PROBLEMS OF DISTRIBUTION AND THEIR SOLUTION. 169 



extent as again to unite the island with the continent, it is evident 

 that a very complex result might be produced ; for, besides the relics 

 of the ancient fauna, we might have successive immigrations from 

 surrounding lands, reaching down to the era of existing species." 

 Thus, in the life of Madagascar, we see the results of isolation 

 interrupted by periods of connection with large continental areas. 

 The fact that the lemurs of Madagascar exist likewise in West 

 Africa, in the Indian region, Ceylon, and the Malay Archipelago, is 

 explicable not by supposing a direct land-connection occupying 

 the site of the Indian Ocean but by regarding these animals as 

 presenting us, in Madagascar, with the remnants, secured from harm 

 by isolation, of a once widely distributed lemur-population. This 

 group of animals, doubtfully classified to-day as the lowest order of 

 the monkey-tribe, as we know from the evidence of fossils, over- 

 ran Europe in the Eocene period of geology. We know that Africa 

 was separated from Europe and Asia in the Tertiary period by a large 

 sea-area. Thus, late in its history, were outlined the bounds of the 

 Ethiopia which the biologist has defined, and which, as we have seen, 

 has the desert region as its northern and natural boundary. Joined 

 to Africa in its earlier phases as an island, Madagascar doubtless 

 received from Africa the lower quadrupeds, reptiles, insects, and 

 other forms bearing evidence of a distant Australian or New World 

 relationship. Then came the separation of Madagascar from the 

 African continent a phase of its history which left that island to 

 mature and develop the modified and peculiar species we see 

 within its limits to-day. At the same time this separation protected 

 it from the inroads of the higher animals coming from the north, 

 which we now find amongst the existing African fauna. 



Similarly, the problem of the likenesses and differences between 

 the life of New Zealand and Australia are explicable only upon the 

 idea supported by strong geological evidence of land changes 

 of curious and complex character. Thus Eastern Australia must 

 have been separated from Western Australia in the Chalk period; 

 and whilst New Zealand was connected by shallow water with tropical 

 Australia, it was sharply demarcated from temperate Australia by 

 a deep sea. Thus is explained the fact of the plants which are 

 common to Australia and New Zealand being tropical and sub- 

 tropical in their nature. Direct land-connection between the two 

 countries, but a connection which at the same time was anything 

 but equivalent to continuity with existing Australia seeing that 

 the latter was practically halved in the Chalk period explains the 

 means whereby the underlying likeness between the life of these 

 islands was established. 



By way of establishing still more firmly the truth of the axiom 

 that physical change forms one of the two main factors involved 



