CLASSIFICATION AND DISTRIBUTION OF ANIMALS. 349 



enced by astronomical changes (variations in exceritricity of earth's 

 orbit and movements of precession, as advanced by Croll). 



All the preceding changes must have exerted a profound 

 influence upon organisms, and throw light upon many problems 

 of distribution. 



Areas of Distribution. May be mapped out for species, genera, 

 families, and orders. In all cases : (1) Size and nature of bound- 

 aries very variable. (2) Need not be continuous. 



(a) Exs. of Limited Areas. The marmot only found in the 

 Alps. A species of humming-bird confined to the crater of the 

 extinct volcano Chiriqui in Veragua. 



Six genera of Lemurs are peculiar to Madagascar. The family 

 GaleopithecidcB (including the single genus Galeopithecus) is limited 

 to Malacca, Sumatra, Borneo, and the Philippines. The order 

 Monotremata only occurs in Australia, Tasmania, and New Guinea. 



(b) Exs. of Extensive Areas. The Leopard is distributed through 

 the whole of Africa and S. Asia to Borneo and E. China. 

 The genus Felis (cat, lion, leopard, &c.) ranges over most of the 

 globe except Australia, the Pacific Islands, W. Indies, Mada- 

 gascar, and the more northerly parts of North America and Asia. 

 The family Pesperttiionidce, including 200 species of small insect- 

 eating bats, occurs everywhere within the tropical and temperate 

 /ones; while the family Muridce (rats, mice, &c.) is only absent 

 from Polynesia and New Zealand. 2. Discontinuity is generally 

 a sign of antiquity, the two or more parts being remains of a once 

 continuous distributional area, in part of which extinction has 

 occurred. Changes in the distribution of land and sea have 

 broken up many once continuous areas. Examples. The variable 

 hare (Lepus variabilis), Europe and Asia N. of 55; Alps, 

 Pyrenees, and Caucasus. The genus Tapirus, S. America, S. E. 

 Asia. Centetidce (a family of the Insectivora), Madagascar, Cuba. 

 Hayti. 



Ganoid fishes are now represented by genera with the fol- 

 lowing distribution : Acipenser, N. temperate and Arctic regions. 

 Most species marine, others are found in the Caspian Sea, Black 

 Sea, and N. American lakes, with their rivers, also in the 

 Danube, Mississippi, and Columbia. Scaphirhynchus, Mississippi 

 and tributaries. Polyodon, Mississippi and Yang-tse-Kiang. 

 Polypterus, Nile and W. African rivers. Calamoichthys, rivers 

 of Old Calabar. Amia, fresh-water, United 



