P R E F A C E .
A m o n g s t the Reptiles and Amphibians obtained by Mr. Darwin, in the Voyage
of the Beagle, there are several of great interest, not merely on account of their
novelty as newly discovered species, of which there are nearly thirty, or as
forming the types of genera not previously known, or of any remarkable peculiarity
of form, structure, or habit, although in all these respects many of them
are highly interesting ; but more particularly as serving to establish or confirm
several points connected with their geographical distribution.
From the structure of most of these animals and their consequent habits of
life, circumscribed as they are for the most p a rt in their locomotive powers, it
might reasonably be predicated th a t they would, upon the whole, exhibit as
distinct examples of restriction, with regard to their geographical boundaries,
as any class of vertebrated animals ; and th a t the intervention of seas and of
mountains would be sufficient to limit the range of a species. Such is in fact
usually the case; and not only is the same species not found in the Old and New
Continents, but, with very few exceptions, not even on the opposite sides of the
South American Continent, in which range Mr. Darwin’s discoveries have
principally been made. The occurrence, however, of Bufo Chilensis a t Rio
Janeiro and at Buenos Ayres on the eastern, and at Valparaiso and the Archipelago
of Chonos on the western side of the continent, shows an extent of distribution
exceedingly unusual if not absolutely unparalleled in this family. I t is,
however, still possible th a t further and more extended researches into the
characters of the animals in question, and an examination of individuals from
each locality a t various ages, may prove th a t there are two species, which have
been confounded with each other, and the anomaly may thus be removed.
B ut although the circumscribed range of a species may be accounted for by
the reasons above mentioned, and others of a restrictive nature, it is not so easy
to refer to any known or obvious cause the remarkable fact of a whole genus,
consisting of numerous species, being thus geographically limited. Vet this is a