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 Linnteus, derive 
each species from a pair, but supposed them to be 
created in suitable numbers of individuals in thcir 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” ®), Buffon had already remarked the repe- 
tition of the African in the American fauna; how, for 
example, the lamais 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. 
