stones, logs of wood, &c., such as Land-Planarians, 

 Peripatus, Centipedes, and Woodlice. 



Lastly, we have the Aerial Fauna, including animals capable 

 of sustaining themselves for an indefinite period in the air, such 

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