1 82 EVOLUTION OF TO-DAY. 



paradise, consisting of nineteen or twenty genera 

 and thirty-five species, are confined to New Guinea 

 and the adjacent islands. In this case, it is neces- 

 sary to suppose that the entire family has arisen 

 since New Guinea has been an island. Neither 

 continuous nor discontinuous family areas can be 

 considered the rule. 



When we come to larger groups, the rule is re- 

 versed, and continuous restricted areas are never 

 found. Orders are very old divisions, becoming 

 separated from each other at the very earliest period 

 in the history of mammals, and no instance can be 

 found where there has not been very wide disper- 

 sion. If we take into consideration fossil remains, 

 there is hardly an order which does not show world- 

 wide distribution. To-day the distribution may be 

 very different, for families and genera have been 

 dropped out, leaving the present ones widely sep- 

 arated. 



In short, the present distribution of groups of 

 organisms upon our continents is parallel with 

 their anatomical relationship and their antiquity. 

 Species, which are of most recent origin, have almost 

 always a continuous area of habitation, as if they 

 had dispersed from some central point. Genera, 

 being somewhat older, show a wider distribution, 

 with more frequent breaks in the continuity, but 

 still give evidence of a central point of origin. 

 Families, older still, have ranged much more widely, 

 while orders, the oldest of all, have had always a 

 world-wide distribution, which in some cases they 

 preserve, but in others have lost by extinction. 



