314 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



ble have been contrasted, and erroneous deductions have been the 

 result. In the division of the northern hemisphere into two primary 

 regions, the so-called (i Nearctic" and " Pala3aretic", no account has been 

 taken of the almost homogeneous character of life throughout the 

 Arctic and Sub- Arctic regions, and the equally important principle of 

 temperature as a powerful limiting agent, nor of the facts of the rapid 

 increase of organic forms and the consequent differentiation of life from 

 the Arctic regions toward the Equatorial in an ever increasing ratio 

 in proportion to the extent and divergence of the principal land-areas. 

 At the northward, this method of division separates, into primary life- 

 regions, areas of the closest ontological resemblances, while at the 

 southward these divisions each embrace faunae so unlike those of their 

 northern portions respectively that the two extremes of either region 

 have little in common, scarcely more than have the southern portions of 

 these two regions as compared with each other. It is the neglect of the 

 above-stated fundamental facts and principles that forms the fatal 

 weakness of the scheme of life-regions proposed by Dr. Sclater, and so" 

 widely and thoughtlessly accepted. That the facts and principles above 

 alluded to are fundamental, in other words, that life is distributed in 

 circumpolar zones under the controlling influence of climate and mainly 

 of temperature, I propose to show by a tabular presentation of the 

 facts of distribution of mammalian life in the northern hemisphere. 



One of the reasons given by Mr. Wallace for adopting Dr. Sclater's 

 regions is that " it is a positive, and by no means an unimportant 

 advantage to have our named regions approximately equal in size, and 

 with easily defined, and therefore easily remembered, boundaries", pro- 

 viding that u we do not violate any clear affinities or produce any glar- 

 ing irregularities". It is further claimed that " all elaborate definitions 

 of interpenetrating frontiers, as well as regions extending over three 

 fourths of the land surface of the globe, and including places which are 

 the antipodes of each other, would be most inconvenient, even if there 

 were not such difference of opinion about them".* 



These arguments can be scarcely characterized as otherwise than 

 trivial, since they imply that truth, at least to a certain degree, should 

 be regarded as secondary to convenience. They further show that the 

 author of these propositions has not worked out in detail the distribu- 

 tion of life, species by species, over a diversified area of considerable 

 extent, like, for instance, that of Eastern North America, where an in- 

 terdigitation of the lesser faunal areas is one of the marked features of 

 the region, as it is elsewhere wherever there is a varied topography and 

 consequent inequality of climate under the same parallels of latitude. 

 Again, Mr. Wallace says, 4< On two main points every system yet 

 proposed, or that probably can be proposed, is open to objection ; 

 they are, Istly, that the several regions are not of equal rank; 2ndly, 

 that they are not equally applicable to all classes of animals. As 

 to the first objection, it will be found impossible to form any three 

 * Geogr. Dist. Anim., vol. i, pp. 63, 64. 



