DISTRIBUTION. 319 



veiling, for instance, from north to south never fails to be 

 struck by the manner in which successive groups of beings, 

 specifically distinct, yet clearly related, replace each other. 

 He hears from closely allied, yet distinct kinds of birds, 

 notes nearly similar, and sees their nests similarly constructed, 

 but not quite alike, with eggs coloured in nearly the same 

 manner. The plains near the Straits of Magellan are inhabit- 

 ed by one species of Rhea (American Ostrich), and north- ward 

 the plains of La Plata by another species of the same genus ; 

 and not by a true ostrich or emeu, like those found in Africa 

 and Australia under the same latitude. On these same plains 

 of La Plata, we see the agouti and bizcacha, animals having 

 nearly the same habits as our hares and rabbits and belonging 

 to the same order of Rodents, but they plainly display an 

 American type of structure. We ascend the lofty peaks of 

 the Cordillera and we find an alpine species of bizcacha ; we 

 look to the waters, and we do not find the beaver or musk- 

 rat, but the coypu and capybara, rodents of the American 

 type. Innumerable other instances could be given. If we 

 look to the islands off the American shore, however much 

 they may differ in geological structure, the inhabitants, though 

 they may be all peculiar species, are essentially American." 



"What is the generalization that expresses these two groups 

 of facts ? On the one hand, we have similarly-conditioned, 

 and sometimes nearly-adjacent, areas, occupied by quite dif- 

 ferent Faunas. On the other hand, we have areas remote from 

 eaoh other in latitude, and contrasted in soil as well as climate, 

 which are occupied by closely-allied Faunas. Clearly then, aa 

 like organisms are not universally, or even generally, found 

 in like habitats ; nor very unlike organisms, in very unlike 

 habitats ; there is no manifest pre-determined adaptation of 

 the organisms to the habitats. The organisms do not occur 

 in such and such places, solely because they are either spe- 

 cially fit for these places, or more fit for them than all other 

 organisms. 



The induction under which these facts come, and which 



