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CHAP. XXIII.] SUMMARY AND CONCLUSION. 553
forms and their habitats, are entirely unnoticed, owing to the
productions of the same locality never being associated in our
museums and collections. A few such relations have been
brought to light by modern scientific travellers, but many more
remain to be discovered ; and there is probably no fresher and
more productive field still unexplored in Natural History. Most
of these curious and suggestive relations are to be found in the
productions of islands, as compared with each other, or with the
continents of which they form appendages ; but these can never
be properly studied, or even discovered, unless they are visibly
grouped together. When the birds, the more conspicuous families
of insects, and the land-shells of islands, are kept together so as
to be readily compared with similar associations from the adja-
cent continents or other islands, it is believed that in almost every
case there will be found to be peculiarities of form or colour
running through widely different groups, and strictly indicative
of local or geographical influences. Some of these coincident
variations have been alluded to in various parts of this work,
but they have never been systematically investigated. They
constitute an unworked mine of wealth for the enterprising
explorer ; and they may not improbably lead to the discovery of
some of the hidden laws (supplementary to Natural Selection),
which seem to be required, in order to account for many of the
external characteristics of animals.
In concluding his task, the author ventures to suggest, that
naturalists who are disposed to turn aside from the beaten track
of research, may find in the line of study here suggested a new
and interesting pursuit, not inferior in attractions to the lofty
heights of transcendental anatomy, or the bewildering mazes of
modern classification. And it is a study which will surely lead
them to an increased appreciation of the beauty and the harmony
of nature, and to a fuller comprehension of the complex relations
and mutual interdependence, which link together every animal
and vegetable form, with the ever-changing earth which supports
them, into one grand organic whole.