ALLEN ON GEOGRAPHICAL DISTRIBUTION OF MAMMALS. 329 



based on it can have " little bearing on the great features of zoological 

 geography — the limitation of groups of genera and families to certain 

 areas". 



II.— MAMMALIAN EEGIONS OF THE GLOBE. 



The influence of temperature as a limiting agent in the distribution 

 of life, as well the ^^aic of the distribution of life in circumsolar zones^\ 

 was fully recognized by Humboldt nearly three-fourths of a century 

 ago, and later, practically if not explicitly, by Ritter, De Candolle, 

 Agassiz, Wagner, Forbes, Dana, Glinther, Meyen, Middendorff, and 

 many other leading zoologists and botanists. While this law must 

 incontrovertibly underlie every philosophic scheme of lief-regions, the 

 number of zones to be recognized, as w^ll as their boundaries, must iu 

 a measure be open to diversity of opinion. Professor Dana, in 1852, 

 recognized five primary zones for marine animals, namely, a torrid, a 

 north and a south temperate, and a north and a south frigid. The torrid 

 and temperate were subdivided, the first into three, the others each into 

 five sub-zones, the two frigid being left undivided. Mr. A. Agassiz, in 

 treating of the distribution of the JEchini,* recognizes also fiv^e zones, a 

 torrid, two temperate, and two frigid. These five primary zones prove 

 to be applicable also to the mammalia, and even their subdivisions may 

 be readily traced, but are rather too detailed for practical use. Owing 

 to the irregular surface of the land-areas, occasioned by elevated pla- 

 teaus and mountain-chains, these zones of distribution have of course 

 a less regular breadth and trend than they preserve over the oceans. 

 Their boundaries, however, approximate to the courses of the isotherms, 

 by certain of which they may be considered as in a general way limited. 



In recognition of these zones, and also of the law of difi'erentiation 

 of life with the relative isolation of the principal land-areas, I proposed 

 in a former paper [1. c, p. 380) a division of the land-areas into eight 

 "Eealms", namely: I, Arctic; II, North Temperate; III, American 

 Tropical; IV, Indo -African ; V, South American Temj^erate; VI, Afri- 

 can Temperate; VII, Antarctic; VHI, Australian. A subdivision of 

 most of these primary regions was provisionally suggested, but only 

 the North American was treated with any degree of detail, and this 

 mainly with reference to the birds, and more especially those of its 

 t*astern portion. Subsequent study of the distribution of mammalian 

 life over the globe has led me to modify some of the views then ex- 

 pressed, especially in relation to the divisions of the Australian Eealm, 

 and to unite the South African Temperate with the Indo-African, as a 

 division of the latter, and also to recognize Madagascar and the Masca- 

 reue Islands as forming together an independent primary region, in 

 accordanca with the views of Sclater, Wallace, and others. Whether 

 or not the Arctic and Antarctic Regions should stand as primary divi- 

 sions seems also open to question. While perhaps tenable on general 



* Illustr. Cat. Mus. Comp. Zool., No. vii, 1872, pis. A-F. 

 Bull. iv. No. 2 2 



