INTRODUCTORY. [CHAP. 



are now islands were once parts of continents, and vice versa. 

 Such connections and disconnections, by allowing migrations at 

 one time, and preventing them from taking place in the reverse 

 direction at a subsequent epoch, have been the chief factors which 

 have resulted in the present very remarkable difference in the 

 faunas of different parts of the globe. And it is solely due to such 

 changes that many of the lower types of mammalian life, like the 

 marsupials of Australia, and the lemurs and insectivores of Mada- 

 gascar, have been preserved at the present day ; their insulation 

 having afforded them protection from the invasion of the larger 

 and more specialised mammals of other parts of the world, by 

 which they would inevitably have been swept away, had the two 

 groups ever come in contact. It is in regard to these migratory 

 movements of animals and changes in the land-surface of the 

 globe that zoology and geography are brought into such close 

 relationship ; the former science sometimes helping to explain the 

 alterations that have taken place in the contours of the land, while 

 in other cases the present distribution of the land explains the 

 past history of the animals by which it is inhabited. 



To understand rightly the present distribution of animals, it is, 

 im ortance however, essential to study their past history as 

 of Paiaeonto- recorded by the preservation of their fossilised 

 remains in the strata of the earth's crust ; as with- 

 out such history it would be quite impossible to grasp the reason 

 of many apparent anomalies in their present distribution. How, 

 for instance, without the aid of palaeontology would it be possible 

 to understand how it came about that tapirs are now found only 

 in tropical America and the Malayan countries, or that marsupials 

 occur solely in America and Australasia at the present day ? And 

 here it may be well to mention that the science of geographical 

 distribution depends essentially upon a belief on the part of the 

 student that all animals are genetically connected one with 

 another, and that the existing forms have originated from earlier 

 kinds by some mode of evolution. Were this belief not accepted, 

 the whole science of distribution would fall to pieces ; as if animals 

 were separately created, there would be nothing calling for special 

 explanation in the fact of tapirs being restricted to the two areas 

 mentioned. 



