INTRODUCTION. 



may so express m\-self, the raw material which all 

 the various influences tliat can brin-- about more or 

 less well-defined variations, have worked up within 

 the limits assigned by the distribution of land and 

 water. 



The present geographical distributionof mammals 

 is thus intimately related to their origin. Land 

 mammals descended from aucestors which were 

 restricted to a continent, forming an island sur- 

 rounded by the waters of the ocean, have not been 

 able to develop on another continent inaccessible 

 to them, however favourable the conditions of life 

 there might be. Broad rix'ers, high mountain chains, 

 deserts, and marshes could not but hinder the 

 advance of certain t_\-pes, and ha\-e actuall}' pre- 

 vented their introduction into regions which were 

 cut off by barriers of that nature. 



E\-ery species, howe\'er strong or weak its pow ers 

 of reproduction and organs of motion ma\- be, 

 would actually be distributed over the whole earth 

 through its multiplication in geometrical progres- 

 sion and its conscc^uent migrations, if it were not 

 confined b)- such barriers, and had not its ranks 

 thinned by enemies and by the absence of the con- 

 ditions of existence. The \-arious causes ha\'e 

 acted in former times just as the)- are acting at the 

 present da}', and their combined eft'ects and mutual 

 action and reaction are expressed in the present 

 geographical distribution of animals. 



In his admirable work on the Geographical Dis- 

 tribution of Animals Wallace adopts six great 

 regions ^ in which the animals are grouped in a 

 special manner. Three of these belong to the Old 

 World, two to America, and one to Australia. 

 Each of these regions has besides a certain number 

 of sub-regions. The great Paiaearctic region 

 comprises the whole of the Eurasian continent, 

 except the south-east, together with the islands of 

 Japan, Iceland, Great Britain, the Azores, the Can- 

 ary Islands, and the islands of the Mediterranean. 

 It comprises the whole of Europe, Africa as far as 

 the Sahara and the Cataracts of the Nile, also Asia 

 JMinor, Arabia, and the entire continent of Asia as 

 far as the large mountain chains of the Himala}'as 

 — an enormous region, in ■which Wallace endeavours 

 to distinguish a European, a Mediterranean, a Sibe- 

 rian, and a JManchoorian sub-region. The great 

 /Ethiopian region comprises the African con- 

 tinent south of the Sahara, and in addition to that, 

 as a sub-region, the island of Madagascar. The 



' They are adoptcil with certnin inodilications iVom a division of the 

 earth originally proposed l>y Mr. P. L. Sclater lor birds. — Tr. 



great Oriental region embraces Asia to the south 

 of the Himala)-as, together with the Sunda Islands 

 and the Philippines. The Australian region is 

 not restricted b\- Wallace to the large island ol 

 Australia with Tasmania, but extends also o\er all 

 the islands from Celebes to the Sandwich group. 

 South America, with ^Mexico, Guatemala, and the 

 Antilles, form the Neotropical region, and the 

 rest of North America hnall\- constitutes the sixth, 

 the Nearctic region. 



Of these regions, as of all others that ha\e been 

 adopted, it ma\- be said that none of them is limited 

 by precise boundaries, e\en if we leave out of ac- 

 count the more or less cosmopolitan animals, and 

 devote our attention onh' to forms confined within 

 narrow limits. If we \\ould represent these regions 

 on maps, we must surround each of them with a 

 prett}- extensi\e zone in which the forms ha\e 

 intermingled or passed from one region into the 

 other. Besides there are in this scheme areas 

 which ha\e been ranked as sub-regions, and which 

 yet deser\e a separate independent position, at 

 least in respect of their mammalian iorms. 



Thus we must undoubtedl}- adopt a Circum- 

 polar region, embracing the north of Siberia, 

 Lapland, Greenland, the Hudson's Bay Territories, 

 and all the islands adjacent to these portions of the 

 mainland. In all parts of this region are found the 

 same, or at an)- rate ver)- closel)- allied, species: to 

 it belongs the territor)- of the polar bear, the rein- 

 deer, the glutton, the lemming, and other charac- 

 teristic forms. The island of Madagascar is totall)- 

 dift'erent from the mainland of Africa in respect of 

 its mammalian fauna, and, in general, is one of the 

 best characterized regions. The Antilles also 

 have scarcely anything in common with the neigh- 

 bouring mainland. If these three regions are 

 separated oft" as of equal value with the great 

 leading regions above named, we then have nine 

 regions marked oft" for the geographical distribu- 

 tion of mammals, and each of these is distinguished 

 b)- a separate assemblage of animals, by its own 

 peculiar fauna. 



In order to understand the parti)' strange parti)- 

 uncertain boundaries of these regions we must have 

 recourse to the indications furnished, on the one 

 hand, b)- geolog)- as to the relations between land 

 and water in earlier epochs, and, on the other hand, 

 by pala;ontolog)' concerning the existence and dis- 

 tribution of mammals which li\-ed in those epochs. 

 In many cases these indications are still ver)- incom- 

 plete, in others more or less uncertain. In such 



