DISTRIBUTION OF ORGANISMS. 209 



character of the neighbouring continents. In regions, on the 

 other hand, sufficiently distant to be involved in the influence 

 of diverse foci of life, we are to expect differences propor- 

 tioned to the difference of original elements, and also of con- 

 ditions attending the development of the various lines ; there 

 we may only expect to see such ultimate parities attained as 

 those between the emeu of Australia and the rhea of America, 

 or the jaguar and puma of the latter continent and the tiger of 

 Asia. Here it is important, to observe that the cetacea and 

 the marine birds in the neighbourhood of the different conti- 

 nents, present less variation than do the land mammals and 

 birds : they have advanced less way along the lines, and have 

 been less exposed to the conditions productive of external 

 variations. In the case of a well-defined zoological region, 

 such as the northern parts of North America, we see the 

 indigenous animals expressly confined to those families which 

 our plan sets forth as springing from the marine tribes 

 above adverted to. There is the polar bear, with his 

 various progeny, the brown bear, black bear, the wolf, fox, 

 and dog ; these from a phocal ancestry. The sea-otter, 

 sprung from an allied stock, gives birth to the few musteline 

 animals which dwell in these dreary regions. Then we have 

 herbivorous cetes, giving rise to the moose deer and musk 

 ox, these again being the progenitors of the goat and sheep. 

 And finally, we have the unusually numerous rodents from 

 the aquatic birds, which nowhere are seen in greater numbers 

 than on the borders of the Arctic Ocean. Such, with the 

 mole, is the whole show of mammalia in this province : it is, 

 it will be observed, of a limited kind ; but it is interesting to 

 remark that it presents nearly all the animals of that class, 

 which we have supposed from their affinities to be descended 

 from the marine families of which there is such abundance 

 upon the adjacent ocean. And, supposing this ocean to be 

 the berceau of these land animals, we can easily see why they 

 should be more akin to the terrestrial mammalia of Northern 

 Europe than to those of South America. The Northern Ocean, 

 spreading in one character of climate along the confines of 

 the two first regions, enables a set of maritime animals which 

 p 



