i] HISTORICAL 15 



many peculiar forms. Madagascar, also considered 

 as a region by some authorities, became an island 

 about mid-Tertiary times. Therefore, concerning 

 mammals, the world would not have been affected in 

 the least if neither Madagascar nor Australia had 

 ever existed. How different is the case of Africa. This 

 ancient and radiating centre has had an enormous 

 effect upon the fauna ,of well-nigh the rest of the 

 world. 



There may be regions of birds, others of fishes 

 and others of beasts, but the search for generally 

 applicable regions is a mare's nest. 



What, then, is the object of the study of Geo- 

 graphical Distribution? It is nothing less than the 

 history of life in space and time. The attempt 

 to account for the present range of any group of 

 animals (the special scope of Zoo-geography) involves 

 the aid of every branch of science. Our subject 

 began in a mild statistical way, restricting itself to 

 the present faunas and floras, and to the present con- 

 figuration of land and water. Next came Oceano- 

 graphy concerned with the depths of the seas, their 

 currents and temperatures ; then inquiries into 

 climatic changes, culminating in irreconcilable astro- 

 nomical hypotheses as to glacial epochs, the causes 

 of which are still a mystery ; theories about changes 

 of the level of the seas, from the point of view of the 

 geologist, the physicist and the astronomer. Then 



