THE DISTRIBUTION OF ANIMAL LIFE. 89 



now in use. They suggest forcibly that they belong 

 to a past period of time, when the latest patents in 

 anatomical structure had not yet been taken out 

 by nature's " 'prentice hand." Instances of such 

 types are found in the marsupial animals of the 

 Australian region, which present the lowest form of 

 the true mammalian type. 



The reason why old-fashioned types persist in iso- 

 lated lands and seas is believed to be because in these 

 places the struggle for existence is not quite so keen. 

 In a large area, the strongest types, which become 

 developed in any part of it, quickly make their way to 

 every other part ; and naturally the kinds with what 

 I call the last patent improvements in structure 

 will soon crowd out the old-fashioned kinds. In the 

 isolated places such new intruders from other parts 

 cannot enter, and so the old-fashioned inhabitants get 

 a chance to survive. Bat if, by accident or artificial 

 means, animals from the mainland are introduced on 

 an island, it is usually found that they are so much 

 stronger, that they spread with surprising rapidity, 

 and drive the aboriginal kinds away, these latter being 

 weaker, because, as already said, they have been bred 

 in a place where the struggle for existence is not 

 so keen. An instance of this sort is the recent spread 

 of the rabbit in Australia. At home, in Europe, the 

 rabbits are kept in check by weasels and other car- 

 nivora ; but in Australia there are only sham carnivora 

 — marsupial animals modified by carnivorous habits, 

 often weaker than the true carnivora — and not very 



