104 EVOL UTION AND NA TUEAL THEOL OGY. 



productions of the various parts of the world, 

 we find that they fall under five or six great 

 faunas and floras, which appear at first sight 

 as if they might have originated in as many 

 centres. 



A naturalist can generally tell at a glance 

 from which continent, and often from what 

 country or even district, any collection of 

 natural objects has been brought. 



On descending to particulars, we find that 

 those species which have the greatest mutual re- 

 semblance generally inhabit adjacent countries, 

 whereas those which show less resemblance, are 

 brought from regions which are more widely 

 separated. Mountain ranges, and sometimes 

 even rivers, present an almost impassible barrier 

 to the spread of many species. An island near 

 a continent usually possesses very few species as 

 compared with the main land ; and these will be 

 nearly all identical, though some will probably 

 present at least well-marked varieties. But an 

 islan^ the middle of the ocean, which has 

 b' .rated from the main land for a long 



indeed, they were ever connected), 

 / produces still fewer species, nearly all 

 'i (except those which may happen to 



