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tliey came into existence ^ Why are uot the same spe- 

 cies found in the same climates all over the Avorld? 

 The general explanation given is, that as the aucient 

 species becaine extinct , new ones were created in each 

 country or district, adapted to the physical conditions 

 of that district. Sir C. Lyell, who has \yritten more 

 fally, and with more ability, on this subject than most 

 naturalists , adopts this view. He illustrates it by spe- 

 culating on the vast physical changes that might be 

 effected in North Africa by the upheaval of a chain 

 of mountains in the Sahara. //Then," he savs, //the 

 animals and plants of Northern Africa would disappear, 

 and the region would gradually beconie fitted for the 

 reception of apopulation of s^QO.'iQ'^ perfectly dissitnilar in 

 their fornis , liabits , and organization'^ Now this theory 

 implies, that weshallfinda general similarity in the pro- 

 ductions of countries which resemble each other in climate 

 and general aspect , while there shall be a complete dissi- 

 milarity between those which are totally opposed in these 

 respects. And if this is the general law which has determi- 

 iied the distribution of theexisting organic world, there 

 must be no exceptions, no striking contradictions. Now 

 we have seen how totally the productions of New Guinea 

 difFer from those of the Western Tslands of the Archipe- 

 lago , say Borneo , as type of the rest , and as almost exactly 

 equal in area to New Guinea. This difFerence, it must 

 be well remarked, is not one of species, but of genera, 

 families, and whole orders. Yet it would be difficult 

 to point out two countries more exactly resembling 

 each other in climate and physical features. In nei- 

 ther is there any marked dry season , rain falling more 

 or less all the year round; both are near the equator, 



