VICARIOUS FORMS. 



22j 



the geographical horizon and the profundity of special 

 research was the more careful ascertainment of the 

 regions of distribution of animal and vegetal families, 

 and of their more prominent species, in which, as we 

 have already said, either no questions were asked as to 

 the causes of distribution, or the matter was facihtated, 

 as by Louis Agassiz, who did not, like Linnaeus, derive 

 each species from a pair, but supposed them to be cre- 

 ated in suitable numbers of individuals in their own 

 regions of distribution. It cannot be expected that any 

 solution was hereby given to the questions which now 

 force themselves upon us, such as why, under like natural 

 conditions, like species are not always to be found, and 

 conversely? Why very similar species frequently appear 

 under external conditions entirely dissimilar? What is 

 to be thought of the mutual relations of the so-called 

 vicarious forms? &c. 



As Riitimeyer has recently observed, in his excellent 

 treatise " On the Derivation of the Animal World of 

 Switzerland " (" Ueber die Herkunft der schweizerischen 

 Thierwelt " *"), Bufifon had already remarked the repeti- 

 tion of the African in the American fauna; how, for ex- 

 ample, the lama is a juvenescent and feeble copy of the 

 camel; and how the puma of the New represents the 

 lion of the Old World. Still, by the mere word " repre- 

 sentative " or " vicarious form " nothing is gained, and 

 a true apprehension of these facts is obtained singly and 

 solely if we theet the inquiry with the assumption that 

 camel and lama, puma and lion, are of common deriva- 

 tion, and that their diverse development was in the lapse 

 of time favoured and determined by the separation of 

 the habitats of their progenitors. 



