VICARIOUS FORMS. 223 



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 facilitated, 

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

 each species from a pair, but supposed them to be 

 created 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 fre- 

 quently appear under external conditions entirely dis- 

 similar ? 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 " **), Buffbn had already remarked the repe- 

 tition of the African in the American fauna ; how, for 

 example, 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 meet 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 separa- 

 tion of the habitats of their progenitors. 



