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Geographical Distribution of Crustacea. A8 
Oriental tropies, as well as in the European temperate regions, 
and the ''emperate zone of the South Pacific and Indian Oceans. 
XII. With respect to the creation of identical species in dis- 
fant regions, we would again point to its direct dependence on a 
near identity of physical condition. Although we cannot admit 
that cireumstances or physical forces have ever created a species 
(as like can only beget like, and physical force must result sim- 
ply in physical force), and while we see in all nature the free act 
of the Divine Being, we may still believe the connexion between 
the calling into existence of a species and the physical eircum- 
stances surrounding it to be as intimate nearly as cause and effect. 
The Creator has, in infinite skill, adapted each species to its place, 
and the whole into a system of admirable harmony and perfection. 
In His wisdom, any difference of physical condition and kind of 
food at hand, is sufficient to require some modification of the in- 
timate structure of species, and this difference is expressed in 
the form of the body or members, so as to produce an exactness 
of adaptation, which we are far from fully perceiving or compre- 
hending with our present knowledge of the relations of species 
to their habitats. 3g 
When therefore we find the same species in regions of unlike 
physical character, as, for example, in the seas of the Canaries 
and Great Britain—regions physically so unlike—we have strong 
. reason for attributing the diffusion of the species to migration. 
'l'he difference between the Mediterranean and Great Britain 
may require the same conclusion for the species common to these 
| seas. 'lhey are so far different, that we doubt whether species 
| created independently in the two could have been identical, or 
| even have had that resemblance that exists between varieties ; 
for this resemblance 1s usually of the most trivial kind, and affects 
only the least essential of the parts of a species. 
E 'l'he continental species of Crustacea from the interior of dif- 
| — ferent continents, are not in any case known to be identical ; and 
-it is well understood that the zoological provinces and districts of 
the land are of far more limited extent than those of the ocean. 
" 'he physical differences of the former are far more striking than 
"those of the latter. As we have observed elsewhere, the varie- 
ties of climate are greater; the elevation above the sea may vary 
widely ; and numberless are the diversities of soil and its condi- 
tions, and the circumstances above and within it. Hence, as the 
creation of each species has had reference most intimately to each 
| . and all of these conditions, as well as to other prospective ends, an 
| identity between distant continental regions is seldom to be found, 
| and the characteristic groups of genera are very widely diverse. 
Comparatively few genera of Insects have as wide a range as those 
of Crustacea ; and species with rare exceptions, have very narrow 
limits. Where the range of a species in this class is great, we 
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