FUNDAMENTAL RELATIONS OF ANIMALS 41 



entirely disconnected areas. Why the animals and plants of North 

 America should present such a strong resemblance to those of Europe 

 and Northern Asia, while those of Australia are so entirely different 

 from those of Africa and South America under the same latitudes, is 

 certainly a problem of great interest in connection with the study of 

 the influence of physical agents upon the character of animals and 

 plants in different parts of the world. North America certainly does 

 not resemble Europe and Northern Asia, more than parts of Aus- 

 tralia resemble certain parts of Africa or of South America; and 

 even if a greater difference should be conceded between the latter 

 than between the former, these disparities are in no way commensur- 

 ate with the difference or similarity of their organized beings, nor in 

 any way rationally dependent one upon the other. Why should the 

 identity of species prevailing in the Arctics not extend to the temper- 

 ate zone, when many species of this zone, though different, are as diffi- 

 cult to distinguish as it is difficult to prove the identity of certain 

 arctic species in the different continents converging to the north, and 

 when besides, those of the two zones mingle to a great extent at their 

 boundaries? Why are the antarctic species not identical with those of 

 the arctic regions? And why should a further increase of the average 

 temperature introduce such completely new types, when even in the 

 Arctics, there are in different continents such strikingly peculiar 

 types (Rhytina for instance) combined with those that are identical 

 over the whole arctic area? ^® 



It may at first sight seem very natural that the arctic species should 

 extend over the three northern continents converging toward the 

 north pole, as there can be no insuperable barrier to the widest dis- 

 semination over this whole area for animals living in a glacial ocean 

 or upon parts of three continents which are almost bound together 

 by ice. Yet the more we trace this identity in detail, the more sur- 

 prising does it appear, as we find in the Arctics as well as every- 



^ I beg not to be misunderstood. I do not impute to all naturalists the idea of 

 ascribing all the differences or all the similarities of the organic world to climatic in- 

 fluences; I wish only to remind them that even the truest picture of the correlations 

 of climate and geographical distribution does not yet touch the question of origin, 

 which is the point under consideration. Too little attention has thus far been paid 

 to the facts bearing upon the peculiarities of structure of animals in connection with 

 the range of their distribution. Such investigations are only beginning to be made as 

 native investigators are studying comparatively the anatomy of animals of different 

 continents. 



