1893- THE BRITISH ASSOCIATION ADDRESSES. 297 



The Polar Basin. 



The address of Mr. Seebohm to the Geographical Section is 

 perhaps the most readable, but it contains nothing new beyond six 

 beautiful maps, illustrating the River Basins, Temperature, Rain and 

 Snow, Heights and Depchs, and Vegetation, prepared under the 

 direction of Mr. E. G. Ravenstein. The general reader, however, will 

 perhaps obtain a clearer broad view of the Arctic Regions from this 

 carefully-prepared address, than from any previously-published 

 description. 



Zoo-geographical Regions. 



Incidentally Mr. Seebohm expresses his views on the possibility 

 of dividing the earth's surface into regions, and then makes some 

 interesting remarks on the special case of the Polar Basin. " The 

 fact is that life areas, or zoo-geographical regions, are more or less 

 fanciful generalisations. The geographical distribution of animals, and 

 probably also that of plants, is almost entirely dependent upon two 

 factors, climate and isolation, the one playing quite as important a part 

 as the other. The climate varies in respect of rainfall and temperature, 

 and species are isolated from each other by seas and mountain 

 ranges. The geographical facts w r hich govern the zoological provinces 

 consequently range themselves under these four heads. It is at once 

 obvious that the influences which determine the geographical 

 distribution of fishes must be quite different from those which 

 determine the distribution of mammals, since the geographical 

 features which isolate the species in the one case, are totally different 

 from those which form impassable barriers in the other. It is equally 

 obvious that the climatic conditions which influence the geographical 

 range of mammals, must include the winter cold as well as the summer 

 heat, while those which determine the geographical distribution of 

 birds, most of which are migratory in the Arctic Regions, is entirely 

 independent of any amount of cold which may descend upon their 

 breeding grounds during the months which they spend in their tropic 

 or sub-tropic winter quarters. Hence all attempts to divide the 

 Polar Basin into zoological regions or provinces are futile. Nearly 

 every group of animals has zoological regions of its own, determined 

 by geographical features peculiar to itself, and any generalisations 

 from these different regions can be little more than a curiosity of 

 science. The mean temperature or distribution of heat can be easily 

 ascertained. It is easy to generalise so as to arrive at an average 

 between the summer heat and the winter cold, because they can be 

 both expressed in the same terms. When, however, we seek to 

 generalise upon the distribution of animal or vegetable life, how is it 

 possible to arrive at a mean geographical distribution of animals ? 

 How many genera of molluscs are equal to a genus of mammals, or 

 how many butterflies are equal to a bird ? If there be any region of 

 the world with any claim to be a life area, it is that part of the Polar 



