Distribution of Mammalia. 19 



the highest in structure, are alogether tropical, and the Ba- 

 trachians^ which rank lowest, especially the salam android 

 forms, are rather types of the colder temperate zone than of 

 the warm, &c. From these facts it is plain, that the geo- 

 graphical distribution of all groups has a direct reference to 

 atmospheric and hydrostatic pressure on one side, and also 

 to the intensity of light and heat over the surface of the 

 globe. 



The special adaptation of minor groups begins very early in 

 the history of our globe, and extends at present all over its 

 surface. In the same manner as animals are adapted to 

 natural limits in their large primitive groups which we call 

 classes, we find also the minor divisions more closely adapted 

 to particular circumstances of the physical condition of all 

 parts of the globe. Among Mammalia, the great type of 

 Marsupialia is placed in New Holland, and extends little 

 beyond that continent into the adjacent islands. A very few 

 representatives of that family are found in America. Asia, 

 Africa, the colder parts of North America, and its southern 

 extremity, are entirely deprived of this type. The family of 

 Edentata, again, has its centre of development in South 

 America, where the sloth, dasypus, ant-eaters, &c., form cha- 

 racteristic types, of which a few analogues occur in Africa, 

 along its southern extremity and western coast. Now it is 

 a fact upon which we cannot insist too strongly, that the 

 same districts of New Holland and South America were, 

 during an earlier geological period comparatively recent, the 

 seat of an equally wide development of the same animals in 

 the same extensive proportion as at present. We need only 

 refer to the beautiful investigations of Dr Lund, upon the 

 fossil mammalia of Brazil, and to those, no less important, of 

 Professor Owen, upon the fossil remains of mammalia of 

 New Holland, to leave not a shadow of doubt upon this 

 adaptation, which indicates distinctly these two regions, at 

 two distinct periods remote from each other,' as the points of 

 development of two distinct families, which have never spread 

 over other parts of the globe at any period since the time of 

 their existence, indicating at least two distinct foci of crea- 

 tion, with the same characters, at two successive epochs ; a 



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