THE ADTANCEMEFT Ol" SCIEITCE. 79 



metrical ratio, to the bulk of the species. If a dry season be gradually prolonged, 

 the large mammal will suffer from the drought soor.er than the small cue : if such 

 alteratiDn of climate affect the quantity of vegetable food, the bulky herbivore 

 ■will first feel the effects of stinted nourishment; if neAV eiieinies are introduced, 

 the large and conspicuous quadruped or bird will fall a prey, while the smaller 

 species conceal themselves and escape. Smaller animals are usually also more 

 prolific than larger ones. '• The actual presence, therefore, of small species of 

 animals in countries where larger species of the same natural families formerly 

 existed, is not the con?equenee of any gradual diminution of the size of such 

 species, but is the result of circumstances which may be illustrated by the fable 

 of the ' Oak and the Reed ;' the smaller and feebler animals have bent and accom- 

 modated themselves to changes which have destroyed the larger species." No 

 doubt the type-form of any species is that r/bich is best adapted to ths? conditions 

 under which such species at the time exists j and as long as those conditions re- 

 main unchanged, so long will the type remain ; all varieties departing therefrom 

 being in the same ratio less adapted to the environing conditions of existence. 

 But, if those conditions change, then the variety of the species at an antecedent 

 date and state of things will become the type-form of the species at a later date, 

 and in an altered state of things. Observation of animals in a state of nature is 

 required to show their degree of plasticity, or the extent to which varieties do 

 arise: whereby grounds may be had for judging of the probability of the elastic 

 ligaments and joint-structnres of a feline foot, for example, being superinduced 

 upon tiie more simple structure of the toe with the nou retractile claw, according 

 to the principle of a succession of varieties in time. Observation of fossil re- 

 mains is also still needed to make known the ante-type=i, in which varieties, analo- 

 gous to the observed ones in existing species, might have occurred, so as to give 

 rise ultimately to such extreme forms as the Giraffe, for example. The aboriginal 

 laws of the geographical distribution of plants and animals have been modified 

 from of old by geological and the concomitant climatal changes; but they have 

 been much more disturbed by man since his introduction upon the globe. The 

 serviceable plants and animals which he has carried with him in his migrations' 

 have flourished and multiplied in lands the most remote from the habitats of the 

 aboriginal species. Man has, also, been the most potent and intelligible cause of 

 extirpation of species within historic times. He alone, with one of the beasts 

 which he has domesticated — the dog — is cosmopolitan. The human species ia 

 represented by a few well-marked varieties ; and there is a certain amount of cor- 

 respondence between their localities and general zoological provinces. But, with 

 regard to the alleged conformity between the geographical distribution of mars 

 and animals, which has of late been systematically enunciated, and made by 

 Agassiz, in Gliddon & Nott's ' Varieties of Mankind,' the basis of deductions a» 

 to the origin and distinction of the human varieties : many facts might be cited, 

 affecting the conformity of the distribution of man with that of the lower animal* 

 and plants, as absolutely enunciated in some recent works. Nor can we be sur- 

 prised to find that the migratory instincts of the human species, with the peculiar 

 endowment of adaptiveness to all climates, should have produced modifications iq 

 geographical distribution to which the lower forms of living nature have not been 



