136 THE VICTORIAN NATURALIST. 



driven backwards and forwards, from east to west, north to south, 

 from one side of a continent to another. 



How can we read the story of these changes ? In only one 

 way — by the study of the flora and fauna, living and fossil, of 

 each country. These are the visible outcome and residual 

 product of the whole past history of the earth. Geographical 

 distribution appeals alike to the geologist and to the biologist. In 

 comparing the past with the present distribution of life upon the 

 globe, one cannot fail to notice a well-marked difference. Broad 

 distribution appears to have been far more prevalent in the early 

 period of the earth's history than now, and argues strongly for a 

 predominance of more uniform conditions. This can be explained 

 by the conclusion that greater facilities for dispersal, and more 

 equable conditions of climate, existed then. 



All the chief types of animal life seem to have originated in 

 the great northern continents, and to have spread south. In the 

 northern, more ancient and more extensive lands, development 

 has been more rapid, and has given rise to higher types ; while 

 southern lands have produced modifications of lower grades of 

 organization, whose ancestors came from north. As the first 

 forms spread outward, they were not able to extend equally in all 

 directions, meeting with various barriers on the way, such as 

 oceans, rivers, climate, mountains, and deserts. Different animals 

 would succeed in reaching different countries according to their 

 powers of overcoming these barriers. Those which could swim 

 or fly would have an obvious advantage where water was con- 

 cerned ; others, as birds, insects, might be driven by wind, or 

 carried on logs by currents, &c. Even when they arrived in the 

 new country, the climate and food might be suitable, or death 

 might result. Connections between the different countries con- 

 tinually changing, the animals after arrival may be isolated for 

 ages. The degree of peculiarity is an index to the length of 

 the isolation. So we find that different countries have different 

 animals. Certain animals and plants are peculiar to each, and 

 others are more abundant there than elsewhere. Thus Africa is 

 the home of the lion ; sheep and goats characterize Europe 

 and Asia : the whole world can be mapped out into zoological 

 regions, each of which has a number of animals peculiar to itself. 

 These regions are as follows : — I. Palaearctic; II. Ethiopian; III. 

 Oriental ; IV. Nearctic ; V. Neotropical ; VI. Australian. The 

 Australian region includes Australia, Tasmania, New Zealand, 

 New Guinea, and other islands. Its real limit lies between 

 the islands of Bali and Lombok. Let us consider in what 

 way the struggle has been carried on in this region, and its past 

 history. 



I. Flora. — Professor Tate has analyzed the Australian flora into 

 the following elements: — (i) An immigrant part, derived from two 



