duction. We must proceed to establish inferences from particular
facts, and fro nil a survey of what actually is known in
respect to each different department of the animal creation.
From the known facts we shall be enabled to draw inferences
which will be sound and firm, as far as they relate to particular
^departments of nature, whatever may be the case in
other regions yet involved in obscurity.
I shall now trace the phenomena connected with the dispersion
of animals, arranging them according to the elements
and the departments of the world inhabited severally by particular
tribes, rather than the order of the zoological system:
I proceed, first, to insects and birds; secondly, to marine
animals; thirdly, to animals of the land, including mammifers
and reptiles.
Section I I.— O f the dispersion o f Insects.
The local existence of insects is closely connected' with
that of the plants and animals, which afford them sustenance,
and which, in many instances, furnish them their only places
of concealment and abode.' We should, therefore, previous
to any inquiry respecting facts which particularly relate to insects;
expect to find the same laws prevailing: in this p art'o f
the creation, as in the dispersion of vegetable tribes, and in
that of other animals. A great number of inseets are espe*.
cially limited in the sphere of their existence by the presence
of particular plants. With the exception of mosses, Edges,
and lichenosae, whieh are, in a great measure, exempted from
contributing to the-support of the insect tribes, -there are few
species in the vegetable creation which are not destined
to afford habitation and sustenance to one- or more species,
and in numerous. examples, several different kinds of insects
are appropriated to one plant. One half at least of the insect
tribes are thus limited to particular regions, since it appears,
according to M. M. Kirby and Spence, that phytiborous
and carnivorous insects exist in nearly equal proportions.
But the remaining half are not much more at large with
respect to the sphere of their existence, since the animals on
which they feed can in general be supported only under given
conditions of nutriment and -climate, which are themselves
determined by localities. The noxious inseets which man
carries with him are said to be the only kinds which are universal.
Fabricius had some knowledge of the geographical distribution
of the insect tribes and of tjieir local relations, but the
subject had never been fully investigated until this, as well
as most other questions in the natural history of-the- insects
land arachnides occupied the attention-of M. Latreille. The
^following are the general conclusions of thisocelebrated naturalist,
with respect to the dispersion of species in this department
of nature;*
1 . The whole'Or a very great number of the arachnides and
insects inhabiting countries of which the temperature and the
soil are the same, but separated^ by/grëàt^distanc.^s| are composed,
in général; n f differfent species, if the'countries are
under the same parallels. AlL th ë ; insëèts and arachnides
which have beCn brought from the eastern parts of '#siâ,-fas
China, are distinct from tKbsb *of Europe and Africa, whatever
the latitudes and temperaturd#éf the Asiatiecbuntriesimay be.
2. The greatest part of the$sMie animals differ,-bèsidès, specifically,
when-the’countries whiéh they inhabit having a Similarity
in the ’ soil andytempèrature are separated one from
another, the differences of latitude being of no consequence;
by natural barriers which interrupt the communication between
these animals ô'r render it difficult ; SUC® as seaè, lofty chains
of mountains, and va?st deserts. The arachnides; -insects;!and
even the reptiles of America and of New' Holland, cannot be
confounded with the animals of the* same' classes inhabiting
the old continent. The insects of the United States, although
often very similar to ours, are different in- some characters.
Thus the tribes which inhabit the kingdoms of New Grenada,
and of Peru, countries near to Guiana and likewise equinoctial,
are yet in a great measure différent from those Of Guiana,
separated from them by the Cordillera which d iv id ^ the climates
of these countries. In passirigfrom Piémont into France
* Introductiöh à la Géographie Géhérale des Insectes et des Arachnides; par
P . A. Latreille. Memoires du Muséum d’Hist. .Nat. toih. ii£ U