Ian & Stuart's Australian Mac: Not for Sale/Another.not.for.sale (Australia).iso/hold me in your arms/ES Cyberama/Wallace-On New Species

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                                      1855
         ON THE LAW WHICH HAS REGULATED THE INTRODUCTION OF NEW SPECIES
                            by Alfred Russel Wallace
                                 February, 1855
                     (also known as the Sarawack Law. ed.)
      Geographical Distribution dependent on Geologic Changes.

  EVERY naturalist who has directed his attention to the subject of
the geographical distribution of animals and plants, must have been
interested in the singular facts which it presents. Many of these
facts are quite different from what would have been anticipated, and
have hitherto been considered as highly curious, but quite
inexplicable. None of the explanations attempted from the time of
Linnaeus are now considered at all satisfactory; none of them have
given a cause sufficient to account for the facts known at the time,
or comprehensive enough to include all the new facts which have
since been, and are daily being added. Of late years, however, a great
light has been thrown upon the subject by geological investigations,
which have shown that the present state of the earth and of the
organisms now inhabiting it, is but the last stage of a long and
uninterrupted series of changes which it has undergone, and
consequently, that to endeavour to explain and account for its present
condition without any reference to those changes (as has frequently
been done) must lead to very imperfect and erroneous conclusions.
  The facts proved by geology are briefly these:- That during an
immense, but unknown period, the surface of the earth has undergone
successive changes; land has sunk beneath the ocean, while fresh
land has risen up from it; mountain chains have been elevated; islands
have been formed into continents, and continents submerged till they
have become islands; and these changes have taken place, not once
merely, but perhaps hundreds, perhaps thousands of times:- That all
these operations have been more or less continuous, but unequal in
their progress, and during the whole series the organic life of the
earth has undergone a corresponding alteration. This alteration also
has been gradual, but complete; after a certain interval not a
single species existing which had lived at the commencement of the
period. This complete renewal of the forms of life also appears to
have occurred several times:- That from the last of the geological
epochs to the present or historical epoch, the change of organic
life has been gradual: the first appearance of animals now existing
can in many cases be traced, their numbers gradually increasing in the
more recent formations, while other species continually die out and
disappear, so that the present condition of the organic world is
clearly derived by a natural process of gradual extinction and
creation of species from that of the latest geological periods. We may
therefore safely infer a like gradation and natural sequence from
one geological epoch to another.
  Now, taking this as a fair statement of the results of geological
inquiry, we see that the present geographical distribution of life
upon the earth must be the result of all the previous changes, both of
the surface of the earth itself and of its inhabitants. Many causes,
no doubt, have operated of which we must ever remain in ignorance, and
we may, therefore, expect to find many details very difficult of
explanation, and in attempting to give one, must allow ourselves to
call into our service geological changes which it is highly probable
may have occurred, though we have no direct evidence of their
individual operation.
  The great increase of our knowledge within the last twenty years,
both of the present and past history of the organic world, has
accumulated a body of facts which should afford a sufficient
foundation for a comprehensive law embracing and explaining them
all, and giving a direction to new researches. It is about ten years
since the idea of such a law suggested itself to the writer of this
essay, and he has since taken every opportunity of testing it by all
the newly-ascertained facts with which he has become acquainted, or
has been able to observe himself. These have all served to convince
him of the correctness of his hypothesis. Fully to enter into such a
subject would occupy much space, and it is only in consequence of some
views having been lately promulgated, he believes, in a wrong
direction, that he now ventures to present his ideas to the public,
with only such obvious illustrations of the arguments and results as
occur to him in a place far removed from all means of reference and
exact information.


    A Law deduced from well-known Geographical and Geological Facts.

    The following propositions in Organic Geography and Geology give
the main facts on which the hypothesis is founded.


                             GEOGRAPHY
  1. Large groups, such as classes and orders, are generally spread
over the whole earth, while smaller ones, such as families and genera,
are frequently confined to one portion, often to a very limited
district.
  2. In widely distributed families the genera are often limited in
range; in widely distributed genera, well marked groups of species are
peculiar to each geographical district.
  3. When a group is confined to one district, and is rich in species,
it is almost invariably the case that the most closely allied
species are found in the same locality or in closely adjoining
localities, and that therefore the natural sequence of the species
by affinity is also geographical.
  4. In countries of a similar climate, but separated by a wide sea or
lofty mountains, the families, genera and species of the one are often
represented by closely allied families, genera and species peculiar to
the other.


                                GEOLOGY
  5. The distribution of the organic world in time is very similar
to its present distribution in space.
  6. Most of the larger and some small groups extend through several
geological periods.
  7. In each period, however, there are peculiar groups, found nowhere
else, and extending through one or several formations.
  8. Species of one genus, or genera of one family occurring in the
same geological time, are more closely allied than those separated
in time.
  9. As generally in geography no species or genus occurs in two
very distant localities without being also found in intermediate
places, so in geology the life of a species or genus has not been
interrupted. In other words, no group or species has come into
existence twice.
  10. The following law may be deduced from these facts:- Every
species has come into existence coincident both in space and time with
a pre-existing closely allied species.

  This law agrees with, explains and illustrates all the facts
connected with the following branches of the subject:- 1st. The system
of natural affinities. 2nd. The distribution of animals and plants
in space. 3rd. The same in time, including all the phaenomena of
representative groups, and those which Professor Forbes supposed to
manifest polarity. 4th. The phaenomena of rudimentary organs. We
will briefly endeavour to show its bearing upon each of these.


  The Form of a true system of Classification determined by this Law.

  If the law above enunciated be true, it follows that the natural
series of affinities will also represent the order in which the
several species came into existence, each one having had for its
immediate antitype a closely allied species existing at the time of
its origin. It is evidently possible that two or three distinct
species may have had a common antitype, and that each of these may
again have become the antitypes from which other closely allied
species were created. The effect of this would be, that so long as
each species has had but one new species formed on its model, the line
of affinities will be simple, and may be represented by placing the
several species in direct succession in a straight line. But if two or
more species have been independently formed on the plan of a common
antitype, then the series of affinities will be compound, and can only
be represented by a forked or many branched line. Now, all attempts at
a Natural classification and arrangement of organic beings show,
that both these plans have obtained in creation. Sometimes the
series of affinities can be well represented for a space by a direct
progression from species to species or from group to group, but it
is generally found impossible so to continue. There constantly occur
two or more modifications of an organ or modifications of two distinct
organs, leading us on to two distinct series of species, which at
length differ so much from each other as to form distinct genera or
families. These are the parallel series or representative groups of
naturalists, and they often occur in different countries, or are found
fossil in different formations. They are said to have an analogy to
each other when they are so far removed from their common antitype
as to differ in many important points of structure, while they still
preserve a family resemblance. We thus see how difficult it is to
determine in every case whether a given relation is an analogy or an
affinity, for it is evident that as we go back along the parallel or
divergent series, towards the common antitype, the analogy which
existed between the two groups becomes an affinity. We are also made
aware of the difficulty of arriving at a true classification, even
in a small and perfect group;- in the actual state of nature it is
almost impossible, the species being so numerous and the modifications
of form and structure so varied, arising probably from the immense
number of species which have served as antitype for the existing
species, and thus produced a complicated branching of the lines of
affinity, as intricate as the twigs of a gnarled oak or the vascular
system of the human body. Again, if we consider that we have only
fragments of this vast system, the stem and main branches being
represented by extinct species of which we have no knowledge, while
a vast mass of limbs and boughs and minute twigs and scattered
leaves is what we have to place in order, and determine the true
position each originally occupied with regard to the others, the whole
difficulty of the true Natural System of classification becomes
apparent to us.
  We shall thus find ourselves obliged to reject all those systems
of classification which arrange species or groups in circles, as
well as those which fix a definite number for the divisions of each
group. The latter class have been very generally rejected by
naturalists, as contrary to nature, notwithstanding the ability with
which they have been advocated; but the circular system of
affinities seems to have obtained a deeper hold, many eminent
naturalists having to some extent adopted it. We have, however,
never been able to find a case in which the circle has been closed
by a direct and close affinity. In most cases a palpable analogy has
been substituted, in others the affinity is very obscure or altogether
doubtful. The complicated branching of the lines of affinities in
extensive groups must also afford great facilities for giving a show
of probability to any such purely artificial arrangements. Their
death-blow was given by the admirable paper of the lamented Mr.
Strickland, published in the "Annals of Natural History," in which
he so cleverly showed the true synthetical method of discovering the
Natural System.


             Geographical Distribution of Organisms.

  If we now consider the geographical distribution of animals and
plants upon the earth, we shall find all the facts beautifully in
accordance with, and readily explained by, the present hypothesis. A
country having species, genera, and whole families peculiar to it,
will be the necessary result of its having been isolated for a long
period, sufficient for many series of species to have been created
on the type of pre-existing ones, which, as well as many of the
earlier-formed species, have become extinct, and thus made the
groups appear isolated. If in any case the antitype had an extensive
range, two or more groups of species might have been formed, each
varying from it in a different manner, and thus producing several
representative or analogous groups. The Sylviadae of Europe and the
Sylvicolidae of North America, the Heliconidae of South America and
the Euploeas of the East, the group of Trogons inhabiting Asia, and
that peculiar to South America, are examples that may be accounted for
in this manner.
  Such phaenomena as are exhibited by the Galapagos Islands, which
contain little groups of plants and animals peculiar to themselves,
but most nearly allied to those of South America, have not hitherto
received any, even a conjectural explanation. The Galapagos are a
volcanic group of high antiquity, and have probably never been more
closely connected with the continent than they are at present. They
must have been first peopled, like other newly-formed islands, by
the action of winds and currents, and at a period sufficiently
remote to have had the original species die out, and the modified
prototypes only remain. In the same way we can account for the
separate islands having each their peculiar species, either on the
supposition that the same original emigration peopled the whole of the
islands with the same species from which differently modified
prototypes were created, or that the islands were successively peopled
from each other, but that new species have been created in each on the
plan of the pre-existing ones. St. Helena is a similar case of a
very ancient island having obtained an entirely peculiar, though
limited, flora. On the other hand, no example is known of an island
which can be proved geologically to be of very recent origin (late
in the Tertiary, for instance), and yet possess generic or family
groups, or even many species peculiar to itself.
  When a range of mountains has attained a great elevation, and has so
remained during a long geological period, the species of the two sides
at and near their bases will be often very different, representative
species of some genera occurring, and even whole genera being peculiar
to one side, as is remarkably seen in the case of the Andes and
Rocky Mountains. A similar phaenomena occurs when an island has been
separated from a continent at a very early period. The shallow sea
between the Peninsula of Malacca, Java, Sumatra and Borneo was
probably a continent or large island at an early epoch, and may have
become submerged as the volcanic ranges of Java and Sumatra were
elevated. The organic results we see in the very considerable number
of species of animals common to some or all of these countries,
while at the same time a number of closely allied representative
species exist peculiar to each, showing that a considerable period has
elapsed since their separation. The facts of geographical distribution
and of geology may thus mutually explain each other in doubtful cases,
should the principles here advocated be clearly established.
  In all those cases in which an island has been separated from a
continent, or raised by volcanic or coralline action from the sea,
or in which a mountain-chain has been elevated in a recent
geological epoch, the phaenomena of peculiar groups or even of
single representative species will not exist. Our own island is an
example of this, its separation from the continent being
geologically very recent, and we have consequently scarcely a
species which is peculiar to it; while the Alpine range, one of the
most recent mountain elevations, separates faunas and floras which
scarcely differ more than may be due to climate and latitude alone.
  The series of facts alluded to in Proposition (3), of closely allied
species in rich groups being found geographically near each other,
is most striking and important. Mr. Lovell Reeve has well
exemplified it in his able and interesting paper on the Distribution
of the Bulimi. It is also seen in the Hummingbirds and Toucans, little
groups of two or three closely allied species being often found in the
same or closely adjoining districts, as we have had the good fortune
of personally verifying. Fishes give evidence of a similar kind:
each great river has its peculiar genera, and in more extensive genera
its groups of closely allied species. But it is the same throughout
Nature; every class and order of animals will contribute similar
facts. Hitherto no attempt has been made to explain these singular
phaenomena, or to show how they have arisen. Why are the genera of
Palms and of Orchids in almost every case confined to one
hemisphere? Why are the closely allied species of brownbacked
Trogons all found in the East, and the green-backed in the West? Why
are the Macaws and the Cockatoos similarly restricted? Insects furnish
a countless number of analogous examples;- the Goliathi of Africa, the
Ornithopterae of the Indian Islands, the Heliconidae of South America,
the Danaidae of the East, and in all, the most closely allied
species found in geographical proximity. The question forces itself
upon every thinking mind,- why are these things so? They could not
be as they are had no law regulated their creation and dispersion. The
law here enunciated not merely explains, but necessitates the facts we
see to exist, while the vast and long-continued geological changes
of the earth readily account for the exceptions and apparent
discrepancies that here and there occur. The writer's object in
putting forward his views in the present imperfect manner is to submit
them to the test of other minds, and to be made aware of all the facts
supposed to be inconsistent with them. As his hypothesis is one
which claims acceptance solely as explaining and connecting facts
which exist in nature, he expects facts alone to be brought to
disprove it, not a priori arguments against its probability.


            Geological Distribution of the Forms of Life.

  The phaenomena of geological distribution are exactly analogous to
those of geography. Closely allied species are found associated in the
same beds, and the change from species to species appears to have been
as gradual in time as in space. Geology, however, furnishes us with
positive proof of the extinction and production of species, though
it does not inform us how either has taken place. The extinction of
species, however, offers but little difficulty, and the modus operandi
has been well illustrated by Sir C. Lyell in his admirable
"principles." Geological changes, however gradual, must occasionally
have modified external conditions to such an extent as to have
rendered the existence of certain species impossible. The extinction
would in most cases be effected by a gradual dying-out, but in some
instances there might have been a sudden destruction of a species of
limited range. To discover how the extinct species have from time to
time been replaced by new ones down to the very latest geological
period, is the most difficult, and at the same time the most
interesting problem in the natural history of the earth. The present
inquiry, which seeks to eliminate from known facts a law which has
determined, to a certain degree, what species could and did appear
at a given epoch, may, it is hoped, be considered as one step in the
right direction towards a complete solution of it.


  High Organization of very ancient Animals consistent with this Law.

  Much discussion has of late years taken place on the question,
whether the succession of life upon the globe has been from a lower to
a higher degree of organization. The admitted facts seem to show
that there has been a general, but not a detailed progression.
Mollusca and Radiata existed before Vertebrata, and the progression
from Fishes to Reptiles and Mammalia, and also from the lower
mammals to the higher, is indisputable. On the other hand, it is
said that the Mollusca and Radiata of the very earliest periods were
more highly organized than the great mass of those now existing, and
that the very first fishes that have been discovered are by no means
the lowest organised of the class. Now it is believed the present
hypothesis will harmonize with all these facts, and in a great measure
serve to explain them; for though it may appear to some readers
essentially a theory of progression, it is in reality only one of
gradual change. It is, however, by no means difficult to show that a
real progression in the scale of organization is perfectly
consistent with all the appearances, and even with apparent
retrogression, should such occur.
  Returning to the analogy of a branching tree, as the best mode of
representing the natural arrangement of species and their successive
creation, let us suppose that at an early geological epoch any group
(say a class of the Mollusca) has attained to a great richness of
species and a high organization. Now let this great branch of allied
species, by geological mutations, be completely or partially
destroyed. Subsequently a new branch springs from the same trunk, that
is to say, new species are successively created, having for their
antitypes the same lower organized species which had served as the
antitypes for the former group, but which have survived the modified
conditions which destroyed it. This new group being subject to these
altered conditions, has modifications of structure and organization
given to it, and becomes the representative group of the former one in
another geological formation. It may, however, happen, that though
later in time, the new series of species may never attain to so high a
degree of organization as those preceding it, but in its turn become
extinct, and give place to yet another modification from the same
root, which may be of higher or lower organization, more or less
numerous in species, and more or less varied in form and structure
than either of those which preceded it. Again, each of these groups
may not have become totally extinct, but may have left a few
species, the modified prototypes of which have existed in each
succeeding period, a faint memorial of their former grandeur and
luxuriance. Thus every case of apparent retrogression may be in
reality a progress, though an interrupted one: when some monarch of
the forest loses a limb, it may be replaced by a feeble and sickly
substitute. The foregoing remarks appear to apply to the case of the
Mollusca, which, at a very early period, had reached a high
organization and a great development of forms and species in the
testaceous Cephalopoda. In each succeeding age modified species and
genera replaced the former ones which had become extinct, and as we
approach the present aera, but few and small representatives of the
group remain, while the Gasteropods and Bivalves have acquired an
immense preponderance. In the long series of changes the earth has
undergone, the process of peopling it with organic beings has been
continually going on, and whenever any of the higher groups have
become nearly or quite extinct, the lower forms which have better
resisted the modified physical conditions have served as the antitypes
on which to found the new races. In this manner alone, it is believed,
can the representative groups at successive periods, and the rising
and fallings in the scale of organization, be in every case explained.


             Objections to Forbes' Theory of Polarity.

  The hypothesis of polarity, recently put forward by Professor Edward
Forbes to account for the abundance of generic forms at a very early
period and at present, while in the intermediate epochs there is a
gradual diminution and impoverishment, till the minimum occurred at
the confines of the Palaeozoic and Secondary epochs, appears to us
quite unnecessary, as the facts may be readily accounted for on the
principles already laid down. Between the Palaeozoic and Neozoic
periods of Professor Forbes, there is scarcely a species in common,
and the greater part of the genera and families also disappear to be
replaced by new ones. It is almost universally admitted that such a
change in the organic world must have occupied a vast period of
time. Of this interval we have no record; probably because the whole
area of the early formations now exposed to our researches was
elevated at the end of the Palaeozoic period, and remained so
through the interval required for the organic changes which resulted
in the fauna and flora of the Secondary period. The records of this
interval are buried beneath the ocean which covers three-fourths of
the globe. Now it appears highly probable that a long period of
quiescence or stability in the physical conditions of a district would
be most favourable to the existence of organic life in the greatest
abundance, both as regards individuals and also as to variety of
species and generic group, just as we now find that the places best
adapted to the rapid growth and increase of individuals also contain
the greatest profusion of species and the greatest variety of
forms,- the tropics in comparison with the temperate and arctic
regions. On the other hand, it seems no less probable that a change in
the physical conditions of a district, even small in amount if
rapid, or even gradual if to a great amount, would be highly
unfavourable to the existence of individuals, might cause the
extinction of many species, and would probably be equally unfavourable
to the creation of new ones. In this too we may find an analogy with
the present state of our earth, for it has been shown to be the
violent extremes and rapid changes of physical conditions, rather than
the actual mean state in the temperate and frigid zones, which renders
them less prolific than the tropical regions, as exemplified by the
great distance beyond the tropics to which tropical forms penetrate
when the climate is equable, and also by the richness in species and
forms of tropical mountain regions which principally differ from the
temperate zone in the uniformity of their climate. However this may
be, it seems a fair assumption that during a period of geological
repose the new species which we know to have been created would have
appeared, that the creations would then exceed in number the
extinctions, and therefore the number of species would increase. In
a period of geological activity, on the other hand, it seems
probable that the extinctions might exceed the creations, and the
number of species consequently diminish. That such effects did take
place in connexion with the causes to which we have imputed them, is
shown in the case of the Coal formation, the faults and contortions of
which show a period of great activity and violent convulsions, and
it is in the formation immediately succeeding this that the poverty of
forms of life is most apparent. We have then only to suppose a long
period of somewhat similar action during the vast unknown interval
at the termination of the Palaeozoic period, and then a decreasing
violence or rapidity through the Secondary period, to allow for the
gradual repopulation of the earth with varied forms, and the whole
of the facts are explained. We thus have a clue to the increase of the
forms of life during certain periods, and their decrease during
others, without recourse to any causes but these we know to have
existed, and to effects fairly deducible from them. The precise manner
in which the geological changes of the early formations were
effected is so extremely obscure, that when we can explain important
facts by a retardation at one time and an acceleration at another of a
process which we know from its nature and from observation to have
been unequal,- a cause so simple may surely be preferred to one so
obscure and hypothetical as polarity.
  I would also venture to suggest some reasons against the very nature
of the theory of Professor Forbes. Our knowledge of the organic
world during any geological epoch is necessarily very imperfect.
Looking at the vast numbers of species and groups that have been
discovered by geologists, this may be doubted; but we should compare
their numbers not merely with those that now exist upon the earth, but
with a far larger amount. We have no reason for believing that the
number of species on the earth at any former period was much less than
at present; at all events the aquatic portion, with which geologists
have most acquaintance, was probably often as great or greater. Now we
know that there have been many complete changes of species; new sets
of organisms have many times been introduced in place of old ones
which have become extinct, so that the total amount which have existed
on the earth from the earliest geological period must have borne about
the same proportion to those now living, as the whole human race who
have lived and died upon the earth, to the population at the present
time. Again, at each epoch, the whole earth was no doubt, as now, more
or less the theatre of life, and as the successive generations of each
species died, their exuviae and preservable parts would be deposited
over every portion of the then existing seas and oceans, which we have
reason for supposing to have been more, rather than less, extensive
than at present. In order then to understand our possible knowledge of
the early world and its inhabitants, we must compare, not the area
of the whole field of our geological researches with the earth's
surface, but the area of the examined portion of each formation
separately with the whole earth. For example, during the Silurian
period all the earth was Silurian, and animals were living and
dying, and depositing their remains more or less over the whole area
of the globe, and they were probably (the species at least) nearly
as varied in different latitudes and longitudes as at present. What
proportion do the Silurian districts bear to the whole surface of
the globe, land and sea (for far more extensive Silurian districts
probably exist beneath the ocean than above it), and what portion of
the known Silurian districts has been actually examined for fossils?
Would the area of rock actually laid open to the eye be the thousandth
or the ten-thousandth part of the earth's surface? Ask the same
question with regard to the Oolite or the Chalk, or even to particular
beds of these when they differ considerably in their fossils, and
you may then get some notion of how small a portion of the whole we
know.
  But yet more important is the probability, nay almost the certainty,
that whole formations containing the records of vast geological
periods are entirely buried beneath the ocean, and for ever beyond our
reach. Most of the gaps in the geological series may thus be filled
up, and vast numbers of unknown and unimaginable animals, which
might help to elucidate the affinities of the numerous isolated groups
which are a perpetual puzzle to the zoologist, may there be buried,
until future revolutions may raise them in their turn above the
waters, to afford materials for the study of whatever race of
intelligent beings may then have succeeded us. These considerations
must lead us to the conclusion, that our knowledge of the whole series
of the former inhabitants of the earth is necessarily most imperfect
and fragmentary,- as much so as our knowledge of the present organic
world would be, were we forced to make our collections and
observations only in spots equally limited in area and in number
with those actually laid open for the collection of fossils. Now,
the hypothesis of Professor Forbes is essentially one that assumes
to a great extent the completeness of our knowledge of the whole
series of organic beings which have existed on the earth. This appears
to be a fatal objection to it, independently of all other
considerations. It may be said that the same objections exist
against every theory on such a subject, but this is not necessarily
the case. The hypothesis put forward in this paper depends in no
degree upon the completeness of our knowledge of the former
condition of the organic world, but takes what facts we have as
fragments of a vast whole, and deduces from them something of the
nature and proportions of that whole which we can never know in
detail. It is founded upon isolated groups of facts, recognizes
their isolation, and endeavours to deduce from them the nature of
the intervening portions.


                        Rudimentary Organs.

  Another important series of facts, quite in accordance with, and
even necessary deductions from, the law now developed, are those of
rudimentary organs. That these really do exist, and in most cases have
no special function in the animal economy, is admitted by the first
authorities in comparative anatomy. The minute limbs hidden beneath
the skin in many of the snake-like lizards, the anal hooks of the
boa constrictor, the complete series of jointed finger-bones in the
paddle of the Manatus and whale, are a few of the most familiar
instances. In botany a similar class of facts has long been
recognised. Abortive stamens, rudimentary floral envelopes and
undeveloped carpels, are of the most frequent occurrence. To every
thoughtful naturalist the question must arise, What are these for?
What have they to do with the great laws of creation? Do they not
teach us something of the system of Nature? If each species has been
created independently, and without any necessary relations with
pre-existing species, what do these rudiments, these apparent
imperfections mean? There must be a cause for them; they must be the
necessary results of some great natural law. Now, if, as it has been
endeavoured to be shown, the great law which has regulated the
peopling of the earth with animal and vegetable life is, that every
change shall be gradual; that no new creature shall be formed widely
differing from anything before existing; that in this, as in
everything else in Nature, there shall be gradation and harmony,- then
these rudimentary organs are necessary, and are an essential part of
the system of Nature. Ere the higher Vertebrata were formed, for
instance, many steps were required, and many organs had to undergo
modifications from the rudimental condition in which only they had
as yet existed. We still see remaining an antitypal sketch of a wing
adapted for flight in the scaly flapper of the penguin, and limbs
first concealed beneath the skin, and then weakly protruding from
it, were the necessary gradations before others should be formed fully
adapted for locomotion. Many more of these modifications should we
behold, and more complete series of them, had we a view of all the
forms which have ceased to live. The great gaps that exist between
fishes, reptiles, birds, and mammals would then, no doubt, be softened
down by intermediate groups, and the whole organic world would be seen
to be an unbroken and harmonious system.


                               Conclusion.

  It has now been shown, though most briefly and imperfectly, how
the law that "Every species has come into existence coincident both in
time and space with a pre-existing closely allied species," connects
together and renders intelligible a vast number of independent and
hitherto unexplained facts. The natural system of arrangement of
organic beings, their geographical distribution, their geological
sequence, the phaenomena of representative and substituted groups in
all their modifications, and the most singular peculiarites of
anatomical structure, are all explained and illustrated by it, in
perfect accordance with the vast mass of facts which the researches of
modern naturalists have brought together, and, it is believed, not
materially opposed to any of them. It also claims a superiority over
previous hypotheses, on the ground that it not merely explains, but
necessitates what exists. Granted the law, and many of the most
important facts in Nature could not have been otherwise, but are
almost as necessary deductions from it, as are the elliptic orbits
of the planets from the law of gravitation.


                                -THE END-
.