xiv DISTRIBUTION 601 



Sturgeons, migrate to the sea at certain seasons. The Dipnoi are 

 exclusively fluviatile, and the perennibranchiate Amphibia, as well 

 as the larva? 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, characterized by their extreme 

 transparency. Mention must also be made of animals dwelling in 

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

 the blind urodele of the caves of Carniola, the blind Fish 

 (Amblyopsis spelceus) of the Mammoth caves of Kentucky, numerous 

 Insects, etc. These, like abyssal species, are blind, and usually 

 colourless, and are obviously specialized 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, Ccelenterates, or Echinoderms. Among 

 Platyhelminthes we have the numerous species of Land Planarians 

 and the Land Nemertineans, and among Chsetopods 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 Caduci- 

 branch Urodeles, the Anura, and the Gymnophiona are all terrestrial 

 or semi-terrestrial. The Lacertilia, Hatteria, 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 

 live under stones, logs of wood, etc., 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 



