202 CRITIQUES AND ADDRESSES. [ix. 



The evolutionist, therefore, is bound to grapple with 

 the following problem whenever it is clearly put before 

 him : Here are the Faunae of the same area during 

 successive epochs. Show good cause for believing 

 either that these Faunae have been derived from one 

 another by gradual modification, or that the Faunae 

 have reached the area in question by migration from 

 some area in which they have undergone their deve- 

 lopment. 



I propose to attempt to deal with this problem, so far 

 as it is exemplified by the distribution of the terrestrial 

 Vertebrata, and I shall endeavour to show you that it is 

 capable of solution in a sense entirely favourable to the 

 doctrine of evolution. 



I have elsewhere 1 stated at length the reasons which 

 lead me to recognize four primary distributional provinces 

 for the terrestrial Vertebrata in the present world, namely, 

 first, the Novozelanian, or New-Zealand province ; 

 secondly, the Australian province, including Australia, 

 Tasmania, and the Negrito Islands ; thirdly, Austro- 

 Columbia, or South America plus North America as far 

 as Mexico ; and fourthly, the rest of the world, or Arc- 

 tog ceo,, in which province America north of Mexico con- 

 stitutes one sub-province, Africa south of the .Sahara a 

 second, Hindostan a third, and the remainder of the Old 

 World a fourth. 



Now the truth which Mr. Darwin perceived and pro- 

 mulgated as "the law of the succession of types" is, 

 that, in all these provinces, the animals found in Plio- 

 cene or later deposits are closely affined to those which 

 now inhabit the same provinces ; and that, conversely, 

 the forms characteristic of other provinces are absent. 

 North and South America, perhaps, present one or 



1 " On the Classification and Distribution of the Alectoromorphse ; " Proceed- 

 ings of the Zoological Society, 1868. 



