re THE
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“ORIGIN OF SPECIES
BY MEANS OF NATURAL SELECTION
OR THE PRESERVATION OF FAVORED RACES IN
THE STRUGGLE FOR LIFE
OU BY
CHARLES DARWIN, M. ne trp. a R.S.
|
WITH ADDITIONS AND CORRECTIONS
FROM SIXTH AND LAST ENGLISH EDITION
IN TWO VOLUMES
VOLUME II
NEW YORK
D. APPLETON AND. COMP-AWN ¥
1889
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CONTENTS OF VOL. IL.
CHAPTER IX,
HYBRIDISM.
Distinction between the sterility of first crosses and of hybrids—
Sterility various in degree, not universal, affected by close
interbreeding, removed by domestication—Laws governing the
sterility of hybrids—Sterility not a special endowment, but.
incidental on other differences, not accumulated by natural
selection—Causes of the sterility of first crosses and of hybrids
—Parallelism between the effects of changed conditions of
life and of crossing—Dimorphism and Trimorphism—Fertility
- of varieties when crossed, and of their mongrel offspring not
universal—Hybrids and mongrels compared independently of
their fertility—Summary «<2. s,s o » Page 1
CHAPTER Xe
ON THE IMPERFECTION OF THE GEOLOGICAL RECORD.
On the absence of intermediate varieties at the present day—On
the nature of extinct intermediate varieties; on their number
—On the lapse of time, as inferred from the rate of denudation
and of deposition—On the lapse of time as estimated by years
—On the poorness of our paleontological collections—On the
intermittence of geological formations—On the denudation of
granitic areas—On the absence of intermediate varieties in any
one formation—On the sudden appearance of groups of species
—On their sudden appearance in the lowest known fossiliferous
strata—Antiquity of the habitable earth .. .. .. wo 48
iv
CONTENTS.
CHAPTER Xi.
On THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS.
On the slow and successive appearance of new species—On their
different rates of change—Species once lost do not reappear—
Groups of species follow the same general rules in their appear-
ance and disappearance as do single species—On Extinction—
On simultaneous changes in the forms of life throughout the
world—On the affinities of extinct species to each other and to
living species—On the state of development of ancient forms—
On the succession of the same types within the same areas—
Summary of preceding and present chapter . . Page 89
CHAPTER XI.
GEOGRAPHICAL DISTRIBUTION.
Present distribution cannot be accounted for by differences in
physical conditions—Importance of barriers—Affinity of the
productions of the same continent—Centres of creation—Means
of dispersal, by changes of climate and of the level of the land,
and by occasional means—Dispersal during the Glacial period
—Alternate Glacial periods in the north and south .. 129
CHAPTER XII.
GEOGRAPHICAL DistTrRIsuTION—continued.
Distribution of fresh-water productions—On the inhabitants of
oceanic islands—Absence of Batrachians and of terrestrial
Mammals—On the relation of the inhabitants of islands to
those of the nearest mainland—On colonisation from the nearest
source with subsequent modification—Summary of the last and
present chapier’..° «. es “so on cs os as aeeuee
CONTENTS. V
CHAPTER XIV.
MoutruaL AFFINITIES OF OrGANIC BEINGS : MorRPHOLOGY :
EMBRYOLOGY : RUDIMENTARY ORGANS.
CLASSIFICATION, groups subordinate to groups—Natural system—
Rules and difficulties in classification, explained on the theory
of descent with modification—Classification of varieties—
Descent always used in classification—Analogical or adaptive
characters—A ffinities, general, complex, and radiating—Ex-
tinction separates and defines groups—MorpHonoey, between
members of the same class, between parts of the same
individual—Emsryro.oey, laws of, explained by variations not
supervening at any early age, and being inherited at a
corresponding age—RUDIMENTARY ORGANS; their origin ex-
plained— summary, “<50- 6 ee ne sy een en ae 202
CHAPTER XV.
RECAPITULATION AND CONCLUSION.
Recapitulation of the objections to the theory of Natural Selection
—Recapitulation of the general and special circumstances in
its favour—Causes of the general belief in the immutability of
species—How far the theory of Natural Selection may be
extended—Effects of its adcption on the study of Natural
History—Concluding remarks :. .. .. «ss «0 0 200
GLOSSARY OF ScCrENTIFIC: TERMS). (2. os ES ee en
INDEX oe se te ae ne asp ae be ao aq at ae 323
ORIGIN OF SPECIES.
CHAPTER IX.
HYBRIDISM.
Distinction between the sterility of first crosses and of hybrids—
Sterility various in degree, not universal, affected by close inter-
breeding, removed by domestication—Laws governing the
sterility of hybrids—Sterility not a special endowment, but
incidental on other differences, not accumulated by natural
selection—Causes of the sterility of first crosses and of hybrids
—Parallelism between the effects of changed conditions of life
and of crossing—Dimorphism and trimorphism—Fertility of
varieties when crossed and of their mongrel offspring not uni-
versal— Hybrids and mongrels compared independently of their
fertility Summary.
THE view commonly entertained by naturalists is that
species, when intercrossed, have been specially endowed
with sterility, in order to prevent their confusion. This
view certainly seems at first highly probable, for species
living together could hardly have been kept distinct had
they been capable of freely crossing. The subject is in
many ways important for us, more especially as the
sterility of species when first crossed, and that of their
hybrid offspring, cannot have been acquired, as I shall
show, by the preservation of successive profitable
2 HYBRIDISM. (Cuap. IX.
degrees of sterility. It is an incidental result of
differences in the reproductive systems of the parent-
species.
In treating this subject, two classes of facts, to a large
extent fundamentally different, have generally been
confounded ; namely, the sterility of species when first
crossed, and the sterility of the hybrids produced from
them.
Pure species have of course their organs of reproduc-
tion in a perfect condition, yet when intercrossed they
produce either few or no offspring. Hybrids, on the
other hand, have their reproductive organs functionally
impotent, as may be clearly seen in the state of the
male element in both plants and animals; though the
formative organs themselves are perfect in structure, as
far as the microscope reveals. In the first case the two
sexual elements which go to form the embryo are
perfect; in the second case they are either not at all
developed, or are imperfectly developed. This distinc-
tion is important, when the cause of the sterility, which
is common to the two cases, has to be considered. The
distinction probably has been slurred over, owing to the
sterility in both cases being looked on as a special
endowment, beyond the province of our reasoning
powers.
The fertility of varieties, that is of the forms known
or believed to be descended from common parents, when
crossed, and likewise the fertility of their mongrel
offspring, is, with reference to my theory, of equal
importance with the sterility of species; for it seems
to make a broad and clear distinction between varieties
and species.
Degrees of Sterility —First, for the sterility of species
Cuap. IX.] DEGREES OF STERILITY. 3
when crossed and of their hybrid offspring. It is
impossible to study the several memoirs and works
of those two conscientious and admirable observers,
Koélreuter and Gartner, who almost devoted their lives
to this subject, without being deeply impressed with the
high generality of some degree of sterility. Kolreuter
makes the rule universal; but then he cuts the knot,
for in ten cases in which he found two forms, considered
by most authors as distinct species, quite fertile
together, he unhesitatingly ranks them as varieties.
Gartner, also, makes the rule equally universal; and he
disputes the entire fertility of Kolreuter’s ten cases.
But in these and in many other cases, Gartner is
obliged carefully to count the seeds, in order to show
that there is any degree of sterility. He always
compares the maximum number of seeds produced by
two species when first crossed, and the maximum
produced by their hybrid offspring, with the average
number produced by both pure parent-species in a state
of nature. But causes of serious error here intervene:
a plant, to be hybridised, must be castrated, and, what
is often more important, must be secluded in order to
prevent pollen being brought to it by insects from other
plants. Nearly all the plants experimented on by
Gartner were potted, and were kept in a chamber in his
house. That these processes are often injurious to the
fertility of a plant cannot be doubted; for Gartner gives
in his table about a score of cases of plants which he
castrated, and artificially fertilised with their own
pollen, and (excluding all cases such as the Leguminose,
in which there is an acknowledged difficulty in the
manipulation) half of these twenty plants had their
fertility in some degree impaired. Moreover, as
4 HYBRIDISM. ' [Cuap. IX.
Gartner repeatedly crossed some forms, such as the
common red and blue pimpernels (Anagallis arvensis
and ccerulea), which the best botanists rank as varieties,
and found them absolutely sterile, we may doubt
whether many species are really so sterile, when
intercrossed, as he believed.
It is certain, on the one hand, that the ee of
various species when crossed is so different in degree
and graduates away so insensibly, and, on the other
hand, that the fertility of pure species is so easily
affected by various circumstances, that for all practical
purposes it is most difficult to say where perfect fertility
ends and sterility begins. I think no better evidence
of this can be required than that the two most
experienced observers who have ever lived, namely
K6lreuter and Gartner, arrived at diametrically opposite
conclusions in regard to some of the very same forms.
It is also most instructive to compare—but I have not
space here to enter on details—the evidence advanced
by our best botanists on the question whether certain
doubtful forms should be ranked as species or varieties,
with the evidence from fertility adduced by different
hybridisers, or by the same observer from experiments
made during different years. It can thus be shown
that neither sterility nor fertility affords any certain
distinction between species and varieties. The evidence
from this source graduates away, and is doubtful in the
same degree as is the evidence derived from other
constitutional and structural differences.
In regard to the sterility of hybrids in successive
generations ; though Gartner was enabled to rear some
hybrids, carefully guarding them from a cross with
either pure parent, for six or seven, and in one ease for
Cuap. IX.] DEGREES OF STERILITY. 5
ten generations, yet he asserts positively that their
fertility never increases, but generally decreases greatly
and suddenly. With respect to this decrease, it may
first be noticed that when any deviation in structure or
constitution is common to both parents, this is often -
transmitted in an augmented degree to the offspring;
and both sexual elements in hybrid plants are already
affected in some degree. But I believe that their
fertility has been diminished in nearly all these cases
by an independent cause, namely, by too close inter-
breeding. I have made so many experiments and
collected so many facts, showing on the one hand that
an occasional cross with a distinct individual or variety
increases the vigour and fertility of the offspring, and on
the other hand that very close interbreeding lessens
their vigour and fertility, that I cannot doubt the
correctness of this conclusion. Hybrids are seldom
raised by experimentalists in great numbers; and as the
parent-species, or other allied hybrids, generally grow
in the same garden, the visits of insects must be
carefully prevented during the flowering season: hence
hybrids, if left to themselves, will generally be fertilised
during each generation by pollen from the same flower ;
and this would probably be injurious to their fertility,
already lessened by their hybrid origin. I am strength-
ened in this conviction by a remarkable statement
repeatedly made by Gartner, namely, that if even the —
less fertile hybrids be artificially fertilised with hybrid
pollen of the same kind, their fertility, notwithstanding
the frequent ill effects from manipulation, sometimes
decidedly increases, and goes on increasing. Now, in
the process of artificial fertilisation, pollen is as often
taken by chance (as I know from my own experience)
6 HYBRIDISM. (Car. IX.
from the anthers of another flower, as from the anthers
of the flower itself which is to be fertilised; so that a
cross between two flowers, though probably often on the
same plant, would be thus effected. Moreover, when-
ever complicated experiments are in progress, so careful
an observer as Gartner would have -castrated his
hybrids, and this would have ensured in each generation
a cross with pollen from a distinct flower, either from
the same plant or from another plant of the same hybrid
nature. And thus, the strange fact of an increase of fer-
tility in the successive generations of artificially fertilised
hybrids, in contrast with those spontaneously self-
fertilised, may, as I believe, be accounted for by too close
interbreeding having been avoided.
Now let us turn to the results arrived at by a third
most experienced hybridiser, namely, the Hon. and Rev.
W. Herbert. He is as emphatic in his conclusion that
some hybrids are perfectly fertile—as fertile as the pure
parent-species—as are Kolreuter and Gartner that some
degree of sterility between distinct species is a universal
law of nature. He experimented on some of the very
same species as did Gartner. The difference in their
results may, I think, be in part accounted for by
Herbert’s great horticultural skill, and by his having
hot-houses at his command. Of his many important
statements I will here give only a single one as an
example, namely, that “every ovule in a pod of Crinum
capense fertilised by C. revolutum produced a plant,
which I never saw to occur in a case of its natural
fecundation.” So that here we have perfect or even
more than commonly perfect fertility, in a first cross
between two distinct species.
This case of the Crinum leads me to refer to a
Cuar. IX.J DEGREES OF STERILITY. 7
singular fact, namely, that individual plants of certain
species of Lobelia, Verbascum and Passiflora, can easily
be fertilised by pollen from a distinct species, but not
by pollen from the same plant, though this pollen can
be proved to be perfectly sound by fertilising other
plants or species. In the genus Hippeastrum, in
Corydalis as shown by Professor Hildebrand, in various
orchids as shown by Mr. Scott and Fritz Miller, all the
individuals are in this peculiar condition. So that with
some species, certain abnormal individuals, and in other
species all the individuals, can actually be hybridised
much more readily than they can be fertilised by pollen
from the same individual plant! To give one instance,
a bulb of Hippeastrum aulicum produced four flowers ;
three were fertilised by Herbert with their own pollen,
and the fourth was subsequently fertilised by the pollen
of a compound hybrid descended from three distinct
species: the result was that “the ovaries of the three
first flowers soon ceased to grow, and after a few days
perished entirely, whereas the pod impregnated by the
pollen of the hybrid made vigorous growth and rapid
progress to maturity, and bore good seed, which
vegetated freely.” Mr. Herbert tried similar experi-
ments during many years, and always with the same
result. These cases serve to show on what slight and
mysterious causes the lesser or greater fertility of a
species sometimes depends.
The practical experiments of horticulturists, though
not made with scientific precision, deserve some notice.
It is notorious in how complicated a manner the
species of Pelargonium, Fuchsia, Calceolaria, Petunia,
Rhododendron, &c., have been crossed, yet many of
these hybrids seed freely. For instance, Herbert
19
8 HYBRIDISM. [Cuap. IX,
asserts that a hybrid from Calceolaria integrifolia and
plantaginea, species most widely dissimilar in general
habit, “reproduces itself as perfectly as if it had been a
natural species from the mountains of Chili” TI have
taken some pains to ascertain the degree of fertility of
some of the complex crosses of Rhododendrons, and I
am assured that many of them are perfectly fertile.
Mr. C. Noble, for instance, informs me that he raises
stocks for grafting from a hybrid between Rhod.
ponticum and catawbiense, and that this hybrid “seeds
as freely as it is possible to imagine.” Had hybrids
when fairly treated, always gone on decreasing in fertility
in each successive generation, as Gartner believed to be
the case, the fact would have been notorious to nursery-
men. MHorticulturists raise large beds of the same
hybrid, and such alone are fairly treated, for by insect
agency the several individuals are allowed to cross
freely with each other, and the injurious influence of
close interbreeding is thus prevented. Any one may
readily convince himself of the efficiency of insect-
agency by examining the flowers of the more sterile
kinds of hybrid Rhododendrons, whieh produce no
pollen, for he will find on their stigmas plenty of pollen
brought from other flowers.
In regard to animals, much fewer experiments have
been carefully tried than with plants. If our systematic
arrangements can be trusted, that is, if the genera of
animals are as distinct from each other as are the genera
of plants, then we may infer that animals more widely
distinct in the scale of nature can be crossed more
easily than in the case of plants; but the hybrids
themselves are, I think, more sterile. It should,
however, be borne in mind that, owing to few animals
Cuar. IX.] PEGREES OF STERILITY. 9
breeding freely under confinement, few experiments
have been fairly tried: for instance, the canary-bird has
been crossed with nine distinct species of finches, but,
as not one of these breeds freely in confinement, we
have no right to expect that the first crosses between
them and the canary, or that their hybrids, should be
perfectly fertile. Again, with respect to the fertility
in successive generations of the more fertile hybrid
animals, I hardly know of an instance in which two
families of the same hybrid have been raised at the
same time from different parents, so as to avoid the ill
effects of close interbreeding. On the contrary, brothers
and sisters have usually been crossed in each successive
generation, in opposition to the constantly repeated
admonition of every breeder. And in this case, it is
not at all surprising that the inherent sterility in the
hybrids should have gone on increasing.
Although I know of hardly any thoroughly well-
authenticated cases of perfectly fertile hybrid animals, I
have reason to believe that the hybrids from Cervulus
vaginalis and Reevesii, and from Phasianus colchicus
with P. torquatus, are perfectly fertile. M. Quatrefages
states that the hybrids from two moths (Borabyx
cynthia and arrindia) were proved in Paris to be fertile
inter se for eight generations. It has lately been
asserted that two such distinct species as the hare and
rabbit, when they can be got to breed together, produce
offspring, which are highly fertile when crossed with
one of the parent-species. The hybrids from the
common and Chinese geese (A. cygnoides), species
which are so different that they are generally ranked in
distinct genera, have often bred in this country with
either pure parent, and in one single instance they have
10 HYBRIDISM ~ fCuap. IX.
bred inter se. This was effected by Mr. Eyton, who
raised two hybrids from the same parents, but from
different hatches; and from these two birds he raised
no less than eight hybrids (grandchildren of the pure
geese) from one nest. In India, however, these cross-
bred geese must be far more fertile; for I am assured
by two eminently capable judges, namely Mr. Blyth and
Capt. Hutton, that whole flocks of these crossed geese
are kept in various parts of the country; and as they
are kept for profit, where neither pure parent-species
exists, they must certainly be highly or perfectly fertile.
With our domesticated animals, the various races
when crossed together are quite fertile; yet in many
cases they are descended from two or more wild species.
From this fact we must conclude either that the
aboriginal parent-species at first produced perfectly
fertile hybrids, or that the hybrids subsequently reared
under domestication became quite fertile. This latter
alternative, which was first propounded by Pallas, seems
by far the most probable, and can, indeed, hardly be
doubted. It is, for instance, almost certain that our
dogs are descended from several wild stocks; yet. with
perhaps the exception of certain indigenous domestic
dogs of South America, all are quite fertile together;
but analogy makes me greatly doubt, whether the
several aboriginal species would at first have freely bred
together and have produced quite fertile hybrids. So
again I have lately acquired decisive evidence that the
crossed offspring from the Indian humped and common
cattle are inter se perfectly fertile; and from the
observations by Riitimeyer on their important osteo-
logical differences, as well as from those by Mr. Blyth
on their differences in habits, voice, constitution, &c.,
Cuap. IX.] DEGREES OF STERILITY. 11
these two forms must be regarded as good and distinct
species. The same remarks may be extended to the two
chief races of the pig. We must, therefore, either give
up the belief of the universal sterility of species when
crossed ; or we must look at this sterility in animals,
not as an indelible characteristic, but as one capable of
being removed by domestication.
Finally, considering all the ascertained facts on the
intercrossing of plants and animals, it may be concluded
that some degree of sterility, both in first crosses and in
hybrids, is an extremely general result; but that it
cannot, under our present state of knowledge, be con-
sidered as absolutely universal.
Laws governing the Sterility of first Crosses and of
Hybrids.
=
We will now consider a little more in detail the laws
governing the sterility of first crosses and of hybrids.
Our chief object will be to see whether or not these
laws indicate that species have been specially endowed
with this quality, in order to prevent their crossing and
blending together in utter confusion. The following
conclusions are drawn up chiefly from Gartner’s ad-
mirable work on the hybridisation of plants. I have
taken much pains to ascertain how far they apply to
animals, and, considering how scanty our knowledge is
in regard to hybrid animals, i have been surprised to
find how generally the same rules apply to both
kingdoms.
It has been already remarked, that the decree of
fertility, both of first crosses and of hybrids, graduates
from zero to perfect fertility. It is surprising in how
{2 LAWS GOVERNING THE STERILITY (Cuap. IX.
many curious ways this gradation can be shown; but
only the barest outline of the facts can here be given.
When pollen from a plant of one family is placed on
the stigma of a plant of a distinct family, it exerts no
more influence than so much inorganic dust. From
this absolute zero of fertility, the pollen of different
species applied to the stigma of some one species of the
same genus, yields a perfect gradation in the number
of seeds produced, up to nearly complete or even quite
complete fertility; and, as we have seen, in certain
abnormal cases, even to an excess of fertility, beyond
that which the plant’s own pollen produces. So in
hybrids themselves, there are some which never have
produced, and probably never would produce, even
with the pollen of the pure parents, a single fertile
seed: but in some of these cases a first trace of fertility
may be detected, by the pollen of one of the pure
parent-species causing the flower of the hybrid to
wither earlier than it otherwise would have done;
and the early withering of the flower is well known
to be a sign of incipient fertilisation. From this
extreme degree of sterility we have self-fertilised
hybrids producing a greater and greater number of
seeds up to perfect fertility.
The hybrids raised from two species which are very
difficult to cross, and which rarely produce any off-
spring, are generally very sterile; but the parallelism
between the difficulty of making a first cross, and the
sterility of the hybrids thus produced—two classes of
facts which are generally confounded together—is by
no means strict. There are many cases, in which two
pure species, as in the genus Verbascum, can be united
with unusual facility, and produce numerous hybrid-
Cuar. IX.}] OF FIRST CROSSES AND OF HYBRIDS. 13
offspring, yet these hybrids are remarkably sterile.
On the other hand, there are species which can be
crossed very rarely, or with extreme difficulty, but
the hybrids, when at last produced, are very fertile.
Even within the limits of the same genus, for instance
in Dianthus, these two opposite cases occur.
The fertility, both of first crosses and of hybrids, is
more easily affected by unfavourable conditions, than
is that of pure species. But the fertility of first crosses
is likewise innately variable; for it is not always the
same in degree when the same two species are crossed
under the same circumstances; it depends in part upon
the constitution of the individuals which happen to
have been chosen for the experiment. So it is with
hybrids, for their degree of fertility is often found to
differ greatly in the several individuals raised from
seed out of the same capsule and exposed to the same
conditions.
By the term systematic affinity is meant, the general
resemblance between species in structure and constitu-
tion. Now the fertility of first crosses, and of the
hybrids produced from them, is largely governed by
their systematic affinity. This is clearly shown by
hybrids never having been raised between species
ranked by systematists in distinct families; and on
the other hand, by very closely allied species generally
uniting with facility. But the correspondence between
systematic affinity and the facility of crossing is by no
means strict. A multitude of cases could be given of
very closely allied species which will not unite, or only
with extreme difficulty ; and on the other hand of very
distinct species which unite with the utmost facility.
In the same family there may be a genus, as Dianthus,
2 LAWS GOVERNING THE STERILITY ([Cuar. IX.
in which very many species can most readily be crossed ;
and another genus, as Silene, in which the most perse-
vering efforts have failed to produce between extremely
close species a single hybrid. Even within the limits
of the same genus, we meet with this same difference;
for instance, the many species of Nicotiana have been
more largely crossed than the species of almost any -
other genus; but Gartner found that N. acuminata,
which is not a particularly distinct species, obstinately
failed to fertilise, or to be fertilised by no less than
eight other species of Nicotiana. Many analogous facts
could be given
No one has been able to point out what kind or what
amount of difference, in any recognisable character, is
suificient to prevent two species crossing. It can be
shown that plants most widely different in habit and
general appearance, and having strongly marked differ-
ences In every part of the flower, even in the pollen, in
the fruit, and in the cotyledons, can be crossed. Annual
and perennial plants, deciduous and evergreen trees,
plants inhabiting different stations and fitted for ex-
tremely different climates, can often be crossed with
ease.
By a reciprocal cross between two species, I mean
the case, for instance, of a female-ass being first crossed
by a stallion, and then a mare by a male-ass; these two
species may ‘hen be said to have been reciprocally
crossed. There is often the widest possible difference
in the facility of making reciprocal crosses. Such
cases are highly important, for they prove that the
capacity in any two species to cross is often completely
independent of their systematic affinity, that is of any
difference in their structure or constitution, excepting
Cuar. IX.] OF FIRST CROSSES AND OF HYBRIDS. 19
in their reproductive systems. The diversity of the
result in reciprocal crosses between the same two
Species was long ago observed by Ko6lreuter. To give
an instance: Mirabilis jalapa can easily be fertilised
by the pollen of M. longiflora, and the hybrids thus
produced are sufficiently fertile; but Kolreuter tried
more than two hundred times, during eight following
years, to fertilise reciprocally M. longiflora with the
pollen of M. jalapa, and utterly failed. Several other
equally striking cases could be given. Thuret has
observed the same fact with certain sea-weeds or Fuci.
Gartner, moreover, found that this difference of facility
in making reciprocal crosses is extremely common in a
lesser degree. He has observed it even between closely
related forms (as Matthiola annua and glabra) which
many botanists rank only as varieties. It is also a
remarkable fact, that hybrids raised from reciprocal
crosses, though of course compounded of the very same
two species, the one species having first been used as
the father and then as the mother, though they rarely
differ in external characters, yet generally differ in
fertility in a small, and occasionally in a high degree.
Several other singular rules could be given from
Gartner: for instance, some species have a remarkable
power of crossing with other species; other species of
the same genus have a remarkable power of impressing
their likeness on their hybrid offspring ; but these two
powers do not at all necessarily go together. There are
certain hybrids which, instead of having, as is usual,
an intermediate character between their two parents,
always closely resemble one of them; and such hybrids,
though externally so like one of their pure parent-
Species, are with rare exceptions extremely sterile. So
16 LAWS GOVERNING THE STERILITY ([Caap. IX.
again amongst hybrids which are usually intermediate
in structure between their parents, exceptional and
abnormal individuals sometimes are born, which closely
resemble one of their pure parents; and these hybrids
are almost always utterly sterile, even when the other
hybrids raised from seed from the same eapsule have a
eonsiderable degree of fertility. These facts show how
completely the fertility of a hybrid may be independent
of its external resemblance to either pure parent.
Considering the several rules now given, which
govern the fertility of first erosses and of hybrids, we
see that when forms, which must be considered as good
and distinct species, are united, their fertility graduates
from zero to perfect fertility, or even to fertility under
certain conditions in excess ; that their fertility, besides
being eminently susceptible to favourable and un-
favourable conditions, is innately variable ; that it is by
no means always the same in degree im the first cross
and in the hybrids produced from this cross; that the
fertility of hybrids is not related to the degree in which
they resemble in external appearance either parent ; and
lastly, that the facility of making a first cross between
any two species is not always governed by their
systematic affinity or degree of resemblance to each
other. This latter statement is clearly proved by the
difference in the result of reciprocal crosses between
the same two species, for, according as the one species
or the other is used as the father or the mother, there is
generally some difference, and occasionally the widest
possible difference, in the facility of effecting an union.
The hybrids, moreover, produced from reciprocal crosses
often differ in fertility.
Now do these complex and singular rules indicate
Cuar. IX.] OF FIRST CROSSES AND OF HYBRIDS. 17
that species have been endowed with sterility simply
to prevent their becoming confounded in nature? I
think not. For why should the sterility be so
extremely different in degree, when various species
are crossed, all of which we must suppose it would
be equally important to keep from blending together ?
Why should the degree of sterility be innately variable
in the individuals of the same species? Why should
some species cross with facility, and yet produce very
sterile hybrids; and other species cross with extreme
difficulty, and yet produce fairly fertile hybrids? Why
should there often be so great a difference in the result
of a reciprocal.cross between the same two species ?
“Why, it may even be asked, has the production of
hybrids been permitted? To grant to species the
special power of producing hybrids, and then to stop
their further propagation by different degrees of sterility,
not strictly related to the facility of the first union
between their parents, seems a strange arrangement.
The foregoing rules and facts, on the other hand,
appear to me clearly to indicate that the sterility both
of first crosses and of hybrids is simply incidental or
dependent on unknown differences in their reproductive
systems; the differences being of so pecular and
limited a nature, that, in reciprocal crosses between the
same two species, the male sexual element of the one
will often freely act on the female sexual element of the
other, but not in a reversed direction. It will be
advisable to explain a little more fully by an example
what I mean by sterility being incidental on other
differences, and not a specially endowed quality. As
the capacity of one plant to be grafted or budded on
another is unimportant for their welfare in a state of
18 LAWS GOVERNING THE STERILITY [Cuar. IX,
nature, I presume that no one will suppose that this
capacity is a specially endowed quality, but will admit
that it is incidental on differences in the laws of growth
of the two plants. We can sometimes see the reason
why one tree will not take on another, from differences
in their rate of growth, in the hardness of their wood,
in the period of the flow or nature of their sap, &c.;
but in a multitude of cases we can assign no reason
whatever. Great diversity in the size of two plants,
one being woody and the other herbaceous, one being
evergreen and the other deciduous, and adaptation to
widely different climates, do not always prevent the
two grafting together. As in hybridisation, so with
crafting, the capacity is limited by systematic affinity,
for no one has been able to graft together trees
belonging to quite distinct families; and, on the other
hand, closely allied species, and varieties of the same
species, can usually, but not invariably, be grafted with
ease. But this capacity, as in hybridisation, is by
no means absolutely governed by systematic affinity.
Although many distinct genera within the same family
have been grafted together, in other cases species of the
same genus will not take on each other. The pear can
be grafted far more readily on the quince, which is
ranked as a distinct genus, than on the apple, which is
a member of the same genus. Even different varieties
of the pear take with different degrees of facility on the
quince; so do different varieties of the apricot and
peach on certain varieties of the plum.
As Gartner found that there was sometimes an
innate difference in different individuals of the same
two species in crossing; so Sageret believes this to be
the case with different individuals of the same two
Cuar. IX.] OF FIRST CROSSES AND OF HYBRIDS. 19
species in being grafted together. As in reciprocal
crosses, the facility of effecting an union is often very
far from equal, so it sometimes is in grafting; the
common gooseberry, for instance, cannot be grafted on
the currant, whereas the currant will take, though with
difficulty, on the gooseberry.
We have seen that the sterility of hybrids, which
have their reproductive organs in an imperfect con-
dition, is a different case from the difficulty of uniting
two pure species, which have their reproductive organs
perfect ; yet these two distinct classes of cases run to
a large extent parallel. Something analogous occurs
in grafting; for Thouin found that three species of
“Robinia, which seeded freely on their own roots, and
which could be grafted with no great difficulty on a
fourth species, when thus grafted were rendered barren.
On the other hand, certain species of Sorbus, when
grafted on other species yielded twice as much fruit as
when on their own roots. We are reminded by this
latter fact of the extraordinary cases of. Hippeastrum,
Passiflora, &c., which seed much more freely when
fertilised with the pollen of a distinct species, than
when fertilised with pollen from the same plant.
We thus see, that, although there is a clear and great
difference between the mere adhesion of grafted stocks,
and. the union of the male and female elements in the
act of reproduction, yet that there is a rude decree of
parallelism in the results of grafting and of crossing
distinct species. And as we must look at the curious
and complex laws governing the facility with which
trees can be grafted on each other as incidental on
unknown differences in their vegetative systems, so I
believe that the still more complex laws governing the
cA, Meg CAUSES OF THE STERILITY [Cuap. IX.
facility of first crosses are incidental on unknown
differences in their reproductive systems. These
differences in both cases, follow to a certain extent, as
might have been expected, systematic affinity, by which
term every kind of resemblance and dissimilarity
between organic beings is attempted to be expressed.
The facts by no means seem to indicate that the greater
or lesser difficulty of either grafting or crossing various
species has been a special endowment; although in the
case of crossing, the difficulty is as important for the
endurance and stability of specific forms, as in the case
of grafting it is unimportant for their welfare.
Origin and Causes of the Sterility of first Crosses
and of Hybrids.
At one time it appeared to me probable, as it has to
others, that the sterility of first crosses and of hybrids
might have been slowly acquired through the natural
selection of slightly lessened degrees of fertility, which,
like any other variation, spontaneously appeared in
certain individuals of one variety when crossed with
those of another variety. For it would clearly be
advantageous to two varieties or incipient species, if
they could be kept from blending, on the same
principle that, when man is selecting at the same time
two varieties, it is necessary that he should keep them
separate. In the first place, it may be remarked that
species inhabiting distinct regions are often sterile
when crossed; now it could clearly have been of no
advantage to such separated species to have been
rendered mutually sterile, and consequently this could
not have been effected through natural selection ; but
Cuar. IX.] OF FIRST CROSSES AND OF HYBRIDS. 21
it may perhaps be argued, that, if a species was rendered
sterile with some one compatriot, sterility with other
species would follow as a necessary contingency. In
the second place, it is almost as much opposed to the
theory of natural selection as to that of special creation,
that in reciprocal crosses the male element of one form
should have been rendered utterly impotent on a
second form, whilst at the same time the male element
of this second form is enabled freely to fertilise the
first form ; for this peculiar state of the reproductive
system could hardly have been advantageous to either
species.
In considering the probability of natural selection
having come into action, in rendering species mutually
sterile, the greatest difficulty will be found to lie in the
existence of many graduated steps from slightly lessened
fertility to absolute sterility. It may be admitted that
it would profit an incipient species, if it were rendered
in some slight degree sterile when crossed with its
parent form or with some other variety ; for thus fewer
bastardised and deteriorated offspring would be pro-
duced to commingle their blood with the new species
in process of formation. But he who will take the
trouble to reflect on the steps by which this first degree
of sterility could be increased through natural selection
to that high degree which is common with so many
species, and which is universal with species which
have been differentiated to a generic or family rank, will
find the subject extraordinarily complex. After mature
reflection it seems to me that this could not have been
effected through natural selection. Take the case of
any two species which, when crossed, produced few and
sterile offspring; now, what is there which could favour
22, CAUSES OF THE STERILITY (Cuap. IX,
the survival of those individuals which happened to
be endowed in a slightly higher degree with mutual
infertility, and which thus approached by one small
step towards absolute sterility? Yet an advance of
this kind, if the theory of natural selection be brought to
bear, must have incessantly occurred with many species,
for a multitude are mutually quite barren. With
sterile neuter insects we have reason to believe that
modifications in their structure and fertility have been
slowly accumulated by natural selection, from an
advantage having been thus indirectly given to the
community to which they belonged over other com-
munities of the same species ; but an individual animal
not belonging to a social community, if rendered slightly
sterile when crossed with some other variety, would not
thus itself gain any advantage or indirectly give any
advantage to the other individuals of the same variety,
thus leading to their preservation.
But it would be superfluous to discuss this question in
detail; for with plants we have conclusive evidence
that the sterility of crossed species must be due to
some principle, quite independent of natural selection.
Both Gartner and Kélreuter have proved that in genera
including numerous species, a series can be formed from
species which when crossed yield fewer and fewer seeds,
to species which never produce a single seed, but yet
are affected by the pollen of certain other species, for
the germen swells. It is here manifestly impossible to
select the more sterile individuals, which have already
ceased to yield seeds; so that this acme of sterility,
when the germen alone is affected, cannot have been
gained through selection ; and from the laws governing
the various grades of sterility being so uniform through-
ie
Cuap. IX.] OF FIRST CROSSES AND OF HYBRIDS. 23
out the animal and vegetable kingdoms, we may infer
that the cause, whatever it may be, is the same or
nearly the same in all cases.
~
We will now look a little closer at the probable
nature of the differences between species which induce
sterility in first crosses and in hybrids. In the case of
first crosses, the greater or less difficulty in effecting an
union and in obtaining offspring apparently depends on
several distinct causes. There must sometimes be a
physical impossibility in the male element reaching
the ovule, as would be the case with a plant having a
pistil too long for the pollen-tubes to reach the ovarium.
It has also been observed that when the pollen of one
species 1s placed on the stigma of a distantly allied
species, though the pollen-tubes protrude, they do not
penetrate the stigmatic surface. Again, the male
element may reach the female element but be incapable
of causing an embryo to be developed, as seems to have
been the case with some of Thuret’s experiments on
Fuci. No explanation can be given of these facts, any
more than why certain trees cannot be grafted on others.
Lastly, an embryo may be developed, and then perish
at an early period. This latter alternative has not been
sufficiently attended to; but I believe, from observations
communicated to me by Mr. Hewitt, who has had great
experience in hybridising pheasants and fowls, that the
early death of the embryo is a very frequent cause of
sterility in first crosses. Mr. Salter has recently given
the results of an examination of about 500 egos
produced from various crosses between three species
of Gallus and their hybrids; the majority of these eggs
had been fertilised ; and in the majority of the fertilised
24 CAUSES OF THE STERILITY [Cuap. IX.
eggs, the embryos had either been partially developed
and had then perished, or had become nearly mature,
but the young chickens had been unable to break
through the shell. Of the chickens which were born,
more than four-fifths died within the first few days, or
at latest weeks, “ without any obvious cause, apparently
from mere inability to live;” so that from the 500
egos only twelve chickens were reared. With plants,
hybridised embryos probably often perish in a like
manner; at least it is known that hybrids raised from
very distinct species are sometimes weak and dwarfed,
and perish at an early age; of which fact Max Wichura
has recently given some striking cases with hybrid
willows. It may be here worth noticing that in some
cases of parthenogenesis, the embryos within the eggs
of silk moths which had not been fertilised, pass
through their early stages of development and then
perish like the embryos produced by a cross between
distinct species. Until becoming acquainted with these
facts, I was unwilling to believe in the frequent early
death of hybrid embryos; for hybrids, when once born,
are generally healthy and long-lived, as we see in the
case of the common mule. Hybrids, however, are
differently cireumstanced before and after birth: when
born and lying in a country where their two parents
live, they are generally placed under suitable conditions
of life. But a hybrid partakes of only half of the
nature and constitution of its mother; it may therefore
before birth, as long as it is nourished within its
mother’s womb, or within the egg or seed produced by
the mother, be exposed to conditions in some degree
unsuitable, and consequently be liable to perish at an
early period; more especially as all very young beings
Cuap. IX.] OF FIRST CROSSES AND OF HYBRIDS. 25
are eminently sensitive to injurious or unnatural
conditions of life. But after all, the cause more
probably lies in some imperfection in the original act of
impregnation, causing the embryo to be imperfectly
developed, rather than in the conditions to which it is
subsequently exposed.
In regard to the sterility of hybrids, in which the
sexual elements are imperfectly developed, the case is
somewhat different. I have more than once alluded to
a large body of facts showing that, when animals and
plants are removed from their natural conditions, they
are extremely liable to have their reproductive systems
seriously affected. This, in fact, is the great bar to
the domestication of animals. Between the sterility
thus superinduced and that of hybrids, there are many
points of similarity. In both cases the sterility is
independent of general health, and is often accompanied
by excess of size or great luxuriance. In both cases
the sterility occurs in various degrees; in both, the
male element is the most liable to be affected; but
sometimes the female more than the male. In both,
the tendency goes to a certain extent with systematic
affinity, for whole groups of animals and plants are
rendered impotent by the same unnatural conditions ;
and whole groups of species tend to produce sterile
hybrids. On the other hand, one species in a group
will sometimes resist great changes of conditions with
unimpaired fertility; and certain species in a group
will produce unusually fertile hybrids. No one can
tell, till he tries, whether any particular animal will
breed under confinement, or any exotic plant seed
freely under culture; nor can he tell till he tries,
whether any two species of a genus will produce more
26 | CAUSES OF THE STERILITY (Cuar. 1X
or less sterile hybrids. Lastly, when organic beings
are placed during several generations under conditions
not natural to them, they are extremely lable to vary,
which seems to be partly due to their reproductive
systems having been specially affected, though in a
lesser degree than when sterility ensues. So it is with
hybrids, for their offspring in successive generations
are eminently hable to vary, as every experimentalist
has observed.
Thus we see that when organic beings are placea
under new and unnatural conditions, and when hybrids
are produced by the unnatural crossing of two species,
the reproductive system, independently of the general
state of health, is affected In a very similar manner.
In the one case, the conditions of life have been dis-
turbed, though often in so slight a degree as to be in-
appreciable by us; in the other case, or that of hybrids,
the external conditions have remained the same, but
the organisation has been disturbed by two distinct
structures and constitutions, including of course the
reproductive systems, having been blended into one.
For it is scarcely possible that two organisations should
be compounded into one, without some disturbance
occurring in the development, or periodical action, or
mutual relations of the different parts and organs one
to another or to the conditions of life. When hybrids
are able to breed inter se, they transmit to their off-
spring from generation to generation the same com-
pounded organisation, and hence we need not be sur-
prised that their sterility, though in some degree
variable, does not diminish ; it is even apt to increase,
this being generally the result, as before explained,
of too close interbreeding. The above view of the
Cuar. IX.] OF FIRST CROSSES AND OF HYBRIDS. 27
sterility of hybrids being caused by two constitutions
being compounded into one has been strongly main-
tained by Max Wichura.
It must, however, be owned that we cannot under-
stand, on the above or any other view, several facts
with respect to the sterility of hybrids; for instance,
the unequal fertility of hybrids produced from recipro-
cal crosses; or the increased sterility in those hybrids
which occasionally and exceptionally resemble closely
either pure parent. Nor do I pretend that the fore-
going remarks go to the root of the matter; no explana-
tion is offered why an organism, when placed under
unnatural conditions, is rendered sterile. All that I
have attempted to show is, that in two cases, in some
respects allied, sterility is the common -result,—in the
one case from the conditions of life having been dis-
turbed, in the other case from the organisation having
been disturbed by two organisations being compounded
into one.
A similar parallelism holds good with an allied yet
very different class of facts. It is an old and almost ©
universal belief founded on a considerable body of
evidence, which I have elsewhere given, that slight
changes in the conditions of life are beneficial to all
living things. We see this acted on by farmers and
gardeners in their frequent exchanges of seed, tubers,
&c., from one soil or climate to another, and back again.
During the convalescence of animals, great benefit is
derived from almost any change in their habits of life.
Again, both with plants and animals, °there is the
clearest evidence that a cross between individuals of the
same species, which differ to a certain extent, gives
vigour and fertility to the offspring; and that clese~
. ATARRIC*A WN BE’ TEETER }
: AMERICAN ETHNO
/
28 STERILITY OF HYBRIDS. (Cuar. TX.
interbreeding continued during several generations
between the nearest relations, if these be kept under
the same conditions of lfe, almost always leads to
decreased size, weakness, or sterility. -
Hence it seems that, on the one hand, slight changes
in the conditions of life benefit all organic beings, and
on the other hand, that slight crosses, that is crosses
between the males and females of the same species,
which have been subjected to slightly different con-
ditions, or which have slightly varied, give vigour and
fertility to the offspring. But, as we have seen, organic
beings long habituated to certain uniform conditions
under a state of nature, when subjected, as under con-
finement, to a considerable change in their conditions,
very frequently are rendered more or less sterile; and
we know that a cross between two forms, that have
become widely or specifically different, produce hybrids
which are almost always in some degree sterile. I am
fully persuaded that this double parallelism is by no
means an accident or an illusion. He who is able to
explain why the elephant and a multitude of other
animals are incapable of breeding when kept under
only partial confinement in their native country, will
be able to explain the primary cause of hybrids being
so generally sterile. He will at the same time be able
to explain how it is that the races of some of our do-
mesticated animals, which have often been subjected
to new and not uniform conditions, are quite fertile
together, although they are descended from distinct
species, which would probably have been sterile if
aboriginally crossed. The above two parallel series of
facts seem to be connected together by some common
but unknown bond, which is essentially related to the
Cuar. IX.] DIMORPHISM AND TRIMORPHISM. 29
principle of life; this principle, according to Mr. Herbert
Spencer, being that life depends on, or consists in, the
incessant action and reaction of various forces, which,
as throughout nature, are always tending towards an
equilibrium ; and when this tendency is slightly dis-
turbed by any change, the vital forces gain in power.
Reciprocal Dimorphism and Trimorphism.
This subject may be here briefly discussed, and will
be found to throw some light on hybridism. Several
plants belonging to distinct orders present two forms,
which exist in about equal numbers and which differ
in no respect except in their reproductive organs; one
form having a long pistil with short stamens, the other
a short pistil with long stamens; the two having
differently sized pollen-grains. With trimorphic plants
there are three forms likewise differing in the lengths
of their pistils and stamens, in the size and colour of
the pollen-grains, and in some other respects; and as
in each of the three forms there are two sets of stamens,
the three forms possess altogether six sets of stamens
and three kinds of pistils. These organs are so pro-
portioned in length to each other, that half the stamens
in two of the forms stand on a level with the stigma of
the third form. Now I have shown, and the result has
been confirmed by other observers, that, in order to
obtain full fertility with these plants, it is necessary
that the stigma of the one form should be fertilised by
pollen taken from the stamens of corresponding height
in another form. So that with dimorphic species two
unions, which may be called legitimate, are fully fertile ;
and two, which may be called illegitimate, are more or
less infertile. With trimorphic species six unions are
30 RECIPROCAL DIMORPHISM [Cuar. IX,
legitimate, or fully fertile,—and twelve are illegitimate,
or more or less infertile.
The infertility which may be observed in various
dimorphic and trimorphic plants, when they are il-
lecitimately fertilised, that is by pollen taken from
stamens not corresponding in height with the pistil,
differs much in degree, up to absolute and utter
sterility ; Just in the same manner as occurs In crossing
distinct species. As the degree of sterility in the
latter case depends in an eminent degree on the con-
ditions of life being more or less favourable, so I have
found it with illegitimate unions. It is well known
that if pollen of a distinct species be placed on the stigma
of a flower, and its own pollen be afterwards, even after
a considerable interval of time, placed on the same
stigma, its action is so strongly prepotent that it
generally annihilates the effect of the foreign pollen;
so it is with the pollen of the several forms of the same
species, for legitimate pollen is strongly prepotent over
illegitimate pollen, when both are placed on the same
stigma. I ascertained this by fertilising several flowers,
first illegitimately, and twenty-four hours afterwards
legitimately, with pollen taken from a_ peculiarly
coloured variety, and all the seedlings were similarly
coloured ; this shows that the legitimate pollen, though
applied twenty-four hours subsequently, had wholly
destroyed or prevented the action of the previously
applied illegitimate pollen. Again, as in making re-
ciprocal crosses between the same two species, there is
occasionally a great difference in the result, so the same
thing occurs with trimorphic plants; for instance, the
mid-styled form of Lythrum salicaria was illegitimately
fertilised with the greatest ease by pollen from the
Cuap, IX.] AND TRIMORPHISM. 31
longer stamens of the short-styled form, and yielded
many seeds; but the latter form did not yield a single
seed when fertilised by the longer stamens of the mid-
styled form.
In all these respects, and in others which might be
added, the forms of the same undoubted species when
illegitimately united behave in exactly the same
manner as do two distinct species when crossed. This
led me carefully to observe during four years many
seedlings, raised from several illegitimate unions. The
chief result is that these illegitimate plants, as they
may be called, are not fully fertile. It is possible to
raise from dimorphic species, both long-styled and
shori-styled illegitimate plants, and from trimorphic
plants all three illegitimate forms. These can then be
properly united in a legitimate manner. When this is
done, there is no apparent reason why they should not
yield as many seeds as did their parents when legiti-
mately fertilised. But such is not the case. They are .
all infertile, in various degrees ; some being so utterly
and incurably sterile that they did not yield during four
seasons a single seed or even seed-capsule. The
sterility of these illegitimate plants, when united with
each other in a legitimate manner, may be strictly
compared with that of hybrids when crossed inter se,
If, on the other hand, a hybrid is crossed with either
pure parent-species, the sterility is usually much
lessened: and so it is when an illegitimate plant is
fertilised by a legitimate plant. In the same manner
as the sterility of hybrids does not always run parallel
with the difficulty of making the first cross between the
two parent-species, so the sterility of certain illegiti-
mate plants was unusually great, whilst the sterility of
21
32 - RECIPROCAL DIMORPHISM [Cuap. IX.
the union from which they were derived was by no
means great. With hybrids raised from the same seed-
capsule the degree of sterility is innately variable, so it
is in a marked manner with illegitimate plants. Lastly,
many hybrids are profuse and persistent flowerers,
whilst other and more sterile hybrids produce few
flowers, and are weak, miserable dwarfs; exactly
similar cases occur with the illegitimate offspring of
various dimorphic and trimorphic plants.
_ Altogether there is the closest identity in character and
behaviour between illegitimate plants and hybrids. Itis
hardly an exaggeration to maintain that illegitimate
plants are hybrids, produced within the limits of the same
species by the improper union of certain forms, whilst
ordinary hybrids are produced from an improper union
between so-called distinct species. We have also already
seen that there is the closest similarity in all respects
between first illegitimate unions and first crosses between
distinct species. This will perhaps be made more fully
apparent by an illustration; we may suppose that a
botanist found two well-marked varieties (and such
occur) of the long-styled form of the trimorphic Lythrum
salicaria, and that he determined to try by crossing
whether they were specifically distinct. He would find
that they yielded only about one-fifth of the proper
number of seed, and that they behaved in all the other
above specified respects as if they had been two distinet
species. But to make the case sure, he would raise
plants from his supposed hybridised seed, and he would
find that the seedlings were miserably dwarfed and
utterly sterile, and that they behaved in all other
respects like ordinary hybrids. He might then main-
tain that he had actually proved, in accordance with
Cuap. IX.] AND TRIMORPHISM. 33
the common view, that his two varieties were as good
and as distinct species as any in the world; but he
would be completely mistaken.
The facts now given on dimorphic and _ trimorphic
plants are important, because they show us, first, that
the physiological test of lessened fertility, both in first
crosses and in hybrids, is no safe criterion of specific
distinction ; secondly, because we may conclude that
there is some unknown bond which connects the in-
fertility of illegitimate unions with that of their illegiti-
mate offspring, and we are led to extend the same view
to first crosses and hybrids; thirdly, because we find,
and this seems to me of especial importance, that two
or three forms of the same species may exist and may
differ in no respect whatever, either in structure or in
constitution, relatively to external conditions, and yet
be sterile when united in certain ways. For we must
remember that it is the union of the sexual elements of
individuals of the same form, for instance, of two long-
styled forms, which results in sterility ; whilst it is the
union of the sexual elements proper to two distinct
forms which is fertile. Hence the case appears at first
sight exactly the reverse of what occurs, in the ordinary
unions of the individuals of the same species and
with crosses between distinct species. It is, however,
doubtful whether this is really so; but I will not en-
large on this obscure subject.
We may, however, infer as probable from the con-
sideration of dimorphic and trimorphic plants, that the
sterility of distinct species when crossed and of their
hybrid progeny, depends exclusively on the nature of
their sexual elements, and not on any difference in their
structure or general constitution. We are also led to
34 FERTILITY OF VARIETIES (Cuap. IX. |
this same conclusion by considering reciprocal crosses,
in which the male of one species cannot be united,
or can be united with great difficulty, with the female
of a second species, whilst the converse cross can be
effected with perfect facility. That excellent observer,
Gartner, likewise concluded that species when crossed
are sterile owing to differences confined to their repro-
ductive systems.
Fertility of Varieties when Crossed, and of their
Mongrel Offspring, not universal.
It may be urged, as an overwhelming argument, that
there must be some essential distinction between species
and varieties, Inasmuch as the latter, however much
they may differ from each other in external appearance,
cross with perfect facility, and yield perfectly fertile
offsprmg. With some exceptions, presently to be
given, I fully admit that this is the rule. But the
subject is surrounded by difficulties, for, looking to
varieties produced under nature, if two forms hitherto
reputed to be varieties be found in any degree sterile
together, they are at once ranked by most naturalists
as species. For instance, the blue and red pimpernel,
which are considered by most botanists as varieties, are
said by Gartner to be quite sterile when crossed, and
he consequently ranks them as undoubted species. If
we thus argue in a circle, the fertility of all varieties
produced under nature will assuredly have to be
granted.
If we turn to varieties, produced, or supposed to have
been produced, under domestication, we are still in-
volved in some doubt. For when it is stated, for
Cuap. IX.] WHEN CROSSED. a)
instance, that certain South American indigenous do-
mestic dogs do not readily unite with European dogs,
the explanation which will occur to every one, and
probably the true one, is that they are descended from
aboriginally distinct species. Nevertheless the perfect
fertility of so many domestic races, differing widely
from each other in appearance, for instance those of the
pigeon, or of the cabbage, is a remarkable fact; more
especially when we reflect how many species there are,
which, though resembling each other most closely, are
utterly sterile when intercrossed. Several considera-
tions, however, render the fertility of domestic varieties
less remarkable. In the first place, it may be observed
that the amount of external difference between two
species is no sure guide to their degree of mutual
sterility, so that similar differences in the case of
varieties would be no sure guide. It is certain that with
species the cause lies exclusively in differences in their
sexual constitution. Now the varying conditions to
which domesticated animals and cultivated plants have
been subjected, have had so little tendency towards
modifying the reproductive system in a manner leading
to mutual sterility, that we have good grounds for ad-
mitting the directly opposite doctrine of Pallas, namely,
that such conditions generally eliminate this tendency ;
so that the domesticated descendants of species, which
in their natural state probably would have been in
some degree sterile when crossed, become perfectly
fertile together. With plants, so far is cultivation from
giving a tendency towards sterility between distinct
species, that in several well-authenticated cases already
alluded to, certain plants have been affected in an
opposite manner, for they have become self-impotent
36 FERTILITY OF VARIETIES (Cuar. TX
whilst still retaining the capacity of fertilising, and
being fertilised by, other species. If the Pallasian
doctrine of the elimination of sterility through long-
continued domestication be admitted, and it can hardly
be rejected, it becomes in the highest degree improbable
that similar conditions long-continued should likewise
induce this tendency; though in certain cases, with
species having a peculiar constitution, sterility might
occasionally be thus caused. Thus, as I believe, we
can understand why with domesticated animals varieties
have not been produced which are mutually sterile;
and why with plants only a few such cases, immediately
to be given, have been observed.
The real difficulty in our present subject is not, as it
appears to me, why domestic varieties have not become
mutually infertile when crossed, but why this has so
generally occurred with natural varieties, as soon as
they have been permanently modified in a sufficient
degree to take rank as species. We are far from
precisely knowing the cause; nor is this surprising,
seeing how profoundly ignorant we are in regard to the
normal and abnormal action of the reproductive system.
But we can see that species, owing to their struggle for
existence with numerous competitors, will have been
exposed during long periods of time to more uniform
conditions, than have domestic varieties; and this may
well make a wide difference in the result. For we
know how commonly wild animals and plants, when
taken from their natural conditions and subjected to
captivity, are rendered sterile; and the reproductive
functions of organic beings which have always lived
under natural conditions would probably in like
manner be eminently sensitive to the influence of an
Cuap. IX.] WHEN CROSSED. Sl
unnatural cross. Domesticated productions, on the other
hand, which, as shown by the mere fact of their domesti-
cation, were not originally highly sensitive to changes
in their conditions of life, and which can now generally
resist with undiminished fertility repeated changes of
conditions, might be expected to produce varieties,
which would be little lable to have their reproductive
powers injuriously affected by the act of crossing with
other varieties which had originated in a like manner.
I have as yet spoken as if the varieties of the same
species were invariably fertile when intercrossed. But
it is impossible to resist the evidence of the existence
of a certain amount of sterility in the few following.
cases, which I will briefly abstract. The evidence is
at least as good as that from which we believe in the
sterility of a multitude of species. The evidence is,
also, derived from hostile witnesses, who in all other
cases consider fertility and sterility as safe criterions of
specific distinction. Gartner kept during several years
a dwarf kind of maize with yellow seeds, and a tall
variety with red seeds growing near each other in his
garden; and although these plants have separated
sexes, they never naturally crossed. He then fertilised
thirteen flowers of the one kind with pollen of the
other; but only a single head produced any seed, and
this one head produced only five grains. Manipulation
in this case could not have been injurious, as the plants
have separated sexes. No one, I believe, has suspected
that these varieties of maize are distinct species ; and it
is important to notice that the hybrid plants thus
raised were themselves perfectly fertile; so that even
Gartner did not venture to consider the two varieties as
specifically distinct.
paste 2,2
38 FERTILITY OF VARIETIES [Cuap. IX.
Girou de Buzareingues crossed three varieties of
gourd, which like the maize has separated sexes, and he
asserts that their mutual fertilisation is by so much the
less easy as their differences are greater. How far these
experiments may be trusted, I know not; but the forms
experimented on are ranked by Sageret, who mainly
founds his classification by the test of infertility, as
varieties, and Naudin has come to the same conclusion.
The following case is far more remarkable, and seems
at first incredible; but it is the result of an astonishing
number of experiments made during many years on
nine species of Verbascum, by so good an observer and
so hostile a witness as Gartner: namely that the yellow
and white varieties when crossed produce less seed than
the similarly coloured varieties of the same species.
Moreover, he asserts that, when yellow and white
varieties of one species are crossed with yellow and
white varieties of a distinct species, more seed is
produced by the crosses between the similarly coloured
flowers, than between those which are differently
coloured. Mr. Scott also has experimented on the
species and varieties of Verbascum; and although
unable to confirm Girtner’s results on the crossing of
the distinct species, he finds that the dissimilarly
coloured varieties of the same species yield fewer seeds,
in the proportion of 86 to 100, than the similarly
coloured varieties. Yet these varieties differ in no
respect except in the colour of their flowers; and one
variety can sometimes be raised from the seed of another.
KGélreuter, whose accuracy has been confirmed by
every subsequent observer, has proved the remarkable
fact, that one particular variety of the common tobacco
was more fertile than the other varieties, when crossed
Cuar. IX.] WHEN CROSSED. 39
with a widely distinct species. He experimented on
five forms which are commonly reputed to be varieties,
and which he tested by the severest trial, namely, by
reciprocal crosses, and he found their mongrel offspring
perfectly fertile. But one of these five varieties, when
used either as the father or mother, and crossed with
the Nicotiana glutinosa, always yielded hybrids not so
sterile as those which were produced from the four
other varieties when crossed with N. glutinosa. Hence
the reproductive system of this one variety must have
been in some manner and in some degree modified.
From these facts it can no longer be maintained that
varieties when crossed are invariably quite fertile.
From the great difficulty of ascertaining the infertility
of varieties in a state of nature, for a supposed variety,
if proved to be infertile in any degree, would almost
universally be ranked as a species ;—from man attend-
ing only to external characters in his domestic varieties,
and from such varieties not having been exposed for
very long periods to uniform conditions of life ;—from
these several considerations we may conclude that
fertility does not constitute a fundamental distinction
between varieties and species when crossed. The
general sterility of crossed species may safely be looked
at, not as a special acquirement or endowment, but as
incidental on changes of an unknown nature in their
sexual elements.
Hybrids and Mongrels compared, independently of their
fertility.
Independently of the question of fertility, ie off-
spring of species and of varieties when crossed may be
40 HYBRIDS AND MONGRELS COMPARED. ([Caap. IX.
compared in several other respects. Gartner, whose
strong wish it was to draw a distinct line between
species and varieties, could find very few, and, as it
seems to me, quite unimportant differences between the
so-called hybrid offspring of species, and the so-called
mongrel offspring of varieties. And, on the other hand,
they agree most closely in many important respects.
I shall here discuss this subject with extreme brevity.
The most important distinction is, that in the first
generation mongrels are more variable than hybrids ;
but Gartner admits that hybrids from species which
have long been cultivated are often variable in the
first generation; and I have myself seen striking
instances of this fact. Girtner further admits that
hybrids between very closely allied species are more
variable than those from very distinct species; and
this shows that the difference in the degree of variability
graduates away. When mongrels and the more fertile
hybrids are propagated for several generations, an extreme
amount of variability in the offspring in both cases is
notorious ; but some few instances of both hybrids and
mongrels long retaining a uniform character could be
given. The variability, however, in the successive
generations of mongrels is, perhaps, greater than in
hybrids.
This greater variability in mongrels than in hybrids
does not seem at all surprising. For the parents of
mongrels are varieties, and mostly domestic varieties
(very few experiments having been tried on natural
varieties), and this implies that there has been recent
variability, which would often continue and would
augment that arising from the act of crossing. The
slight variability of hybrids in the first generation, in
Cuar. IX.] HYBRIDS AND MONGRELS COMPARED. 41
contrast with that in the succeeding generations, is a
curious fact and deserves attention. For it bears on
the view which I have taken of one of the causes of
ordinary variability; namely, that the reproductive
system from being eminently sensitive to changed
conditions of life, fails under these circumstances to
perform its proper function of producing offspring
closely similar in all respects to the parent-form. Now
hybrids in the first generation are descended from
species (excluding those long-cultivated) which have
not had their reproductive systems in any way affected,
and they are not variable; but hybrids themselves have
their reproductive systems seriously affected, and their
descendants are highly variable.
But to return to our comparison of mongrels and
hybrids: Gartner states that mongrels are more liable
than hybrids to revert to either parent-form ; but this,
if it be true, is certainly only a difference in degree.
Moreover, Gartner expressly states that hybrids from
long cultivated plants are more subject to reversion
than hybrids from species in their natural state; and
this probably explains the singular difference in the
results arrived at by different observers: thus Max
Wichura doubts whether hybrids ever revert to their
parent-forms, and he experimented on uncultivated
species of willows; whilst Naudin, on the other hand,
insists in the strongest terms on the almost universal
tendency to reversion in hybrids, and he experimented
chiefly on cultivated plants. Gartner further states
that when any two species, although most closely allied
to each other, are crossed with a third species, the
hybrids are widely different from each other ; whereas
if two very distinct varieties of one species are crossed
42, HYBRIDS AND MONGRELS COMPARED. ([Cuap. IX.
with another species, the hybrids do not differ much.
But this conclusion, as far as I can make out, is
founded on a single experiment; and seems directly
opposed to the results of several experiments made by
Kolreuter.
Such alone are the unimportant differences which
Gartner is able to point out between hybrid and
mongrel plants. On the other hand, the degrees and
kinds of resemblance in mongrels and in hybrids to
their respective parents, more especially in hybrids
produced from nearly related species, follow according
to Gartner the same laws. When two species are
crossed, one has sometimes a prepotent power of
impressing its likeness on the hybrid. So I believe
it to be with varieties of plants; and with animals one
variety certainly often has this prepotent power over
another variety. Hybrid plants produced from a
reciprocal cross, generally resemble each other closely ;
and so it is with mongrel plants from a reciprocal cross.
Both hybrids and mongrels can be reduced to either
pure parent-form, by repeated crosses in successive
generations with either parent.
These several remarks are apparently applicable to
animals ; but the subject is here much complicated,
partly owing to the existence of secondary sexual
characters ; but more especially owing to prepotency in
transmitting hkeness running more strongly in one sex
than in the other, both when one species is crossed with
another, and when one variety is crossed with another
variety. For imstance, I think those authors are right
who maintain that the ass has a prepotent power over
the horse, so that both the mule and the hinny resemble
more closely the ass than the horse; but that the pre-
Cuar. IX.] HYBRIDS AND MONGRELS COMPARED. 43
potency runs more strongly in the male than in the
female ass, so that the mule, which is the offspring of
the male ass and mare, is more like an ass, than is
the hinny, which is the offspring of the female ass and
stallion.
Much stress has been laid by some authors on the
supposed fact, that it is only with mongrels that the
offspring are not intermediate in character, but closely
resemble one of their parents; but this does sometimes
occur with hybrids, yet I grant much less frequently
than with mongrels. Looking to the cases which I
have collected of cross-bred animals closely resembling
one parent, the resemblances seem chiefly confined to
characters almost monstrous in their nature, and which
have suddenly appeared—such as albinism, melanism,
deficiency of tail or horns, or additional fingers and
toes; and do not relate to characters which have been
slowly acquired through selection. A tendency to
sudden reversions to the perfect character of either
parent would, also, be much more likely to occur with
mongrels, which are descended from varieties often
suddenly produced and semi-monstrous in character,
than with hybrids, which are descended from species
slowly and naturally produced. On the whole, I
entirely agree with Dr. Prosper Lucas, who, after
arranging an enormous body of facts with respect to
animals, comes to the conclusion that the laws of
resemblance of the child to its parents are the same,
whether the two parents differ little or much from each
other, namely, in the union of individuals of the same
variety, or of different varieties, or of distinct species.
Independently of the question of fertility and sterility,
in all other respects there seems to be a general and
22
44 | SUMMARY, Tent
close similarity in the offspring of crossed species, and
of crossed varieties. If we look at species as having
been specially created, and at varieties as having been
produced by secondary laws, this similarity would be
an astonishing fact. But it harmonises perfectly with
the view that there is no essential distinction between
species and varieties.
Summary of Chapter.
First crosses between forms, sufficiently distinct to
be ranked as species, and their hybrids, are very
generally, but not universally, sterile. The sterility
is of all degrees, and is often so slight that the most
careful experimentalists have arrived at diametrically
opposite conclusions in ranking forms by this test.
The sterility is innately variable in individuals of the
same species, and is eminently susceptible to the action
of favourable and unfavourable conditions. The degree
of sterility does not strictly follow systematic affinity,
but is governed by several curious and complex laws.
It is generally different, and sometimes widely different
in reciprocal crosses between the same two species. It
is not always equal in degree in a first cross and in the
hybrids produced from this cross.
In the same manner as in grafting trees, the capacity
in one species or variety to take on another, is incidental
on differences, generally of an unknown nature, in their
vegetative systems, so in crossing, the greater or less
facility of one species to unite with another is incidental
on unknown differences in their reproductive systems.
There is no more reason to think that species have been
specially endowed with various degrees of sterility to
prevent their crossing and blending in nature, than to
Cuap. IX.] SUMMARY. 45.
think that trees have been specially endowed with
various and somewhat analogous degrees of difficulty
in boing grafted together in order to prevent their
inarching in our forests.
The sterility of first crosses and of their hybrid
progeny has not been acquired through natural se-
lection. In the case of first crosses it seems to depend
on several circumstances; in some instances in chief
part on the early death of the embryo. In the case of
hybrids, it apparently depends on their whole or-
ganisation having been disturbed by being compounded
from two distinct forms; the sterility being closely
-allied to that which so frequently affects pure species,
when exposed to new and unnatural conditions of
life. He who will explain these latter cases will
be able to explain the sterility of hybrids. This
view is strongly supported by a parallelism of another
kind: namely, that, firstly, slight changes in the
conditions of life add to the vigour and fertility of all
organic beings; and secondly, that the crossing of
forms, which have been exposed to slightly different
conditions of life or which have varied, favours the size,
vigour, and fertility of their offspring. The facts given
on the sterility of the illegitimate unions of dimorphic
and trimorphic plants and of their illegitimate progeny,
perhaps render it probable that some unknown bond in
all cases connects the degree of fertility of first unions
with that of their offspring. The consideration of these
facts on dimorphism, as well as of the results of reci-
procal crosses, clearly leads to the conclusion that the
primary cause of the sterility of crossed species is
confined to differences in their sexual elements. But
why, in the case of distinct species, the sexual elements
46 | SUMMARY. (Cuap. IX.
should so generally have become more or less modified,
leading to their mutual infertility, we do not know ; but
it seems to stand in some close relation to species having
been exposed for long periods of time to nearly uniform
conditions of life.
It is not surprising that the difficulty in crossing any
two species, and the sterility of their hybrid offspring,
should in most cases correspond, even if due to distinct
causes: for both depend on the amount of difference
between the species which are crossed. Nor is it
surprising that the facility of effecting a first cross, and
the fertility of the hybrids thus produced, and the
capacity of being grafted together—though this latter
capacity evidently depends on widely different circum-
stances—should all run, to a certain extent, parallel
with the systematic affinity of the forms subjected to
experiment; for systematic affinity includes resem-
blances of all kinds.
First crosses between forms known to be varieties, or
sufficiently alike to be considered as varieties, and their
mongrel offspring, are very generally, but not, as is so
often stated, invariably fertile. Nor is this almost
universal and perfect fertility surprismg, when it is
remembered how liable we are to argue in a circle with
respect to varieties in a state of nature; and when we
remember that the greater number of varieties have
been produced under domestication by the selection of
mere external differences, and that they have not been
long exposed to uniform conditions of life. It should
also be especially kept in mind, that long-continued
domestication tends to eliminate sterility, and is there-
fore little likely to induce this same quality. Indepen-
dently of the question of fertility, in all other respects
Cuap. IX.] SUMMARY. 47
there is the closest general resemblance between hybrids
and mongrels,—in their variability, in their power of
absorbing each other by repeated crosses, and in their
inheritance of characters from both parent-forms.
Finally, then, although we are as ignorant of the
precise cause of the sterility of first crosses and of
hybrids as we are why animals and plants removed
from their natural conditions become sterile, yet the
facts given in this chapter do not seem to me opposed
to the belief that species aboriginally existed as
varieties.
4$ IMPERFECTION OF THE (Cuar. X.
CHAPTER ke
ON THE IMPERFECTION OF THE GEOLOGICAL RECORD.
On the absence of intermediate varieties at the present day—On
the nature of extinct intermediate varieties ; on their number—
On the lapse of time, as inferred from the rate of denudation
and of deposition—On the lapse of time as estimated by years
—On the poorness of our paleontological collections—On the
intermittence of geological formations—On the denudation of
granitic areas—On the absence of intermediate varieties in any
one formation—On the sudden appearance of groups of species—
On their sudden appearance in the lowest known fossiliferous
strata—Antiquity of the habitable earth.
IN the sixth chapter I enumerated the chief objections
which might be justly urged against the views main-
tained in this volume. Most of them have now been
discussed. One, namely the distinctness of specific
forms, and their not being blended together by innumer-
able transitional links, is a very obvious difficulty. I
assigned reasons why such links do not commonly occur
at the present day under the circumstances apparently
most favourable for their presence, namely on an
extensive and continuous area with graduated physical
conditions. I endeavoured to show, that the life of
each species depends in a more important manner on
the presence of other already defined organic forms,
than on climate, and, therefore, that the really governing
conditions of life do not graduate away quite insensibly
like heat or moisture. I endeavoured, also, to show
Cuap. X.] GEOLOGICAL RECORD. 49
that intermediate varieties, from existing in lesser
numbers than the forms which they connect, will
generally be beaten out and exterminated during the
course of further modification and improvement. The
main cause, however, of innumerable intermediate links
not now occurring everywhere throughout nature,
depends on the very process of natural selection, through
which new varieties continually take the places of and
supplant their parent-forms. But just in proportion as
this process of extermination has acted on an enormous
scale, so must the number of intermediate varieties,
which have formerly existed, be truly enormous. Why
then is not every geological formation and every stratum
full of such intermediate links ? Geology assuredly does
not reveal any such finely-graduated organic chain ; and
this, perhaps, is the most obvious and serious objection
which can be urged against the theory. The explanation
lies, as I believe, in the extreme imperfection of the
geological record.
In the first place, it. should always be borne in mind
what sort of intermediate forms must, on the theory,
have formerly existed. I have found it difficult, when
looking at any two species, to avoid picturing to
myself forms directly intermediate between them. But
this is a wholly false view ; we should always look for
forms intermediate between each species and a common
but unknown progenitor; and the progenitor will gen-
erally have differed in some respects from all its
modified descendants. To give a simple illustration:
the fantail and pouter pigeons are both descended from
the rock-pigeon ; if we possessed all the intermediate
varieties which have ever existed, we should have an
extremely close series between both and the rock-
50 IMPERFECTION OF THE [Cuar. X
pigeon; but we should have no varieties directly
intermediate between the fantail and pouter; none,
for instance, combining a tail somewhat expanded with
a crop somewhat enlarged, the characteristic features of
these two breeds. These two breeds, moreover, have
become so much modified, that, if we had no historical
or indirect evidence regarding their origin, it would not
have been possible to have determined, from a mere
comparison of their structure with that of the rock-
pigeon, C. livia, whether they had descended from this
species or from some other allied form, such as C. oenas.
So, with natural species, if we look to forms very
distinct, for instance to the horse and tapir, we have
no reason to suppose that links directly intermediate
between them ever existed, but between each and an
unknown common parent. The common parent will
have had in its whole organisation much general re-
semblance to the tapir and to the horse; but in some
points of structure may have differed considerably from
both, even perhaps more than they differ from each
other. Hence, in all such cases, we should be unable
to recognise the parent-form of any two or more species,
even if we closely compared the structure of the parent
with that of its modified descendants, unless at the
same time we had a nearly eae chain of the inter-
mediate links.
It is just possible by the Boe that one of two
living forms might have descended from the other; for
instance, a horse from a tapir; and in this case direct
intermediate links will have existed between them.
But such a case would imply that one form had
remained for a very long period unaltered, whilst its
descendants had undergone a vast amount of change;
Cuap. X.] GEOLOGICAL RECORD. 51
and the principle of competition between organism and
organism, between child and parent, will render this a
very rare event; for in all cases the new and improved
forms of life tend to supplant the old and unimproved
forms.
By the theory of natural selection all living species
have been connected with the parent-species of each
genus, by differences not greater than we see between
the natural and domestic varieties of the same species
at the present day; and these parent-species, now
generally extinct, have in their turn been similarly
connected with more ancient forms; and so on back-
wards, always converging to the common ancestor of
each great class. So that the number of intermediate
and transitional links, between all living and extinct
species, must have been inconceivably great. But
assuredly, if this theory be true, such have lived upon
the earth.
On the Lapse of Time, as inferred from the rate of
Deposition and extent of Denudation.
Independently of our not finding fossil remains of
such infinitely numerous connecting links, it may be
objected that time cannot have sufficed for so great an
amount of organic change, all changes having been
effected slowly. It is hardly possible for me to recall
to the reader who is not a practical geologist, the facts
leading the mind feebly to comprehend the lapse of time.
He who can read Sir Charles Lyell’s grand work on the
Principles of Geology, which the future historian will
recognise aS having produced a revolution in natural
science, and yet does not admit how vast have been the
52 , THE LAPSE OF TIME. (Cuar. X-
past periods of time, may at once close this volume.
Not that it suffices to study the Principles of Geology,
or to read special treatises by different observers on
separate formations, and to mark how each author
attempts to give an inadequate idea of the duration of
each formation, or even of each stratum. We can best
gain some idea of past time by knowing the agencies at
work, and learning how deeply the surface of the land
has been denuded, and how much sediment has been
deposited. As Lyell has well remarked, the extent and
thickness of our sedimentary formations are the result
and the measure of the denudation which the earth’s
crust has elsewhere undergone. Therefore a man
should examine for himself the great piles of super-
imposed strata, and watch the rivulets brmging down
mud, and the waves wearing away the sea-cliffs, in
order to comprehend something about the duration of
past time, the monuments of which we see all around
us.
It is good to wander along the coast, when formed of
moderately hard rocks, and mark the process of degrad-
ation. The tides in most cases reach the cliffs only for
a short time twice a day, and the waves eat into them
only when they are charged with sand or pebbles;
for there is good evidence that pure water effects
nothing in wearing away rock. At last the base of the
cliff is undermined, huge fragments fall down, and
these, remaining fixed, have to be worn away atom by
atom, until after being reduced in size they can be
rolled about by the waves, and then they are more
quickly ground into pebbles, sand, or mud. But how
often do we see along the bases of retreating cliffs
rounded boulders, all thickly clothed by marine pro-
Cap. X.] THE LAPSE OF TIME. 53
ductions, showing how little they are abraded and how
seldom they are rolled about! Moreover, if we follow
for a few miles any line of rocky cliff, which is under-
going degradation, we find that it is only here and there,
along a short length or round a promontory, that the
cliffs are at the present time suffering. + The appearance
of the surface and the vegetation show that elsewhere
years have elapsed since the waters washed their base.
We have, however, recently learnt from the obser-
vations of Ramsay, in the van of many excellent
observers—of Jukes, Geikie, Croll, and others, that
subaerial degradation is a much more important agency
than coast-action, or the power of the waves. The
whole surface of the land is exposed to the chemical
action of the air and of the rain-water with its dissolved
carbonic acid, and in colder countries to frost; the
disintegrated matter is carried down even gentle slopes
during heavy rain, and to a greater extent than might
be supposed, especially in arid districts, by the wind ; it
is then transported by the streams and rivers, which
when rapid deepen their channels, and triturate the
fragments. On a rainy day, even in a gently undula-
ting country, we see the effects of subaerial degradation
in the muddy rills which flow down every slope.
Messrs. Ramsay and Whitaker have shown, and the
observation is a most striking one, that the great lines
of escarpment in the Wealden district and those ranging
across England, which formerly were looked at as
ancient sea-coasts, cannot have been thus formed, for
each line is composed of one and the same formation,
whilst our sea-cliffs are everywhere formed by the
intersection of various formations. This being the case,
we are compelled to admit that the escarpments owe
54 , THE LAPSE OF TIME. — [Cmap. X.
their origin in chief part to the rocks of which they are
composed having resisted subaerial denudation better
than the surrounding surface ; this surface consequently
has been gradually lowered, with the lines of harder
rock left projecting. Nothing impresses the mind with
the vast duration of time, according to our ideas of time,
more forcibly than the conviction thus gained that
subaerial agencies which apparently have so little
power, and which seem to work so slowly, have pro-
duced great results.
When thus impressed with the slow rate at which
the land is worn away through subaerial and littoral
action, it 1s good, in order to appreciate the past
duration of time, to consider, on the one hand, the
masses of rock which have been removed over many
extensive areas, and on the other hand the thickness of
our sedimentary formations. 1 remember having been
much struck when viewing volcanic islands, which have
been worn by the waves and pared all round into
perpendicular cliffs of one or two thousand feet in
height ; for the gentle slope of the lava-streams, due to
their formerly liquid state, showed at a glance how far
the hard, rocky beds had once extended into the open
ocean. The same story is told still more plainly by
faults,-—_those great cracks along which the strata have
been upheaved on one side, or thrown down on the
other, to the height or depth of thousands of feet; for
since the crust cracked, andit makes no great difference
whether the upheaval was sudden, or, as most geologists
now believe, was slow and effected by many starts, the
surface of the land has been so completely planed down
that no trace of these vast dislocations is externally
visible. The Craven fault, for instance extends for
Cuap. X.) THE LAPSE OF TIME. | 55
upwards of 30 miles, and along this line the vertical
displacement of the strata varies from 600 to 3000 feet.
Professor Ramsay has published an account of a down-
throw in Anglesea of 2300 feet; and he informs me
that he fully believes that there is one in Merioneth-
shire of 12,000 feet ; yet in these cases there is nothing
on the surface of the land to show such prodigious
movements; the pile of rocks on either side of the
crack having been smoothly swept away.
On the other hand, in all parts of the world the piles
of sedimentary strata are of wonderful thickness. In
the Cordillera I estimated one mass of conglomerate at
ten thousand feet; and although conglomerates have
probably been accumulated at a quicker rate than finer
sediments, yet from being formed of worn and rounded
pebbles, each of which bears the stamp of time, they
are good to show how slowly the mass must have been
heaped together. Professor Ramsay has given me the
maximum thickness, from actual measurement in most
cases, of the successive formations in different parts of
Great Britain; and this is the result :—
Feet,
Palzozoic strata (not including igneous beds) .. .. 57,154
PECOMGALY SEIAtAe ce, (es) 6- uel) | sits oo 1, Sede, a0) owe LOMO
RSE IEE SEE ALR cs oo) fae ens wed sek it 00) Seah ete sagen
—making altogether 72,584 feet; that is, very nearly
thirteen and three-quarters British miles. Some of the
formations, which are represented in England by thin
beds, are thousands of feet in thickness on the Con-
tinent. Moreover, between each successive formation,
we have, in the opinion of most geologists, blank
periods of enormous length. So that the lofty pile of
sedimentary rocks in Britain gives but an inadequate
23
56 | THE LAPSE OF TIME. (Cuar. X.
idea of the time which has elapsed during their accumula-
tion. The consideration of these various facts impresses
the mind almost in the same manner as does the vain
endeavour to grapple with the idea of eternity.
Nevertheless this impression is partly false. Mr.
Croll, in an interesting paper, remarks that we do not.
err “in forming too great a conception of the length of
“ceological periods,” but in estimating them by years.
When geologists look at large and complicated phe-
nomena, and then at the figures representing several
million years, the two produce a totally different effect
on the mind, and the figures are at once pronounced too
small. In regard to subaerial denudation, Mr. Croll
shows, by calculating the known amount of sediment
annually brought down by certain rivers, relatively to
their areas of drainage, that 1000 feet of solid rock, as
it became gradually disintegrated, would thus be re-
moved from the mean level of the whole area in the
course of six million years. This seems an astonishing
result, and some considerations lead to the suspicion
that it may be too large, but even if halved or quartered
it is still very surprising. Few of us, however, know
what a million really means: Mr. Croll gives the
following illustration: take a narrow strip of paper, 83
feet 4 inches in length, and stretch it along the wall of
a large hall; then mark off at one end the tenth of an
inch. This tenth of an inch will represent one hundred
years, and the entire strip a million years. But let it
be borne in mind, in relation to the subject of this work,
what a hundred years implies, represented as it is by a
measure utterly insignificant in a hall of the above
dimensions. Several eminent breeders, during a single
lifetime, have so largely modified some of the higher
Cuar. X.] THE LAPSE OF TIME. | Ds
animals, which propagate their kind much more slowly
than most of the lower animals, that they have formed
what well deserves to be called a new sub-breed. Fewmen
have attended with due care to any one strain for more
than half a century, so that’'a hundred years represents
the work of two breeders in succession. It is not to be
supposed that species in a state of nature ever change
so quickly as domestic animals under the guidance of
methodical selection. The comparison would be in
every way fairer with the effects which follow from
unconscious selection, that is the preservation of the
most useful or beautiful animals, with no intention of
modifying the breed; but by this process of unconscious
selection, various breeds have been sensibly changed in
the course of two or three centuries.
Species, however, probably change much more slowly,
and within the same country only a few change at the
same time. This slowness follows from all the inhabit-
ants of the same country being already so well adapted
to each other, that new places in the polity of nature do
not occur until after long intervals, due to the occur-
rence of physical changes of some kind, or through the
immigration of new forms. Moreover variations or
individual differences of the right nature, by which
some of the inhabitants might be better fitted to their
new places under the altered circumstances, would not
always occur at once. Unfortunately we have no means
of determining, according to the standard of years, how
long a period it takes to modify a species; but to the
subject of time we must return.
58 _ THE POORNESS OF OUR -(Coar. X
On the Poorness of Paleontological Collections.
Now let us turn to our richest geological museums,
and what a paltry display we behold! That our col-
lections are imperfect is admitted by every one. The
remark of that admirable paleontologist, Edward Forbes,
should never be forgotten, namely, that very many fossil
species are known and named from single and often
broken specimens, or from a few specimens collected on
some one spot. Only a small portion of the surface of
the earth has been geologically explored, and no part
with sufficient care, as the important discoveries made
every year in Europe prove. No organism wholly soft
can be preserved. Shells and bones decay and disappear
when left on the bottom of the sea, where sediment is
not accumulating. We probably take a quite erroneous
view, when we assume that sediment is being deposited
over nearly the whole bed of the sea, at a rate
sufficiently quick to embed and preserve fossil remains.
Throughout an enormously large proportion of the ocean,
the bright blue tint of the water bespeaks its purity.
The many cases on record of a formation conformably
covered, after an immense interval of time, by another
and later formation, without the underlying bed haying
suffered in the interval any wear and tear, seem
explicable only on the view of the bottom of the sea not
rarely lying for ages in an unaltered condition. The
remains which do become embedded, if in sand or
gravel, will, when the beds are upraised, generally be
dissolved by the percolation of rain-water charged with
carbolic acid. Some of the many kinds of animals
which live on the beach between high and low water
mark seem to be rarely preserved. For instance, the
Cap. X.] PALMONTOLOGICAL COLLECTIONS. 59
several species of the Chthamaline (a sub-family of
sessile cirripedes) coat the rocks all over the world in
infinite numbers: they are all strictly littoral, with the
exception of a single Mediterranean species, which
inhabits deep water, and this has been found fossil in
Sicily, whereas not one other species has hitherto been
found in any tertiary formation: yet it is known that
the genus Chthamalus existed during the Chalk period.
Lastly, many great deposits requiring a vast length of
time for their accumulation, are entirely destitute of
organic remains, without our being able to assign any
reason: one of the most striking instances is that of the
Flysch formation, which consists of shale and sandstone,
several thousand, occasionally even six thousand feet in
thickness, and extending for at least 300 miles from
Vienna to Switzerland; and although this great mass
has been most carefully searched, no fossils, except a
few vegetable remains, have been found.
With respect to the terrestrial productions which lived
during the Secondary and Paleozoic periods, it is super-
fluous to state that our evidence is fragmentary in an
extreme degree. For instance, until recently not a land-
shell was known belonging to either of these vast
periods, with the exception of one species discovered by
Sir C. Lyell and Dr. Dawson in the carboniferous strata
of North America; but now land-shells have been found
in the lias. In regard to mammiferous remains, a
glance at the historical table published in Lyell’s
Manual will bring home the truth, how accidental and
rare is their preservation, far better than pages of detail.
Nor is their rarity surprising, when we remember how
large a proportion of the bones of tertiary mammals
have been discovered either in caves or in lacustrine
60 _ THE POORNESS OF OUR [Crar. X.
deposits; and that not a cave or true lacustrine bed is
known belonging to the age of our secondary or
paleozoic formations.
But the imperfection in the geological record largely
results from another and more important cause than
any of the foregoing; namely, from the several forma-
tions being separated from each other by wide intervals
of time. This doctrine has been emphatically admitted
by many geologists and palzontologists, who, like E.
Forbes, entirely disbelieve in the change of species.
When we see the formations tabulated in written
works, or when we follow them in nature, it is difficult
to avoid believing that they are closely consecutive.
But we know, for instance, from Sir R. Murchison’s
great work on Russia, what wide gaps there are in that
country between the superimposed formations ; so it is
in North America, and in many other parts of the
world. The most skilful geologist, if his attention had
been confined exclusively to these large territories,
would never have suspected that, during the periods
which were blank and barren in his own country, great
piles of sediment, charged with new and peculiar forms
of life, had elsewhere been accumulated. And if, in
each separate territory, hardly any idea can be formed
of the length of time which has elapsed between the
consecutive formations, we may infer that this could
nowhere be ascertained. The frequent and great
changes in the mineralogical composition of consecutive
formations, generally implying great changes in the
geography of the surrounding lands, whence the sedi-
ment was derived, accord with the belief of vast inter-
vals of time having elapsed between each formation.
We can, I think, see why the geological formations
Cuap. X.] PALZONTOLOGICAL COLLECTIONS. 61
of each region are almost invariably intermittent ; that
is, have not followed each other in close sequence.
Scarcely any fact struck me more when examining
many hundred miles of the South American coasts,
which have been upraised several hundred feet within
the recent period, than the absence of any recent de-
posits sufficiently extensive to last for even a short
geological period. Along the whole west coast, which is
inhabited by a peculiar marine fauna, tertiary beds are
so poorly developed, that no record of several successive
and peculiar marine faunas will probably be preserved
to a distant age. A little reflection will explain why,
along the rising coast of the western side of South
America, no extensive formations with recent or ter-
tiary remains can anywhere be found, though the supply
of sediment must for ages have been great, from the
enormous degradation of the coast-rocks and from
muddy streams entering the sea. The explanation, no
doubt, is, that the littoral and sub-littoral deposits are
continually worn away, as soon as they are brought up
by the slow and gradual rising of the land within the
erinding action of the coast-waves.
We may, I think, conclude that sediment must be
accumulated in extremely thick, solid, or extensive
masses, in order to withstand the incessant action of
the waves, when first upraised and during successive
oscillations of level, as well as the subsequent subaerial
degradation. Such thick and extensive accumulations
of sediment may be formed in two ways; either in pro-
found depths of the sea, in which case the bottom will
not be inhabited by so many and such varied forms of
life, as the more shallow seas; and the mass when
upraised will give an imperfect record of the organisms
62 THE POORNESS OF OUR [Cuar. X.
which existed in the neighbourhood during the period
of its accumulation. Or, sediment may be deposited to
any thickness and extent over a shallow bottom, if it
continue slowly to subside. In this latter case, as long
as the rate of subsidence and the supply of sediment
nearly balance each other, the sea will remain shallow
and favourable for many and varied forms, and thus
a rich fossiliferous formation, thick enough, when up-
raised, to resist a large amount of denudation, may be
formed. .
I am convinced that nearly all our ancient formations,
which are throughout the greater part of their thickness
rich in fossils, have thus been formed during subsidence.
Since publishing my views on this subject in 1845, I
have watched the progress of Geology, and have been
surprised to note how author after author, in treating
of this or that great formation, has come to the con-
clusion that it was accumulated during subsidence. I
may add, that the only ancient tertiary formation on
the west coast of South America, which has been bulky
enough to resist such degradation as it has as yet
suffered, but which will hardly last to a distant
geological age, was deposited during a downward
oscillation of level, and thus gained considerable
thickness.
All geological facts tell us plainly that each area
has undergone numerous slow oscillations of level,
and apparently these oscillations have affected wide
spaces. Consequently, formations rich in fossils and
sufficiently thick and extensive to resist subsequent
degradation, will have been formed over wide spaces
during periods of subsidence, but only where the
supply of sediment was sufficient to keep the sea
Cuar. X.] PALHONTOLOGICAL COLLECTIONS. 63
shallow and to embed and preserve the remains before
they had time to decay. On the other hand, as long as
the bed of the sea remains stationary, thick deposits
cannot have been accumulated in the shallow parts,
which are the most favourable to life. Still less can
this have happened during the alternate periods of
elevation ; or, to speak more accurately, the beds which
‘were then accumulated will generally have been
destroyed by being upraised and brought within the
- limits of the coast-action.
These remarks apply chiefly to littoral and sublittoral
deposits. In the case of an extensive and shallow sea,
such as that within a large part of the Malay Archi-
pelago, where the depth varies from 30 or 40 to 60
fathoms, a widely extended formation might be formed
during a period of elevation, and yet not suffer exces-
sively from denudation during its slow upheaval; but
the thickness of the formation could not be great, for
owing to the elevatory movement it would be less than
the depth in which it was formed; nor would the
deposit be much consolidated, nor be capped by over-
lying formations, so that 1t would run a good chance of
being worn away by atmospheric degradation and by
the action of the sea during subsequent oscillations
of level. It has, however, been suggested by Mr.
Hopkins, that if one part of the area, after rising and
before being denuded, subsided, the deposit formed
during the risimg movement, though not thick, might
afterwards become protected by fresh accumulations,
and thus be preserved for a long period.
Mr. Hopkins also expresses his belief that sedimentary
beds of considerable horizontal extent have rarely been
completely destroyed. But all geologists, excepting
>
64 . THE POORNESS OF OUR -[Cuar. X.
the few who believe that our present metamorphic
schists and plutonic rocks once formed the primordial
nucleus of the globe, will admit that these latter rocks
have been stript of their covering to an enormous
extent. For it is scarcely possible that such rocks
could have been solidified and crystallized whilst
uncovered ; but if the metamorphic action occurred at
profound depths of the ocean, the former protecting
mantle of rock may not have been very thick. Ad-
mitting then that gneiss, mica-schist, granite, diorite,
&c., were once necessarily covered up, how can we
account for the naked and extensive areas of such rocks
in many parts of the world, except on the belief that
they have subsequently been completely denuded of all
overlying strata? That such extensive areas do exist
cannot be doubted: the granitic region of Parime is
described by Humboldt as being at least nineteen times
as large as Switzerland. South of the Amazon, Boué
colours an area composed of rocks of this nature as
equal to that of Spain, France, Italy, part of Germany,
and the British Islands, all conjomed. This region has
not been carefully explored, but from the concurrent
testimony of travellers, the granitic area is very large:
thus, Von Eschwege gives a detailed section of these
rocks, stretching from Rio de Janeiro for 260 geo-
graphical miles inland in a straight line; and I
travelled for 150 miles in another direction, and saw
nothing but granitic rocks. Numerous specimens,
collected along the whole coast from near Rio Janeiro to
the mouth of the Plata, a distance of 1100 geographical
miles, were examined by me, and they all belonged to
this class. Inland, along the whole northern bank of
the Plata I saw, besides modern tertiary beds, only one
Car. X.} PALAONTOLOGICAL COLLECTIONS. 65
small patch of slightly metamorphosed rock, which
alone could have formed a part of the original capping
of the granitic series. Turning to a well-known region,
namely, to the United States and Canada, as shown in
Professor H. D. Rogers’s beautiful map, I have estimated
the areas by cutting out and weighing the paper, and I
find that the metamorphic (excluding “the semi-meta-
“morphic”) and granitic rocks exceed, in the proportion
of 19 to 12:5, the whole of the newer Paleozoic
formations. In many regions the metamorphic and
granitic rocks would be found much more widely
extended than they appear to be, if all the sedimentary
beds were removed which rest unconformably on them,
and which could not have formed part of the original
mantle under which they were crystallized. Hence it
is probable that in some parts of the world whole
formations have been completely denuded, with not a
wreck left behind.
One remark is here worth a passing notice. During
periods of elevation the area of the land and of the
adjoining shoal parts of the sea will be increased, and
new stations will often be formed :—all circumstances
favourable, as previously explained, for the formation of
new varieties and species; but during such periods
there will generally be a blank in the geological record.
On the other hand, during subsidence, the inhabited
area and number of inhabitants will decrease (excepting
on the shores of a continent when first broken up into
an archipelago), and consequently during subsidence,
though there will be much extinction, few new varieties
or species will be formed ; and it is during these very
periods of subsidence, that the deposits which are
richest in fossils have been accumulated.
Pe ee ay
Sine
66 ABSENCE OF INTERMEDIATE VARIETIES [Caar. X.
On the Absence of Numerous Intermediate Varieties in
any Single Formation.
From these several considerations, it cannot be
doubted that the geological record, viewed as a whole,
is extremely imperfect; but if we confine our attention
to any one formation, it becomes much more difficult to
understand why we do not therein find closely graduated
varieties between the allied species which lived at its
commencement and at its close. Several cases are on
record of the same species presenting varieties in the
upper and lower parts of the same formation ; thus,
Trautschold gives a number of instances with Am-
monites ; and Hilgendorf has described a most curious
case of ten graduated forms of Planorbis multiformis in
the successive beds of a fresh-water formation in
Switzerland. Although each formation has indispu-
tably required a vast number of years for its deposition,
several reasons can be given why each should not
commonly include a graduated series of links between
the species which lived at its commencement and close;
but I cannot assign due proportional weight to the
following considerations.
Although each formation may mark a very long lapse
of years, each probably is short compared with the
period requisite to change one species into another. I
am aware that two paleontologists, whose opinions are
worthy of much deference, namely Bronn and Wood-
ward, have concluded that the average duration of each
formation is twice or thrice as long as the average
duration of specific forms. But insuperable difficulties,
as it seems to me, prevent us from coming to any just
conclusion on this head. When we see a species first
Cuap. X.j IN ANY SINGLE FORMATION. 67
appearing in the middle of any formation, it would be
rash in the extreme to infer that it had not elsewhere
previously existed. So again when we find a species
disappearing before the last layers have been deposited,
it would be equally rash to suppose that it then became
extinct. We forget how small the area of Europe is
compared with the rest of the world; nor have the
several stages of the same formation throughout Europe
been correlated with perfect accuracy.
~ We may safely infer that with marine animals of all
kinds there has been a large amount of migration due
to climatal and other changes; and when we see a
species first appearing in any formation, the probability
is that it only then first immigrated into that area. It
is well-known, for instance, that several species appear
somewhat earlier in the paleozoic beds of North
America than in those of Europe; time having appa-
rently been required for their migration from the
American to the European seas. In examining the
latest deposits in various quarters of the world, it has
everywhere been noted, that some few still existing
species are common in the deposit, but have become
extinct in the immediately surrounding sea; or, con-
versely, that some are now abundant in the neighbouring
sea, but are rare or absent in this particular deposit.
It is an excellent lesson to reflect on the ascertained
amount of migration of the inhabitants of Europe
during the glacial epoch, which forms only a part ot
one whole geological period; and likewise to reflect on
the changes of level, on the extreme change of climate,
and on the great lapse of time, all included within this
same glacial period. Yet it may be doubted whether,
in any quarter of the world, sedimentary deposits,
24
68 ABSENCE OF INTERMEDIATE VARIETIES [Cuap. X.
including fossil remains, have gone on accumulating
within the same area during the whole of this period.
Jt is not, for instance, probable that sediment was
deposited during the whole of the glacial period near
the mouth of the Mississippi, within that limit of depth
at which marine animals can best flourish: for we
know that great geographical changes occurred in
other parts of America during this space of time.
When such beds as were deposited in shallow water
near the mouth of the Mississippi during some part of
the glacial period shall have been upraised, organic
remains will probably first appear and disappear at
different levels, owing to the migrations of species and
to geographical changes. And in the distant future, a
geologist, examining these beds, would be tempted to
conclude that the average duration of life of the
embedded fossils had been less than that of the glacial
period, instead of having been really far greater, that is,
extending from before the glacial epoch to the present day.
In order to get a perfect gradation between two forms
in the upper and lower parts of the same formation, the
deposit must have gone on continuously accumulating
during a long period, sufficient for the slow process of
modification; hence the deposit must be a very thick
one; and the species undergoing change must have
lived in the same district throughout the whole time.
But we have seen that a thick formation, fossiliferous
throughout its entire thickness, can accumulate only
during a period of subsidence; and to keep the depth
approximately the same, which is necessary that the
same marine species may live on the same space, the
supply of sediment must nearly counterbalance the
amount of subsidence. But this same movement of
Cuap. X.} IN ANY SINGLE FORMATION. 69
subsidence will tend to submerge the area whence the
sediment is derived, and thus diminish the supply,
whilst the downward movement continues. In fact,
this nearly exact balancing between the supply of
sediment and the amount of subsidence is probably a
rare contingency ; for it has been observed by more than
one palontologist, that very thick deposits are usually
barren of organic remains, except near their upper or
lower limits.
It would seem that each separate formation, like the
whole pile of formations in any country, has generally
been intermittent in its accumulation. When we see,
as is so often the case, a formation composed of beds
of widely different mineralogical composition, we may
reasonably suspect that the process of deposition has
been more or less interrupted. Nor will the closest
inspection of a formation give us any idea of the length
of time which its deposition may have consumed.
Many instances could be given of beds only a few feet
in thickness, representing formations, which are else-
where thousands of feet in thickness, and which must
have required an enormous period for their accumu-
lation; yet no one ignorant of this fact would have
even suspected the vast lapse of time represented by
the thinner formation. Many cases could be given of
the lower beds of a formation having been upraised,
denuded, submerged, and then re-covered by the upper
beds of the same formation,—facts, showing what wide,
yet easily overlooked, intervals have occurred in its
accumulation. In other cases we have the plainest
evidence in great fossilised trees, still standing upright
as they grew, of many long intervals of time and
changes of level during the process of deposition, which
70 ABSENCE OF INTERMEDIATE VARIETIES [Cuap. X.
would not have been suspected, had not the trees been
preserved: thus Sir C. Lyell and Dr. Dawson found
carboniferous beds 1400 feet thick in Nova Scotia, with
ancient root-bearing strata, one above the other at no
less than sixty-eight different levels. Hence, when the
same species occurs at the bottom, middle, and top of a
formation, the probability is that it has not lived on the
same spot during the whole period of deposition, but
has disappeared and reappeared, perhaps many times,
during the same geological period. Consequently if it
were to undergo a considerable amount of modification
during the deposition of any one geological formation,
a section would not include all the fine intermediate
gradations which must on our theory have existed, but
abrupt, though perhaps slight, changes of form.
It is all-important to remember that naturalists have
no golden rule by which to distinguish species and
varieties; they grant some little variability to each
species, but when they meet with a somewhat greater
amount of difference between any two forms, they rank
both as species, unless they are enabled to connect
them together by the closest intermediate gradations ;
and this, from the reasous just assigned, we can seldom
hope to effect in any one geological section. Supposing
B and C to be two species, and a third, A, to be found
in an older and underlying bed; even if A were strictly
intermediate between B and C, it would simply be
ranked as a third and distinct species, unless at the
same time it could be closely connected by interme-
diate varieties with either one or both forms. Nor
should it be forgotten, as before explained, that A
might be the actual progenitor of B and C, and yet
would not necessarily be strictly-intermediate between
Cuar. XJ IN ANY SINGLE FORMATION. 71
them in all respects. So that we might obtain the
parent-species and its several modified descendants
from the lower and upper beds of the same formation,
and unless we obtained numerous transitional grada-
tions, we should not recognise their blood-relationship,
and should consequently rank them as distinct species.
It is notorious on what excessively slight differences
many palzontologists have founded their species; and
they do this the more readily if the specimens come
from different sub-stages of the same formation. Some
experienced conchologists are now sinking many of the.
very fine species of D’Orbigny and others into the rank
of varieties; and on this view we do find the kind of
evidence of change which on the theory we ought to
find. Look again at the later tertiary deposits, which
include many shells believed by the majority of natu-
ralists to be identical with existing species; but some
excellent naturalists, as Agassiz and Pictet, maintain
that all these tertiary species are specifically distinct,
though the distinction is admitted to be very slight ;¢
so that here, unless we believe that these eminent
naturalists have been misled by their imaginations,
and that these late tertiary species really present no
difference whatever from their living representatives, or
unless we admit, in opposition to the judgment of
most naturalists, that these tertiary species are all
truly distinct from the recent, we have evidence of the
frequent occurrence of slight modifications of the kind
required. If we look to rather wider intervals of time,
namely, to distinct but consecutive stages of the same
great formation, we find that the embedded fossils,
though universally ranked as specifically different, yet
are far more closely related to each other than are the
72 ABSENCE OF INTERMEDIATE VARIETIES ([Cuar. X.
species found in more widely separated formations; so
that here again we have undoubted evidence of change
in the direction required by the theory; but to this
latter subject I shall return in the following chapter
With animals and plants that propagate rapidly and
do not wander much, there is reason to suspect, as we
have formerly seen, that their varieties are generally at
first local; and that such local varieties do not spread
widely and supplant their parent-forms until they
have been modified and perfected in some considerable
degree. According to this view, the chance of dis-
covering in a formation in any one country all the
early stages of transition between any two forms, is
small, for the successive changes are supposed to have
been local or confined to some one spot. Most marine
animals have a wide range; and we have seen that
with plants it is those which have the widest range,
that oftenest present varieties ; so that, with shells and
other marine animals, it is probable that those which
had the widest range, far exceeding the limits of the
known geological formations in Europe, have oftenest
given rise, first to local varieties and ultimately to new
species ; and this again would greatly lessen the chance
of our being able to trace the stages of transition in
any one geological formation.
It is a more important consideration, leading to the
same result, as lately insisted on by Dr. Falconer,
namely, that the period during which each species
underwent modification, though long as measured by
years, was probably short in comparison with that
during which it remained without undergoing any change,
It should not be forgotten, that at the present day,
with perfect specimens for examination, two forms
Cuar. X.] IN ANY SINGLE FORMATION. 73
can seldom be connected by intermediate varieties,
and thus proved to be the same species, until many
specimens are collected from many places; and with
fossil species this can rarely be done. We _ shall,
perhaps, best perceive the improbability of our being
enabled to connect species by numerous, fine, inter-
mediate, fossil links, by asking ourselves whether, for
instance, geologists at some future period will be able
to prove that our different breeds of cattle, sheep,
horses, and dogs are descended from a single stock or
from several aboriginal stocks; or, again, whether
certain sea-shells inhabiting the shores of North
America, which are ranked by some conchologists as
distinct species from their European representatives,
and by other conchologists as only varieties, are really
varieties, or are, as it is called, specifically distinct.
This could be effected by the future geologist only by
his discovering in a fossil state numerous intermediate
gradations; and such success is improbable in the
_ highest degree.
It has been asserted over and over again, by writers
who believe in the immutability of species, that geology
yields no linking forms. This assertion, as we shall
see in the next chapter, is certainly erroneous. As Sir
J. Lubbock has remarked, “ Every species is a link
“between other allied forms.” If we take a genus
having a score of species, recent and extinct, and
destroy four-fifths of them, no one doubts that the
remainder will stand much more distinct from each
other. If the extreme forms in the genus happen to
have been thus destroyed, the genus itself will stand
more distinct from other allied genera. What geo-
logical research has not revealed, is the former existence
74 ABSENCE OF INTERMEDIATE VARIETIES ([Cuap. X.
of infinitely numerous gradations, as fine as existing
varieties, connecting together nearly all existing and
extinct species. But this ought not to be expected ; yet
this has been repeatedly advanced as a most serious
objection against my views.
It may-be worth while to sum up the foregoing
remarks on the causes of the imperfection of the
geological record under an imaginary illustration. The
Malay Archipelago is about the size of Europe from the
North Cape to the Mediterranean, and from Britain to
Russia; and therefore equals all the geological forma-
tions which have been examined with any accuracy,
excepting those of the United States of America. I
fully agree with Mr. Godwin-Austen, that the present
condition of the Malay Archipelago, with its numerous
large islands separated by wide and shallow seas, pro-
bably represents the former state of Europe, whilst
most of our formations were accumulating. The Malay
Archipelago is one of the richest regions in organic
beings; yet if all the species were to be collected which
have ever lived there, how imperfectly would they
represent the natural history of the world}
But we have every reason to believe that the
terrestrial productions of the archipelago would be
preserved in an extremely imperfect manner in the
formations which we suppose to be there accumulating.
Not many of the strictly littoral animals, or of those
which lived on naked submarine rocks, would be em-
bedded ; and those embedded in gravel or sand would
not endure to a distant epoch. Wherever sediment did
not accumulate on the bed of the sea, or where it did
not accumulate at a sufficient rate to protect organic
bodies from decay, no remains could be preserved.
ec ha
se
Cuap. X.] IN ANY SINGLE FORMATION. 75
Formations rich in fossils of many kinds, and of
thickness sufficient to last to an age as distant in
futurity as the secondary formations lie in the past,
would generally be formed in the archipelago only
during periods of subsidence. These periods of subsi-
dence would be separated from each other by immense
intervals of time, during which the area would be
either stationary or rising; whilst rising, the fossili-
ferous formations on the steeper shores would be de-
stroyed, almost as soon as accumulated, by the incessant
coast-action, aS we now see on the shores of South -
America. Even throughout the extensive and shallow
seas within the archipelago, sedimentary beds could
hardly be accumulated of great thickness during the
periods of elevation, or become capped and protected
by subsequent deposits, so as to have a good chance of
enduring to a very distant future. During the periods
of subsidence, there would probably be much extinction
of life; during the periods of elevation, there would be
much variation, but the geological record would then be
less perfect.
It may be doubted whether the duration of any one
great period of subsidence over the whole or part of the
archipelago, together with a contemporaneous accumula-
tion of sediment, would exceed the average duration of
the same specific forms; and these contingencies are
indispensable for the preservation of all the transitional
gradations between any two or more species. If such
gradations were not all fully preserved, transitional
varieties would merely appear as so many new, though
closely allied species. It is also probable that each
great period of subsidence would be interrupted by
oscillations of level, and that slight climatal changes
76 ABSENCE OF INTERMEDIATE VARIETIES [Cuap. X.
would intervene during such lengthy periods; and in
these cases the inhabitants of the archipelago would
migrate, and no closely consecutive record of their
modifications could be preserved in any one formation.
Very many of the marine inhabitants of the archi-
pelago now range thousands of miles beyond its con-
fines; and analogy plainly leads to the belief that it
would be chiefly these far-ranging species, though only
some of them, which would oftenest produce new
varieties ; and the varieties would at first be local or
confined to one place, but if possessed of any decided
advantage, or when further modified and improved, they
would slowly spread and supplant their parent-forms.
When such varieties returned to their ancient homes,
as they would differ from their former state in a nearly
uniform, though perhaps extremely slight degree, and
as they would be found embedded in slightly different
sub-stages of the same formation, they would, according
to the principles followed by many palzontologists, be
ranked as new and distinct species.
If then there be some degree of truth in these re-
marks, we have no right to expect to find, in our
geological formations, an infinite number of those fine
transitional forms which, on our theory, have connected
all the past and present species of the same group into
one long and branching chain of life. We ought only
to look for a few links, and such assuredly we do find
—some more distantly, some more closely, related to
each other; and these links, let them be ever so close,
if found in different stages of the same formation,
would, by many paleontologists, be ranked as distinct
species. But I do not pretend that I should ever have
suspected how poor was the record in the best preserved
Cuap. X.] IN ANY SINGLE FORMATION. 77
geological sections, had not the absence of innumerable
transitional links between the species which lived at
the commencement and close of each formation, pressed
so hardly on my theory.
On the sudden Appearance of whole Groups of
allied Species.
The abrupt manner in which whole groups of species
suddenly appear in certain formations, has been urged
by several palzontologists—for instance, by Agassiz,
Pictet, and Sedgwick—as a fatal objection to the belief
in the transmutation of species. If numerous species,
belonging to the same genera or families, have really
started into life at once, the fact would be fatal to the
theory of evolution through natural selection. For the
development by this means of a group of forms, all of
which are descended from some one progenitor, must
have been an extremely slow process; and the progeni-
tors must have lived long before their modified descen-
dants. But we continually overrate the perfection of
the geological record, and falsely infer, because certain
genera or families have not been found beneath a
certain stage, that they did not exist before that stage.
In all cases positive paleontological evidence may be
implicitly trusted; negative evidence is worthless, as
experience has so often shown. We continually forget
how large the world is, compared with the area over
which our geological formations have been carefully
examined ; we forget that groups of species may else-
where have long existed, and have slowly multiplied,
before they invaded the ancient archipelagoes of Europe
and the United States. We do not make due allowance
8 SUDDEN APPEARANCE OF [Cuar. X.
for the intervals of time which have elapsed between our
consecutive formations,—longer perhaps in many cases
than the time required for the accumulation of each
formation. These intervals will have given time for
the multiplication of species from some one parent-
form: and in the succeeding formation, such groups or
species will appear as if suddenly created.
I may here recall a remark formerly made, namely,
that it might require a long succession of ages to adapt
an organism to some new and peculiar line of life, for
instance, to fly through the air; and consequently that
the transitional forms would often long remain con-
fined to some one region; but that, when this adaptation
had once been effected, and a few species had thus
acquired a great advantage over other organisms, a
comparatively short time would be necessary to produce
many divergent forms, which would spread rapidly and
widely, throughout the world. Professor Pictet, in his
excellent Review of this work, in commenting on early
transitional forms, and taking birds as an illustration,
cannot see how the successive modifications of the
anterior imbs of a supposed prototype could possibly
have been of any advantage. But look at the penguins
of the Southern Ocean; have not these birds their front
limbs in this precise intermediate state of “neither true
“arms nor true wings”? Yet these birds hold their
place victoriously in the battle for life; for they exist
in infinite numbers and of many kinds. I do not
suppose that we here see the real transitional grades
through which the wings of birds have passed; but
what special difficulty is there in believing that it
might profit the modified descendants of the penguin,
first to become enabled to flap along the surface of the
Caap. X.] GROUPS OF ALLIED SPECIES. 719
sea like the logger-headed duck, and ultimately to rise
from its surface and glide through the air ?
I will now give a few examples to illustrate the
foregoing remarks, and to show how liable we are to
error In supposing that whole groups of species have
suddenly been produced. Even in so short an interval
as that between the first and second editions of Pictet’s
great work on Paleontology, published in 1844-46 and
in 1853-57, the conclusions on the first appearance and
disappearance of several groups of animals have been
considerably modified; and a third edition would
require still further changes. I may recall the well-
known fact that in geological treatises, published not
many years ago, mammals were always spoken of as
having abruptly come in at the commencement of the
tertiary series. And now one of the richest known ac-
cumulations of fossil mammals belongs to the middle of
the secondary series; and true mammals have been
discovered in the new red sandstone at nearly the com-
mencement of this great series. Cuvier used to urge that
no monkey occurred in any tertiary stratum; but now
extinct species have been discovered in India, South
America and in Europe, as far back as the miocene stage.
Had it not been for the rare accident of the preservation
of footsteps in the new red sandstone of the United States,
who would have ventured to suppose that no less than
at least thirty different bird-like animals, some of
gigantic size, existed during that period? Not a frag-
ment of bone has been discovered in these beds. Not
long ago, paleontologists maintained that the whole
class of birds came suddenly into existence during the
eocene period; but now we know, on the authority of
Professor ie that a bird certainly lived during the
80 SUDDEN APPEARANCE OF [Caar. X.
deposition of the upper greensand; and still more
recently, that strange bird, the Archeopteryx, with a
long lizard-like tail, bearing a pair of feathers on each
joint, and with its wings furnished with two free claws,
has been discovered in the oolitic slates of Solenhofen.
Hardly any recent discovery shows more forcibly than
this, how little we as yet know of the former inhabitants
. of the world.
I may give another instance, which, from having
passed under my own eyes, has much struck me. Ina
memoir on Fossil Sessile Cirripedes, I stated that, from
the large number of existing and extinct tertiary
species ; from the extraordinary abundance of the in-
dividuals of many species all over the world, from the
Arctic regions to the equator, inhabiting various zones of
depths from the upper tidal limits to 50 fathoms ; from
the perfect manner in which specimens are preserved
in the oldest tertiary beds; from the ease with which
even a fragment of a valve can be recognised; from all
these circumstances, [ inferred that, had sessile cirripedes _
existed during the secondary periods, they would
certainly have been preserved and discovered; and as
not one species had then been discovered in beds of
this age, I concluded that this great group had been
suddenly developed at the commencement of the ter-
tiary series. This was a sore trouble to me, adding as
I then thought one more instance of the abrupt ap-
pearance of a great group of species. But my work had
hardly been published, when a skilful palzontologist,
M. Bosquet, sent me a drawing of a perfect specimen
of an unmistakeable sessile cirripede, which he had
himself extracted from the chalk of Belgium. And, as
if to make the case as striking as possible, this cirripede
Cuap. X.] GROUPS OF ALLIED SPECIES. 81
was a Chthamalus, a very common, large, and ubi-
quitous genus, of which not one species has as yet
been found even in any tertiary stratum. Still more
recently, a Pyrgoma, a member of a distinct sub-family
of sessile cirripedes, has been discovered by Mr. Wood-
ward in the upper chalk; so that we now have abun-
dant evidence of the existence of this group of animals
during the secondary period.
The case most frequently insisted on by paleonto-
logists of the apparently sudden appearance of a whole
group of species, is that of the teleostean fishes, low
down, according to Agassiz, in the Chalk period. This
group includes the large majority of existing species.
But certain Jurassic and Triassic forms are now com-
monly admitted to be teleostean; and even some
paleeozoic forms have thus been classed by one high
authority. If the teleosteans had really appeared
suddenly in the northern hemisphere at the commence-
ment of the chalk formation. the fact would have been
highly remarkable ; but it would not have formed an
insuperable difficulty, unless it could likewise have
been shown that at the same period the species were
suddenly and simultaneously developed in other
quarters of the world. It is almost superfluous to
remark that hardly any fossil-fish are known from south
of the equator ; and by running through Pictet’s Paleeon-
tology it will be seen that very few species are known
from several formations in Europe. Some few families
of fish now have a confined range ; the teleostean fishes
might formerly have had a similarly confined range,
and after having been largely developed in some one
sea, have spread widely. Nor have we any right to
suppose that the seas of the world have always been
82 GROUPS OF ALLIED SPECIES [Cuar. X.
so freely open from south to north as they are at
present. Even at this day, if the Malay Archipelago
were converted into land, the tropical parts of the
Indian Ocean would form a large and perfectly enclosed
basin, In which any great group of marine animals
might be multiplied; and here they would remain
confined, until some of the species became adapted to
a cooler climate, and were enabled to double the
Southern capes of Africa or Australia, and thus reach
other and distant seas.
From these considerations, from our ignorance of the
geology of other countries beyond the confines of
Europe and the United States, and from the revolution
in our paleontological knowledge effected by the dis-
coveries of the last dozen years, it seems to me to be
about as rash to dogmatize on the succession of organic
forms throughout the world, as it would be for a natura-
list to land for five minutes on a barren point in
Australia, and then to discuss the number and range of
its productions.
On the sudden Appearance of Groups of allied Species
in the lowest known Fossiliferous Strata.
There is another and allied difficulty, which is much
more serious. I allude to the manner in which species
belonging to several of the main divisions of the animal
kingdom suddenly appear in the lowest known fossili-
ferous rocks. Most of the arguments which have
convinced me that all the existing species of the same
group are descended from a single progenitor, apply
with equal force to the earliest known species. For
instance, it cannot be doubted that all the Cambrian
Cuap. X.}| IN LOWEST FOSSILIFEROUS STRATA. 83
and Silurian trilobites are descended from some one
crustacean, which must have lived long before the
Cambrian age, and which probably differed greatly from
any known animal. Some of the most ancient animals,
as the Nautilus, Lingula, &., do not differ much from
living species ; and it cannot on our theory be supposed,
that these old species were the progenitors of all the
species belonging to the same groups which have
subsequently appeared, for they are not in any degree
intermediate in character.
Consequently; if the theory be true, it is indisputable
that before the lowest Cambrian stratum was deposited
long periods elapsed, as long as, or probably far longer
than, the whole interval from the Cambrian age to the
present day; and that during these vast periods the
world swarmed with living creatures. Here we en-
counter a formidable objection ; for it seems doubtful
whether the earth, in a fit state for the habitation of
living creatures, has lasted long enough. Sir W.
Thompson concludes that the consolidation of the crust
can hardly have occurred less than 20 or more than
400 million years ago, but probably not less than 98 or
more than 200 million years. These very wide limits
show how doubtful the data are; and other elements
may have hereafter to be introduced into the problem.
Mr. Croll estimates that about 60 million years have
elapsed since the Cambrian period, but this, judging
from the small amount of organic change since the
commencement of the Glacial epoch, appears a very
short time for the many and great mutations of life, which
have certainly occurred since the Cambrian formation ;
and the previous 140 million years can hardly be con-
sidered as sufficient for the development of the varied
84 GROUPS OF ALLIED SPECIES [Cuar. X
forms of life which already existed during the Cam-
brian period. It is, however, probable, as Sir William
Thompson insists, that the world at a very early period
was subjected to more rapid and violent changes in
its physical conditions than those now occurring; and
such changes would have tended to induce changes
at a corresponding rate in the organisms which then
existed.
To the question why we do not find rich fossiliferous
deposits belonging to these assumed earliest periods
prior to the Cambrian system, I can give no satisfactory
answer. Several eminent geologists, with Sir R.
Murchison at their head, were until recently convinced
that we beheld in the organic remains of the lowest
Silurian stratum the first dawn of life. Other highly
competent judges, as Lyell and E. Forbes, have disputed
this conclusion. We should not forget that only asmall
portion of the world is known with accuracy. Not
very long ago M. Barrande added another and lower
stage, abounding with new and peculiar species, beneath
the then known Silurian system; and now, still lower
down in the Lower Cambrian formation, Mr. Hicks has
found in South Wales beds rich in trilobites, and con-
taining various molluscsand annelids. The presence of
phosphatic nodules and bituminous matter, even in
some of the lowest azoic rocks, probably indicates life
at these periods ; and the existence of the Eozoon in the
Laurentian formation of Canada is generally admitted.
There are three great series of strata beneath the Silurian
system in Canada, in the lowest of which the Eozoon is
found. Sir W. Logan states that their “ united thickness
“may possibly far surpass that of all the succeeding
‘rocks, from the base of the paleozoic series to the
Cuap. X.] IN LOWEST FOSSILIFEROUS STRATA. 85
“present time. We are thus carried back to a period
“so remote, that the appearance of the so-called
“Primordial fauna (of Barrande) may by some be
“considered as a comparatively modern event.” The
Eozoon belongs to the most lowly organised of all
classes of animals, but is highly organised for its class ;
it existed in countless numbers, and,as Dr. Dawson has
remarked, certainly preyed on other minute organic
beings, which must have lived in great numbers. Thus
the words, which I wrote in 1859, about the existence
of living beings long before the Cambrian period, and
which are almost the same with those since used by Sir
W. Logan, have proved true. Nevertheless, the difficulty
of assigning any good reason for the absence of vast
piles of strata rich in fossils beneath the Cambrian
system is very great. It does not seem probable that
the most ancient beds have been quite worn away by
denudation, or that their fossils have been wholly
obliterated by metamorphic action, for if this had been
the case we should have found only small remnants of
the formations next succeeding them in age, and these
would always have existed in a partially metamorphosed
condition. But the descriptions which we possess of
the Silurian deposits over immense territories in Russia
and in North America, do not support the view, that
the older a formation is, the more invariably it has
suffered extreme denudation and metamorphism.
The case at present must remain inexplicable; and
may be truly urged as a valid argument against the
views here entertained. To show that it may hereafter
receive some explanation, I will give the following
hypothesis. From the nature of the organic remains
which do not appear to have inhabited profound depths,
86 GROUPS OF ALLIED SPECIES [Cuar. X.
in the several formations of Europe and of the United
States; and from the amount of sediment, miles in
thickness, of which the formations are composed, we
may infer that from first to last large islands or tracts
of land, whence the sediment was derived, occurred in
the neighbourhood of the now existing continents of
Europe and North America. This same view has since
been maintained by Agassiz and others. But we do not
know what was the state of things in the intervals
between the several successive formations; whether
Europe and the United States during these intervals
existed as dry land, or as a submarine surface near land,
on which sediment was not deposited, or as the bed of
an open and unfathomable sea.
Looking to the existing oceans, which are thrice as
extensive as the land, we see them studded with many
islands; but hardly one truly oceanic island (with the
exception of New Zealand, if this can be called a truly
oceanic island) is as yet known to afford even a remnant
of any palzozoic or secondary formation. Hence we
may perhaps infer, that during the palozoic and
secondary periods, neither continents nor continental
islands existed where our oceans now extend; for had
they existed, palzeozoic and secondary formations would
in all probability have been accumulated from sediment
derived from their wear and tear; and these would have
been at least partially upheaved by the oscillations of
level, which must have intervened during these enor-
mously long periods. If then we may infer anything
from these facts, we may infer that, where our oceans
now extend, oceans have extended from the remotest
period of which we have any record; and on the other
hand, that where continents now exist, large tracts of
Cuap. X.] IN LOWEST FOSSILIFEROUS STRATA. 87
land have existed, subjected no doubt to great oscilla-
tions of level, since the Cambrian period. The coloured
map appended to my volume on Coral Reefs, led me to
conclude that the great oceans are still mainly areas of
subsidence, the great archipelagoes still areas of oscilla-
tions of level, and the continents areas of elevation.
But we have no reason to assume that things have thus
remained from the beginning of the world. Our contin-
ents seem to have been formed by a preponderance, during
many oscillations of level, of the force of elevation ; but
may not the areas of preponderant movement have
changed in the lapse of ages ? Ata period long antecedent
to the Cambrian epoch, continents may have existed where
oceans are now spread out; and clear and open oceans
may have existed where our continents now stand. Nor
should we be justified in assuming that if, for instance,
the bed of the Pacific Ocean were now converted into a
continent we should there find sedimentary formations in
a recognisable condition older than the Cambrian strata,
supposing such to have been formerly deposited ; for it
might well happen that strata which had subsided some
miles nearer to the centre of the earth, and which had
been pressed on by an enormous weight of superincum-
bent water, might have undergone far more metamorphic
action than strata which have always remained nearer
to the surface. The immense areas in some parts of the
world, for instance in South America, of naked meta-
morphic rocks, which must have been heated under
great pressure, have always seemed to me to require
some special explanation; and we may perhaps believe
that we see in these large areas, the many formations
long anterior to the Cambrian epoch in a completely
metamorphosed and denuded condition.
88 IMPERFECTION OF GEOLOGICAL RECORD. [Cnapr. X.
The several difficulties here discussed, namely—that,
though we find in our geological formations many links
between the species which now exist and which formerly
existed, we do not find infinitely numerous fine transi-
tional forms closely joming them all together ;—the
sudden manner in which several groups of species first
appear in our European formations ;—the almost entire
absence, as at present known, of formations rich in fossils
beneath the Cambrian strata,—are all undoubtedly of the
most serious nature. We see this in the fact that the
most eminent paleontologists, namely, Cuvier, Agassiz
Barrande, Pictet, Falconer, E. Forbes, &c., and all our
greatest geologists, as Lyell, Murchison, Sedgwick, &c.,
have unanimously, often vehemently, maintained the
immutability of species. But Sir Charles Lyell now
gives the support of his high authority to the opposite
side ; and most geologists and paleontologists are much
shaken in their former belief. Those who believe that
the geological record is in any degree perfect, will un-
doubtedly at once reject the theory. For my part,
following out Lyell’s metaphor, I look at the geological
record as a history of the world imperfectly kept, and
written in a changing dialect ; of this history we possess
the last volume alone, relating only to two or three
countries. Of this volume, only here and there a short
chapter has been preserved; and of each page, only here
and there a few lines. Each word of the slowly-changing
language, more or less different in the successive chapters,
may represent the forms of life, which are entombed in
our consecutive formations, and which falsely appear
to have been abruptly introduced. On this view, the
difficulties above discussed are greatly diminished, or
even disappear.
| p
Cuap. XI.J SUCCESSION OF ORGANIC BEINGS. $9
CHAPTER XI.
ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS.
On the slow and successive appearance of new species—On their
different rates of change—Species once lost do not reappear—
Groups of species follow the same general rules in their ap-
pearance and disappearance as do single species—On extinction
—On simultaneous changes in the forms of life throughout the
world—On the affinities of extinct species to each other and to
living species—On the state of development of ancient forms—
On the succession of the same types within the same areas—
Summary of preceding and present chapter.
LET us now see whether tho several facts and laws
relating to the geological succession of organic beings
accord best with the common view of the immutability
of species, or with that of their slow and gradual modi-
fication, through variation and natural selection.
New species have appeared very slowly, one after
another, both on the land and in the waters. Lyell has
shown that it is hardly possible to resist the evidence on
this head in the case of the several tertiary stages; and
every year tends to fill up the blanks between the stages,
and to make the proportion between the lost and existing
forms more gradual. In some of the most recent beds,
though undoubtedly of high antiquity if measured by
years, only one or two species are extinct, and only one
or two are new, having appeared there for the first time,
either locally, or, as far as we know, on the face of
the earth. The secondary formations are more broken ;
90 THE GEOLOGICAL SUCCESSION ([Czap. XI.
but, as Bronn has remarked, neither the appearance
nor disappearance of the many species embedded in
each formation has been simultaneous.
Species belonging to different genera and classes have
not changed at the same rate, or in the same degree.
In the older tertiary beds a few living shells may still
be found in the midst of a multitude of extinct forms.
Falconer has given a striking instance of a similar fact,
for an existing crocodile is associated with many lost
mammals and reptiles in the sub-Himalayan deposits.
The Silurian Lingula differs but little from the living
species of this genus ; whereas most of the other Silurian
Molluscs and all the Crustaceans have changed greatly.
The productions of the land seem to have changed at a
quicker rate than those of the sea, of which a striking
instance has been observed in Switzerland. There is
some reason to believe that organisms high in the scale,
change more quickly than those that are low: though
there are exceptions tothisrule. The amount of organic
change, as Pictet has remarked, is not the same in each
successive so-called formation. Yet if we compare any
but the most closely related formations, all the species
will be found to have undergone some change. When
a species has once disappeared from the face of the earth,
we have no reason to believe that the same identical
form ever reappears. The strongest apparent exception
to this latter rule is that of the so-called “colonies ” of
M. Barrande, which intrude for a period in the midst of
an older formation, and then allow the pre-existing
fauna to reappear ; but Lyell’s explanation, namely, that
it is a case of temporary migration from a distinct geo-
eraphical province, seems satisfactory.
These several facts accord well with our theory, which
Cuap, XI.) OF ORGANIC BEINGS. 91
includes no fixed law of development, causing all the
inhabitants of an area to change abruptly, or simul-
taneously, or to an equal degree. The process of modifi-
cation must be slow, and will generally affect only a
few species at the same time; for the variability of each
species is independent of that of all others. Whether
such variations or individual differences as may arise will
be accumulated through natural selection in a greater
or less degree, thus causing a greater or less amount of
permanent modification, will depend on many complex
contingencies—on the variations being of a beneficial
nature, on the freedom of intercrossing, on the slowly
changing physical conditions of the country, on the
immigration of new colonists, and on the nature of the
other inhabitants with which the varying species come
into competition. Hence it is by no means surprising
that one species should retain the same identical form
much longer than others; or, if changing, should change
in a less degree. We find similar relations between the
existing inhabitants of distinct countries; for instance,
the land-shells and coleopterous insects of Madeira have
come to differ considerably from their nearest allies on
the continent of Europe, whereas the marine shells and
birds have remained unaltered. We can perhaps under-
stand the apparently quicker rate of change in terrestrial
and in more highly organised productions compared
with marine and lower productions, by the more complex
relations of the higher beings to their organic and in-
organic conditions of life, as explained in a former
chapter. When many of the inhabitants of any area
have become modified and improved, we can understand,
on the principle of competition, and from the all-import-
ant relations of organism to organism in the struggle for
26
=
92 THE GEOLOGICAL SUCCESSION [Cxap. XL
life, that any form which did not become in some degree
modified and improved, would be liable to extermination.
Hence we see why all the species in the same region do
at last, if we look to long enough intervals of time, be-
come modified, for otherwise they would become extinct.
In members of the same class the average amount of
change, during long and equal periods of time, may,
perhaps, be nearly the same; but as the accumulation
of enduring formations, rich in fossils, depends on great
masses of sediment being deposited on subsiding areas,
our formations have been almost necessarily accumulated
at wide and irregularly intermittent intervals of time;
consequently the amount of organic change exhibited by
the fossils embedded in consecutive formations is not
equal. Each formation, on this view, does not mark a new
and complete act of creation, but only an occasional scene,
taken almost at hazard, in an ever slowly changing drama.
We can clearly understand why a species when once
lost should never reappear, even if the very same con-
ditions of life, organic and inorganic, should recur. For
though the offspring of one species might be adapted
(and no doubt this has occurred in innumerable in-
stances) to fill the place of another species in the economy
of nature, and thus supplant it; yet the two forms—
the old and the new—would not be identically the
same; for both would almost certainly inherit different
characters from their distinct progenitors ; and organisms
already differing would vary in a different manner,
For instance, it is possible, if all our fantail pigeons
were destroyed, that fanciers might make a new breed
hardly distinguishable from the present breed ; but if
the parent rock-pigeon were likewise destroyed, and
under nature we have every reason to believe that
Cap. X1.] ‘OF ORGANIC BEINGS. 93
parent-forms are generally supplanted and exterminated
by their improved offspring, it is incredible that a fantail,
identical with the existing breed, could be raised from
any other species of pigeon, or even from any other well-
established race of the domestic pigeon, for the successive
variations would almost certainly be in some degree
different, and the newly-formed variety would probably
inherit from its progenitor some characteristic differences.
Groups of species, that is, genera and families, follow
the same general rules in their appearance and dis-
appearance as do single species, changing more or less
quickly, and in a greater or lesser degree. A group,
when it has once disappeared, never reappears; that is,
its existence, as long as it lasts, is continuous. I am
aware that there are some apparent exceptions to this
rule, but the exceptions are surprisingly few, so few that
E. Forbes, Pictet, and Woodward (though all strongly
opposed to such views as I maintain) admit its truth;
and the rule strictly accords with the theory. For all
the species of the same group, however long it may
have lasted, are the modified descendants one from the
other, and all from a common progenitor. In the genus
Lingula, for instance, the species which have successively
appeared at all ages must have been connected by an
unbroken series of generations, from the lowest Silurian
stratum to the present day.
We have seen in the last chapter that whole groups
of species sometimes falsely appear to have been abruptly
developed; and I have attempted to give an explana-
tion of this fact, which if true would be fatal to my
views. But such cases are certainly exceptional; the
general rule being a gradual increase in number, until
the group reaches its maximum, and then, sooner or
94 EXTINCTION. (Cuar. XI.
later, a gradual decrease. If the number of the species
included within a genus, or the number of the genera
within a family, be represented by a vertical line of vary-
ing thickness, ascending through the successive geological
formations, in which the species are found, the line will
sometimes falsely appear to begin at its lower end, not
in a sharp point, but abruptly ; it then gradually thickens
upwards, often keeping of equal thickness for a space,
and ultimately thins out in the upper beds, marking the
decrease and final extinction of the species. This gradual
increase in number of the species of a group is strictly
conformable with the theory, for the species of the same
genus, and the genera of the same family, can mcerease
only slowly and progressively ; the process of modifica-
tion and the production of a number of allied forms
necessarily being a slow and gradual process,—one
species first giving rise to two or three varieties, these
being slowly converted into species, which in their turn
produce by equally slow steps other varieties and species,
and so on, like the branching of a great tree from asingle
stem, till the group becomes large.
On Extinction.
We have as yet only spoken incidentally of the dis-
appearance of species and of groups of species. On the
theory of natural selection, the extinction of old forms
and the production of new and improved forms are
intimately connected together. The old notion of all
the inhabitants of the earth having been swept away by
catastrophes at successive periods is very generally
given up, even by those geologists, as Elie de Beaumont,
Murchison, Barrande, &c., whose general views would
Crap. XI.] EXTINCTION. 95
naturally lead them to this conclusion. On the contrary,
we have every reason to believe, from the study of the
tertiary formations, that species and groups of species
eradually disappear, one after another, first from one spot,
then from another, and finally from the world. Insome
few cases however, as by the breaking of an isthmus
and the consequent irruption of a multitude of new
inhabitants into an adjoining sea, or by the final subsi-
dence of an island, the process of extinction may have
been rapid. Both single species and whole groups of
species last for very unequal periods; some groups,
as we have seen, have endured from the earliest known
dawn of life to the present day ; some have disappeared
‘before the close of the paleozoic period. No fixed law
seems to determine the length of time during which
any single species or any single genus endures. There
is reason to believe that the extinction of a whole group
of species is generally a slower process than their pro-
duction: if their appearance and disappearance be re-
presented, as before, by a vertical line of varying thick-
ness the line is found to taper more gradually at its upper
end, which marks the progress of extermination, than
at its lower end, which marks the first appearance and
the early increase in number of the species. In some
cases, however, the extermination of whole groups, as
of ammonites, towards the close of the secondary period,
has been wonderfully sudden.
The extinction of species has been involved in the
most gratuitous mystery. Some authors have even sup-
posed that, as the individual has a definite length of
life, so have species a definite duration. No one can
have marvelled more than I have done at the extinction
of species. When I found in La Plata the tooth of a
96 EXTINCTION. [Cuar. XI.
horse embedded with the remains of Mastodon, Mega-
therium, Toxodon, and other extinct monsters, which
all co-existed with still living shells at a very late geo-
logical period, I was filled with astonishment ; for, seeing
that the horse, since its introduction by the Spaniards
into South America, has run wild over the whole
country and has increased in numbers at an unparalleled
rate, I asked myself what could so recently have exter-
minated the former horse under conditions of life ap-
parently so favourable. But my astonishment was
groundless. Professor Owen soon perceived that the
tooth, though so like that of the existing horse, belonged
to an extinct species. Had this horse been still living,
but in some degree rare, no naturalist would have felt
the least surprise at its rarity ; for rarity is the attribute
of a vast number of species of all classes, in all countries.
If we ask ourselves why this or that species is rare, we
answer that something is unfavourable in its conditions
of life; but what that something is we can hardly ever
tell. On the supposition of the fossil horse still existing
as a rare species, we might have felt certain, from the
analogy of all other mammals, even of the slow-breeding
elephant, and from the history of the naturalisation of
the domestic horse in South America, that under more
favourable conditions it would in a very few years have
stocked the whole continent. But we could not have
told what the unfavourable conditions were which
checked its increase, whether some one or several con-
tingencies, and at what period of the horse’s life, and in
what degree they severally acted. If the conditions had
gone on, however slowly, becoming less and less favour-
able, we assuredly should not have perceived the fact,
yet the fossil horse would certainly have become rarer
Cuap, XI} EXTINCTION. 97
and rarer, and finally extinct ;—its place being seized
on by some more successful competitor. |
It is most difficult always to remember that the in-
crease of every creature is constantly being checked
by unperceived hostile agencies; and that these same
unperceived agencies are amply sufficient to cause rarity,
and finally extinction. So little is this subject under-
stood, that I have heard surprise repeatedly expressed
at such great monsters as the Mastodon and the more
ancient Dinosaurians having become extinct; as if mere
bodily strength gave victory in the battle of life. Mere
size, on the contrary, would in some cases determine, as
has been remarked by Owen, quicker extermination-from
the greater amount of requisite food. Before man in-
habited India or Africa, some cause must have checked
the continued increase of the existing elephant. <A
highly capable judge, Dr. Falconer, believes that it is
chiefly insects which, from incessantly harassing and
weakening the elephant in India, check its increase ; and
this was Bruce’s conclusion with respect to the African
elephant in Abyssinia. It is certain that insects and
blood-sucking bats determine the existence of the larger
naturalized quadrupeds in several parts of S. America.
We see in many cases in the more recent tertiary for-
mations, that rarity precedes extinction; and we know
that this has been the progress of events with those
animals which have been exterminated, either locally or
wholly, through man’s agency. I may repeat what I
published in 1845, namely, that to admit that species
generally become rare before they become extinct—to feel
no surprise at the rarity of a species, and yet to marvel
greatly when the species ceases to exist, is much the same
as to admit that sickness in the individual is the fore-
98 EXTINCTION. (Cuar. XI.
runner of death—to feel no surprise at sickness, but,
when the sick man dies, to wonder and to suspect that
he died by some deed of violence.
The theory of natural selection is grounded on the
belief that each new variety and ultimately each new
species, is produced and maintained by having some
advantage over those with which it comes into competi-
tion ; and the consequent extinction of the less-favoured
forms almost inevitably follows. It is the same with
our domestic productions; when a new and slightly
improved variety has been raised, it at first supplants
the less improved varieties in the same neighbourhood ;
when much improved it is transported far and near, like
our short-horn cattle, and takes the place of other breeds
in other countries. Thus the appearance of new forms
and the disappearance of old forms, both those naturally
and those artificially produced, are bound together. In
flourishing groups, the number of new specific forms
which have been produced within a given time has at
some periods probably been greater than the number of
the old specific forms which have been exterminated ;
but we know that species have not gone on indefinitely
increasing, at least during the later geological epochs, so
that, looking to later times, we may believe that the
production of new forms has caused the extinction of
about the same number of old forms.
The competition will generally be most severe, as
formerly explained and illustrated by examples, between
the forms which are most like each other in all respects.
Hence the improved and modified descendants of a species
will generally cause the extermination of the parent-
species; and if many new forms have been developed
from any one species, the nearest allies of that species,
Cuap. XI] EXTINCTION. 99
v.é. the species of the same genus, will be the most liable
to extermination. Thus, as I believe, a number of new
species descended from one species, that is a new genus,
comes to supplant an old genus, belonging to the same
family. But it must often have happened that a new
species belonging to some one group has seized on the
place occupied by a species belonging to a distinct group,
and thus have caused its extermination. If many allied
forms be developed from the successful intruder, many
will have to yield their places; and it will generally be
the allied forms, which will suffer from some inherited
inferiority in common. JBut whether it be species
belonging to the same or to a distinct class, which have
yielded their places to other modified and improved
species, a few of the sufferers may often be preserved
for a long time, from being fitted to some peculiar line
of life, or from inhabiting some distant and isolated
station, where they will have escaped severe competi-
tion. For instance, some species of Trigonia, a great
genus of shells in the secondary formations, survive in
the Australian seas; and a few members of the great and
almost extinct group of Ganoid fishes still inhabit our
fresh waters. Therefore the utter extinction of a group
is generally, as we have seen, a slower process than its
production.
With respect to the apparently sudden extermination
of whole families or orders, as of Trilobites at the close
of the palzeozoic period and of Ammonites at the close of
the secondary period, we must remember what has been
already said on the probable wide intervals of time
between our consecutive formations; and in these
intervals there may have been much slow extermina-
tion. Moreover, when, by sudden immigration or by
100 FORMS OF LIFE CHANGING (Cuap. XI.
unusually rapid development, many species of a new
group have taken possession of an area, many of the
older species will have been exterminated in a corre-
spondingly rapid manner; and the forms which thus
yield their places will commonly be allied, for they will
partake of the same inferiority in common.
Thus, as it seems to me, the manner in which single
species and whole groups of species become extinct
accords well with the theory of natural selection. We
need not marvel at extinction ; if we must marvel, let
it be at our own presumption in imagining for a
moment that we understand the many complex con-
tingencies on which the existence of each species
depends. If we forget for an instant that each species
tends to increase inordinately, and that some check is
always in action, yet seldom perceived by us, the whole
economy of nature will be utterly obscured. Whenever
we can precisely say why this species is more abundant
in individuals than that; why this species and not
another can be naturalised in a given country; then,
and not until then, we may justly feel surprise why we
cannot account for the extinction of any particular
species or group of species.
On the Forms of Life changing almost simultaneously
throughout the World.
Scarcely any paleontological discovery is more
striking than the fact that the forms of life change
almost simultaneously throughout the world. Thus our
European Chalk formation can be recognised in many
distant regions, under the most different climates, where
not a fragment of the mineral chalk itself can be found ;
namely in North America, in equatorial South America,
Cuap. XI] THROUGHOUT THE WORLD. 101
in Tierra del Fuego, at the Cape of Good Hope, and in
the peninsula of India. For at these distant points,
the organic remains in certain beds present an unmis-
takeable resemblance to those of the Chalk. Itis not
that the same species are met with; for in some cases
not one species is identically the same, but they be-
long to the same families, genera, and sections of
genera, and sometimes are similarly characterised in
such trifling points as mere superficial sculpture. More-
over, other forms, which are not found in the Chalk of
Europe, but which occur in the formations either above
or below, occur in the same order at these distant
points of the world. In the several successive paleo-
zoic formations of Russia, Western Europe, and North
America, a similar parallelism in the forms of life has
been observed by several authors; so it is, according
to Lyell, with the European and North American
tertiary deposits. Even if the few fossil species which
are common to the Old and New Worlds were kept
wholly out of view, the general parallelism in the
successive forms of life, in the paleozoic and tertiary
stages, would still be manifest, and the several forma-
tions could be easily correlated.
These observations, however, relate to the marine
inhabitants of the world: we have not sufficient data
to judge whether the productions of the land and of
fresh water at distant points change in the same parallel
manner. We may doubt whether they have thus
changed: if the Megatherium, Mylodon, Macrauchenia,
and Toxodon had been brought to Europe from La
Plata, without any information in regard to their geo-
logical position, no one would have suspected that they
had co-existed with sea-shells all still living; but as
102 FORMS OF LIFE CHANGING (Cuar. XL
these anomalous monsters co-existed with the Mastodon
and Horse, it might at least have been inferred that
they had lived during one of the later tertiary stages.
When the marine forms of life are spoken of as
having changed simultaneously throughout the world,
it must not be supposed that this expression relates to
the same year, or to the same century, or even that it
has a very strict geological sense; for if all the marine
animals now living in Europe, and all those that lived
in Europe during the pleistocene period (a very remote
period as measured by years, including the whole
glacial epoch) were compared with those now existing
in South America or in Australia, the most skilful
naturalist would hardly be able to say whether the
present or the pleistocene inhabitants of Europe re-
sembled most closely those of the southern hemisphere.
So, again, several highly competent observers maintain
that the existing productions of the United States are
more closely related to those which lived in Europe
during certain late tertiary stages, than to the present
inhabitants of Europe; and if this be so, it is evfdent
that fossiliferous beds now deposited on the shores of
North America would hereafter be lable to be classed
with somewhat older European beds. Nevertheless,
looking to a remotely future epoch, there can be little
doubt that all the more modern marine formations,
namely, the upper pliocene, the pleistocene and strictly
modern beds of Europe, North and South America, and
Australia, from containing fossil remains in some
degree allied, and from not including those forms which
are found only in the older underlying deposits, would
be correctly ranked as simultaneous in a geological sense.
The fact of the forms of life changing simultaneously,
Cuar. XI] THROUGHOUT THE WORLD. 103
in the above large sense, at distant parts of the world,
has greatly struck those admirable observers, MM. de
Verneuil and d’Archiac. After referring to the parallel-
ism of the paleeozoic forms of life in various parts of
Europe, they add, “If, struck by this strange sequence,
we turn our attention to North America, and there
discover a series of analogous phenomena, it will appear
certain that all these modifications of species, their
extinction, and the introduction of new ones, cannot
be owing to mere changes in marine currents or other
causes more or less local and temporary, but depend on
general laws which govern the whole animal kingdom.”
M. Barrande has made forcible remarks to precisely
the same effect. It is, mdeed, quite futile to look to
changes of currents, climate, or other physical con-
ditions, as the cause of these great mutations in the
forms of life throughout the world, under the most
different climates. We must, as Barrande has re-
marked, look to some special law. We shall see this
more clearly when we treat of the present distribution
of organic beings, and find how slight is the relation
between the physical conditions of various countries
and the nature of their inhabitants.
This great fact of the parallel succession of the forms
of life throughout the world, is explicable on the theory
of natural selection. Newspecies are formed by having
some advantage over older forms; and the forms, which
are already dominant, or have some advantage over
the other forms in their own country, give birth to the
greatest number of new varieties or incipient species.
We have distinct evidence on this head, in the plants
which are dominant, that is, which are commonest and
most widely diffused, producing the greatest number of
27
104 FORMS OF LIFE CHANGING (Cuar. XL
new varieties. It is also natural that the dominant,
varying, and far-spreading species, which have already
invaded to a certain extent the territories of other
species, should be those which would have the best
chance of spreading still further, and of giving rise in
new countries to other new varieties and species. The
process of diffusion would often be very slow, depending
on climatal and geographical changes, on strange acci-
dents, and on the gradual acclimatisation of new species
to the various climates through which they might have to
pass, but in the course of time the dominant forms would
generally succeed in spreading and would ultimately
prevail. The diffusion would, it is probable, be slower
with the terrestrial inhabitants of distinct continents
than with the marine inhabitants of the continuous sea.
We might therefore expect to find, as we do find, a less
strict degree of parallelism in the succession of the pro-
ductions of the land than with those of the sea.
Thus, as it seems to me, the parallel, and, taken in a
large sense, simultaneous, succession of the same forms
of life throughout the world, accords well with the
principle of new species having been formed by domi-
nant species spreading widely and varying; the new
species thus produced being themselves dominant,
owing to their having had some advantage over their
already dominant parents, as well as over other species,
and again spreading, varying, and producing new forms.
The old forms which are beaten and which yield their
places to the new and victorious forms, will generally
be allied in groups, from inheriting some inferiority in
common; and therefore, as new and improved groups
spread throughout the world, old groups disappear from
the world; and the succession of forms everywhere
Cuap. XI.) THROUGHOUT THE WORLD. 105
tends to correspond both in their first appearance and
final disappearance.
There is one other remark connected with this subject
worth making. I have given my reasons for believing
that most of our great formations, rich in fossils, were
deposited during periods of subsidence; and that blank
intervals of vast duration, as far as fossils are concerned,
occurred during the periods when the bed of the sea
was either stationary or rising, and likewise when sedi-
ment was not thrown down quickly enough to embed
and preserve organic remains. During these long and
blank intervals I suppose that the inhabitants of each
region underwent a considerable amount of. modification
and extinction, and that there was much migration
from other parts of the world. As we have reason to
believe that large areas are affected by the same move-
ment, it is probable that strictly contemporaneous
formations have often been accumulated over very wide
spaces in the same quarter of the world; but we are
very far from having any right to conclude that this
has invariably been the case, and that large areas have
invariably been affected by the same movements. When
two formations have been deposited in two regions
during nearly, but not exactly, the same period, we
should find in both, from the causes explained in the
foregoing paragraphs, the same general succession in
the forms of life; but the species would not exactly
correspond ; for there will have been a little more time
in the one region than in the other for modification,
extinction, and immigration.
I suspect that cases of this nature occur in Hurope.
Mr. Prestwich, in his admirable Memoirs on the eocene
deposits of England and France, is able to draw a close
106 AFFINITIES OF EXTINCT SPECIES. ([Cuap. XI.
general parallelism between the successive stages in
the two countries ; but when he compares certain stages
in England with those in France, although he finds in
both a curious accordance in the numbers of the species
belonging to the same genera, yet the species them-
selves differ in a manner very difficult to account for
considering the proximity of the two areas——unless,
indeed, it be assumed that an isthmus separated two
seas inhabited by distinct, but contemporaneous, faunas.
Lyell has made similar observations on some of the
later tertiary formations. Barrande, also, shows that
there is a striking general parallelism in the successive
Silurian deposits of Bohemia and Scandinavia; never-
theless he finds a surprising amount of difference in
the species. If the several formations in these regions
have not been deposited during the same exact periods,
—a formation in one region often corresponding with a
blank interval in the other,—and if in both regions the
species have gone on slowly changing during the accu-
mulation of the several formations and during the long
intervals of time between them ; in this case the several
formations in the two regions could be arranged in the
same order, In accordance with the general succession
of the forms of life, and the order would falsely appear
to be strictly parallel; nevertheless the species would
not be all the same in the apparently corresponding
stages in the two regions.
On the Affinities of Extinct Species to each other, and
to Living Forms.
Let us now look to the mutual affinities of extinct
and living species. All fall into a few grand classes;
and this fact is at once explained on the principle of
Cuar. XI] AFFINITIES OF EXTINCT SPECIES. 107
descent. The more ancient any form is, the more, as
a general rule, it differs from living forms. But, as
Buckland long ago remarked, extinct species can all be
classed either in still existing groups, or between them.
That the extinct forms of life help to fill up the
intervals between existing genera, families, and orders,
is certainly true; but as this statement has often been
ignored or even denied, it may be well to make some
remarks on this subject, and to give some instances.
If we confine our attention either to the living or to the
extinct species of the same class, the series is far less
perfect than if we combine both into one general
system. In the writings of Professor Owen we con-
tinually meet with the expression of generalised forms,
as applied to extinct animals; and in the writings of
Agassiz, of prophetic or synthetic types; and these
terms imply that such forms are in fact intermediate or
connecting links. Another distinguished paleontologist,
M. Gaudry, has shown in the most striking manner that
many of the fossil mammals discovered by him in Attica
serve to break down the intervals between existing —
genera. Cuvier ranked the Ruminants and Pachyderms,
as two of the most distinct orders of mammals: but so
many fossil links have been disentombed that Owen
has had to alter the whole classification, and has placed
certain pachyderms in the same sub-order with rumi-
nants; for example, he dissolves. by gradations the
apparently wide interval between the pig and the
camel. The Ungulata or hoofed quadrupeds are now
divided into the even-toed or odd-toed divisions ; but
the Macrauchenia of 8. America connects to a certain
extent these two grand divisions. No one will deny
that the Hipparion is intermediate between the existing
108 AFFINITIES OF EXTINCT SPECIES. (Cuap. XI.
horse and certain older ungulate forms. What a won-
derful connecting link in the chain of mammals is
the Typotherium from 8. America, as the name given
to it by Professor Gervais expresses, and which cannot
be placed in any existing order. The Sirenia form a
very distinct group of mammals, and one of the most
remarkable peculiarities in the existing dugong and
lamentin is the entire absence of hind limbs without
even arudiment being left; but the extinct Halitherium
had, according to Professor Flower, an ossified thigh-
bone “articulated to a well-defined acetabulum in the
pelvis,” and it thus makes some approach to ordinary
hoofed quadrupeds, to which the Sirenia are in other
respects allied. The cetaceans or whales are widely
different from all other mammals, but the tertiary Zeug-
lodon and Squalodon, which have been placed by some
naturalists in an order by themselves, are considered by
Professor Huxley to be undoubtedly cetaceans, “and to
constitute connecting links with the aquatic carnivora.”
Even the wide interval between birds and reptiles
has been shown by the naturalist just quoted to be
partially bridged over in the most unexpected manner,
on the one hand, by the ostrich and extinct Archeo-
pteryx, and on the other hand, by the Compsognathus,
one of the Dinosaurians—that group which includes
the most gigantic of all terrestrial reptiles. Turning to
the Invertebrata, Barraude asserts, a higher authority
could not be named, that he is every day taught that,
although palzozoic animals can certainly be classed
under existing groups, yet that at this ancient period
the groups were not so distinctly separated from each
other as they now are.
Some writers have objected to any extinct species,
Cuap. XI] AFFINITIES OF EXTINCT SPECIES. 109
or group of species, being considered as intermediate
between any two living species, or groups of species.
If by this term it is meant that an extinct form is
directly intermediate in all its characters between two
living forms or groups, the objection is probably valid.
But in a natural classification many fossil species
certainly stand between living species, and some extinct
genera between living genera, even between genera
belonging to distinct families. The most common case,
especially with respect to very distinct groups, such as
fish and reptiles, seems to be, that, supposing them to
be distinguished at the present day by a score of cha-
racters, the ancient members are separated by a some-
what lesser number of characters ; so that the two groups
formerly made a somewhat nearer approach to each
other than they now do.
It is a common belief that the more ancient a form
is, by so much the more it tends to connect by some of
its characters groups now widely separated from each
other. This remark no doubt must be restricted to
those groups which have undergone much change in
the course of geological ages; and it would be difficult
to prove the truth of the proposition, for every now and
then even a living animal, as the Lepidosiren, is dis-
covered having affinities directed towards very distinct
groups. Yet if we compare the older Reptiles and
Batrachians, the older Fish, the older Cephalopods, and
the eocene Mammals, with the more recent members of
the same classes, we must admit that there is truth in
the remark.
Let us see how far these several facts and inferences
accord with the theory of descent with modification.
As the subject is somewhat complex, I must request
110 AFFINITIES OF EXTINCT SPECIES. ([Cuapr. XI
the reader to turn to the diagram in the fourth chapter.
We may suppose that the numbered letters in italics
represent genera, and the dotted lines diverging from
them the species in each genus. The diagram is much
too simple, too few genera and too few species being
given, but this is unimportant for us. The horizontal
lines may represent successive geological formations,
and all the forms beneath the uppermost line may be
considered as extinct. The three existing genera a™,
q*, p*, will form a small family; 6* and /™ a closely
allied family or sub-family; and o™, ce“, m™, a third
family. These three families, together with the many
extinct genera on the several lines of descent diverging
from the parent-form (A) will form an order, for all
will have inherited something in common from their
ancient progenitor. On the principle of the continued
tendency to divergence of character, which was formerly
illustrated by this diagram, the more recent any form
is, the more it will generally differ from its ancient
progenitor. Hence we can understand the rule that
the most ancient fossils differ most from existing forms.
We must not, however, assume that divergence of
character is a necessary contingency ; it depends solely
on the descendants from a species being thus enabled
to seize on many and different places in the economy of
nature. Therefore it is quite possible, as we have seen
in the case of some Silurian forms, that a species might
go on being slightly modified in relation to its slightly
altered conditions of life, and yet retain throughout a
vast period the same general characteristics. This is
represented in the diagram by the letter F*.
All the many forms, extinct and recent, descended
from (A), make, as before remarked, one order; and
Cuap. XI] AFFINITIES OF EXTINCT SPECIES. 111
this order, from the continued effects of extinction and
divergence of character, has become divided into several
sub-families and families, some of which are supposed
to have perished at different periods, and some to have
endured to the present day.
By looking at the diagram we can see that if many
of the extinct forms supposed to be imbedded in the
successive formations, were discovered at several points
low down in the series, the three existing families on
the uppermost line would be rendered less distinct
from each other. If, for instance, the genera a}, a®, a}°,
F®, m3, m®, m*, were disinterred, these three families
would be so closely linked together that they probably
would have to be united into one great family, in
nearly the same manner as has occurred with rumi-
nants and certain pachyderms. Yet he who objected
to consider as intermediate the extinct genera, which
thus link together the living genera of three families,
would be partly justified, for they are intermediate, not
directly, but only by a long and circuitous course
through many widely different forms. If many ex-
tinct forms were to be discovered above one of the
middle horizontal lines or geological formations—for
instance, above No. VI.—but none from beneath this
line, then only two of the families (those on the left
hand, a, &c., and 6', &.) would have to be united
into one; and there would remain two families, which
would be less distinct from each other than they were
before the discovery of the fossils. So again if the three
families formed of eight genera (a to m*), on the
uppermost line, be supposed to differ from each other
by half-a-dozen important characters, then the families
which existed at the period marked VI. would certainly
112 AFFINITIES OF EXTINCT SPECIES. ([Caar. XL
have differed from each other by a less number of cha-
racters; for they would at this early stage of descent
have diverged in a less degree from their common
progenitor. Thus it comes that ancient and extinct
genera are often in a greater or less degree intermediate
in character between their modified descendants, or
between their collateral relations.
Under nature the process will be far more complicated
than is represented in the diagram; for the groups will
have been more numerous; they will have endured for
extremely unequal lengths of time, and will have been
modified in various degrees. As we possess only the
last volume of the geological record, and that in a very
broken condition, we have no right to expect, except in
rare cases, to fill up the wide intervals in the natural
system, and thus to unite distinct families or orders.
All that we have a right to expect is, that those groups
which have, within known geological periods, undergone
much modification, should in the older formations make
some slight approach to each other; so that the older
members should differ less from each other in some of
their characters than do the existing members of the
same groups; and this by the concurrent evidence of
our best paleontologists is frequently the case.
Thus, on the theory of descent with modification, the
main facts with respect to the mutual affinities of the
extinct forms of life to each other and to living forms,
are explained in a satisfactory manner. And they are
wholly inexplicable on any other view.
On this same theory, it is evident that the fauna
during any one great period in the earth’s history will be
intermediate in general character between that which
preceded and that which succeeded it. Thus the species
Cuap. XL] AFFINITIES OF EXTINCT SPECIES. 113
which lived at the sixth great stage of descent in the
diagram are the modified offspring of those which lived
at the fifth stage, and are the parents of those which
became still more modified at the seventh stage; hence
they could hardly fail to be nearly intermediate in
character between the forms of life above and below.
We must, however, allow for the entire extinction of
some preceding forms, and in any one region for the
immieration of new forms from other regions, and for a
large amount of modification during the long and blank
intervals between the successive formations. Subject
to these allowances, the fauna of each geological period
undoubtedly is intermediate in character, between the
preceding and succeeding faunas. I need give only one
instance, namely, the manner in which the fossils of the
Devonian system, when this system was first discovered,
were at once recognised by paleontologists as inter-
mediate in character between those of the overlying
carboniferous, and underlying Silurian systems. But
each fauna is not necessarily exactly intermediate, as
unequal intervals of time have elapsed between conse-
cutive formations.
It is no real objection to the truth of the statement that
the fauna of each period as a whole is nearly intermediate
in character between the preceding and succeeding
faunas, that certain genera offer exceptions to the rule.
For instance, the species of mastodons and elephants,
when arranged by Dr. Falconer in two series,—in the
first place according to their mutual affinities, and in
the second place according to their periods of existence,
—do not accord in arrangement. The species extreme
in character are not the oldest or the most recent; nor
are those which are intermediate in character, inter-
114 ~~ AFFINITIES OF EXTINCT SPECIES. ([Caap. XI.
mediate in age. But supposing for an instant, in this
and other such cases, that the record of the first appear-
ance and disappearance of the species was complete,
which is far from the case, we have no reason to believe
that forms successively produced necessarily endure for
corresponding lengths of time. A very ancient form
may occasionally have lasted much longer than a form
elsewhere subsequently produced, especially im the case
of terrestrial productions inhabiting separated districts.
To compare small things with great; if the principal
living and extinct races of the domestic pigeon were
arranged in serial affinity, this arrangement would not
closely accord with the order in time of their produc-
tion, and even less with the order of their disappearance ;
for the parent rock-pigeon still lives ; and many varieties
between the rock-pigeon and the carrier have become
extinct; and carriers which are extreme in the impor-
tant character of length of beak originated earlier than
short-beaked tumblers, which are at the opposite end of
the series in this respect.
Closely connected with the statement, that the organic
remains from an intermediate formation are in some
degree intermediate in character, is the fact, insisted on
by all paleontologists, that fossils from two consecutive
formations are far more closely related to each other,
than are the fossils from two remote formations. Pictet
gives as a well-known instance, the general resem-
blance of the organic remains from the several stages
of the Chalk formation, though the species are dis-
tinct in each stage. This fact alone, from its generality,
seems to have shaken Professor Pictet in his belief
in the immutability of species. He who is acquainted
with the distribution of existing species over the globe,
Oxap. XI.] AFFINITIES OF EXTINCT SPECIES. 115
will not attempt to account for the close resemblance of
distinct species in closely consecutive formations, by
the physical conditions of the ancient areas having
remained nearly the same. Let it be remembered that
the forms of life, at least those inhabiting the sea, have
changed almost simultaneously throughout the world,
and therefore under the most different climates and con-
ditions. Consider the prodigious vicissitudes of climate
during the pleistocene period, which includes the whole
glacial epoch, and note how little the specific forms of
the inhabitants of the sea have been affected.
On the theory of descent, the full meaning of the
fossil remains from closely consecutive formations being
closely related, though ranked as distinct species, is
obvious. As the accumulation of each formation has
often been interrupted, and as long blank intervals have
intervened between successive formations, we ought not
to expect to find, as I attempted to show in the last
chapter, in any one or in any two formations, all the
intermediate varieties between the species which
appeared at the commencement and close of these
periods: but we ought to find after intervals, very long
as measured by years, but only moderately long as
measured geologically, closely allied forms, or, as they
have been called by some authors, representative species;
and these assuredly we do find. We find, in short, such
evidence of the slow and scarcely sensible mutations of
specific iorms, as we have the right to expect.
28
(116 STATE OF DEVELOPMENT OF (Cuap. XI,
On the State of Development of Ancient compared with
Living Forms.
We have seen in the fourth chapter that the degree
of differentiation and specialisation of the parts in
organic beings, when arrived at maturity, is the best
standard, as yet suggested, of their degree of perfection -
or highness. We have also seen that, as the speciali-
sation of parts is an advantage to each being, so natural
selection will tend to render the organisation of each
being more specialised and perfect, and in this sense
higher; not but that it may leave many creatures with
simple and unimproved structures fitted for simple con-
ditions of life, and in some cases will even degrade or
simplify the organisation, yet leaving such degraded
beings better fitted for their new walks of life. In
another and more general manner, new species become
superior to their predecessors; for they have to beat in
the struggle for life all the older forms, with which they
come into close competition. We may therefore con-
clude that if under a nearly similar climate the eocene
inhabitants of the world could be put into competition
with the existing inhabitants, the former would be beaten
and exterminated by the latter, as would the secondary
by the eocene, and the palzozoic by the secondary
forms. So that by this fundamental test of victory in
the battle for life, as well as by the standard of the
specialisation of organs, modern forms ought, on the
theory of natural selection, to stand higher than ancient
forms. Isthis the case? A large majority of paleon-
tologists would answer in the affirmative ; and it seems
that this answer must be admitted as true, though
difficult of proof.
Cuap. XT] ANCIENT AND LIVING FORMS. 117
It is no valid objection to this conclusion, that certain
Brachiopods have been but slightly modified from an
extremely remote geological epoch; and that certain
land and fresh-water shells have remained nearly the
same, from the time when, as far as is known, they
first appeared. Itis not an insuperable difficulty that
Foraminifera have not, as insisted on by Dr. Carpenter,
progressed in organisation since even the Laurentian
epoch ; for some organisms would have to remain fitted
for simple conditions of life, and what could be better
fitted for this end than these lowly organised Protozoa ?
Such objections as the above would be fatal to my view,
if it included advance in organisation as a necessary
contingent. They would likewise be fatal, if the above
Foraminifera, for instance, could be proved to have
first come into existence during the Laurentian epoch,
or the above Brachiopods during the Cambrian forma-
tion; for in this case, there would not have been time
sufficient for the development of these organisms up to
the standard which they had then reached. When
advanced up to any given point, there is no necessity,
on the theory of natural selection, for their further
continued progress; though they will, during each
successive age, have to be slightly modified, so as to
hold their places in relation to slight changes in their
conditions. The foregoing objections hinge on the
question whether we really know how old the world
is, and at what period the various forms of life first
appeared ; and this may well be disputed.
The problem whether organisation on the whole has
advanced is In many ways excessively intricate. The
geological record, at all times imperfect, does not
extend far enough back, to shew with unmistakeable
118 STATE OF DEVELOPMENT OF (CHar. XI.
clearness that within the known history of the world
organisation has largely advanced. Even at the present
day, looking to members of the same class, naturalists
are not unanimous which forms ought to be ranked as
highest: thus, some look at the selaceans or sharks,
from their approach in some important points of struc-
ture to reptiles, as the highest fish; others look at
the teleosteans as the highest. The ganoids stand
intermediate between the selaceans and teleosteans;
the latter at the present day are largely preponderant
in number; but formerly selaceans and ganoids alone
existed; and in this case, according to the standard of
highness chosen, so will it be said that fishes have
advanced or retrograded in organisation. To attempt
to compare members of distinct types in the scale of
highness seems hopeless; who will decide whether a
cuttle-fish be higher than a bee—that insect which the
great Von Baer believed to be “in fact more highly
organised than a fish, although upon another type” ?
In the complex struggle for life it is quite credible that
crustaceans, not very high in their own class, might beat
cephalopods, the highest molluscs ; and such crustaceans,
though not highly developed, would stand very high in
the scale of invertebrate animals, if judged by the most
decisive of all trials—the law of battle. Beside these
inherent difficulties in deciding which forms are the
most advanced in organisation, we ought not solely to
compare the highest members of a class at any two
periods—though undoubtedly this is one and perhaps
the most important element in striking a balance—but
we ought to compare all the members, high and low, at the
two pericds. Atan ancient epoch the highest and lowest
molluscoidal animals, namely, cephalopods and brachio<
Cuap. XI] ANCIENT AND LIVING FORMS. 119
pods, swarmed in numbers; at the present time both
groups are greatly reduced, whilst others, intermediate
in organisation, have largely increased; consequently
some naturalists maintain that molluscs were formerly
more highly developed than at present; but a stronger
case can be made out on the opposite side, by consider-
ing the vast reduction of brachiopods, and the fact
that our existing cephalopods, though few in number,
are more highly organised than their ancient represen-
tatives. We ought also to compare the relative propor-
tional numbers at any two periods of the high and low
classes throughout the world: if, for instance, at the
_ present day fifty thousand kinds of vertebrate animals
exist, and if we knew that at some former period only
ten thousand kinds existed, we ought to look at this in-
crease in number in the highest class, which implies a
great displacement of lower forms, as a decided advance
in the organisation of the world. We thus see how
hopelessly difficult it is to compare with perfect fair-
ness under such extremely complex relations, the stan-
dard of organisation of the imperfectly-known faunas of
successive periods.
We shall appreciate this difficulty more clearly, by
looking to certain existing faunas and floras. From the
extraordinary manner in which European productions
have recently spread over New Zealand, and have seized
on places which must have been previously occupied by
the indigenes, we must believe, that if all the animals
and plants of Great Britain were set free in New
Zealand, a multitude of British forms would in the
course of time become thoroughly naturalised there,
and would exterminate many of the natives. On the
other hand, from the fact that hardly a single inhabitant
120 STATE OF DEVELOPMENT OF [Cuap. XI.
of the southern hemisphere has become wild in any part
of Europe, we may well doubt whether, if all the
productions of New Zealand were set free in Great
Britain, any considerable number would be enabled to
seize on places now occupied by our native. plants and
animals. Under this point of view, the productions of
Great Britain stand much higher in the scale than'those
of New Zealand. Yet the most skilful naturalist, from
an examination of the species of the two countries,
could not have foreseen this result. ;
Agassiz and several other highly competent judges
insist that ancient animals resemble to a certain extent
the embryos of recent animals belonging to the same
classes; and that the geological succession of extinct
forms is nearly parallel with the embryological de-
velopment of existing forms. This view accords ad-
mirably well with our theory. In a future chapter I
shall attempt to show that the adult differs from its
embryo, owing to variations having supervened at a not
early age, and having been inherited at a corresponding
age. This process, whilst it leaves the embryo almost
unaltered, continually adds, in the course of successive
generations, more and more difference to the adult.
Thus the embryo comes to be left as a sort of picture,
preserved by nature, of the former and less modified
condition of the species. This view may be true, and
yet may never be capable of proof. Seeing, for instance,
that the oldest known mammals, reptiles, and fishes
strictly belong to their proper classes, though some of
these old forms are in a slight degree less distinct from
each other than are the typical members of the same
groups at the present day, it would be vain to look for
animals having the common embryological character of
Cuap. XI] ANCIENT AND LIVING FORMS. 121
the Vertebrata, until beds rich in fossils are discovered
far beneath the lowest Cambrian strata—a discovery of
which the chance is small.
On the Succession of the same Types within the same
Areas, during the later Tertiary periods.
Mr. Clift many years ago showed that the fossil
mammals from the Australian caves were closely allied
to the living marsupials of that continent. In South
America, a similar relationship is manifest, even to an
uneducated eye, in the gigantic pieces of armour, like
those of the armadillo, found in several parts of La
Plata; and Professor Owen: has shown in the most
striking manner that most of the fossil mammals, buried
therein such numbers, are related to South American
types. This relationship is even more clearly seen in
the wonderful collection of fossil bones made by MM.
Lund and Clausen in the caves of Brazil. I was so
much impressed with these facts that I strongly insisted,
in 1839 and 1845, on this “law of the succession of
types,’ —on “this wonderful relationship in the same
continent between the dead and the living.” Professor
Owen has subsequently extended the same generalisation
to the mammals of the Old World. We see the same
law in this author’s restorations of the extinct and
gigantic birds of New Zealand. We see it also in the
birds of the caves of Brazil. Mr. Woodward has shown
that the same law holds good with sea-shells, but, from
the wide distribution of most molluscs, it is not well
displayed by them. Other cases could be added, as the
relation between the extinct and living land-shells of
Madeira ; and between the extinct and living brackish
water-shells of the Aralo-Caspian Sea.
122 SUCCESSION OF THE (Cuap. XI.
Now what does this remarkable law of the succession
of the same types within the same areas mean? He
would be a bold man who, after comparing the present
climate of Australia and of parts of South America,
under the same latitude, would attempt to account, on
the one hand through dissimilar physical conditions, for
the dissimilarity of the inhabitants of these two con-
tinents; and, on the other hand through similarity of
conditions, for the uniformity of the same types in each
continent during the later tertiary periods. Nor can it
be pretended that it is an immutable law that marsupials
should have been chiefly or solely produced in Australia ;
or that Edentata and other American types should have
been solely produced in South America. For we know
that Europe in ancient times was peopled by numerous
marsupials ; and I have shown im the publications above
alluded to, that in America the law of distribution of
terrestrial mammals was formerly different from what it
now is. North America formerly partook strongly of
the present character of the southern half of the con-
tinent ; and the southern half was formerly more closely
allied, than it is at present, to the northern half. In a
similar manner we know, from Falconer and Cautley’s
discoveries, that Northern India was formerly more
closely related in its mammals to Africa than it is at
the present time. Analogous facts could be given in
relation to the distribution of marine animals.
On the theory of descent with modification, the great
law of the long enduring, but not immutable, succession
of the same types within the same areas, is at once ex-
plained ; for the inhabitants of each quarter of the world
will obviously tend to leave in that quarter, during the
next succeeding period of time, closely allied though in
Cuap. XI.] SAME TYPES IN THE SAME AREAS. 128
some degree modified descendants. If the inhabitants
of one continent formerly differed greatly from those of
another continent, so will their modified descendants still
differ in nearly the same manner and degree. But after
very long intervals of time, and after great geographical
changes, permitting much intermieration, the feebler
will yield to the more dominant forms, and there will
be nothing immutable in the distribution of organic
beings.
It may be asked in ridicule, whether I suppose that
the megatherium and other allied huge monsters, which
formerly lived in South America, have left behind them
the sloth, armadillo, and anteater, as their degenerate
descendants. This cannot for an instant be admitted.
These huge animals have become wholly extinct, and
have left no progeny. But in the caves of Brazil, there
are many extinct species which are closely allied in size
and in all other characters to the species still living in
South America; and some of these fossils may have been
the actual progenitors of the living species. It must not
be forgotten that, on our theory, all the species of the
same genus are the descendants of some one species; so
that, if six genera, each having eight species, be found in
one geological formation, and in a succeeding formation
there be six other allied or representative genera each
with the same number of species, then we may conclude
that generally only one species of each of the older
genera has left modified descendants, which constitute
the new genera containing the several species; the other
seven species of each old genus having died out and left
no progeny. Or, and this will be a far commoner case,
two or three species in two or three alone of the six older
genera will be the parents of the new genera: the other
—_—sre | we zt = * a ie ie ean oe a a EN oe weal ta ca Si aaa
‘a 7 = ~ ee Se
124 SUMMARY OF THE {Cuap. XI.
species and the other old genera having become utterly
extinct. In failing orders, with the genera and species
decreasing in numbers as is the case with the Edentata
of South America, still fewer genera and species will
leave modified blood-descendants.
Summary of the preceding and present Chapters.
I have attempted to show that the geological record is
extremely imperfect; that only a small portion of the
globe has been geologically explored with care; that
only certain classes of organic beings have been largely
: preserved in a fossil state; that the number both of
specimens and of species, preserved in our museums, is
absolutely as nothing compared with the number of
generations which must have passed away even during a
single formation; that, owing to subsidence being almost
necessary for the accumulation of deposits rich in fossil
species of many kinds, and thick enough to outlast future
degradation, great intervals of time must have elapsed
between most of our successive formations; that there
has probably been more extinction during the periods of
subsidence, and more variation during the periods of
elevation, and during the latter the record will have been
least perfectly kept; that each single formation has not
been continuously deposited ; that the duration of each
formation is probably short compared with the average
duration of specific forms; that migration has played an
important part in the first appearance of new forms in
any one area and formation ; that widely ranging species
are those which have varied most frequently, and have
oftenest given rise to new species; that varieties have
at first been local; and lastly, although each species
Cuap. XI.] PRECEDING AND PRESENT CHAPTERS. 125
must have passed through numerous transitional stages,
it is probable that the periods, during which each
underwent modification, though many and long as
measured by years, have been short in comparison with
the periods during which each remained in an unchanged
condition. ‘These causes, taken conjointly, will to a large
extent explain why—though we do find many links—we
do not find interminable varieties, connecting together all
extinct and existing forms by the finest graduated steps.
It should also be constantly borne in mind that any
linking variety between two forms, which might be found,
would be ranked, unless the whole chain could be
perfectly restored, as a new and distinct species; for it
is not pretended that we have any sure criterion by which
Species and varieties can be discriminated.
He who rejects this view of the imperfection of the
geological record, will rightly reject the whole theory.
For he may ask in vain where are the numberless
transitional links which must formerly have connected
the closely allied or representative species, found in
the successive stages of the same great formation? He
may disbelieve in the immense intervals of time which
must have elapsed between our consecutive formations ;
he may overlook how important a part migration has
played, when the formations of any one great region,
as those of Europe, are considered; he may urge the
apparent, but often falsely apparent, sudden coming in
of whole groups of species. He may ask where are the
remains of those infinitely numerous organisms which
must have existed long before the Cambrian system
was deposited? We now know that at least one animal
did then exist; but I can answer this last question
only by supposing that where our oceans now extend
126 SUMMARY OF THE [Cuar. XL
they have extended for an enormous period, and where
our oscillating continents now stand they have stood
since the commencement of the Cambrian system; but
that, long before that epoch, the world presented a
widely different aspect; and that the older continents,
formed of formations older than any known to us, exist
now only as remnants in a metamorphosed condition,
or lie stili buried under the ocean.
Passing from these difficulties, the other great leading
facts in paleontology agree admirably with the theory
of descent with modification through variation and
natural selection. We can thus understand how it is
that new species come in slowly and successively ; how
species of different classes do not necessarily change
together, or at the same rate, or in the same degree;
yet in the long run that all undergo modification to
some extent. The extinction of old forms is the almost
inevitable consequence of the production of new forms.
We can understand why, when a species has once dis-
appeared, it never reappears. Groups of species Increase
in numbers slowly, and endure for unequal periods of
time; for the process of modification is necessarily
slow, and depends on many complex contingencies.
The dominant species belonging to large and dominant
groups tend to leave many modified descendants, which
form new sub-groups and groups. As these are formed,
the species of the less vigorous groups, from their in-
feriority inherited from a common progenitor, tend to
become extinct together, and to leave no modified off-
spring on the face of the earth. But the utter extinc-
tion of a whole group of species has sometimes been a
slow process, from the survival of a few descendants,
lingering in protected and isolated situations. When a
CuaP. XI] PRECEDING AND PRESENT CHAPTERS. 127
group has once wholly disappeared, it does not reappear ;
for the link of generation has been broken.
We can understand how it is that dominant forms
which spread widely and yield the greatest number of
varieties tend to people the world with allied, but
modified, descendants; and these will generally succeed
in displacing the groups which are their inferiors in
the struggle for existence. Hence, after long intervals
of time, the productions of the world appear to have
changed simultaneously.
We can understand how it is that all the forms of
life, ancient and recent, make together a few grand
classes. We can understand, from the continued ten-
dency to divergence of character, why the more ancient
a form is, the more it generally differs from those now
living; why ancient and extinct forms often tend to
fill up gaps between existing forms, sometimes blending
two groups, previously classed as distinct, into one; but
more commonly bringing them only a little closer
together. The more ancient a form is, the more often
it stands in some degree intermediate between groups
now distinct ; for the more ancient a form is, the more
nearly it will be related to, and consequently resemble,
the common progenitor of groups, since become widely
divergent. Extinct forms are seldom directly inter-
mediate between existing forms; but are intermediate
only by a long and circuitous course through other
extinct and different forms. We can clearly see why
the organic remains of closely consecutive formations
are Closely allied; for they are closely linked together
by generation. We can clearly see why the remains of
an intermediate formation are intermediate in character.
The inhabitants of the world at each successive
128 SUMMARY OF CHAPTERS. (Cear. XI.
period in its history have beaten their predecessors
in the race for life, and are, in so far, higher in the
scale, and their structure has generally become more
specialised; and this may account for the common
belief held by so many paleontologists, that organisa-
tion on the whole has progressed. Extinct and ancient
animals resemble to a certain extent the embryos of
the more recent animals belonging to the same classes,
and this wonderful fact receives a simple explanation
according to our views. The succession of the same
types of structure within the same areas during the
later geological periods ceases to be mysterious, and is
intelligible on the principle of inheritance.
If then the geological record be as imperfect as many
believe, and it may at least be asserted that the record
cannot be proved to be much more perfect, the main
objections to the theory of natural selection are greatly
diminished or disappear. On the other hand, all the
chief laws of palzeontology plainly proclaim, as it seems
to me, that species have been produced by ordinary -
generation: old forms having been supplanted by new
and improved forms of life, the products of Variation
and the Survival of the Fittest.
Cuar. XII.] GEOGRAPHICAL DISTRIBUTION. 129
CHAPTER XIL
GEOGRAPHICAL DISTRIBUTION,
Present distribution cannot be accounted for by differences in
physical conditions—Importance of barriers—Affinity of the pro-
ductions of the same continent—Centres of creation—Means of
dispersal by changes of climate and of the level of the land, and
by occasional means—Dispersal during the Glacial period—
Alternate Glacial periods in the North and South,
In considering the distribution of organic beings over
the face of the globe, the first great fact which strikes
us is, that neither the similarity nor the dissimilarity
of the inhabitants of various regions can be wholly
accounted for by climatal and other physical conditions.
Of late, almost every author who has studied the subject
has come to this conclusion. The case of America
alone would almost suffice to prove its truth; for if we
exclude the arctic and northern temperate parts, all
authors agree that one of the most fundamental divisions
in geographical distribution is that between the New and
Old Worlds; yet if we travel over the vast American
continent, from the central parts of the United States
to its extreme southern point, we meet with the most
diversified conditions; humid districts, arid deserts,
lofty mountains, grassy plains, forests, marshes, lakes,
and great rivers, under almost every temperature.
There is hardly a climate or condition in the Old
World which cannot be paralleled in the New—at
130 GEOGRAPHICAL DISTRIBUTION. [Cuapr, XIL
least as closely as the same species generally require.
No doubt small areas can be pointed out in the Old
World hotter than any in the New World; but these
are not inhabited by a fauna different from that of the
surrounding districts; for it is rare to find a group of
organisms confined toa small area, of which the con-
ditions are peculiar in only a slight degree. Notwith-
standing this general parallelism in the conditions of
the Old and New Worlds, how widely different are
their living productions!
In the southern hemisphere, if we compare large
tracts of land in Australia, South Africa, and western
South America, between latitudes 25° and 35°, we shall
find parts extremely similar in all their conditions, yet
it would not be possible to point out three faunas and
floras more utterly dissimilar. Or, again, we may com-
pare the productions of South America south of lat.
35° with those north of 25°, which consequently are
separated by a space of ten degrees of latitude, and are
exposed to considerably different conditions; yet they
are incomparably more closely related to each other
than they are to the productions of Australia or Africa
under nearly the same climate. Analogous facts could
be given with respect to the inhabitants of the sea.
A second great fact which strikes us in our general
review is, that barriers of any kind, or obstacles to
free migration, are related in a close and important
manner to the differences between the productions of
various regions. We see this in the great difference
in nearly all the terrestrial productions of the New
and Old Worlds, excepting in the northern parts, where
the land almost joins, and where, under a slightly
different climate, there might have been free migration
Cuap. XII.) GEOGRAPHICAL DISTRIBUTION. 131
for the northern temperate forms, as there now is for
the strictly arctic productions. We see the same fact
in the great difference between the inhabitants of
Australia, Africa, and South America under the same
latitude ; for these countries are almost as much isolated
from each other as is possible. On each continent,
also, we see the same fact; for on the opposite sides of
lofty and continuous mountain-ranges, of great deserts
and even of large rivers, we find different productions ;
though as mountain-chains, deserts, &c, are not as
impassable, or likely to have endured so long, as the
oceans separating continents, the differences are very
inferior in degree to those characteristic of distinct
continents.
Turning to the sea, we find the same law. The
marine inhabitants of the eastern and western shores
of South America are very distinct, with extremely
few shells, crustacea, or echinodermata in common ;
but Dr. Ginther has recently shown that about thirty
per cent. of the fishes are the same on the opposite
sides of the isthmus of Panama; and this fact has led
naturalists to believe that the isthmus was formerly
open. Westward of the shores of America, a wide
space of open ocean extends, with not an island as a
halting-place for emigrants; here we have a barrier of
another kind, and as soon as this is passed we meet in
the eastern islands of the Pacific with another and
totally distinct fauna. So that three marine faunas
range far northward and southward in parallel lines
not far from each other, under corresponding climates ;
but from being separated from each other by impass-
able barriers, either of land or open sea, they are almost
wholly distinct. On the other hand, proceeding still
Le GEOGRAPHICAL DISTRIBUTION. ([Cuapr. XII.
farther westward from the eastern islands of the tropical
parts of the Pacific, we encounter no impassable barriers,
and we have innumerable islands as halting-places, or
continuous coasts, until, after travelling over a hemi-
sphere, we come to the shores of Africa; and over this
vast space we meet with no well-defined and distinct
marine faunas. Although so few marine animals are
common to the above-named three approximate faunas
of Eastern and Western America and the eastern
Pacific islands, yet many fishes range from the Pacific
into the Indian Ocean, and many shells are common
to the eastern islands of the Pacific and the eastern
shores of Africa on almost exactly opposite meridians
of longitude.
A third great fact, partly included in the foregoing
statement, is the affinity of the productions of the same
continent or of the same sea, though the species them-
selves are distinct at different points and stations. It
is a law of the widest generality, and every continent
offers innumerable instances. Nevertheless the natural-
ist, in travelling, for instance, from north to south,
never fails to be struck by the manner in which suc-
cessive groups of beings, specifically distinct, though
nearly related, replace each other. He hears from
closely allied, yet distinct kinds of birds, notes nearly
similar, and sees their nests similarly constructed, but
not quite alike, with eggs coloured in nearly the same
manner. The plains near the Straits of Magellan are
inhabited by one species of Rhea (American ostrich),
and northward the plains of La Plata by another species
of the same genus; and not by a true ostrich or emu,
like those inhabiting Africa and Australia under the
same latitude. On these same plains of La Plata we
Cuap. XII.) GEOGRAPHICAL DISTRIBUTION. 133
see the agouti and bizcacha, animals having nearly
the same habits as our hares and rabbits, and belonging
to the same order of Rodents, but they plainly display
an American type of structure. We ascend the lofty
peaks of the Cordillera, and we find an alpine species
of bizcacha; we look to the waters, and we do not find
the beaver or musk-rat, but the coypu and capybara,
rodents of the S. American type. Innumerable other
instances could be given. If we look to the islands off
the American shore, however much they may differ in
geological structure, the inhabitants are essentially
American, though they may be all peculiar species.
We may look back to past ages, as shown in the last
chapter, and we find American types then prevailing
on the American continent and in the American seas.
We see in these facts some deep organic bond, through-
out space and time, over the same areas of land and
water, independently of physical conditions. The
naturalist must be dull who is not led to inquire what
this bond is.
The bond is simply inheritance, that cause which
alone, as far as we positively know, produces organisms
quite like each other, or, as we see in the case of
varieties, nearly alike. The dissimilarity of the in-
habitants of different regions may be attributed to
modification through variation and natural selection,
and probably in a subordinate degree to the definite
influence of different physical conditions. The degrees
of dissimilarity will depend on the migration of the
more dominant forms of life from one region into
another having been more or less effectually prevented,
at periods more or less remote;—on the nature and
number of the former immigrants ;—and on the action
134 GEOGRAPHICAL DISTRIBUTION. [Cuar. XII.
of the inhabitants on each other in leading to the
preservation of different modifications ; the relation of
organism to organism in the struggle for life being, as
I have already often remarked, the most important of
all relations. Thus the high importance of barriers
comes into play by checking migration; as does time
for the slow process of modification through natural
selection. Widely-ranging species, abounding in in-
dividuals, which have already triumphed over many
competitors in their own widely-extended homes, will
have the best chanee of seizing on new places, when
they spread into new countries. In their new homes
they will be exposed to new cenditions, and will fre-
quently undergo further modification and improvement;
and thus they will become still further victorious, and
will produce groups of modified descendants. On this
principle of inheritance with modification we can under-
stand how it is that sections of genera, whole genera,
and even families, are confined to the same areas, as is
so commonly and notoriously the case.
There is no evidence, as was remarked in the last
chapter, of the existence of any law of necessary
development. As the variability of each species is an
independent property, and will be taken advantage of
by natural selection, only so far as it profits each in-
dividual in its complex struggle for life, so the amount
of modification in different species will be no uniform
quantity. If a number of species, after having long
competed with each other in their old home, were to
migrate in a body into a new and afterwards isolated
country, they would be little hable to modification ; for
neither migration nor isolation in themselves effect
anything. These principles come into play only by
Cuar. XII.) SINGLE CENTRES OF CREATION. 135
bringing organisms into new relations with each other
and in a lesser degree with the surrounding physical
conditions. As we have seen in the last chapter that
some forms have retained nearly the same character
from an enormously remote geological period, so certain
species have migrated over vast spaces, and have not
become greatly or at all modified.
According to these views, it is obvious that the
several species of the same genus, though inhabiting
the most distant quarters of the world, must originally
have proceeded from the same source, as they are
descended from the same progenitor. In the case of
those species which have undergone during whole geo-
logical periods little modification, there is not much
difficulty in believing that they have migrated from
the same region; for during the vast geographical and
clmatal changes which have supervened since ancient
times, almost any amount of migration is possible. But
in many other cases, in which we have reason to believe
that the species of a genus have been produced within
comparatively recent times, there is great difficulty on
this head. It is also obvious that the individuals of
the same species, though now inhabiting distant and
isolated regions, must have proceeded from one spot,
where their parents were first produced: for, as hag
been explained, it is incredible that individuals iden-
tically the same should have been produced from
parents specifically distinct.
Single Centres of supposed Creation—We are thus
brought to the question which has been largely dis-
cussed by naturalists, namely, whether species have
been created at one or more points of the earth’s sur-
face. Undoubtedly there are many cases of extreme
136 SINGLE CENTRES OF CREATION. (Cua. XI.
- difficulty in understanding how the same species could
possibly have migrated from some one point to the
several distant and isolated points, where now found.
Nevertheless the simplicity of the view that each
species was first produced within a single region cap-
tivates the mind. He who rejects it, rejects the vera
causa of ordinary generation with subsequent migra-
tion, and calls in the agency of a miracle. It is
universally admitted, that in most cases the area in-
habited by a species is continuous; and that when a
plant or animal inhabits two points so distant from
each other, or with an interval of such a nature, that
the space could not have been easily passed over by
migration, the fact is given as something remarkable
and exceptional. The incapacity of migrating across a
wide sea is more clear in the case of terrestrial mam-
mals than perhaps with any other organic beings; and,
accordingly, we find no inexplicable instances of the
same mammals inhabiting distant points of the world.
No geologist feels any difficulty in Great Britain pos-
sessing the same quadrupeds with the rest of Europe,
for they were no doubt once united. But if the same
species can be produced at two separate points, why do
we not find a single mammal common to Europe and
Australia or South America? The conditions of life
are nearly the same, so that a multitude of European
animals and plants have become naturalised in America
and Australia; and some of the aboriginal plants are
identically the same at these distant poimts of the
northern and southern hemispheres? The answer, as
I believe, is, that mammals have not been able to
migrate, whereas some plants, from their varied means
of dispersal, have migrated across the wide and broken
Cuar. XII] SINGLE CENTRES OF CREATION. 137
interspaces. The great and striking influence of barriers
of all kinds, is intelligible only on the view that the
great majority of species have been produced on one
side, and have not been able to migrate to the opposite
side. Some few families, many sub-families, very many
genera, and a still greater number of sections of genera,
are confined toa single region ; and it has been observed
by several naturalists that the most natural genera, or
those genera in which the species are most closely
related to each other, are generally confined to the
same country, or if they have a wide range that their
range is continuous. What a strange anomaly it would
be, if a directly opposite rule were to prevail, when we
go down one step lower in the series, namely, to the
individuals of the same species, and these had not
been, at least at first, confined to some one region !
Hence it seems to me, as it has to many other
naturalists, that the view of each species having been
produced in one area alone, and having subsequently
migrated from that area as far as its powers of migration
and subsistence under past and present conditions
permitted, is the most probable. Undoubtedly many
cases occur, In which we cannot explain how the same
species could have passed from one point to the other.
But the geographical and climatal changes which have
certainly occurred within recent geological times, must
have rendered discontinuous the formerly continuous
range of many species. So that we are reduced to consider
whether the exceptions to continuity of range are so
numerous and of so grave a nature, that we ought to give
up the belief, rendered probable by general considerations,
that each species has been produced within one area, and
has migrated thence as far as it could. It would be
138 SINGLE CENTRES OF CREATION. ([Caap. XII.
hopelessly tedious to discuss all the exceptional cases
of the same species, now living at distant and separated
points, nor do I for a moment pretend that any
explanation could be offered of many instances. But,
after some preliminary remarks, I will discuss a few of
the most striking classes of facts ; namely, the existence
of the same species on the summits of distant mountain
ranges, and at distant points in the arctic and antarctic
regions; and secondly (in the following chapter), the
wide distribution of freshwater productions ; and thirdly,
the occurrence of the same terrestrial species on islands
and on the nearest mainland, though separated by
hundreds of miles of open sea. If the existence of the
same species at distant and isolated peints of the earth’s
surface, can in many instances be explained on the view
of each species having migrated from a single birthplace ;
then, considering our ignorance with respect to former
climatal and geographical changes and to the various
occasional means of transport, the belief that a single
birthplace is the law, seems to me incomparably the
safest.
In discussing this subject, we shall be enabled at the
same time to consider a point equally important for us,
namely, whether the several species of a genus which
must on our theory all be descended from a common
progenitor, can have migrated, undergoing modification
during their migration, from some one area. If, when
most of the species inhabiting one region are different
from those of another region, though closely allied to
them, it can be shown that migration from the one region
to the other has probably occurred at some former period,
our general view will be much strengthened ; for the
explanation is obvious on the principle of descent with
Cuap. XII] SINGLE CENTRES OF CREATION. 139
-modification. A volcanic island, for instance, upheaved
and formed at the distance of a few hundreds of miles
from a continent, would probably receive from it in the
course of time a few colonists, and their descendants,
though modified, would still be related by inheritance to
the inhabitants of that continent. Cases of this nature
are common, and are, as we shall hereafter see, inexplic-
able on the theory of independent creation. This view
of the relation of the species of one region to those of
another, does not differ much from that advanced by Mr.
Wallace, who concludes that “every species has come
into existence coincident both in space and time with a
pre-existing closely allied species.” And it is now well
known that he attributes this coincidence to descent with
modification.
The question of single or multiple centres of creation
differs from another though allied question,—namely,
whether all the individuals of the same species are
descended from a single pair, or single hermaphrodite, or
whether, as some authors suppose, from many individuals
simultaneously created. With organic beings which
never intercross, if such exist, each species must be de-
scended from a succession of modified varieties, that
have supplanted each other, but have never blended with
other individuals or varieties of the same species ; so that,
at each successive stage of modification, all the individuals
of the same form will be descended from a single parent.
But in the great majority of cases, namely, with all
organisms which habitually unite for each birth, or which
occasionally intercross, the individuals of the same
species inhabiting the same area will be kept nearly
uniform by intercrossing; so that many individuals will
go on simultaneously changing, and the whole amount
30
140 _ MEANS OF DISPERSAL. [Cuar. XII.
of modification at each stage will not be due to descent
from a single parent. To illustrate what I mean: our
English race-horses differ from the horses of every
other breed; but they do not owe their difference and
superiority to descent from any single pair, but to
continued care in the selecting and training of many
individuals during each generation.
Before discussing the three classes of facts, which I
have selected as presenting the greatest amount of
difficulty on the theory of “single centres of creation,”
I must say a few words on the means of dispersal.
Means of Dispersal.
Sir C. Lyell and other authors have ably treated
this subject. I can give here only the briefest abstract
of the more important facts. Change of climate must
have had a powerful influence on migration, A region
now impassable to certain organisms from the nature of
its climate, might have been a high road for micration,
when the climate was different. I shall, however,
presently have to discuss this branch of the subject in
some detail. Changes of level in the land must also
have been highly influential: a narrow isthmus now
separates two marine faunas; submerge it, or let it
formerly have been submerged, and the two faunas will
now blend together, or may formerly have blended.
Where the sea now extends, land may at a former period
have connected islands or possibly even continents to-
gether, and thus have allowed terrestrial productions to
pass from one to the other. No geologist disputes that
great mutations of level have occurred within the period
of existing organisms. Edward Forbes insisted that all
the islands in the Atlantic must have been recently
Cuap. XII) MEANS OF DISPERSAL. 141
connected with Europe or Africa, and Europe likewise
with America. Other authors have thus hypothetically
bridged over every ocean, and united almost every island
with some mainland. If indeed the arguments used by
Forbes are to be trusted, it must be admitted that
scarcely a single island exists which has not recently
been united to some continent. This view cuts the
Gordian knot of the dispersal of the same species to the
most distant points, and removes many a difficulty ; but
to the best of my judgment we are not authorised in
admitting such enormous geographical changes within
the period of existing species. It seems to me that we
- have abundant evidence of great oscillations in the level
of the land or sea; but not of such vast changes in the
position and extension of our continents, as to have united
them within the recent period to each other and to the
several intervening oceanic islands. I freely admit the
former existence of many islands, now buried beneath
the sea, which may have served as halting-places for
plants and for many animals during their mieration. In
the coral-producing oceans such sunken islands are now
marked by rings of coral or atolls standing over them.
Whenever it is fully admitted, as it will some day be, that
each species has proceeded from a single birthplace, and
when in the course of time we know something definite
about the means of distribution, we shall be enabled
to speculate with security on the former extension of the
land. But I do not believe that it will ever be proved
that within the recent period most of our continents
which now stand quite separate, have been continuously,
or almost continuously united with each other, and with
the many existing oceanic islands. Several facts in
distribution,—such as the great difference in the marine
142 MEANS OF DISPERSAL. (Guar. XII.
faunas on the opposite sides of almost every continent,
—the close relation of the tertiary inhabitants of several
lands and even seas to their present inhabitants,—the
degree of affinity between the mammals inhabiting
islands with those of the nearest continent, being in
part determined (as we shall hereafter see) by the depth
of the intervening ocean,—these and other such facts are
opposed to the admission of such prodigious geographical
revolutions within the recent period, as are necessary
on the view advanced by Forbes and admitted by his
followers. The nature and relative proportions of the
inhabitants of oceanic islands are likewise opposed to the
belief of their former continuity with continents. Nor
does the almost universally volcanic composition of such.
islands favour the admission that they are the wrecks of
sunken continents ;—if they had originally existed as
continental mountain ranges, some at least of the islands |
would have been formed, like other mountain summits,
of granite, metamorphic schists, old fossiliferous and
other rocks, instead of consisting of mere piles of volcanic
matter.
I must now say a few words on what are called
accidental means, but which more properly should be
called occasional means of distribution. I shall here
confine myself to plants. In botanical works, this or
that plant is often stated to be ill adapted for wide
dissemination ; but the greater or less facilities for
transport across the sea may be said to be almost wholly
unknown. Until I tried, with Mr. Berkeley’s aid, a few
experiments, it was not even known how far seeds could
resist the injurious action of sea-water. To my surprise
I found that out of 87 kinds, 64 germinated after an
immersion of 28 days, and a few survived an immersion
Cuap. XII] MEANS OF DISPERSAL. 143
of 137 days. It deserves notice that certain orders were
far more injured than others: nine Leguminose were
tried, and, with one exception, they resisted the salt-water
badly ; seven species of the allied orders, Hydrophyllaceze
and Polemoniacez, were all killed by a month’s im-
mersion. For convenience’ sake I chiefly tried small
seeds without the capsule or fruit; and as all of these
sank in a few days they could not have been floated
across wide spaces of the sea, whether or not they were
injured by the salt-water. Afterwards I tried some larger
fruits, capsules, &c., and some of these floated for a long
time. It is well known what a difference there is in the
buoyancy of green and seasoned timber ; and it occurred
to me that floods would often wash into the sea dried
plants or branches with seed-capsules or fruit attached
to them. Hence I was led to dry the stems and branches
of 94 plants with ripe fruit, and to place them on gea-
water. The majority sank quickly, but some which,
whilst green, floated for a very short time, when dried
floated much longer ; for instance, ripe hazel-nuts sank
immediately, but when dried they floated for 90 days,
and afterwards when planted germinated ; an asparagus-
plant with ripe berries floated for 23 days, when dried it
floated for 85 days, and the seeds afterwards germinated ;
the ripe seeds of Helosciadium sank in two days, when
dried they floated for above 90 days, and afterwards
serminated. Altogether, out of the 94 dried plants, 18
floated for above 28 days; and some of the 18 floated
for a very much longer period. So that as §4 kinds of
seeds germinated after an immersion of 28 days; andas
7? distinct species with ripe fruit (but not all the same
species as in the foregoing experiment) floated, after
being dried, for above 28 days, we may conclude, as far
144 _ MEANS OF DISPERSAL. (Cuar. XII.
as anything can be inferred from these scanty facts, that
the seeds of =); kinds of plants of any country might be
floated by sea-currents during 28 days, and would re-
tain their power of germination. In Johnston’s Physical
Atlas, the average rate of the several Atlantic currents
is 33 miles per diem (some currents running at the rate
of 60 miles per diem) ; on this average, the seeds of ;}4
plants belonging to one country might be floated across
924 miles of sea to another country, and when stranded,
if blown by an inland gale to a favourable spot, would
germinate.
Subsequently to my experiments, M. Martens tried
similar ones, but in a much better manner, for he placed
the seeds in a box in the actual sea, so that they were
alternately wet and exposed to the air like really float-
ing plants. He tried 98 seeds, mostly different from
mine; but he chose many large fruits and likewise
seeds from plants which live near the sea; and this
would have favoured both the average length of their
flotation and their resistance to the injurious action of
the salt-water. On the other hand, he did not pre-
viously dry the plants or branches with the fruit; and
this, as we have seen, would have caused some of them
to have floated much longer. The result was that 38 of
his seeds of different kinds floated for 42 days, and were
then capable of germination. But I do not doubt that
plants exposed to the waves would float for a less time
than those protected from violent movement as in our
experiments. Therefore it would perhaps be safer to
assume that the seeds of about +4 plants of a flora,
after having been dried, could be floated across a space
of sea 900 miles in width, and would then germinate,
The fact of the larger fruits often floating longer than
Cuap. XII] MEANS OF DISPERSAL. 145
the small, is interesting; as plants with large seeds or
fruit which, as Alph. de Candolle has shown, generally
have restricted ranges, could hardly be transported by
any other means.
Seeds may be occasionally transported in another
manner. Drift timber is thrown up on most islands,
even on those in the midst of the widest oceans; and
the natives of the coral-islands in the Pacific procure
stones for their tools, solely from the roots of drifted
trees, these stones being a valuable royal tax. I find
that when irregularly shaped stones are embedded in
the roots of trees, small parcels of earth are frequently
enclosed in their interstices and behind them,—so
perfectly that not a particle could be washed away
during the longest transport: out of one small portion
of earth thus completely enclosed by the roots of an
oak about 50 years old, three dicotyledonous plants
germinated: I am certain of the accuracy of this obser-
vation. Again, I can show that the carcases of birds,
when floating on the sea, sometimes escape being im-
mediately devoured: and many kinds of seeds in the
crops of floating birds long retain their vitality: peas
and vetches, for instance, are killed by even.a few days’
immersion in sea-water; but some taken out of the
crop of a pigeon, which had floated on artificial sea-
water for 30 days, to my surprise nearly all germinated.
Living birds can hardly fail to be highly effective
agents in the transportation of seeds. I could give
many facts showing how frequently birds of many kinds
are blown by gales to vast distances across the ocean.
We may safely assume that under such circumstances
their rate of flight would often be 35 miles an hour;
and some authors have given a far higher estimate. I
146 3 _ MEANS OF DISPERSAL. (Cuar. XII.
have never seen an instance of nutritious seeds passing
through the intestines of a bird; but hard seeds of fruit
pass uninjured through even the digestive organs of a
turkey. In the course of two months, I picked up in
my garden 12 kinds of seeds, out of the excrement of
small birds, and these seemed perfect, and some of
them, which were tried, germinated. But the following
fact is more important: the crops of birds do not secrete
gastric juice, and do not, as I know by trial, injure in
the least the germination of seeds; now, after a bird
has found and devoured a large supply of food, it is
positively asserted that all the grains do not pass into
the gizzard for twelve or even eighteen hours. <A bird
in this interval might easily be blown to the distance
of 500 miles, and hawks are known to look out for tired
birds, and the contents of their torn crops might thus
readily get scattered. Some hawks and owls bolt their
prey whole, and, after an interval of from twelve to
twenty hours, disgorge pellets, which, as I know from
experiments made in the Zoological Gardens, include
seeds capable of germination. Some seeds of the oat
wheat, millet, canary, hemp, clover, and beet germinated
after having been from twelve to twenty-one hours
in the stomachs of different birds of prey; and two
seeds of beet grew after having been thus retained
for two days and fourteen hours. Fresh-water fish, I
find, eat seeds of many land and water plants ; fish are
frequently devoured by birds, and thus the seeds might
be transported from place to place. I forced many
kinds of seeds into the stomachs of dead fish, and then
gave their bodies to fishing-eagles, storks, and pelicans ;
these birds, after an interval of many hours, either
rejected the seeds in pellets or passed them in their
Cuap. XII.) MEANS OF DISPERSAL. 147
excrement; and several of these seeds retained the
power of germination. Certain seeds, however, were
always killed by this process.
Locusts are sometimes blown to great distances from
the land ; I myself caught one 370 miles from the coast
of Africa, and have heard of others caught at greater dis-
tances. The Rey. R. T. Lowe informed Sir C. Lyell that
in November 1844 swarms of locusts visited the island
of Madeira. They were in countless numbers, as thick
as the flakes of snow in the heaviest snowstorm, and
extended upwards as far as could be seen with a tele-
scope. During two or three days they slowly careered
round and round in an immense ellipse, at least five or
six miles in diameter, and at night alighted on the
taller trees, which were completely coated with them.
They then disappeared over the sea, as suddenly as they
had appeared, and have not since visited the island.
Now, in parts of Natal it is believed by some farmers,
though on insufficient evidence, that injurious seeds are
introduced into their grass-land in the dung left by the
great flights of locusts which often visit that country. In
consequence of this beef Mr. Weale sent me in a letter a
small packet of the dried pellets, out of which I extracted
under the microscope several seeds, and raised from
them seven grass plants, belonging to two species, of
two genera. Hence a swarm of locusts, such as that
which visited Madeira, might readily be the means of
introducing several kinds of plants into an island lying
- far from the mainland.
Although the beaks and feet of birds are generally
clean, earth sometimes adheres to them: in one ease I
removed sixty-one grains, and in another case twenty-two
grains of dry argillaceous earth from the foot of a part-
148 - MEANS OF DISPERSAL. (Cuap. XII.
ridge, and in the earth there was a pebble as large as
the seed of a vetch. Here is a better case: the leg of a
woodcock was sent to me by a friend, with a little cake
of dry earth attached to the shank, weighing only nine
grains; and this contained a seed of the toad-rush
(Juncus bufonius) which germinated and flowered. Mr.
Swaysland, of Brighton, who during the last forty years
has paid close attention to our migratory birds, informs
me that he has often shot wagtails (Motacille), wheat-
ears, and whinchats (Saxicolz), on their first arrival on
our shores, before they had alighted ; and he has several
times noticed little cakes of earth attached to their feet.
Many facts could be given showing how generally soil
is charged with seeds. For instance, Prof. Newton sent
me the leg of a red-legged partridge (Caccabis rufa)
which had been wounded and could not fly, with a bali
of hard earth adhering toit, and weighing six and a half
ounces. The earth had been kept for three years, but
when broken, watered and placed under a bell glass,
no less than 82 plants sprung from it: these consisted
of 12 monocotyledons, including the common oat, and
at least one kind of grass, and of 70 dicotyledons, which
consisted, judging from the young leaves, of at least
three distinct species. With such facts before us, can
we doubt that the many birds which are annually
blown by gales across great spaces of ocean, and
which annually migrate—for instance, the millions of
quails across the Mediterranean—must occasionally
transport a few seeds embedded in dirt adhering to
their feet or beaks? But I shall have to recur to this
subject.
As icebergs are known to be sometimes loaded with
earth and stones, and have even carried brushwood,
Cuap. XII] MEANS OF DISPERSAL. 149
bones, and the nest of a land-bird, it can hardly be
doubted that they must occasionally, as suggested by
Lyell, have transported seeds from one part to another
of the arctic and antarctic regions; and during the
Glacial period from one part of the now temperate
regions to another. In the Azores, from the large
number of plants common to Europe, in comparison
with the species on the other islands of the Atlantic,
which stand nearer to the mainland, and (as remarked
by Mr. H. C. Watson) from their somewhat northern
character in comparison with the latitude, I suspected
that these islands had been partly stocked by ice-borne
seeds, during the Glacial epoch. At my request Sir C.
Lyell wrote to M. Hartung to inquire whether he had
observed erratic boulders on these islands, and he
answered that he had found large fragments of granite
and other rocks, which do not occur in the archipelago.
Hence we may safely infer that icebergs formerly
landed their rocky burthens on the shores of these
mid-ocean islands, and it is at least possible that they
may have brought thither some few seeds of northern
plants.
Considering that these several means of transport,
and that other means, which without doubt remain to
be discovered, have been in action year after year for
tens of thousands of years, it would, I think, be a
marvellous fact if many plants had not thus become
widely transported. These means of transport are
sometimes called accidental, but this is not strictly
correct: the currents of the sea are not accidental, nor
is the direction of prevalent gales of wind. It should
be observed that scarcely any means of transport would
carry seeds for very great distances: for seeds do not
150 - MEANS OF DISPERSAL. (Cuar. XT.
retain their vitality when exposed for a great length of
time to the action of sea-water ; nor could they be long
carried in the crops or intestines of birds. These
means, however, would suffice for occasional transport
across tracts of sea some hundred miles in breadth, or
from island to island, or from a continent to a neigh-
bouring island, but not from one distant continent to
another. The floras of distant continents would not by
such means become mingled; but would remain as
distinct as they now are. The currents, from their
course, would never bring seeds from North America to
Britain, though they might and do bring seeds from
the West Indies to our western shores, where, if not
killed by their very long immersion in salt water, they
could not endure our climate. Almost every year, one
or two land-birds are blown across the whole Atlantic
Ocean, from North America to the western shores of
Ireland and England; but seeds could be transported
by these rare wanderers only by one means, namely, by
dirt adhering to their feet or beaks, which is in itself a
rare accident. Even in this case, how small would be
the chance of a seed falling on favourable soil, and
coming to maturity! But it would be a great error to
argue that because a well-stocked island, like Great
Britain, has not, as far as is known (and it would be
very difficult to prove this), received within the last
few centuries, through occasional means of transport,
immigrants from Europe or any other continent, that a
poorly-stocked island, though standing more remote
from the mainland, would not receive colonists by simi-
lar means. Out of a hundred kinds of seeds or animals
transported to an island, even if far less well-stocked
than Britain, perhaps not more than one would be so
Cuar. XII] THE GLACIAL PERIOD. 151
well fitted to its new home, as to become naturalised
But this is no valid argument against what would be
effected by occasional means of transport, during the
long lapse of geological time, whilst the island was
being upheaved, and before it had become fully stocked
with inhabitants. On almost bare land, with few or no
destructive insects or birds living there, nearly every
seed which chanced to arrive, if fitted for the climate,
would germinate and survive.
Dispersal during the Glacial Period.
The identity of many plants and animals, on moun-
tain-summits, separated from each other by hundreds
of miles of lowlands, where Alpine species, could not
possibly exist, is one of the most striking cases known
of the same species living at distant points, without
the apparent possibility of their having migrated from
one point to the other. It is indeed a remarkable fact
to see so many plants of the same species living on the
snowy regions of the Alps or Pyrenees, andin the
extreme northern parts of Europe; but it is far more
remarkable, that the plants on the White Mountains, in
the United States of America, are all the same with
those of Labrador, and nearly all the same, as we hear
from Asa Gray, with those on the loftiest mountains
of Europe. Even as long ago as 1747, such facts led
Gmelin to conclude that the same species must have
been independently created at many distinct points ;
and we might have remained in this same belief, had
not Agassiz and others called vivid attention to the
Glacial period, which, as we shall immediately see,
affords a simple explanation of these facts. We have
evidence of almost every conceivable kind, organic and
31
152 DISPERSAL DURING (Cuap. XII.
inorganic, that, within a very recent geological period,
central Europe and North America suffered under an
arctic climate. The ruins of a house burnt by fire do
not tell their tale more plainly than do the mountains
of Scotland and Wales, with their scored flanks, polished
surfaces, and perched boulders, of the icy streams with
which their valleys were lately filled. So greatly has
the climate of Europe changed, that in Northern Italy,
gigantic moraines, left by old glaciers, are now clothed
by the vine and maize. Throughout a large part of the
United States, erratic boulders and scored rocks plainly
reveal a former cold period. |
The former influence of the glacial climate on the dis-
tribution of the inhabitants of Europe, as explained by
Edward Forbes, is substantially as follows. But we shall
follow the changes more readily, by supposing a new
glacial period slowly to come on, and then pass away,
as formerly occurred. As the cold came on, and as each
more southern zone became fitted for the inhabitants of
the north, these would take the places of the former
inhabitants of the temperate regions. The latter, at
the same time, would travel further and further south-
ward, unless they were stopped by barriers, in which
case they would perish. The mountains would become
covered with snow and ice, and their former Alpine
inhabitants would descend to the plains. By the time
that the cold had reached its maximum, we should have
an arctic fauna and flora, covering the central parts of
Europe, as far south as the Alps and Pyrenees, and even
stretching into Spain. The now temperate regions of
the United States would likewise be covered by arctic
plants and animals and these would be nearly the same
with those of Europe; for the present circumpolar
Cuap. XII.] THE GLACIAL PERIOD. 153
inhabitants, which we suppose to have everywhere tra-
velled southward, are remarkably uniform round the
world.
As the warmth returned, the arctic forms would
retreat northward, closely followed up in their retreat
by the productions of the more temperate regions.
And as the snow melted from the bases of the moun-
tains, the arctic forms would seize on the cleared and
thawed ground, always ascending, as the warmth in-
creased and the snow still further disappeared, higher
and higher, whilst their brethren were pursuing their
northern journey. Hence, when the warmth had fully
returned, the same species, which had lately lived
together on the European and North American low-
lands, would again be found in the arctic regions of the
Old and New Worlds, and on many isolated mountain-
summits far distant from each other.
Thus we can understand the identity of many plants
at points so immensely remote as the mountains of the
United States and those of Europe. We can thus also
understand the fact that the Alpine plants of each
mountain-range are more especially related to the arctic
forms living due north or néarly due north of them:
for the first migration when the cold came on, and the
re-migration on the returning warmth, would generally
have been due south and north. The Alpine plants,
for example, of Scotland, as remarked by Mr. H. C.
Watson, and those of the Pyrenees, as remarked by
Ramond, are more especially allied to the plants of
northern Seandinavia; those of the United States to
Labrador; those of the mountains of Siberia to the
arctic regions of that country. These views, grounded
as they are on the perfectly well-ascertained occurrence
154 DISPERSAL DURING (Cuap. XII,
of a former Glacial period, seem to me to explain in so
satisfactory a manner the present distribution of the
Alpine and Arctic productions of Europe and America,
that when in other regions we find the same species
on distant mountain-summits, we may almost conclude,
without other evidence, that a colder climate formerly
permitted their migration across the intervening low-
lands, now become too warm for their existence.
As the arctic forms moved first southward and after-
wards backwards to the north, in unison with the
changing climate, they will not have been exposed
during their long migrations to any great diversity of
temperature; and as they all migrated in a body to-
gether, their mutual relations will not have been much
disturbed. Hence, in accordance with the principles
inculeated in this volume, these forms will not have
been liable to much modification. But with the Alpine
productions, left isolated from the moment of the re-
turning warmth, first at the bases and ultimately on
the summits of the mountains, the case will have been
somewhat different ; for it is not likely that all the same
arctic species will have been left on mountain-ranges far
distant from each other, and have survived there ever
since; they will also in all probability, have become
mingled with ancient Alpine species, which must have
existed on the mountains before the commencement of the
Glacial epoch, and which during the coldest period will
have been temporarily driven down to the plains; they
will, also, have been subsequently exposed to somewhat
different climatal influences. Their mutual relations
will thus have been in some degree disturbed ; conse-
quently they will have been lable to modification ; and
they have been modified ; for if we compare the present
Cuap. XII] THE GLACIAL PERIOD. 155
Alpine plants and animals of the several great Euro-
pean mountain-ranges one with another, though many
of the species remain identically the same, some exist
as varieties, some as doubtful forms or sub-species, and
some as distinct yet closely allied species Pepreses ag
each other on the several ranges.
In the foregoing illustration I have assumed that at
the commencement of our imaginary Glacial period,
the arctic productions were as uniform round the polar
regions as they are at the present day. But it is also
necessary to assume that many sub-arctic and some
few temperate forms were the same round the world,
for some of the species which now exist on the lower
mountain-slopes and on the plains of North America
and Europe are the same; and it may be asked how I
account for this degree of uniformity in the sub-arctic
and temperate forms round the world, at the commence-
ment of the real Glacial period. At the present day, the
sub-arctic and northern temperate productions of the Old
and New Worlds are separated from each other by the
whole Atlantic Ocean and by the northern part of the
Pacific. During the Glacial period, when the inhabitants
of the Old and New Worlds lived farther southwards
than they do at present, they must have been still more
completely separated from each other by wider spaces
of ocean ; so that it may well be asked how the same
species could then or previously have entered the two
continents. The explanation, I believe, lies in the
nature of the climate before the commencement of the
Glacial period. At this, the newer Pliocene period, the
majority of the inhabitants of the world were specifi-
cally the same as now, and we have good reason to be-
lieve that the climate was warmer than at the present
Se
156 DISPERSAL DURING [Cuap. XII.
day. Hence we may suppose that the organisms which
now live under latitude 60°, lived during the Pliocene
period farther north under the Polar Circle, in latitude
66°-67°; and that the present arctic productions then
lived on the broken land still nearer to the pole. Now,
if we look at a terrestrial globe, we see under the Polar
Circle that there is almost continuous land from wes-
tern Europe, through Siberia, to eastern America. And
this continuity of the circumpolar land, with the con-
sequent freedom under a more favourable climate for in-
termigration, will account for the supposed uniformity of
the sub-arctic and temperate productions of the Old and
New Worlds, at a period anterior to the Glacial epoch.
Believing, from reasons before alluded to, that our
continents have long remained in nearly the same
relative position, though subjected to great oscillations
of level, I am strongly inclined to extend the above
view, and to infer that during some still earlier and
still warmer period, such as the older Pliocene period,
a large number of the same plants and animals in-
habited the almost continuous circumpolar land; and
that these plants and animals, both in the Old and
New Worlds, began slowly to migrate southwards as
the climate became less warm, long before the com-
mencement of the Glacial period. We now see, as
I believe, their descendants, mostly in a modified con-
dition, in the central parts of Europe and the United
States. On this view we can understand the relation-
ship with very little identity, between the productions
of North America and Europe,—a relationship which is
highly remarkable, considering the distance of the two
areas, and their separation by the whole Atlantic Ocean.
We can further understand the singular fact remarked
Cuap. XII] THE GLACIAL PERIOD, 157
on by several observers that the productions of Europe
and America during the later tertiary stages were more
closely related to each other than they are at the present
time ; for during these warmer periods the northern
parts of the Old and New Worlds will have been
almost continuously united by land, serving as a bridge,
since rendered impassable by cold, for the intermigration
of their inhabitants.
During the slowly decreasing warmth of the Pliocene
period, as soon as the species in common, which in-
habited the New and Old Worlds, migrated south of
the Polar Circle, they will have been completely cut off
from each other. This separation, as far as the more
temperate productions are concerned, must have taken
place long ages ago. As the plants and animals mi-
srated southward, they will have become mingled in the
one great region with the native American productions,
and would have had to compete with them ; and in the
other great region, with those of the Old World. Con-
sequently we have here everything favourable for much
modification,—for far more modification than with the
Alpine productions, left isolated, within a much more
recent period, on the several mountain-ranges and on
the arctic lands of Europe and N. America. Hence it
has come, that when we compare the now living pro-
ductions of the temperate regions of the New and Old
Worlds, we find very few identical species (though Asa
Gray has lately shown that more plants are identical
than was formerly supposed), but we find in every
creat class many forms, which some naturalists rank as
geooraphical races, and others as distinct species; and
a host of closely allied or representative forms which
are ranked by all naturalists as specifically distinct.
158 ALTERNATE GLACIAL PERIODS ([Cuar. XIL
As on the land, so in the waters of the sea, a slow
southern migration of a marine fauna, which, during
the Pliocene or even a somewhat earlier period, was
nearly uniform along the continuous shores of the Polar
Circle, will account, on the theory of modification, for
many closely allied forms now living in marine areas
completely sundered. Thus, I think, we can under-
stand the presence of some closely allied, still existing
and extinct tertiary forms, on the eastern and western
shores of temperate North America; and the still more
striking fact of many closely allied crustaceans (as
described in Dana’s admirable work), some fish and
other marine animals, inhabiting the Mediterranean
and the seas of Japan,—these two areas being now
completely separated by the breadth of a whole con-
tinent and by wide spaces of ocean.
These cases of close relationship in species either
now or formerly inhabiting the seas on the eastern and
western shores of North America, the Mediterranean
and Japan, and the temperate lands of North America
and Europe, are inexplicable on the theory of creation.
We cannot maintain that such species have been created
alike, in correspondence with the nearly similar physical
conditions of the areas ; for if we compare, for instance,
certain parts of South America with parts of South
Africa or Australia, we see countries closely similar in
all their physical conditions, with their inhabitants
utterly dissimilar.
Alternate Glacial Periods in the North and South.
But we must return to our more immediate subject.
I am convinced that Forbes’s view may be largely
Cuar. XII] IN THE NORTH AND SOUTH. 159
extended. In Europe we meet with the plainest
evidence of the Glacial period, from the western shores
of Britain to the Oural range, and southward to the
Pyrenees. We may infer from the frozen mammals
and nature of the mountain vegetation, that Siberia was
similarly affected. In the Lebanon, according to Dr.
Hooker, perpetual snow formerly covered the central
axis, and fed glaciers which rolled 4000 feet down the
valleys. The same observer has recently found great
moraines at a low level on the Atlas range in N. Africa.
Along the Himalaya, at points 900 miles apart, glaciers
have left the marks of their former low descent; and
in Sikkim, Dr. Hooker saw maize growing on ancient
and gigantic moraines. Southward of the Asiatic con-
tinent, on the opposite side of the equator, we know,
from the excellent researches of Dr. J. Haast and Dr.
Hector, that in New Zealand immense glaciers formerly
descended to a low level; and the same plants found
by Dr. Hooker on widely separated mountains in this
island tell the same story of a former cold period.
From facts communicated to me by the Rev. W. B.
Clarke, it appears also that there are traces of former
glacial action on the mountains of the south-eastern
corner of Australia.
Looking to America; in the northern half, ice-borne
fragments of rock have been observed on the eastern
side of the continent, as far south as lat. 36°-387°, and
on the shores of the Pacific, where the climate is now
so different, as far south as lat. 46°. Erratic boulders
have, also, been noticed on the Rocky Mountains. In
the Cordillera of South America, nearly under the
equator, glaciers once extended far below their present
level In Central Chile I examined a vast mound of
/
160 ALTERNATE GLACIAL PERIODS ([Cuap. XIL
detritus with great boulders, crossing the Portillo valley,
which there can hardly be a doubt once formed a huge
moraine; and Mr. D. Forbes informs me that he found
in various parts of the Cordillera, from lat. 13° to 30° S.,
at about the height of 12,000 feet, deeply-furrowed
rocks, resembling those with which he was familiar in
Norway, and likewise great masses of detritus, including
srooved pebbles. Along this whole space of the Cor-
dillera true glaciers do not now exist even at much
more considerable heights. Farther south on both sides
of the continent, from lat. 41° to the southernmost
extremity, we have the clearest evidence of former gla-
cial action, in numerous immense boulders transported
far from their parent source.
From these several facts, namely from the glacial
action having extended all round the northern and
southern hemispheres—from the period having been in
a geological sense recent in both hemispheres—from its
having lasted in both during a great length of time, as
may be inferred from the amount of work effected—
and lastly from glaciers having recently descended toa
low level along the whole line of the Cordillera, it at
one time appeared to me that we could not avoid the
conclusion that the temperature of the whole world
had been simultaneously lowered during the Glacial
period. But now Mr. Croll, ina series of admirable
memoirs, has attempted to show that a glacial con-
dition of climate is the result of various physical causes,
brought into operation by an increase in the eccentricity
of the earth’s orbit. All these causes tend towards the
same end; but the most powerful appears to be the
indirect influence of the eccentricity of the orbit upon
oceanic currents. According to Mr. Croll, cold periods
*
ew
Cuap. X11.) IN THE NORTH AND SOUTH. 161
regularly recur every ten or fifteen thousand years ; and
these at long intervals are extremely severe, owing to
certain contingencies, of which the most important, as Sir
C. Lyell has shown, is the relative position of the land
and water. Mr. Croll believes that the last great Glacial
period occurred about 240,000 years ago, and endured
with slight alterations of climate for about 160,000
years. With respect to more ancient Glacial periods,
several geologists are convinced from direct evidence
that such occurred during the Miocene and Kocene
formations, not to mention still more ancient formations.
But the most important result for us, arrived at by Mr.
Croll, is that whenever the northern hemisphere passes
through a cold period the temperature of the southern
hemisphere is actually raised, with the winters rendered
much milder, chiefly through changes in the direction of
the ocean-currents. So conversely it will be with the
northern hemisphere, whilst the southern passes though
a Glacial period. This conclusion throws so much lhght
on geographical distribution that I am strongly inclined
to trust in it; but I will first give the facts, which
demand an explanation.
In South America, Dr. Hooker has shown that
besides many closely allied species, between forty and
fifty of the flowering plants of Tierra del Fuego, forming
no inconsiderable part of its scanty flora, are common
to North America and Europe, enormously remote as
these areas in opposite hemispheres are from each
other. On the lofty mountains of equatorial America
a host of peculiar species belonging to European
genera occur. On the Organ mountains of Brazil,
some few temperate European, some Antarctic, and
some Andean genera were found by Gardner, which do
162 ALTERNATE GLACIAL PERIODS [Casar. XI.
not exist in the low intervening hot countries. On the
Silla of Caraccas, the illustrious Humboldt long ago
found species belonging to genera characteristic of the
Cordillera.
In Africa, several forms characteristic of Europe and
some few representatives of the flora of the Cape of
Good Hope occur on the mountains of Abyssinia. At
the Cape of Good Hope a very few European species;
believed not to have been introduced by man, and on
the mountains several representative European forms
are found, which have not been discovered in the
intertropical parts of Africa. Dr. Hooker has also
lately shown that several of the plants living on the
upper parts of the lofty island of Fernando Po and on
the neighbouring Cameroon mountains, in the Gulf of
Guinea, are closely related to those on the mountains
of Abyssinia, and likewise to those of temperate Europe.
It now also appears, as I hear from Dr. Hooker,
that some of these same temperate plants have been
discovered by the Rev. R. T. Lowe on the mountains of
the Cape Verde islands. This extension of the same
temperate forms, almost under the equator, across the
whole continent of Africa and to the mountains of the
Cape Verde archipelago, is one of the most astonishing
facts ever recorded in the distribution of plants.
On the Himalaya, and on the isolated mountain-
ranges of the peninsula of India, on the heights of
Ceylon, and on the volcanic cones of Java, many plants
occur, either identically the same or representing each
other, and at the same time representing plants of
Europe, not found in the intervening hot lowlands.
A list of the genera of plants collected on the loftier
peaks of Java, raises a picture of a collection made on
Cuap. XII] IN THE NORTH AND SOUTH. 163
a hillock in Europe! Still more striking is the fact
that peculiar Australian forms are represented by
certain plants growing on the summits of the moun-
tains of Borneo. Some of these Australian forms, as I
hear from Dr. Hooker, extend along the heights of the
peninsula of Malacca, and are thinly scattered on the
one hand over India, and on the other hand as far
north as Japan.
On the southern mountains of Australia, Dr.
F. Miller has discovered several European species ;
other species, not introduced by man, occur on the
lowlands; and a long list can be given, as I am
informed by Dr. Hooker, of European genera, found in
Australia, but not in the intermediate torrid regions.
In the admirable ‘Introduction to the Flora of New
Zealand, by Dr. Hooker, analogous and striking facts
are given in regard to the plants of that large island.
Hence we see that certain plants growing on the more
lofty mountains of the tropics in all parts of the world,
and on the temperate plains of the north and south, are
either the same species or varieties of the same species.
It should, however, be observed that these plants are
not strictly arctic forms; for, as Mr. H. C. Watson
has remarked, “in receding from polar towards equa-
torial latitudes, the Alpine or mountain floras really
become less and less Arctic.” Besides these identical
and closely allied forms, many species inhabiting the
same widely sundered areas, belong to genera not now
found in the intermediate tropical lowlands.
These brief remarks apply to plants alone; but some
few analogous facts could be given in regard to terres-
trial animals. In marine productions, similar cases
likewise ite asan example, I may quote a statement
3
164 ALTERNATE GLACIAL PERIODS [Cuap. XII.
by the highest .authority, Prof. Dana, that “it is cer-
tainly a wonderful fact that New Zealand should have
a closer resemblance in its crustacea to Great Britain,
its antipode, than to any other part of the world.”
Sir J. Richardson, also, speaks of the reappearance on
the shores of New Zealand, Tasmania, &c., of northern
forms of fish. Dr. Hooker informs me that twenty-five
species of Algze are common to New Zealand and to
Europe, but have not been found in the intermediate
tropical seas.
From the foregoing facts, namely, the presence of
temperate forms on the highlands across the whole of
equatorial Africa, and along the Peninsula of India, to
Ceylon and the Malay Archipelago, and in a less well-
marked manner across the wide expanse of tropical
South America, it appears almost certaim that at some
former period, no doubt during the most severe part of
a Glacial period, the lowlands of these great continents
were everywhere tenanted under the equator by a con
siderable number of temperate forms. At this period
the equatorial climate at the level of the sea was pro-
bably about the same with that now experienced at the
height of from five to six thousand feet under the same
latitude, or perhaps even rather cooler. During this, the
coldest period, the lowlands under the equator must
have been clothed with a mingled tropical and temper-
ate vegetation, like that described by Hooker as growing
luxuriantly at the height of from four to five thousand
feet on the lower slopes of the Himalaya, but with
perhaps a still greater preponderance of temperate
forms. So again in the mountainous island of Fernando
Po, in the Gulf of Guinea, Mr. Mann found temperate
European forms beginning to appear at the height of
Cxar. XII.] IN THE NORTH AND SOUTH. 165
about five thousand feet. Onthe mountains of Panama,
at the height of only two thousand feet, Dr. Seemann
found the vegetation like that of Mexico, “with forms
of the torrid zone harmoniously blended with those of
the temperate.”
Now let us see whether Mr. Croll’s conclusion that
when the northern hemisphere suffered from the extreme
cold of the great Glacial period, the southern hemisphere
was actually warmer, throws any clear light on the
present apparently inexplicable distribution of various
organisms in the temperate parts of both hemispheres,
and on the mountains of the tropics. The Glacial
period, as measured by years, must have been very
long ; and when we remember over what vast spaces
some naturalised plants and animals have spread within
a few centuries, this period will have been ample for
any amount of migration. As the cold became more
and more intense, we know that Arctic forms invaded
the temperate regions; and, from the facts just given,
there can hardly be a doubt that some of the more
vigorous, dominant and widest-spreading temperate
forms invaded the equatorial lowlands. The inha-
bitants of these hot lowlands would at the same time
have migrated to the tropical and subtropical regions
of the south, for the southern hemisphere was at this
period warmer. On the decline of the Glacial period,
as both hemispheres gradually recovered their former
temperatures, the northern temperate forms living on
the lowlands under the equator, would have been driven
to their former homes or have been destroyed, being re-
placed by the equatorial forms returning from the south.
Some, however, of the northern temperate forms would.
almost certainly have ascended any adjoining high land,
166 ALTERNATE GLACIAL PERIODS [Cuap. XIL
where, if sufficiently lofty, they would have long sur-
vived like the Arctic forms on the mountains of Europe.
They might have survived, even if the climate was not
perfectly fitted for them, for the change of temperature
must have been very slow, and plants undoubtedly
possess a certain capacity for acclimatisation, as shown
by their transmitting to their offspring different con-
stitutional powers of resisting heat and cold.
In the regular course of events the southern hemi-
sphere would in its turn be subjected to a severe Glacial
period, with the northern hemisphere rendered warmer ;
and then the southern temperate forms would invade
the equatorial lowlands. The northern forms which
had before been left on the mountains would now
descend and mingle with the southern forms. These
latter, when the warmth returned, would return to their
former homes, leaving some few species on the moun-
tains, and carrying southward with them some of the
northern temperate forms which had descended from
their mountain fastnesses. Thus, we should have some
few species identically the same in the northern and
southern temperate zones and on the mountains of the
intermediate tropical regions. But the species left
during a long time on these mountains, or in opposite
hemispheres, would have to compete with many new
forms and would be exposed to somewhat different
physical conditions ; hence they would be eminently
liable to modification, and would generally now exist
as varieties or as representative species; and this is the
ease. We must, also, bear in mind the occurrence in
both hemispheres of former Glacial periods; for these
will account, in accordance with the same principles, for
the many quite distinct species inhabiting the same
Cuar. XII] IN THE NORTH AND SOUTH. 167
widely separated areas, and belonging to genera not now
found in the intermediate torrid zones.
It is a remarkable fact strongly sisted on by Hooker
in regard to America, and by Alph. de Candolle in
regard to Australia; that many more identical or
slightly modified species have migrated from the north
to the south, than in a reversed direction, We see,
however, a few southern forms on the mountains of
Borneo and Abyssinia. Isuspect that this preponderant
migration from the north to the south is due to the
greater extent of land in the north, and to the northern
forms having existed in their own homes in greater
numbers, and having consequently been advanced
through natural selection and competition to a higher
stage of perfection, or dominating power, than the
southern forms. And thus, when the two sets became
commingled in the equatorial regions, during the alter-
nations of the Glacial periods, the northern forms were
the more powerful and were able to hold their places
on the mountains, and afterwards to migrate southward
with the southern forms; but not so the southern in
regard to the northern forms. In the same manner at
the present day, we see that very many European
productions cover the ground in La Plata, New Zealand,
and to a lesser degree in Australia, and have beaten
the natives; whereas extremely few southern forms
have become naturalised in any part of the northern
hemisphere, though hides, wool, and other objects likely
to carry seeds have been largely imported into Europe
during the last two or three centuries from La Plata
and during the last forty or fifty years from Australia.
The Neilgherrie mountains in India, however, offer a
partial exception; for here, as I hear from Dr. Hooker,
168 ALTERNATE GLACIAL PERIODS ([Cuap. XIL.
Australian forms are rapidly sowing themselves and
becoming naturalised. Before the last great Glacial
period, no doubt the intertropical mountains were
stocked with endemic Alpine forms; but these have
almost everywhere yielded to the more dominant forms
generated in the larger areas and more efficient work-
shops of the north. In many islands the native
productions are nearly equalled, or even outnumbered,
by those which have become naturalised; and this is
the first stage towards their extinction. Mountains are
jslands on the land, and their inhabitants have yielded
to those produced within the larger areas of the north,
just in the same way as the inhabitants of real islands
have everywhere yielded and are still yielding to
continental forms naturalised through man’s agency.
The same principles apply to the distribution of
terrestrial animals and of marine productions, in the
northern and southern temperate zones, and on the
intertropical mountains. When, during the height of
the Glacial period, the ocean-currents were widely
different to what they now are, some of the inhabitants
of the temperate seas might have reached the equator ; of
these a few would perhaps at once be able to migrate
southward, by keeping to the cooler currents, whilst
others might remain and survive in the colder depths
until the southern hemisphere was in its turn subjected
to a glacial climate and permitted their further progress ;
in nearly the same manner as, according to Forbes,
isolated spaces inhabited by Arctic productions exist to
the present day in the deeper parts of the northern
temperate seas.
I am far from supposing that all the difficulties in
regard to the distribution and affinities of the identical
Cuap. XII.] IN THE NORTH AND SOUTH. 169
and allied species, which now live so widely separated
in the north and south, and sometimes on the inter-
mediate mountain-ranges, are removed on the views
above given. The exact lines of migration cannot be
indicated. We cannot say why certain species and not
others have migrated ; why certain species have ,been
modified and have given rise to new forms, whilst others
have remained unaltered. We cannot hope to explain
such facts, until we can say why one species and not
another becomes naturalised by man’s agency in a
foreign land; why one species ranges twice or thrice as
far, and is twice or thrice as common, as another species
within their own homes.
Various special difficulties also remain tobe solved ;
for instance, the occurrence, as shown by Dr. Hooker, of
the same plants at points so enormously remote as
Kerguelen Land, New Zealand, and Fuegia ; but icebergs,
as suggested by Lyell, may have been concerned in their
dispersal. The existence at these and other distant
points of the southern hemisphere, of species, which,
though distinct, belong to genera exclusively confined
to the south, is a more remarkable case. Some of these
species are so distinct, that we cannot suppose that there
has been time since the commencement of the last
Glacial period for their migration and subsequent
modification to the necessary degree. The facts seem to
indicate that distinct species belonging to the same
genera have migrated in radiating lines from a common
centre; and I am inclined to look in the southern, as in
the northern hemisphere, to a former and warmer period,
before the commencement of the last Glacial period,
when the Antarctic lands, now covered with ice, supported
a highly peculiar and isolated flora. It may be suspected
170 ALTERNATE GLACIAL PERIODS. ([Cuar. XT.
that before this flora was exterminated during the last
Glacial epoch, a few forms had been already widely
dispersed to various points of the southern hemisphere
by occasional means of transport, and by the aid
as halting-places, of now sunken islands. Thus the
southern shores of America, Australia, and New Zealand
may have become slightly tinted by the same peculiar
forms of life.
Sir C. Lyell in a striking passage has speculated, in
language almost identical with mine, on the effects of
great alterations of climate throughout the world on
geographical distribution. And -we have now seen that
Mr. Croll’s conclusion that successive Glacial periods in
the one hemisphere coincide with warmer periods in the
opposite hemisphere, together with the admission of the
slow modification of species, explains a multitude of facts
in the distribution of the same and of the allied forms
of life in all parts of the globe. The living waters have
flowed during one period from the north and during
another from the south, and in both cases have reached
the equator; but the stream of life has flowed with
greater force from the north than in the opposite direction.
and has consequently more freely inundated the south,
As the tide leaves its drift in horizontal lines, rising
higher on the shores where the tide rises highest, so have
the living waters left their living drift on our mountain
summits, in a line gently rising from the Arctic lowlands
to a great altitude under the equator. The various
beings thus left stranded may be compared with savage
races of man, driven up and surviving in the mountain
fastnesses of almost every land, which serves asa record,
full of interest to us, of the former inhabitants of the
surrounding lowlands.
Cuap. XIII.] FRESH-WATER PRODUCTIONS. 171
CHAPTER XIII.
GEOGRAPHICAL DISTRIBUTION—continued.
Distribution of fresh-water productions—On the inhabitants of
oceanic islands—Absence of Batrachians and of terrestrial Mam-
mals—On the relation of the inhabitants of islands to those of
the nearest mainland—On colonisation from the nearest source
with subsequent modification—Summary of the last and present
chapter.
Fresh-water Productions.
As lakes and river-systems are separated from each
other by barriers of land, it might have been thought
that fresh-water productions would not have ranged
widely within the same country, and as the sea is
apparently a still more formidable barrier, that they
would never have extended to distant countries. But
the case is exactly the reverse. Not only have many
fresh-water species, belonging to different classes, an
enormous range, but allied species prevail in a
remarkable manner throughout the world. When first
collecting in the fresh waters of Brazil, I well remember
feeling much surprise at the similarity of the fresh-
water insects, shells, &c., and at the dissimilarity of the
surrounding terrestrial beings, compared with those of
Britain.
But the wide ranging power of fresh-water productions
can, I think, in most cases be explained by their having
become fitted, in a manner highly useful to them, for
172 FRESH-WATER PRODUCTIONS. [Cuap. XIIL
short and frequent migrations from pond to pond, or
from stream to stream, within their own countries;
and liability to wide dispersal would follow from this
capacity as an almost necessary consequence. We can
here consider only a few cases; of these, some of the
most difficult to explain are presented by fish. It was
formerly believed that the same fresh-water species
never existed on two continents distant from each other.
But Dr. Ginther has lately shown that the Galaxias
attenuatus inhabits Tasmania, New Zealand, the Falk-
land Islands, and the mainland of South America. This
is a wonderful case, and probably indicates dispersal
from an Antarctic centre during a former warm period.
This case, however, is rendered in some degree less
surprising by the species of this genus having the
power of crossing by some unknown means considerable
spaces of open ocean: thus there is one species common
to New Zealand and to the Auckland Islands, though
separated by a distance of about 230 miles. On the same
continent fresh-water fish often range widely, and as if
capriciously ; for in two adjoining river-systems some of
the species may be the same, and some wholly different.
It is probable that they are occasionally transported
by what may be called accidental means. Thus fishes
still alive are not very rarely dropped at distant points
by whirlwinds; and it is known that the ova retain
their vitality for a considerable time after removal from
the water. Their dispersal may, however, be mainly
attributed to changes in the level of the land within the
recent period, causing rivers to flow into each other.
Instances, also, could be given of this having occurred
during floods, without any change of level. The wide
difference of the fish on the opposite sides of most
Cuap. XIII] FRESH-WATER PRODUCTIONS. re
mountain-ranges, which are continuous, and which con-
sequently must from an early period have completely
prevented the inosculation of the river-systems on the
two sides, leads to the same conclusion. Some fresh-
water fish belong to very ancient forms, and in such cases
there will have been ample time for great geographical
changes, and consequently time and means for much
migration. Moreover Dr. Ginther has recently been
led by several considerations to infer that with fishes
the same forms have a long endurance. Salt-water fish
can with care be slowly accustomed to live in fresh
water ; and, according to Valenciennes, there is hardly a
single group of which all the members are confined to
fresh water, so that a marine species belonging to a
fresh-water group might travel far along the shores of
the sea, and could, it is probable, become adapted
without much difficulty to the fresh waters of a distant
land.
Some species of fresh-water shells have very wide
ranges, and allied species which, on our theory, are
descended from a common parent, and must have pro-
ceeded froma single source, prevail throughout the
world. Their distribution at first perplexed me much,
as their ova are not likely to be transported by birds ;
and the ova, as well as the adults, are immediately
killed by sea-water. I could not even understand how
some naturalised species have spread rapidly through-
out the same country. But two facts, which I have
observed—and many others no doubt will be discovered
—throw some lght on this subject. When ducks
suddenly emerge from a pond covered with duck-weed,
I have twice seen these little plants adhering to their
backs; and it has happened to me, in removing a little
174 FRESH-WATER PRODUCTIONS. ([Cuap. XIIL
duck-weed from one aquarium to another, that I have
unintentionally stocked the one with fresh-water shells
from the other. But another agency is perhaps more
effectual: I suspended the feet of a duck in an
ayuarium, where many ova of fresh-water shells were
hatching; and I found that numbers of the extremely
minute and just-hatched shells crawled on the feet, and
clung to them so firmly that when taken out of the
~ water they could not be jarred off, though at a somewhat
more advanced age they would voluntarily drop off.
These just-hatched molluscs, though aquatic in their
nature, survived on the duck’s feet, in damp air, from
twelve to twenty hours; and in this length of timea
duck or heron might fly at least six or seven hundred
miles, and if blown across the sea to an oceanic island,
or to any other distant point, would be sure to alight on
a pool or rivulet. Sir Charles Lyell informs me that a
Dytiscus has been caught with an Ancylus (a fresh-
water shell like a limpet) firmly adhering to it; and a
water-beetle of the same family, a Colymbetes, once flew
on board the ‘ Beagle,’ when forty-five miles distant
from the nearest land: how much farther it might have
been blown by a favouring gale no one can tell
With respect to plants, it has long been known what
enormous ranges many fresh-water, and even marsh
species, have, both over continents and to the most
remote oceanic islands. This is strikingly illustrated,
according to Alph. de Candolle, in those large groups of
terrestrial plants, which have very few aquatic members ;
for the latter seem immediately to acquire, as if in
consequence, a wide range. I think favourable means
of dispersal explain this fact. I have before mentioned
that earth occasionally adheres in some quantity to the
Cuar. XIII] FRESH-WATER PRODUCTIONS. 175
feet and beaks of birds. Wading birds, which frequent
the muddy edges of ponds, if suddenly flushed, would be
the most likely to have muddy feet. Birds of this order
wander more than those of any other; and they are
occasionally found on the most remote and barren
islands of the open ocean; they would not be likely to
alight on the surface of the sea, so that any dirt on their
feet would not be washed off; and when gaining the
land, they would be sure to fly to their natural fresh-
water haunts. I do not believe that botanists are
aware how charged the mud of ponds is with seeds; I
have tried several little experiments, but will here give
only the most striking case: I took in February three
table-spoonfuls of mud from three different points,
beneath water, on the edge of a little pond: this mud
when dried weighed only 62 ounces; I kept it covered
up in my study for six months, pulling up and counting
each plant as it grew ; the plants were of many kinds,
and were altogether 537 in number; and yet the viscid
mud was all contained in a breakfast cup! Considering
these facts, I think it would be an inexplicable cir-
cumstance if water-birds did not transport the seeds
of fresh-water plants to unstocked ponds and streams,
situated at very distant points. The same agency may
have come into play with the eggs of some of the
smaller fresh-water animals.
Other and unknown agencies probably have also
played a part. I have stated that fresh-water fish eat
some kinds of seeds, though they reject many other
kinds after having swallowed them; even small fish
swallow seeds of moderate size, as of the yellow water-
lily and Potamogeton. Herons and other birds, century
after century, have gone on daily devouring fish; they
39
176 FRESH-WATER PRODUCTIONS. [Cuar. XIII.
then take flight and go to other waters, or are blown
across the sea; and we have seen that seeds retain their
power of germination, when rejected many hours after-
wards in pellets or in the excrement. When I saw
the great size of the seeds of that fine water-lily,
the Nelumbium, and remembered Alph. de Candolle’s
remarks on the distribution of this plant, I thought that
the means of its dispersal must remain inexplicable;
but Audubon states that he found the seeds of the great
southern water-lily (probably, according to Dr. Hooker,
the Nelumbium luteum) in a heron’s stomach. Now
this bird must often have flown with its stomach thus
well stocked to distant ponds, and then getting a hearty
meal of fish, analogy makes me believe that it would
have rejected the seeds in a pellet in a fit state for
germination.
In considering these several means of distribution, it
should be remembered that when a pond or stream is
first formed, for instance, on a rising islet, it will be
unoccupied ; and a single seed or egg will have a good
chance of succeeding. Although there will always be a
struggle for life between the inhabitants of the same
pond, however few in kind, yet as the number even in a
well-stocked pond is small in comparison with the
number of species inhabiting an equal area of land, the
competition between them will probably be less severe
than between terrestrial species; consequently an in-
truder from the waters of a foreign country would have
a better chance of seizing on a new place, than in the
case of terrestrial colonists. We should also remember
that many fresh-water productions are low in the scale
of nature, and we have reason to believe that such
beings become modified more slowly than the high;
Cuap. XIII.] INHABITANTS OF OCEANIC ISLANDS. 177
and this will give time for the migration of aquatic
species. We should not forget the probability of many
fresh-water forms having formerly ranged continuously
over immense areas, and then having become extinct
at intermediate points. But the wide distribution of
fresh-water plants and of the lower animals, whether
retaining the same identical form or in some degree
modified, apparently depends in main part on the wide
dispersal of their seeds and eges by animals, more
especially by fresh-water birds, which have great powers
of flight, and naturally travel from one piece of water to
another.
On the Inhabitants of Oceanic Islands.
We now come to the last of the three classes of facts,
which I have selected as presenting the greatest amount
of difficuity with respect to distribution, on the view
that not only all the individuals of the same species
have migrated from some one area, but that allied
species, although now inhabiting the most distant
points, have proceeded from a single area,—the birth-
place of their early progenitors. I have already given
my reasons for disbelieving in continental extensions
within the period of existing species, on so enormous a
scale that all the many islands of the several oceans
were thus stocked with their present terrestrial inhabi-
tants. This view removes many difficulties, but it
does not accord with all the facts in regard to the
productions of islands. In the following remarks T
shall not confine myself to the mere question of
dispersal, but shall consider some other cases bearing
on the truth of the two theories of independent creation
and of descent with modification.
178 INHABITANTS OF OCEANIC ISLANDS. [Cuar. XIII.
The species of all kinds which inhabit oceanic islands
are few in number compared with those on equal con-
tinental areas: Alph. de Candolle admits this for
plants, and Wollaston for insects. New Zealand, for
instance, with its lofty mountains and diversified
stations, extending over 780 miles of latitude, together
with the outlying islands of Auckland, Campbell and
Chatham, contain altogether only 960 kinds of flower-
ing plants; if we compare this moderate number with
the species which swarm over equal areas in South-
Western Australia or at the Cape of Good Hope,
we must admit that some cause, independently of
different physical conditions, has given rise to so great
a difference in number. Even the uniform county of
Cambridge has 847 plants, and the little island of
Anglesea 764, but a few ferns and a few introduced
plants are included in these numbers, and the com-
parison in some other respects is not quite fair. We
have evidence that the barren island of Ascension
aboriginally possessed less than half-a-dozen flowering
plants; yet many species have now become naturalised
on it, as they have in New Zealand and on every other
oceanic island which can be named. In St. Helena
there is reason to believe that the naturalised plants
and animals have nearly or quite exterminated many
native productions. He who admits the doctrine of
the creation of each separate species, will have to admit
that a sufficient number of the best adapted plants and
animals were not created for oceanic islands; for man
has unintentionally stocked them far more fully and
perfectly than did nature.
Although in oceanic islands the species are few in
number, the proportion of endemic kinds (i. ¢. those
Cuar. XII] INHABITANTS OF OCEANIC ISLANDS. 179
found nowhere else in the world) is often extremely
large. If we compare, for instance, the number of
endemic land-shells in Madeira, or of endemic birds in
the Galapagos Archipelago, with the number found on
any continent, and then compare the area of the island
with that of the continent, we shall see that this is
true. This fact might have been theoretically expected,
for, as already explained, species occasionally arriving
after long intervals of time in the new and isolated
district, and. having to compete with new associates,
would be eminently hable to modification, and would
often produce groups of modified descendants. But it
by no means follows that, because in an island: nearly
all the species of one class are peculiar, those of
another class, or of another section of the same class,
are peculiar; and this difference seems to depend
partly on the species which are not modified having
immigated in a body, so that their mutual relations
have not been much disturbed; and partly on the
frequent arrival of unmodified immigrants from the
mother-country, with which the insular forms have
intercrossed. It should be borne in mind that the
offspring of such crosses would certainly gain in
vigour; so that even an occasional cross would produce
more effect than might have been anticipated. I will
give a few illustrations of the foregoing remarks: in
the Galapagos Islands there are 26 land-birds ; of these
21 (or perhaps 23) are peculiar, whereas of the 11
marine birds only 2 are peculiar; and it is obvious that
marine birds could arrive at these islands much more
easily and frequently than land-birds. Bermuda, on
the other hand, which lies at about the same distance
from North America as the Galapagos Islands do from
180 INHABITANTS OF OCEANIC ISLANDS. [Cuar. XIII.
South America, and which has a very peculiar soil,
does not possess a single endemic land-bird; and we
know from Mr. J. M. Jones’s admirable account of
Bermuda, that very many North American birds occa-
sionally or even frequently visit this island. Almost
every year, as I am informed by Mr. E. V. Harcourt,
many European and African birds are blown to
Madeira; this island is inhabited by 99 kinds, of which
one alone is peculiar, though very closely related to a
European form; and three or four other species are
confined to this island and to the Canaries. So that
the Islands of Bermuda and Madeira have been stocked
from the neighbouring continents with birds, which for
long ages have there struggled together, and have
become mutually co-adapted. Hence when settled in
their new homes, each kind will have been kept by
the others to its proper place and habits, and will
consequently have been but little liable to modifi-
cation. Any tendency to modification will also have
been checked by intercrossing with the unmodified
inmigrants, often arriving from the mother-country.
Madeira again is inhabited by a wonderful number of
peculiar land-shells, whereas not one species of sea-
shell is peculiar to its shores: now, though we do not
know how sea-shells are dispersed, yet we can see that
their eggs or larve, perhaps attached to seaweed or
floating timber, or to the feet of wading-birds, might be
transported across three or four hundred miles of open
sea far more easily than land-shells. The different
orders of insects inhabiting Madeira present nearly
parallel cases.
Oceanic islands are sometimes deficient in animals of
certain whole classes, and their places are occupied by
Cuap. XIII.] INHABITANTS OF OCEANIC ISLANDS. 181
other classes; thus in the Galapagos Islands reptiles,
and in New Zealand gigantic wingless birds, take, or
recently took, the place of mammals. Although New
Zealand is here spoken of as an oceanic island, it is in
some degree doubtful whether it should be so ranked ;
it is of large size, and is not separated from Australia
by a profoundly deep sea; from its geological charac-
ter and the direction of its mountain-ranges, the Rev.
W. B. Clarke has lately maintained that this island,
as well as New Caledonia, should be considered as
appurtenances of Australia. Turning to plants, Dr.
Hooker has shown that in the Galapagos Islands the
proportional numbers of the different orders are very -
different from what they are elsewhere. All such
differences in number, and the absence of certain whole
groups of animals and plants, are generally accounted
for by supposed differences in the physical conditions
of the islands; but this explanation is not a little
doubtful. Facility of immigration seems to have been
fully as important as the nature of the conditions.
Many remarkable little facts could be given with
respect to the inhabitants of oceanic islands. For
instance, in certain islands not tenanted by a single
mammal, some of the endemic plants have beautifully
hooked seeds; yet few relations are more manifest than
that hooks serve for the transportal of seeds in the
wool or fur of quadrupeds. But a hooked seed might
be carried to an island by other means; and the plant
then becoming modified would form an endemic species,
still retaining its hooks, which would form a useless
appendage like the shrivelled wings under the soldered
wing-covers of many insular beetles. Again, islands
often possess trees or bushes belonging to orders which
182 ABSENCE OF TERRESTRIAL = (Caap. XUL
elsewhere include only herbaceous species; now trees,
as Alph. de Candolle has shown, generally have, what-
ever the cause may be, confined ranges Hence trees
would be little likely to reach distant oceanic islands 3
and an herbaceous plant, which had no chance of
successfully competing with the many fully developed
trees growing on a continent, might, when established
on an island, gain an advantage over other herbaceous
plants by growing taller and taller and overtopping
them. In this case, natural selection would tend to
add to the stature of the plant, to whatever order it
belonged, and thus first convert it into a bush and then
into a tree.
Absence of Batrachians and Terrestrial Mammals on
Oceanie Islands.
With respect to the absence of whole orders of
animals on oceanic islands, Bory St. Vincent long ago
remarked that Batrachians (frogs, toads, newts) are
never found on any of the many islands with which the
great oceans are studded. I have taken pains to verify
this assertion, and have found it true, with the ex-
ception of New Zealand, New Caledonia, the Andaman
Islands, and perhaps the Salomon Islands and the
Seychelles. But I have already remarked that it is
doubtful whether New Zealand and New Caledonia
ought to be classed as oceanic islands ; and this is still
more doubtful with respect to the Andaman and
Salomon groups and the Seychelles. This general
absence of frogs, toads, and newts on so many true
oceanic islands cannot be accounted for by their
physical conditions: indeed it seems that islands are
peculiarly fitted for these animals; for frogs have been
Cuap. XIIL] MAMMALS ON OCEANIC ISLANDS. 183
introduced into Madeira, the Azores, and Mauritius,
and have multiphed so as to become a nuisance. But
as these animals and their spawn are immediately
killed (with the exception, as far as known, of one
Indian species) by sea-water, there would be great
difficulty in their transportal across the sea, and there-
fore we can see why they do not exist on strictly
oceanic islands. But why, on the theory of creation,
they should not have been created there, it would be
very difficult to explain.
Mammals offer another and similar case. I have
carefully searched the oldest voyages, and have not
found a single instance, free from doubt, of a terrestrial
mammal (excluding domesticated animals kept by the
natives) inhabiting an island situated above 300 miles
from a continent or great continental island; and many
islands situated at a much less distance are equally
barren. The Falkland Islands, which are inhabited by
a wolf-like fox, come nearest to an exception; but this
group cannot be considered as oceanic, as it lies on a
bank in connection with the mainland at the distance
of about 280 miles; moreover, icebergs formerly brought
boulders to its western shores, and they may have
formerly transported foxes, as now frequently happens
in the arctic regions. Yet it cannot be said that small
islands will not support at least small mammals, for
they occur in many parts of the world on very small
islands, when lying close to a continent; and hardly
an island can: be named on which our smaller quad-
rupeds have not become naturalsed and greatly
multiplied. It cannot be said, on the ordinary view of
creation, that there has not been time for the creation
of mammals; many volcanic islands are sufficiently
184 ABSENCE OF TERRESTRIAL = [Cuapr. XIII.
ancient, as shown by the stupendous degradation which
they have suffered, and by their tertiary strata: there
has also been time for the production of endemic species
belonging to other classes; and on continents it is
known. that new species of mammals appear and
disappear at a quicker rate than other and lower
animals. Although terrestrial mammals do not occur
on oceanic islands, aerial mammals do occur on almost
every island. New Zealand possesses two bats found
nowhere else in the world: Norfolk Island, the Viti
Archipelago, the Bonin Islands, the Caroline and
Marianne Archipelagoes, and Mauritius, all possess
their peculiar bats. Why, it may be asked, has the
supposed creative force produced bats and no other
mammals on remote islands? On my view this
question can easily be answered; for no terrestrial
mammal can be transported across a wide space of sea,
but bats can fly across. Bats have been seen wandering
by day far over the Atlantic Ocean; and two North
American species either regularly or occasionally visit
Bermuda, at the distance of 600 miles from the main-
land. I hear from Mr. Tomes, who has specially
studied this family, that many species have enormous
ranges, and are found on continents and on far distant
islands. Hence we have only to suppose that such
wandering species have been modified in their new
homes in relation to their new position, and we can
understand the presence of endemic bats on oceanic
islands, with the absence of all other terrestrial mam-
mals.
Another interesting relation exists, namely between
the depth of the sea separating islands from each other
or from the nearest continent, and the degree of affinity
CuaP. XIIL] MAMMALS ON OCEANIC ISLANDS. 185
of their mammalian inhabitants. Mr. Windsor Earl
has made some striking observations on this head, since
ereatly extended by Mr. Wallace’s admirable researches,
in regard to the great Malay Archipelago, which is
traversed near Celebes by a space of deep ocean, and
this separates two widely distinct mammalian faunas.
On either side the islands stand on a moderately shallow
submarine bank, and these islands are inhabited by the
same or by closely allied quadrupeds. I have not as
yet had time to follow up this subject in all quarters of
the world ; but as far as I have gone, the relation holds
good. For instance, Britain is separated by a shallow
channel from Europe, and the mammals are the same
on both sides; and so it is with all the islands near the
shores of Australia. The West Indian Islands, on the
other hand, stand on a deeply submerged bank, nearly
1000 fathoms in depth, and here we find American
forms, but the species and even the genera are quite
distinct. As the amount of modification which animals
of all kinds undergo partly depends on the lapse of
time, and as the islands which are separated from each
other or from the mainland by shallow channels, are
more likely to have been continuously united within a
recent period than the islands separated by deeper
channels, we can understand how it is that a relation
exists between the depth of the sea separating two
mammalian faunas, and the degree of their affinity,—
a relation which is quite inexplicable on the theory of
independent acts of creation.
The foregoing statements in regard to the inhabitants
of oceanic islands,—namely, the fewness of the species,
with a large proportion consisting of endemic forms—
the members of certain groups, but not those of other
186 ABSENCE OF TERRESTRIAL ([Cuapr. XIII.
groups in the same class, having been modified—the
absence of certain whole orders, as of batrachians and
of terrestrial mammals, notwithstanding the presence of
aerial bats——the singular proportions of certain orders
of plants——herbaceous forms having been developed
into trees, &c.,—seem to me to accord better with the
belief in the efficiency of occasional means of transport,
carried on during a long course of time, than with the
belief in the former connection of all oceanic islands
with the nearest continent; for on this latter view it is
probable that the various classes would have immigrated
more uniformly, and from the species having entered
in a body their mutual relations would not have been
much disturbed, and consequently they would either
have not been modified, or all the species in a more
equable manner.
I do not deny that there are many and serious
difficulties in understanding how many of the in-
habitants of the more remote islands, whether stil]
retaining the same specific form or subsequently modi-
fied, have reached their present homes. But the
probability of other islands having once existed as
halting-places, of which not a wreck now remains,
must not be overlooked. I will specify one difficult
ease. Almost all oceanic islands, even the most isolated
and smallest, are inhabited by land-shells, generally by
endemic species, but sometimes by species found else-
where,—striking instances of which have been given
by Dr. A. A. Gould in relation to the Pacific. Now it
is notorious that land-shells are easily killed by sea-
water ; their eggs, at least such as I have tried, sink in
it and are killed. Yet there must be some unknown,
but occasionally efficient means for their transportal.
Cuap. XIII] MAMMALS ON OCEANIC ISLANDS. 187
Would the just-hatched young sometimes adhere to the
feet of birds roosting on the ground, and thus get
transported ? It occurred to me that land-shells, when
hybernating and having a membranous diaphragm over
the mouth of the shell, might be floated in chinks of
drifted timber across moderately wide arms of the sea.
And I find that several species in this state withstand
uninjured an immersion in sea-water during seven
days: one shell, the Helix pomatia, after having been
thus treated and again hybernating was put into sea-
water for twenty days, and perfectly recovered. During
this length of time the shell might have been carried
by a marine current of average swiftness, to a distance
of 660 geographical miles. As this Helix has a thick
calcareous operculum, I removed it, and when it had
formed a new membranous one, I again immersed it for
fourteen days in sea-water, and again it recovered and
crawled away. Baron Aucapitaine has since tried
similar experiments: he placed 100 land-shells, be-
longing to ten species, in a box pierced with holes, and
immersed it for a fortnight in the sea. Out of the
hundred shells, twenty-seven recovered. The presence
of an operculum seems to have been of importance, as
out of twelve specimens of Cyclostoma elegans, which
is thus furnished, eleven revived. It is remarkable,
seeing how well the Helix pomatia resisted with me the
salt-water, that not one of fifty-four specimens belonging
to four other species of Helix tried by Aucapitaine,
recovered. It is, however, not at all probable that
land-shells have often been thus transported ; the feet
of birds offer a more probabie method.
188 RELATIONS OF THE INHABITANTS OF [Cuap. XII
On the Relations of the Inhabitants of Islands to those of
| the nearest Mainland.
The most striking and important fact for us is the
affinity of the species which inhabit islands to those of
the nearest mainland, without being actually the same.
Numerous instances could be given. The Galapagos
Archipelago, situated under the equator, lies at the
distance of between 500 and 600 miles from the shores
of South America. Here almost every product of the
land and of the water bears the unmistakable stamp of
the American continent. There are twenty-six land-
birds; of these, twenty-one, or perhaps twenty-three
are ranked as distinct species, and would commonly be
assumed to have been here created; yet the close affinity
of most of these birds to American species is manifest
in every character, in their habits, gestures, and tones
of voice. So it is with the other animals, and with a
large proportion of the plants, as shown by Dr. Hooker
in his admirable Flora of this archipelago. The natu-
ralist, looking at the inhabitants of these volcanic
islands in the Pacific, distant several hundred miles
from the continent, feels that he is standing on American
land. Why should this be so? why should the species
which are supposed to have been created in the Gala-
pagos Archipelago, and nowhere else, bear so plainly
the stamp of affinity to those created in America?
There is nothing in the conditions of life, in the
geological nature of the islands, in their height or
climate, or in the proportions in which the several
classes are associated together, which closely resembles
the conditions of the South American coast: in fact,
there is a considerable dissimilarity in all these respects.
Cuap. XTil.] ISLANDS TO THOSE OF THE MAINLAND. 189
On the other hand, there is a considerable degree of
resemblance in the volcanic nature of the soil, in the
climate, height, and size of the islands, between the
Galapagos and Cape Verde Archipelagoes: but what an
entire and absolute difference in their inhabitants!
The inhabitants of the Cape Verde Islands are related
to those of Africa, hke those of the Galapagos to
America. Facts such as these, admit of no sort of
explanation on the ordinary view of independent
creation; whereas on the view here maintained, it is
obvious that the Galapagos Islands would be likely to
receive colonists from America, whether by occasional
means of transport or (though I do not believe in this
doctrine) by formerly continuous land, and the Cape
Verde Islands from Africa; such colonists would be
liable to modification,—the principle of inheritance still
betraying their original birthplace.
Many analogous facts could be given: indeed it is an
almost universal rule that the endemic productions of
islands are related to those of the nearest continent, or
of the nearest large island. The exceptions are few,
and most of them can be explained. Thus although
Kerguelen Land stands nearer to Africa than to America,
the plants are related, and that very closely, as we know
from Dr. Hooker’s account, to these of America: but
on the view that this island has been mainly stocked
by seeds brought with earth and stones on icebergs,
drifted by the prevailing currents, this anomaly dis-
appears. New Zealand in its endemic planes is much
more closely related to Austraha, the nearest mainland,
than to any other region: and this is what might have
been expected ; but it is also plainly related to South
America, which, although the next nearest continent, is
190 RELATIONS OF THE INHABITANTS OF [Cuapr. XIIL
so enormously remote, that the fact becomes an anomaly.
But this difficulty partially disappears on the view that
New Zealand, South America, and the other southern
lands have been stocked in part from a nearly inter-
mediate though distant point, namely from the antarctic
islands, when they were clothed with vegetation, during
a warmer tertiary period, before the commencement of
the last Glacial period. The affinity, which though
feeble, I am assured by Dr. Hooker is real, between the
flora of the south-western corner of Australia and of the
- Cape of Good Hope, is a far more remarkable case; but
this affinity is confined to the plants, and will, no doubt,
some day be explained.
The same law which has determined the relationship
between the inhabitants of islands and the nearest
mainland, is sometimes displayed on a small scale, but
in a most interesting manner, within the limits of the
same archipelago. Thus each separate island of the
Galapagos Archipelago is tenanted, and the fact is a
marvellous one, by many distinct species; but these
species are related to each other in a very much closer
manner than to the inhabitants of the American con-
tinent, or of any other quarter of the world. This is
what might have been expected, for islands situated so
near to each other would almost necessarily receive
immigrants from the same original source, and from
each other. But how is it that many of the immigrants
have been differently modified, though only in a small
degree, in islands situated within sight of each other,
having the same geological nature, the same height,
climate, &c.?. This long appeared to me a great diffi-
culty: but it arises in chief part from the deeply-seated
error of considering the physical conditions of a country
Cnar. XIII.) ISLANDS TO THOSE OF THE MAINLAND. 191
as the most important; whereas it cannot be disputed
that the nature of the other species with which each has
to compete, is at least as important, and generally a far
more important element of success. Now if we look to
the species which inhabit the Galapagos Archipelago,
and are likewise found in other parts of the world, we
find that they differ considerably in the several islands.
This difference might indeed have been expected if the
islands have been stocked by occasional means of
transport—a seed, for instance, of one plant having
been brought to one island, and that of another plant to
another island, though all proceeding from the same
general source. Hence, when in former times an im-
migrant first settled on one of the islands, or when it
subsequently spread from one to another, it would
undoubtedly be exposed to different conditions in the
different islands, for it would have to compete with a
different set of organisms; a plant, for instance, would
find the ground best fitted for it occupied by somewhat
different species in the different islands, and would be
exposed to the attacks of somewhat different enemies.
If then it varied, natural selection would probably
favour different varieties in the different islands. Some
species, however, might spread and yet retain the same
character throughout the group, Just as we see some
species spreading widely throughout a continent and
remaining the same.
The really surprising fact in this case of the Galapagos
Archipelago, and in a lesser degree in some analogous
cases, is that each new species after being formed in any
one island, did not spread quickly to the other islands,
But the islands, though in sight of each other, are
separated by deep arms of the sea, in most cases wider
192 RELATIONS OF THE INHABITANTS OF [Cuapr. XII.
than the British Channel, and there is no reason tw
suppose that they have at any former period been
continuously united. The currents of the sea are rapid
and sweep between the islands, and gales of wind are
extraordinarily rare; so that the islands are far more
effectually separated from each other than they appear
ona map. Nevertheless some of the species, both of
those found in other parts of the world and of those
confined to the archipelago, are common to the several
islands; and we may infer from their present manner
of distribution, that they have spread from one island
to the others. But we often take, I think, an erroneous
view of the probability of closely-allied species invading
each other’s territory, when put into free intereommuni-
cation. Undoubtedly, if one species has any advantage
over another, it will in a very brief time wholly or in
part supplant it ; but if both are equally well fitted for
their own places, both will probably hold their separate
places for almost any length of time. Being familiar
with the fact that many species, naturalised through
man’s agency, have spread with astonishing rapidity
over wide areas, we are apt to infer that most species
would thus spread; but we should remember that the
species which become naturalised in new countries are
not generally closely allied to the aboriginal inhabitants,
but are very distinct forms, belonging in a large pro-
portion of cases, as shown by Alph. de Candolle, to
distinet genera. In the Galapagos Archipelago, many
even of the birds, though so well adapted for flying
from island to island, differ on the different islands ;
thus there are three closely-allied species of mocking-
thrush, each confined to its own island. Now let us
suppose the mocking-thrush of Chatham Island to be
Cuap. XIII.] ISLANDS TO THOSE OF THE MAINLAND. 193
blown to Charles Island, which has its own mocking-
thrush; why should it succeed in establishing itself
there? We may safely infer that Charles Island is
well stocked with its own species, for annually more
egos are laid and young birds hatched, than can possibly
be reared ; and we may infer that the mocking-thrush
peculiar to Charles Island is at least as well fitted for
its home as is the species peculiar to Chatham Island.
Sir C. Lyell and Mr. Wollaston have communicated to
me a remarkable fact bearing on this subject; namely,
that Madeira and the adjoining islet of Porto Santo
possess many distinct but representative species of land-
shells, some of which live in crevices of stone; and
although large quantities of stone are annually trans-
ported from Porto Santo to Madeira, yet this latter
island has not become colonised by the Porto Santo
species ; nevertheless both islands have been colonised
by European land-shells, which no doubt had some
advantage over the indigenous species. From these
considerations I think we need not greatly marvel at
the endemic species which inhabit the several islands of
the Galapagos Archipelago, not having all spread from
island to island. On the same continent, also, pre-
occupation has probably played an important part in
checking the commingling of the species which inhabit
different districts with nearly the same physical condi-
tions. Thus, the south-east and south-west corners of
Australia have nearly the same physical conditions, and
are united by continuous land, yet they are inhabited
by a vast number of distinct mammals, birds, and
plants ; so it is, according to Mr. Bates, with the butter-
flies and other animals inhabiting the great, open, and
continuous valley of the Amazons.
194 RELATIONS OF THE INHABITANTS OF [Cuap. XIIL
The same principle which governs the general char-
acter of the inhabitants of oceanic islands, namely, the
relation to the source whence colonists could have been
mostly easily derived, together with their subsequent
modification, is of the widest application throughout
nature. We see this on every mountain-summit, in
every lake and marsh. For Alpine species, excepting
in as far as the same species have become widely
spread during the Glacial epoch, are related to those
of the surrounding lowlands; thus we have in South
America, Alpine humming-birds, Alpine rodents, Alpine
plants, &c., all strictly belonging to American forms;
and it is obvious that a mountain, as it became slowly
upheaved, would be colonised from the surrounding
lowlands. So it is with the inhabitants of lakes and
marshes, excepting in so far as great facility of trans-
port has allowed the same forms to prevail throughout
large portions of the world. We see this same prin-
ciple in the character of most of the blind animals
inhabiting the caves of America and of Europe. Other
analogous facts could be given. It will, I believe, be
found universally true, that wherever in two regions,
let them be ever so distant, many closely allied or
representative species occur, there will lkewise be
found some identical species; and wherever many
closely-allied species occur, there will be found many
forms which some naturalists rank as distinct species,
and others as mere varieties; these doubtful forms
showing us the steps in the progress of modification.
The relation between the power and extent of
migration in certain species, either at the present or
at some former period, and the existence at remote
points of the world of closely-allied species, is shown
Cxap. XIII.] ISLANDS TO THOSE OF THE MAINLAND. 195
in another and more general way. Mr. Gould re-
marked to me leng ago, that in those genera of birds
which range over the world, many of the species have
very wide ranges. I can hardly doubt that this rule
is generally true, though difficult of proof. Amongst
mammals, we see it strikingly displayed in Bats, and
in a lesser degree in the Felide and Canidz. We see
the same rule in the distribution of butterflies and
beetles. So it is with most of the inhabitants of fresh
water, for many of the genera in the most distinct
classes range over the world, and many of the species
have enormous ranges. It is not meant that all, but
that some of the species have very wide ranges in the
genera which range very widely. Nor is it meant that
the species in such genera have on an average a very
wide range; for this will largely depend on how far
the process of modification has gone; for instance, two
varieties of the same species inhabit America and
Europe, and thus the species has an immense range ;
but, if variation were to be carried a little further,
the two varieties would be ranked as distinct species,
and their range would be greatly reduced. Still less is
it meant, that species which have the capacity of
crossing barriers and ranging widely, as in the case
of certain powerfully-winged birds, will necessarily
range widely ; for we should never forget that to range
widely implies not only the power of crossing barriers,
but the more important power of being victorious in
distant lands in the struggle for lfe with foreign
associates. But according to the view that all the
species of a genus, though distributed to the most
remote points of the world, are descended from a single
progenitor, we ought to find, and I believe as a general
196 RELATIONS OF THE INHABITANTS OF [Cnap. XIII.
rule we do find, that some at least of the species range
very widely. |
We should bear in mind that many genera in all
classes are of ancient origin, and the species in this
case will have had ample time for dispersal and sub-
sequent modification. There is also reason to believe
from geological evidence, that within each great class
the lower organisms change at a slower rate than the
higher; consequently they will have had a_ better
chance of ranging widely and of still retaiming the
same specific character. This fact, together with that
of the seeds and eggs of most lowly organised forms
being very minute and better fitted for distant trans-
portal, probably accounts for a law which has long
been observed, and which has lately been discussed by
Alph. de Candolle in regard to plants, namely, that
the lower any group of organisms stands the more
widely it ranges.
The relations just discussed,—namely, lower organ-
isms ranging more widely than the higher,—some of
the species of widely-ranging genera themselves ranging
widely,—such facts, as alpine, lacustrine, and marsh
productions being generally related to those which live
on the surrounding low lands and dry lands,—the
striking relationship between the inhabitants of islands
and those of the nearest mainland—the still closer
relationship of the distinct inhabitants of the islands in
the same archipelago—are inexplicable on the ordinary
view of the independent creation of each species, but
are explicable if we admit colonisation from the nearest
or readiest suurce, together with the subsequent adap-
tation of the colonists to their new homes.
Czar. XIIL] ISLANDS TO THOSE OF THE MAINLAND. 197
Summary of the last and present Chapters.
In these chapters I have endeavoured to show, that
if we make due allowance for our ignorance of the full
effects of changes of climate and of the level of the
land, which have certainly occurred within the recent
period, and of other changes which have probably
occurred,—if we remember how ignorant we are with
respect to the many curious means of occasional trans-
port,—if we bear in mind, and this is a very important
consideration, how often a species may have ranged
continuously over a wide area, and then have become
extinct in the intermediate tracts,—the difficulty is not
insuperable in believing that all the individuals of the
same species, wherever found, are descended from
common parents. And we are led to this conclusion,
which has been arrived at by many naturalists under
the designation of single centres of creation, by various
general considerations, more especially from the im-
portance of barriers of all kinds, and from the analogical
distribution of sub-genera, genera, and families.
With respect to distinct species belonging to the
same genus, which on our theory have spread from one
parent-source; if we make the same allowances as
before for our ignorance, and remember that some
forms of life have changed very slowly, enormous —
periods of time having been thus granted for their
migration, the difficulties are far from insuperable;
though in this case, as in that of the individuals of the
same species, they are often great.
As exemplifying the effects of climatal changes on
distribution, I have attempted to show how important
a part the last Glacial period has played, which affected
198 SUMMARY OF THE [Cuar. XIU
even the equatorial regions, and which, during the
alternations of the cold in the north and south, allowed
the productions of opposite hemispheres to mingle, and
left some of them stranded on the mountain-summits
in all parts of the world. As showing how diversified
are the means of occasional transport, I have discussed
at some little length the means of dispersal of fresh-
water productions.
If the difficulties be not insuperable in admitting
that in the long course of time all the individuals of
the same species, and likewise of the several species
belonging to the same genus, have proceeded from
some one source; then all the grand leading facts of
geographical distribution are explicable on the theory
of migration, together with subsequent modification and
the multiplication of new forms. We can thus under-
stand the high importance of barriers, whether of land
or water, in not only separating, but in apparently
forming the several zoological and botanical provinces.
We can thus understand the concentration of related
species within the same areas; and how it is that
under different latitudes, for instance in South America,
the inhabitants of the plains and mountains, of the
forests, marshes, and deserts, are linked together in so
mysterious a manner, and are likewise linked to the
extinct beings which formerly inhabited the same
continent. Bearing in mind that the mutual relation
of organism to organism is of the highest importance,
we can see why two areas having nearly the same
physical conditions should often be mhabited by very
different forms of life; for according to the length of
tine which has elapsed since the colonists entered one
of the rezions, or both; according to the nature of the
Cuap. XIII1.] LAST AND PRESENT CHAPTERS. 199
communication which allowed certain forms and not
others to enter, either in greater or lesser numbers;
according or not, as those which entered happened to
come into more or less direct competition with each
other and with the aborigines; and according as the
immigrants were capable of varying more or less
rapidly, there would ensue in the two or more regions,
independently of their physical conditions, infinitely
diversified conditions of life,—there would be an almost
endless amount of organic action and reaction,—and
we should find some groups of beings greatly, and some
only slightly modified,—some developed in great force,
some existing in scanty numbers—and this we do find
in the several great geographical provinces of the
world.
On these same principles we can understand, as I have
endeavoured to show, why oceanic islands should have
few inhabitants, but that of these, a large proportion
should be endemic or peculiar ; and why, in relation to
the means of migration, one group of beings should
have all its species peculiar, and another group, even
within the same class, should have all its species the
same with those in an adjoining quarter of the world.
We can see why whole groups of organisms, as batra-
chians and terrestrial mammals, should be absent from
oceanic islands, whilst the most isolated islands should
possess their own peculiar species of aerial mammals or
bats. We can see why, in islands, there should be
some relation between the presence of mammals, in a
more or less modified condition, and the depth of the
sea between such islands and the mainland. We can
clearly see why all the inhabitants of an archipelago,
though see distinct on the several islets, should
3
200 tr SUMMARY OF THE [Cuap. XTIL
be closely related to each other; and should likewise
be related, but less closely, to those of the nearest
continent, or other source whence immigrants might
have been derived. We can see why, if there exist
very closely allied or representative species in two
areas, however distant from each other, some identical
species will almost always there be found.
As the late Edward Forbes often insisted, there is a
striking parallelism in the laws of lfe throughout time
and space; the laws governing the succession of forms
in past times beg nearly the same with those govern-
ing at the present time the differences in different
areas. We see this in many facts. The endurance of
each species and group of species is continuous in time;
for the apparent exceptions to the rule are so few, that
they may fairly be attributed to our not having as yet
discovered in an intermediate deposit certain forms
which are absent in it, but which occur both above and
below: so in space, it certainly is the general rule that
the area inhabited by a single species, or by a group of
species, is continuous, and the exceptions, which are not
rare, may,as I have attempted to show, be accounted for
by former migrations under different circumstances, or
through occasional means of transport, or by the species
having become extinct in the intermediate tracts.
Both in time and space species and groups of species
have their points of maximum development. Groups
of species, living during the same period of time, or
living within the same area, are often characterised by
trifling features in common, as of sculpture or colour.
In looking to the long succession of past ages; as in
looking to distant provinces throughout the world, we
tind that species in certain classes differ little from each
Cuar. XIII.] LAST AND PRESENT CHAPTERS. 201
other, whilst those in another class, or only in a different
section of the same order, differ greatly from each other.
In both time and space the lowly organised members
of each class generally change less than the highly
organised ; but there are in both cases marked excep-
tions to the rule. According to our theory, these
several relations throughout time and space are intelli-
gible ; for whether we look to the allied forms of life
which have changed during successive ages, or to
those which have changed after having migrated into
distant quarters, in both cases they are connected by
the same bond of ordinary generation; m both cases
the laws of variation have been the same, and modifi-
cations have been accumulated by the same means of
natural selection.
202 CLASSIFICATION. (Cuap. XIV.
CHAPTER XIV.
MoutvuaL AFFINITIES OF ORGANIC Bernas: Mor-
PHOLOGY: EMBRYOLOGY: RUDIMENTARY ORGANS.
CLASSIFICATION, groups subordinate to groups—Natural system—
Rules and difficulties in classification, explained on the theory
of descent with modification—Classification of varieties—Descent
always used in classification—Analogical or adaptive characters
—Affinities, general, complex, and radiating—Extinction
separates and defines groups—MorprHoLoey, between members
of the same class, between parts of the same individual—
Empryouoey, laws of, explained by variations not supervening
at an early age, and being inherited at a corresponding age—
RUDIMENTARY ORGANS; their origin explained—Summary.
Classification.
From the most remote period in the history of the world
organic beings have been found to resemble each other
in descending degrees, so that they can be classed in
groups under groups. This classification is not arbi-
trary like the grouping of the stars in constellations.
The existence of groups would have been of simple
significance, if one group had been exclusively fitted to
inhabit the land, and another the water; one to feed
on fiesh, another on vegetable matter, and so on; but
the case is widely different, for it is notorious how
commonly members of even the same sub-group have
different habits. In the second and fourth chapters, on
Variation and on Natural Selection, I have attempted
Cuap. XIV.] CLASSIFICATION. 203
to show that within each country it is the widely
ranging, the much diffused and common, that is the
dominant species, belonging to the larger genera in each
class, which vary most. The varieties, or incipient
species, thus produced, ultimately become converted
into new and distinct species; and these, on the prin-
ciple of inheritance, tend to produce other new and
dominant species. Consequently the groups which are
now large, and which generally include many dominant
species, tend to go on increasing in size. I further
attempted to show that from the varying descendants
of each species trying to occupy as many and as different
places as possible in the economy of nature, they
constantly tend to diverge in character. This latter
conclusion is supported by observing the great diversity
of forms which, in any small area, come into the closest
competition, and by certain facts in naturalisation.
I attempted also to show that there is a steady
tendency in the forms which are increasing in number
and diverging in character, to supplant and exterminate
the preceding, less divergent and less improved forms.
I request the reader to turn to the diagram illustrating
the action, as formerly explained, of these several prin-
ciples; and he will see that the inevitable result is,
that the modified descendants proceeding from one
progenitor become broken up into groups subordinate
to groups. In the diagram each letter on the uppermost
line may represent a genus including several species;
and the whole of the genera along this upper line form
together one class, for all are descended from one ancient
parent, and, consequently, have inherited something in
common. But the three genera on the left hand have,
on this same principle, much in common, and form a
204 CLASSIFICATION. (Cuar. XIV.
sub-family, distinct from that containing the next two
genera on the right hand, which diverged from a common
parent at the fifth stage of descent. These five genera
have also much in common, though less than when
grouped in sub-families; and they form a family distinct
from that containing the three genera still farther to
the right hand, which diverged at an earlier period.
And all these genera, descended from (A), form an
order distinct from the genera descended from (1). So
that we here have many species descended from a single
progenitor grouped into genera; and the genera into
sub-families, families, and orders, all under one great
class. The grand fact of the natural subordination of
organic beings In groups under groups, which, from its
famiharity, does not always sufficiently strike us, is in
my judgment thus explained. No doubt organic beings,
like all other objects, can be classed in many ways,
either artificially by single characters, or more naturally
by a number of characters. We know, for instance, that
minerals and the elemental substances can be thus
arranged. In this case there is of course no relation to
genealogical succession, and no cause can at present be
assigned for their falling into groups. But with organic
beings the case is different, and the view above given
accords with their natural arrangement in group under
group; and no other explanation has ever been
attempted.
Naturalists, as we have seen, try to arrange the
species, genera, and families in each class, on what is
called the Natural System. But what is meant by this
system ? Some authors look at it merely as a scheme
for arranging together those living objects which are
most alike, and for separating those which are most
Cuap. XIV.] CLASSIFICATION. 205
unlke; or as an artificial method of enunciating, as
briefly as possible, general propositions,—that is, by one
sentence to give the characters common, for instance, to
all mammals, by another those common to all carnivora,
by another those common to the dog-genus, and then,
by adding a single sentence, a full description is given
of each kind of dog. The ingenuity and utility of this
system are indisputable. But many naturalists think
that something more is meant by the Natural System ;
they believe that it reveals the plan of the Creator ;
but unless it be specified whether order in time or
space, or both, or what else is meant by the plan of the
Creator, it seems to me that nothing is thus added to
our knowledge. Expressions such as that famous one
by Linneus, which we often meet with in a more or
less concealed form, namely, that the characters do not
make the genus, but that the genus gives the characters,
seem to imply that some deeper bond is included in our
classifications than mere resemblance. I believe that
this is the case, and that community of descent—the
one known cause of close similarity in organic beings—
is the bond, which though observed by various degrees
of modification, is partially revealed to us by our
classifications.
Let us now consider the rules followed in classifica-
tion, and the difficulties which are encountered on the
view that classification either gives some unknown
plan of creation, or is simply a scheme for enunciating
general propositions and of placing together the forms
most like each other. It might have been thought
(and was in ancient times thought) that those parts of
the structure which determined the habits of life, and
the general place of each being in the economy of
206 | CLASSIFICATION. [Cuar. XIV.
nature, would be of very high importance in classifica-
tion. Nothing can be more false. No one regards the
external similarity of a mouse to a shrew, of a dugong
to a whale, of a whale to a fish, as of any importance.
These resemblances, though so intimately connected
with the whole life of the being, are ranked as merely
“adaptive or analogical characters;” but to the
consideration of these resemblances we shall recur. It
may even be given as a general rule, that the less any
part of the organisation is concerned with special
habits, the more important it becomes for classification.
As an instance: Owen, in speaking of the dugong,
says, “The generative organs, being those which are
most remotely related to the habits and food of an
animal, I have always regarded as affording very clear
indications of its true affinities. We are least likely in
the modifications of these organs to mistake a merely
adaptive for an essential character.” With plants how
remarkable it is that the organs of vegetation, on which
their nutrition and life depend, are of little signification ;
whereas the organs of reproduction, with their product
the seed and embryo, are of paramount importance!
So again in formerly discussing certain morphological
characters which are not functionally important, we
have seen that they are often of the highest service in
classification. This depends on their constancy through-
out many allied groups; and their constancy chiefly
depends on any slight deviations not having been
preserved and accumulated by natural selection, which
acts only on serviceable characters.
That the mere physiological importance of an organ
does not determine its classificatory value, is almost
proved by the fact, that in allied groups, in which the
Cuap. XIV.] CLASSIFICATION. 207
same organ, aS we have every reason to suppose, has
nearly the same physiological value, its classificatory
value is widely different. No naturalist can have
worked long at any group without being struck with
this fact; and it has been fully acknowledged in the
writings of almost every author. It will suffice to
quote the highest authority, Robert Brown, who, in
speaking of certain organs in the Proteacex, says their
generic importance, “like that of all their parts, not
only in this, but, as I apprehend, in every natural
family, is very unequal, and in some cases seems to be
entirely lost.’ Again, in another work he says, the
genera of the Connaraceze “ differ in having one or more
ovaria, in the existence or absence of albumen, in the
imbricate or valvular estivation. Any one of these
characters singly is frequently of more than generic
importance, though here even when all taken together
they appear insufficient to separate Cnestis from
Connarus.” To give an example amongst insects: in
one great division of the Hymenoptera, the antenne, as
Westwood has remarked, are most constant in structure ;
in another division they differ much, and the differences
are of quite subordinate value in classification ; yet no
one will say that the antenne in these two divisions of
the same order are of unequal physiological importance.
Any number of instances could be given of the vary-
ing importance for classification of the same important
organ within the same group of beings.
Again, no one will say that rudimentary or atrophied
organs are of high physiological or vital importance ;
yet, undoubtedly, organs in this condition are often of
much value in classification. No one will dispute that
the rudimentary teeth in the upper jaws of young
208 . CLASSIFICATION. (Cuar. XIV.
Ttuminants, and certain rudimentary bones of the leg,
are highly serviceable in exhibiting the close affinity
between ruminants and pachyderms. Robert Brown
has strongly insisted on the fact that the position of the
rudimentary florets is of the highest importance in the
classification of the grasses. 3
Numerous instances could be given of characters
derived from parts which must be considered of very
trifling physiological importance, but which are univer-
sally admitted as highly serviceable in the definition of
whole groups. For instance, whether or not there is an
open passage from the nostrils to the mouth, the only
character, according to Owen, which absolutely dis-
tinguishes fishes and reptiles—the inflection of the
angle of the lower jaw in Marsupials—the manner in
which the wings of insects are folded—mere colour in
certain Algze—mere pubescence on parts of the flower
in grasses—the nature of the dermal covering, as hair or
feathers, in the Vertebrata. If the Ornithorhynchus
had been covered with feathers instead of hair, this
external and trifling character would have been con-
sidered by naturalists as an important aid in deter-
mining the degree of affinity of this strange creature to
birds.
The importance, for classification, of trifling characters,
mainly depends on their being correlated with many
other characters of more or less importance. The value
indeed of an aggregate of characters is very evident in
natural history. Hence, as has often been remarked, a
species may depart from its allies in several characters,
both of high physiological importance, and of almost
universal prevalence, and yet leave us in no doubt
where it should be ranked. Hence, also, it has been
Cuar. XIV.] CLASSIFICATION. 209
found that a classification founded on any single
character, however important that may be, has always
failed; for no part of the organisation is invariably
constant. The importance of an aggregate of characters,
even when none are important, alone explains the
aphorism enunciated by Linnzus, namely, that the
characters do not give the genus, but the genus gives
the characters; for this seems founded on the apprecia-
tion of many trifling points of resemblance, too slight to
be defined. Certain plants, belonging to the Malpighi-
aces, bear perfect and degraded flowers ; in the latter,
as A. de Jussieu has remarked, “the greater number of
the characters proper to the species, to the genus, to the
family, to the class, disappear, and thus laugh at our
classification.” When Aspicarpa produced in France,
during several years, only these degraded flowers,
departing so wonderfully in a number of the most
important points of structure from the proper type of
the order, yet M. Richard sagaciously saw, as Jussieu
observes, that this genus should still be retained
amongst the Malpighiacese. This case well illustrates
the spirit of our classifications.
Practically, when naturalists are at work, they do
not trouble themselves about the physiological value
of the characters which they use in defining a group
or in allocating any particular species. If they find
a character nearly uniform, and common to a great
number of forms, and not common to others, they use it
as one of high value ; if common to some lesser number,
they use it as of subordinate value. ‘This principle has
been proadly confessed by some naturalists to be the
true one; and by none more clearly than by that
excellent botanist, Aug. St. Hilaire. If several trifling
210 ; CLASSIFICATION. [Caar. XIV.
characters are always found in combination, though no
apparent bond of connection can be discovered between
them, especial value is set on them. As in most groups
of animals, important organs, such as those for pro-
pelling the blood, or for aerating it, or those for pro-
pagating the race, are found nearly uniform, they are
considered as highly serviceable in classification ; but in
some groups all these, the most important vital organs, -
are found to offer characters of quite subordinate value.
Thus, as Fritz Miller has lately remarked, in the same
group of crustaceans, Cypridina is furnished with a
heart, whilst in two closely allied genera, namely
Cypris and Cytherea, there is no such organ; one
species of Cypridina has well-developed branchie,
whilst another species is destitute of them.
We can see why characters derived from the embryo
should be of equal importance with those derived from
the adult, for a natural classification of course includes
all ages. But it is by no means obvious, on the ordi-
nary view, why the structure of the embryo should be
more important for this purpose than that of the adult,
which alone plays its full part in the economy of nature.
Yet it has been strongly urged by those great natural-
ists, Milne Edwards and Agassiz, that embryological
characters are the most important of all; and this
doctrine has very generally been admitted as true.
Nevertheless, their importance has sometimes been
exaggerated, owing to the adaptive characters of larve
not having been excluded; in order to show this, Fritz
Miller arranged by the aid of such characters alone the
oreat class of crustaceans, and the arrangement did not
prove a natural one. But there can be no doubt that
embryonic, excluding larval characters, are of the
Cuap. XIV.] CLASSIFICATION. 211
- highest value for classification, not only with animals
but with plants. Thus the main divisions of flowering
plants are founded on differences in the embryo,—on
the number and position of the cotyledons, and on the
mode of development of the plumule and radicle. We
shall immediately see why these characters possess so
high a value in classification, namely, from the natural
system being genealogical in its arrangement.
Our classifications are often plainly influenced by
chains of affinities. Nothing can be easier than to
define a number of characters common to all birds ; but
with crustaceans, any such definition has hitherto been
found impossible. ‘There are crustaceans at the opposite
ends of the series, which have hardly a character in
common; yet the species at both ends, from being
plainly allied to others, and these to others, and so
onwards, can be recognised as unequivocally belonging
to this, and to no other class of the Articulata.
Geographical distribution has often been used, though
perhaps not quite logically, in classification, more
especially in very large groups of closely allied forms.
Temminck insists on the utility or even necessity of
this practice in certain groups of birds; and it has been
followed by several entomologists and botanists.
Finally, with respect to the comparative value of the
various groups of species, such as orders, sub-orders,
families, sub-families, and genera, they seem to be, at
least at present, almost arbitrary. Several of the best
botanists, such as Mr. Bentham and others, have strongly
insisted on their arbitrary value. Instances could be
given amongst plants and insects, of a group first
ranked by practised naturalists as only a genus, and
‘then raised to the rank of a sub-family or family; and
36
212 CLASSIFICATION. (Cuar. XIV.
this has been done, not because further research has
detected important structural differences, at first over-
looked, but because numerous allied species with slightly
different grades of difference, have been subsequently
discovered.
All the foregoing rules and aids and difficulties in
classification may be explained, if I do not greatly
deceive myself, on the view that the Natural System is
founded on descent with modification ;—that the cha-
racters which naturalists consider as showing true
affinity between any two or more species, are those
which have been inherited from a common parent, all
true classification being genealogical ;—that community
of descent is the hidden bond which naturalists have
been unconsciously seeking, and not some unknown
plan of creation, or the enunciation of general proposi-
tions, and the mere putting together and separating
objects more or less alike.
But I must explain my meaning more fully. I
believe that the arrangement of the groups within each
class, in due subordination and relation to each other,
must be strictly genealogical in order to be natural;
but that the amount of difference in the several branches
or groups, though allied in the same degree in blood to
their common progenitor, may differ greatly, being due
to the different degrees of modification which they have
undergone; and this is expressed by the forms being
ranked under different genera, families, sections, or
orders. The reader will best understand what is meant,
if he will take the trouble to refer to the diagram in the
fourth chapter. We will suppose the letters A to L to
represent allied genera existing during the Silurian
epoch, and descended from some still earlier form. In
Cuap. XIV.] CLASSIFICATION. ~ B18
three of these genera (A, F, and I), a species has trans-
mitted modified descendants to the present day, repre-
sented by the fifteen genera (a" to z*) on the uppermost
horizontal line. Now all these modified descendants
from a single species, are related in blood or descent in
the same degree; they may metaphorically be called
cousins to the same millionth degree; yet they differ
widely and in different degrees from each other. The
forms descended from A, now broken up into two or
three families, constitute a distinct order from those
descended from I, also broken up into two families.
Nor can the existing species, descended from A, be
ranked in the same genus with the parent A; or those
from I, with the parent I. But the existing genus F*
may be supposed to have been but slightly modified ;
and it will then rank with the parent-genus F; just
as some few still living organisms belong to Silurian
genera. So that the comparative value of the differences
between these organic beings, which are all related to
each other in the same degree in blood, has come to
be widely different. Nevertheless their genealogical
arrangement remains strictly true, not only at the
present time, but at each successive period of descent.
All the modified descendants from A will have inherited
something in common from their common parent, as
will all the descendants from I; so will it be with each
subordinate branch of descendants, at each successive
stage. If, however, we suppose any descendant of A,
or of I, to have become so much modified as to have
lost all traces of its parentage, in this case, its place in
the natural system will be lost, as seems to have occurred
with some few existing organisms, All the descendants
of the genus F, along its whole line of descent, are
214 CLASSIFICATION. (Caan xarye
supposed to have been but little modified, and they form
a single genus. But this genus, though much isolated,
will still occupy its proper intermediate position. The
representation of the groups, as here given in the diagram
on a flat surface, is much too simple. The branches
ought to have diverged in all directions. If the names
of the groups had been simply written down in a linear
series, the representation would have been still less
natural; and it is notoriously not possible to represent
in a series, on a flat surface, the affinities which we
discover in nature amongst the beings of the same
eroup. Thus, the natural system is genealogical in its
arrangement, hke a pedigree: but the amount of modifi-
cation which the different groups have undergone has to
be expressed by ranking them under different so-called
genera, sub-families, families, sections, orders, and
classes.
It may be worth while to illustrate this view of
classification, by taking the case of languages. If we
possessed a perfect pedigree of mankind, a genealogical
arrangement of the races of man would afford the best
classification of the various languages now spoken
throughout the world; and if all extinct languages, and
all intermediate and slowly changing dialects, were to
be included, such an arrangement would be the only
possible one. Yet it might be that some ancient
languages had altered very little and had given rise to
few new languages, whilst others had altered much
owing to the spreading, isolation, and state of civilisation
of the several co-descended races, and had thus given
rise to many new dialects and languages. The various
degrees of difference between the languages of the same
stock, would have to be expressed by groups subordinate
Cuar. XIV.] CLASSIFICATION. is)
to groups; but the proper or even the only possible
arrangement would still be genealogical ; and this would
be strictly natural, as it would connect together all
languages, extinct and recent, by the closest affinities,
and would give the filiation and origin of each tongue.
In confirmation of this view, let us glance at the
classification of varieties, which are known or believed ~
to be descended from a single species. These are
grouped under the species, with the sub-varieties under
the varieties; and in some cases, ass with the domestic
pigeon, with several other grades of difference. Nearly
the same rules are followed as in classifying species.
Authors have insisted on the necessity of arranging
varieties on a natural instead of an artificial system ; we
are cautioned, for instance, not to class two varieties of
the pine-apple together, merely because their fruit,
though the most important part, happens to be nearly
identical; no one puts the Swedish and common turnip
together, though the esculent and thickened stems are
so similar. Whatever part is found to be most con-
stant, is used in classing varieties: thus the great
agriculturist Marshall says the horns are very useful for
this purpose with cattle, because they are less variable
than the shape or colour of the body, &c.; whereas with
sheep the horns are much less serviceable, because less
constant. In classing varieties, | apprehend that if we
had a real pedigree, a genealogical classification would
be universally preferred; and it has been attempted in
some cases. For we might feel sure, whether there had
been more or less modification, that the principle of
inheritance would keep the forms together which were
allied in the greatest number of points. In tumbler
pigeons, though some of the sub-varieties differ in the
216 CLASSIFICATION. [Cuar. XIV.
important character of the length of the beak, yet all
are kept together from having the common habit of
tumbling; but the short-faced breed has nearly or quite
lost this habit: nevertheless, without any thought on
the subject, these tumblers are kept in the same group,
because allied in blood and alike in some other respects.
With species in a state of nature, every naturalist has
in fact brought descent into his classification; for he
includes in his lowest grade, that of species, the two
sexes; and how enormously these sometimes differ in
the most important characters, is known to every
naturalist: scarcely a single fact can be predicated in
common of the adult males and hermaphrodites of
certain cirripedes, and yet no one dreams of separating
them. As soon as the three Orchidean forms, Mo-
nachanthus, Myanthus, and Catasetum, which had
previously been ranked as three distinct genera, were
known to be sometimes produced on the same plant,
they were immediately considered as varieties; and
now I have been able to show that they are the male,
female, and hermaphrodite forms of the same species.
The naturalist includes as one species the various larval
stages of the same individual, however much they may
differ from each other and from the adult, as well as the
so-called alternate generations of Steenstrup, which can
only in a technical sense be considered as the same
individual. He includes monsters and varieties, not
from their partial resemblance to the parent-form, but
because they are descended from it.
As descent has universally been used in classing
together the individuals of the same species, though the
males and females and larve are sometimes extremely
different; and as it has been used in classing varieties
Cuap. XIV.] CLASSIFICATION. Heh sf
which have undergone a certain, and sometimes a
considerable amount of modification, may not this same
element of descent have been unconsciously used in
grouping species under genera, and genera under higher
groups, all under the so-called natural system? I
believe it has been unconsciously used; and thus only
can I understand the several rules and guides which
have been followed by our best systematists. As we
have no written pedigrees, we are forced to trace
community of descent by resemblances of any kind.
Therefore we choose those characters which are the least
likely to have been modified,-in relation to the con-
ditions of life to which each species has been recently
exposed. Rudimentary structures on this view are as
good as, or even sometimes better than, other parts of
the organisation. We care not how trifling a character
may be—let it be the mere inflection of the angle of the
jaw, the manner in which an insect’s wing is folded,
whether the skin be covered by hair or feathers—if it
prevail throughout many and different species, especially
those having very different habits of life, it assumes high
value; for we can account for its presence in so many
forms with such different habits, only by inheritance
from a common parent. We may err in this respect in
regard to single points of structure, but when several
characters, let them be ever so trifiing, concur through-
out a large group of beings having different habits, we
may feel almost sure, on the theory of descent, that
these characters have been inherited from a common
ancestor; and we know that such ageregated characters
have especial value in classification.
We can understand why a species or a group of
species may depart from its allies, in several of its most
218 CLASSIFICATION. [Coap. XIV.
important characteristics, and yet be safely classed with
them. This may be safely done, and is often done, as
long as a sufficient number of characters, let them be ever
so unimportant, betrays the hidden bond of community
of descent. Let two forms have not a single character
in common, yet, if these extreme forms are connected
together by a chain of intermediate groups, we may at
once infer their community of descent, and we put them
all into the same class. As we find organs of high
physiological importance—those which serve to preserve
life under the most diverse conditions of existence—are
generally the most constant, we attach especial value to
them; but if these same organs, in another group or
section of a group, are found to differ much, we at once
value them less in our classification. We shall presently
see why embryological characters are of such high classi-
ficatory importance. Geographical distribution may
sometimes be brought usefully into play im classing
large genera, because all the species of the same genus,
inhabiting any distinct and isolated region, are in all
probability descended from the same parents.
Analogical Resemblances—We can understand, on
the above views, the very important distinction between
real affinities and analogical or adaptive resemblances.
Lamarck first called attention to this subject, and he
has been ably followed by Macleay and others. The
resemblance in the shape of the”body and in the fin-like
anterior limbs between dugongs and whales, and between
these two orders of mammals and fishes, are analogical.
So is the resemblance between a mouse and a shrew-
mouse (Sorex), which belong to different orders; and
the still closer resemblance, insisted on by Mr. Mivart,
between the mouse and a small marsupial animal
Cuar. XIV.] ANALOGICAL RESEMBLANCES. 219
(Antechinus) of Australia. These latter resemblances
may be accounted for, as it seems to me, by adaptation
for similarly active movements through thickets and
herbage, together with concealment from enemies.
Amongst insects there are innumerable similar in-
stances; thus Linneus, misled by external appear-
ances, actually classed an homopterous insect as a moth.
We see something of the same kind even with our
domestic varieties, as in the strikingly similar shape
of the body in the improved breeds of the Chinese and
common pig, which are descended from distinct species ;
and in the similarly thickened stems of the common and
specifically distinct Swedish turnip. The resemblance
between the greyhound and the racehorse is hardly more
fanciful than the analogies which have been drawn by
some authors between widely different animals.
On the view of characters being of real importance
for classification, only in so far as they reveal descent,
-we can clearly understand why analogical or adap-
tive characters, although of the utmost importance to
the welfare of the being, are almost valueless to the
systematist. For animals, belonging to two most
distinct lines of descent, may have become adapted to
similar conditions, and thus have assumed a cloge
external resemblance; but such resemblances will not
reveal—will rather tend to conceal their blood-relation-
ship. We can thus also understand the apparent
paradox, that the very same characters are analogical
when one group is compared with another, but give true
affinities when the members of the same group are
compared together: thus, the shape of the body and
fin-like limbs are only analogical when whales are
compared with fishes, being adaptations in both classes
220 CLASSIFICATION. (Cuar. XIV.
for swimming through the water; but between the
several members of the whale family, the shape of the
body and the fin-like limbs offer characters exhibiting
true affinity; for as these parts are so nearly similar
throughout the whole family, we cannot doubt that they
have been inherited from a common ancestor. So it is
with fishes.
Numerous cases could be given of striking resemblances
in quite distinct beings between single parts or organs.
which have been adapted for the same functions. A
good instance is afforded by the close resemblance of the
jaws of the dog and Tasmanian wolf or Thylacinus,—
animals which are widely sundered in the natural sys-
tem. But this resemblance is confined to general appear-
ance, as in the prominence of the canines, and in the
cutting shape of the molar teeth. for the teeth really
differ much: thus the dog has on each side of the upper
jaw four pre-molars and only two molars; whilst the
Thylacinus has three pre-molars and four molars. The
molars also differ much in the two animals in relative
size and structure. The adult dentition is preceded by
a widely different milk dentition. Any one may of
course deny that the teeth in either case have been
adapted for tearing flesh, through the natural selection
of successive variations; but if this be admitted in the
one case, it is unintelligible to me that it should be
denied in the other. Iam glad to find that so high an
authority as Professor Flower has come to this same
conclusion.
The extraordinary cases given in a former chapter, of
widely different fishes possessing electric organs,—of
widely different insects possessing luminous organs,—
and of orchids and asclepiads having pollen-masses
Cuap XIV.] ANALOGICAL RESEMBLANCES. 204
with viscid discs, come under this same head of ana-
logical resemblances. But these cases are so wonderful
that they were introduced as difficulties or objections
to our theory. In all such cases some fundamental
difference in the growth or development of the parts,
and generally in their matured structure, can be
detected. The end gained is the same, but the means,
though appearing superficially to be the same, are
essentially different. The principle formerly alluded to
under the term of analogical variation has probably in
these cases often come into play; that is, the members
of the same class, although only distantly allied, have
inherited so much in common in their constitution,
that they are apt to vary under similar exciting causes
in a similar manner; and this would obviously aid in
the acquirement through natural selection of parts or
organs, strikingly like each other, independently of
their direct inheritance from a common progenitor.
As species belonging to distinct classes have often been
adapted by successive slight modifications to live under
nearly similar circumstances,—to inhabit, for instance,
the three elements of land, air, and water,—we can
perhaps understand how it is that a numerical paral-
lelism has sometimes been observed between the sub-
groups of distinct classes. A naturalist, struck with a
parallelism of this nature, by arbitrarily raising or
sinking the value of the groups in several classes (and
all our experience shows that their valuation is as yet
arbitrary), could easily extend the parallelism over a
wide range; and thus the septenary, quinary, quater-
nary and ternary classifications have probably arisen.
There is another and curious class of cases in which
close external resemblance does not depend on adapta-
993 CLASSIFICATION. (Cuap. XIV.
tion to similar habits of life, but has been gained for
the sake of protection. I allude to the wonderful
manner in which certain butterflies imitate, as first
described by Mr. Bates, other and quite distinct species.
This excellent observer has shown that in some districts
of S. America, where, for instance, an Ithomia abounds
in gaudy swarms, another butterfly, namely, a Leptalis,
is often found mingled in the same flock; and the
latter so closely resembles the Ithomia in every shade
and stripe of colour and even in the shape of its wings,
that Mr. Bates, with his eyes sharpened by collecting
during eleven years, was, though always on his guard,
continually deceived. When the mockers and the
mocked are caught and compared, they are found to be
very different in essential structure, and to belong not
only to distinct genera, but often to distinct families.
Had this mimicry occurred in only one or two in-
stances, it might have been passed over as a strange
coincidence. But, if we proceed from a district where
one Leptalis imitates an Ithomia, another mocking and
mocked species belonging to the same two genera,
equally close in their resemblance, may be found.
Altogether no less than ten genera are enumerated,
which include species that imitate other butterflies.
The mockers and mocked always inhabit the same
region; we never find an imitator living remote from
the form which it imitates. The mockers are almost
invariably rare insects; the mocked in almost every
case abound in swarms. In the same district in which
a species of Leptalis closely imitates an Ithomia, there
are sometimes other Lepidoptera mimicking the same
Ithomia: so that in the same place, species of three
genera of butterflies a.d even a moth are found all
Cap. XIV.] ANALOGICAL RESEMBLANCES, Ds
closely resembling a butterfly belonging to a fourth
genus. It deserves especial notice that many of the
mimicking forms of the Leptalis, as well as of the
mimicked forms, can be shown by a graduated series to
be merely varieties of the same species; whilst others
are undoubtedly distinct species. But why, it may be
asked, are certain forms treated as the mimicked and
others as the mimickers? Mr. Bates satisfactorily
answers this question, by showing that the form which
is imitated keeps the usual dress of the group to which
it belongs, whilst the counterfeiters have changed their
dress and do not resemble their nearest allies.
We are next led to inquire what reason can be
assigned for certain butterflies and moths so often
assuming the dress of another and quite distinct form ;
why, to the perplexity of naturalists, has nature con-
descended to the tricks of the stage? Mr. Bates has,
no doubt, hit on the true explanation. The mocked
forms, which always abound in numbers, must habitu-
ally escape destruction to a large extent, otherwise they
could not exist in such swarms; and a large amount of
evidence has now been collected, showing that they are
distasteful to birds and other insect-devouring animals.
The mocking forms, on the other hand, that inhabit the
same district, are comparatively rare, and belong to
rare groups; hence they must suffer habitually from
some danger, for otherwise, from the number of eggs
laid by all butterflies, they would in three or four
generations swarm over the whole country. Now if a
member of one of these persecuted and rare groups were
to assume a dress so like that of a well-protected species
that it continually deceived the practised eyes of an
entomologist, it would often deceive predaceous birds
37
Q24 CLASSIFICATION. (Cap. XIV.
and insects, and thus often escape destruction. Mr.
Bates may almost be said to have actually witnessed
the process by which the mimickers have come so
closely to resemble the mimicked; for he found that
some of the forms of Leptalis which mimic so many
other butterflies, varied in an extreme degree. In one
district several varieties occurred, and of these one
alone resembled to a certain extent, the common
Ithomia of the same district. In another district there
were two or three varieties, one of which was much
commoner than the others, and this closely mocked
another form of Ithomia. From facts of this nature,
Mr. Bates concludes that the Leptals first varies; and
when a variety happens to resemble in some degree
any common butterfly inhabiting the same district,
this variety, from its resemblance to a flourishing and
little-persecuted kind, has a better chance of escaping
destruction from predaceous birds and insects, and is
consequently oftener preserved ;—“the less perfect
degrees of resemblance being generation after generation
eliminated, and only the others left to propagate their
kind.” So that here we have an excellent illustration
of natural selection.
Messrs. Wallace and Trimen have lkewise described
several equally striking cases of imitation in the
Lepidoptera of the Malay Archipelago and Africa, and
with some other insects. Mr. Wallace has also de-
tected one such case with birds, but we have none
with the larger quadrupeds. The much greater fre-
quency of imitation with insects than with other
animals, is probably the consequence of their small
size; insects cannot defend themselves, excepting
indeed the kinds furnished with a sting, and I have
Cuar. XIV.] ANALOGICAL RESEMBLANCES. 229
never heard of an instance of such kinds mocking other
insects, though they are mocked; insects cannot easily
escape by flight from the larger animals which prey
on them; therefore, speaking metaphorically, they are
reduced, like most weak creatures, to trickery and
dissimulation.
It should be observed that the process of imitation
probably never commenced between forms widely dis-
similar in colour. But starting with species already
somewhat like each other, the closest resemblance, if
beneficial, could readily be gained by the above means ;
and if the imitated form was subsequently and gradu-
ally modified through any agency, the imitating form
would be led along the same track, and thus be altered
to almost any extent, so that it might ultimately
assume an appearance or colouring wholly unlike that
of the other members of the family to which it belonged.
There is, however, some difficulty on this head, for it
is necessary to suppose in some cases that ancient
members belonging to several distinct groups, before
they had diverged to their present extent, accidentally
resembled a member of another and protected group in
a sufficient degree to afford some slight protection ; this
having given the basis for the subsequent acquisition of
the most perfect resemblance.
On the Nature of the Affinities connecting Organic
Beings—As the modified descendants of dominant
species, belonging to the larger genera, tend to inherit
the advantages which made the groups to which they
belong large and their parents dominant, they are
almost sure to spread widely, and to seize on more and
more places in the economy of nature. The larger and
more dominant groups within each class thus tend to
226 _ AFFINITIES CONNECTING — (Cuar. XIV.
go on increasing in size; and they consequently sup-
plant many smaller and feebler groups. Thus we can
account for the fact that all organisms, recent and
extinct, are included under a few great orders, and
under still fewer classes. As showing how few the
higher groups are in number, and how widely they are
spread throughout the world, the fact is striking that
the discovery of Australia has not added an insect
belonging to a new class; and that in the vegetable
kingdom, as I learn from Dr. Hooker, it has added only
two or three families of small size.
In the chapter on Geological Succession I attempted
to show, on the principle of each group having generally
diverged much in character during the long-continued
process of modification, how it is that the more ancient
forms of life often present characters In some degree
intermediate between existing groups. As some few of
the old and intermediate forms have transmitted to
the present day descendants but little modified, these
constitute our so-called osculant or aberrant species.
The more aberrant any form is, the greater must be the
number of connecting forms which have been exter-
minated and utterly Jost. And we have some evidence
of aberrant groups having suffered severely from ex-
tinction, for they are almost always represented by
extremely few species; and such species as do occur
are generally very distinct from each other, which
again implies extinction. The genera Ornithorhynchus
and Lepidosiren, for example, would not have been less
aberrant had each been represented by a dozen species,
instead of as at present by a single one, or by two or
three. We can, I think, account for this fact only by
looking at aberrant groups as forms which have been
Cuar. XIV.] ORGANIC BEINGS. DOT.
conquered by more successful competitors, with a few
members still preserved under unusually favourable
conditions.
Mr. Waterhouse has remarked that, when a member
belonging to one group of animals exhibits an affinity to
_ a quite distinct group, this affinity in most cases is
general and not special; thus, according to Mr. Water-
house, of all Rodents, the bizcacha is most nearly related
to Marsupials ; but in the points in which it approaches
this order, its relations are general, that is, not to any
one marsupial species more than to another. As these
points of affinity are believed to be real and not merely
_adaptive, they must be due in accordance with our view
to inheritance from a common progenitor. Therefore
we must suppose either that all Rodents, including the
bizcacha, branched off from some ancient Marsupial,
which will naturally have been more or less intermediate
in character with respect to all existing Marsupials ; or
that both Rodents and Marsupials branched off from a
common progenitor, and that both groups have since
undergone much modification in divergent directions.
On either view we must suppose that the bizcacha has
retained, by inheritance, more of the characters of its
ancient progenitor than have other Rodents; and there-
fore it will not be specially related to any one existing
Marsupial, but indirectly to all or nearly all Marsupials,
from having partially retained the character of their
common progenitor, or of some early member of the
group. On the other hand, of all Marsupials, as Mr.
Waterhouse has remarked, the Phascolomys resembles
most nearly, not any one species, but the general order
of Rodents. In this case, however, it may be strangly
suspected that the resemblance is only analogical, owing |
228 _ AFFINITIES CONNECTING ([Cuaar. XIV.
to the Phascolomys having become adapted to habits
like those of a Rodent. The elder De Candolle has
made nearly similar observations on the general nature
of the affinities of distinct families of plants.
On the principle of the multiplication and gradual
divergence in character of the species descended from a
common progenitor, together with their retention by
inheritance of some characters in common, we can
understand the excessively complex and radiating
affinities by which all the members of the same family
or higher group are connected together. For the com-
mon progenitor of a whole family, now broken up by
extinction into distinct groups and sub-groups, will have
transmitted some of its characters, modified in various
ways and degrees, to all the species; and they will
consequently be related to each other by circuitous lines
of affinity of various lengths (as may be seen in the
diagram so often referred to), mounting up through
many predecessors. As it is difficult to show the blood-
relationship between the numerous kindred of any
ancient and noble family even by the aid of a genea-
logical tree, and almost impossible to do so without this
aid, we can understand the extraordinary difficulty
which naturalists have experienced in describing, with-
out the aid of a diagram, the various affinities which
they perceive between the many living and extinct
members of the same great natural class.
Extinction, as we have seen in the fourth chapter, has
played an important part in defining and widening the
intervals between the several groups in each class. We
may thus account for the distinctness of whole classes
from each other—for instance, of birds from all other
vertebrate animals—by the belief that many ancient
Cuap. XIV.) ORGANIC BEINGS. 229
forms of life have been utterly lost, through which the
early progenitors of birds were formerly connected with
the early progenitors of the other and at that time less
differentiated vertebrate classes. There has been much
less extinction of the forms of hfe which once connected
fishes with batrachians. There has been still less
within some whole classes, for instance the Crustacea,
for here the most wonderfully diverse forms are still
linked together by a long and only partially broken
chain of affinities. Extinction has only defined the
groups: it has by no means made them; for if every
form which has ever lived on this earth were suddenly
to reappear, though it would be quite impossible to give
definitions by which each group could be distinguished,
still a natural classification, or at least a natural
arrangement, would be possible. We shall see this by
turning to the diagram; the letters, A to L,may represent
eleven Silurian genera, some of which have produced
large groups of modified descendants, with every link in
each branch and sub-branch still alive; and the links
not greater than those between existing varieties. In
this case it would be quite impossible to give definitions
by which the several members of the several groups
could be distinguished from their more immediate
parents and descendants. Yet the arrangement in the
diagram would still hold good and would be natural;
for, on the principle of inheritance, all the forms
descended, for instance, from A, would have something
in common. Ina tree we can distinguish this or that
branch, though at the actual fork the two unite and
blend together. We could not, as I have said, define
the several groups; but we could pick out types, or
forms, representing most of the characters of each group,
230 AFFINITIES CONNECTING (Cuar. XIV.
whether large or small, and thus give a general idea
of the value of the differences between them. This is
what we should be driven to, if we were ever to succeed
in collecting all the forms in any one class which have
lived throughout all time and space. Assuredly we
shall never succeed in making so perfect a collection :
nevertheless, in certain classes, we are tending towards
this end; and Milne Edwards has lately insisted, in an
able paper, on the high importance of looking to types,
whether or not we cau separate and define the groups
to which such types belong.
Finally, we have seen that natural selection, which
follows from the struggle for existence, and which almost
inevitably leads to extinction and divergence of charac-
ter in the descendants from any one parent-species,
explains that great and universal feature in the affinities
of all organic beings, namely, their subordination in
group under group. We use the element of descent in
classing the individuals of both sexes and of all ages
under one species, although they may have but few
characters in common; we use descent in classing
acknowledged varieties, however different they may be
from their parents; and I believe that this element of
descent is the hidden bond of connexion which natur-
alists have sought under the term of the Natural System.
On this idea of the natural system being, in so far as it
has been perfected, genealogical in its arrangement,
with the grades of difference expressed by the terms
genera, families, orders, &c., we can understand the
rules which we are compelled to follow in our classifi-
cation. We can understand why we value certain
resemblances far more than others; why we use
rudimentary and useless organs, or others of trifling
Cuap. XIV.) ORGANIC: BEINGS. P|
physiological importance ; why, in finding the relations
between one group and another, we summarily reject
analogical or adaptive characters, and yet use these
same characters within the lmits of the same group.
We can clearly see how it is that all living and extinct
forms can be grouped together within a few great
classes ; and how the several members of each class are
connected together by the most complex and radiating
lines of affinities. Weshall never, probably, disentangle
the inextricable web of the affinities between the mem-
bers of any one class; but when we have a distinct
object in view, and do not look to some unknown plan
of creation, we may hope to make sure but slow
progress.
Professor Hackel in his ‘Generelle Morphologie’ and
in other works, has recently brought his great knowledge
and abilities to bear on what he calls phylogeny, or the
lines of descent of all organic beings. In drawing up
the several series he trusts chiefly to embryological
characters, but receives aid from homologous and rudi-
mentary organs, as well as from the successive periods
at which the various forms of life are believed to have
first appeared in our geological formations. He has thus
boldly made a great beginning, and shows us how
classification will in the future be treated.
Morphology.
We have seen that the members of the same class,
independently of their habits of life, resemble each other
in the general plan of their organisation. This resem-
blance is often expressed by the term “ unity of type ;”
or by saying that the several parts and organs in the
different species of the class are homologous. The
2
>
> 932 . MORPHOLOGY (Cuap. XIV.
whole subject is included under the general term of
Morphology. This is one of the most interesting de-
partments of natural history, and may almost be said to
be its very soul. What can be more curious than that
the hand of a man, formed for grasping, that of a mole
for digging, the leg of the horse, the paddle of the por-
poise, and the wing of the bat, should all be constructed
on the same pattern, and should include similar bones,
in the same relative positions? How curious it is, to
give a subordinate though striking instance, that the
hind-feet of the kangaroo, which are so well fitted for
bounding over the open plains,—those of the climbing,
leaf-eating koala, equally well fitted for grasping the
branches of trees,—those of the ground-dwelling, insect
or root eating, bandicoots,—and those of some other
Australian marsupials,—should all be constructed on
the same extraordinary type, namely with the bones of
the second and third digits extremely slender and
enveloped within the same skin, so that they appear like
a single toe furnished with two claws. Notwithstand-
ing this similarity of pattern, it 1s obvious that the
hind feet of these several animals are used for as widely
different purposes as it is possible to conceive. The
case is rendered all the more striking by the American
opossums, which follow nearly the same habits of life as
some of their Australian relatives, having feet con-
structed on the ordinary plan. Professor Flower, from
whom these statements are taken, remarks in conclusion:
“We may call this conformity to type, without getting
much nearer to an explanation of the phenomenon ;”
and he then adds “but is it not powerfully suggestive
of true relationship, of inheritance from a common
ancestor ?”
Cuap. XIV.] MORPHOLOGY. 230
Geoffroy St. Hilaire has strongly insisted on the high
importance of relative position or connexion in homo-
logous parts; they may differ to almost any extent in
form and size, and yet remain connected together in the
same invariable order. We never find, for instance, the
bones of the arm and fore-arm, or of the thigh and leg,
transposed. Hence the same names can be given to the
homologous bones in widely different animals. We see
the same great law in the construction of the mouths of
insects: what can be more different than the immensely
long spiral proboscis of a sphinx-moth, the curious
folded one of a bee or bug, and the great jaws of a
beetle ?—yet all these organs, serving for such widely
different purposes, are formed by infinitely numerous
modifications of an upper lip, mandibles, and two pairs
of maxille. The same law governs the construction of
the mouths and limbs of crustaceans. So it is with the
flowers of plants.
Nothing can be more hopeless than to attempt to
explain this similarity of pattern in members of the
same class, by utility or by the doctrine of final causes.
The hopelessness of the attempt has been expressly
admitted by Owen in his most interesting work on the
‘Nature of Limbs. On the ordinary view of the
independent creation of each being, we can only say
that so it is;—that it has pleased the Creator to con-
struct all the animals and plants in each great class on
a uniform plan ; but this is not a scientific: explanation.
The explanation is to a large extent simple on the
theory of the selection of successive slight modifica-
tions,—each modification being profitable in some way
to the modified form, but often affecting by correlation
other parts of the organisation. In changes of thig
- 234 MORPHOLOGY. ([Cuar. XIV.
nature, there will be little or no tendency to alter the
original pattern, or to transpose the parts. The bones
of a limb might be shortened and flattened to any
extent, becoming at the same time enveloped in thick
membrane, so as to serve as a fin; or a webbed hand
might have all its bones, or certain bones, lengthened
to any extent, with the membrane connecting them
increased, so as to serve as a wing; yet all these
modifications would not tend to alter the framework of
the bones or the relative connexion of the parts. If
we suppose that an early progenitor—the archetype as
it may be called—of all mammals, birds, and reptiles,
had its limbs constructed on the existing general
pattern, for whatever purpose they served, we can at
once perceive the plain signification of the homologous
construction of the limbs throughout the class. So
with the mouths of insects, we have only to suppose
that their common progenitor had an upper lip,
mandibles, and two pairs of maxille, these parts
being perhaps very simple in form; and then natural
selection will account for the infinite diversity in the
structure and functions of the mouths of insects.
Nevertheless, it is conceivable that the general pattern
of an organ might become so much obscured as to be
finally lost, by the reduction and ultimately by the
complete abortion of certain parts, by the fusion of
other parts, and by the doubling or multiplication of
others,—variations which we know to be within the
limits of possibility. In the paddles of the gigantic
extinct sea-lizards, and in the mouths of certain
suctorial crustaceans, the general pattern seems thus
to have become partially obscured.
There is another and equally curious branch of our
Cuap. XIV.] MORPHOLOGY. 235
subject ; namely, serial homologies, or the comparison
of the different parts or organs in the same individual,
and not of the same parts or organs in different
members of the same class. Most physiologists believe
that the bones of the skull are homologous—that is,
correspond in number and in relative connexion—with
the elemental parts of a certain number of vertebre.
The anterior and posterior limbs in all the higher
vertebrate classes are plainly homologous. So it is
with the wonderfully complex jaws and legs of crus-
taceans. It is familiar to almost every one, that in
a flower the relative position of the sepals, petals,
stamens, and pistils, as well as their intimate structure,
are intelligible on the view that they consist of meta-
morphosed leaves, arranged in a spire. In monstrous —
plants, we often get direct evidence of the possibility of
one organ being transformed into another ; and we can
actually see, during the early or embryonic stages of
development in flowers, as well as in crustaceans and
many other animals, that organs, which when mature
become extremely different are at first exactly alike.
How inexplicable are the cases of serial homologies
on the ordinary view of creation! Why should the
brain be enclosed in a box composed of such numerous
and such extraordinarily shaped pieces of bone, appa-
rently representing vertebree? As Owen has remarked,
the benefit derived from the yielding of the separate
pieces in the act of parturition by mammals, will by
no means explain the same construction in the skulls
of birds and reptiles. Why should similar bones have
been created to form the wing and the leg of a bat,
used as they are for such totally different purposes,
namely flying and walking? Why should one crus-
38
236 MORPHOLOGY. [Cuar. XTV.
tacean, which has an extremely complex mouth formed
of many parts, consequently always have fewer legs;
or conversely, those with many legs have simpler
mouths ? Why should the sepals, petals, stamens, and
pistils, in each flower, though fitted for such distinct
purposes, be all constructed on the same pattern ?
On the theory of natural selection, we can, to a
certain extent, answer these questions. We need not
here consider how the bodies of some animals first
became divided into a series of segments, or how they
became divided into right and left sides, with corre-
sponding organs, for such questions are almost beyond
investigation. It is, however, probable that some serial
structures are the result of cells multiplying by division,
entailing the multiplication of the parts developed from
such cells. It must suffice for our purpose to bear in
mind that an indefinite repetition of the same part or
organ is the common characteristic, as Owen has
remarked, of all low or little specialised forms; there-
fore the unknown progenitor of the Vertebrata probably
possessed many vertebre ; the unknown progenitor of
the Articulata, many segments; and the unknown
progenitor of flowering plants, many leaves arranged in
one or more spires. We have also formerly seen that
parts many times repeated are eminently liable to vary,
not only in number, but in form. Consequently such
parts, being already present in considerable numbers,
and being highly variable, would naturally afford the
materials for adaptation to the most different purposes ;
yet they would generally retain, through the force of
inheritance, plain traces of their original or fundamental
resemblance. They would retain this resemblance all
the more, as the variations, which afforded the basis for
Cuap. XIV.] MORPHOLOGY. 237
their subsequent modification through natural selection,
would tend from the first to be similar; the parts
being at an early stage of growth alike, and being
subjected to nearly the same conditions. Such parts,
whether more or less modified, unless their common
origin becarne wholly obscured, would be serially
homologous.
In the great class of molluscs, though the parts in
distinct species can be shown to be homologous, only a
few serial homologies, such as the valves of Chitons,
can be indicated ; that is, we are seldom enabled to say
that one part is homologous with another part in the
same individual. And we can understand this fact;
for in molluscs, even in the lowest members of the
class, we do not find nearly so mitch indefinite repetition
of any one part as we find in the other great classes of
the animal and vegetable kingdoms.
But morphology is a much more complex subject
than it at first appears, as has lately been well shown
in a remarkable paper by Mr. E. Ray Lankester, who
has drawn an importasit distinction between certain
classes of cases which have all been equally ranked by
naturalists as homologous. He proposes to call the
structures which resemble each other in distinct
animals, owing to their descent from a common
progenitor with subsequent modification, homogenous ;
and the resemblances which cannot thus be accounted
for, he proposes to call homoplasiic. For instance, he
believes that the hearts of birds and mammals are as a
whole homogenous,—that is, have been derived from a
common progenitor; but that the four cavities of the
heart in the two classes are homoplastic,—that is, have
been independently developed. Mr. Lankester also
238 MORPHOLOGY. (Cuap. XIV.
adduces the close resemblance of the parts on the right
and left sides of the body, and in the successive
segments of the same individual animal; and here we
have parts commonly called homologous, which bear
no relation to the descent of distinct species from a
common progenitor. Homoplastic structures are the
same with those which I nave classed, though in a very
imperfect manner, as analogous modifications or re-
semblances. Their formation may be attributed in part
to distinct organisms, or to distinct parts of the same
organism, having varied in an analogous manner; and
in part to similar modifications, having been preserved
for the same general purpose or function,—of which
many instances have been given.
Naturalists frequently speak of the skull as formed
of metamorphosed vertebre; the jaws of crabs as
metamorphosed legs ; the stamens and pistils in flowers
as metamorphosed leaves; but it would in most cases
be more correct, as Professor Huxley has remarked, to
speak of both skull and vertebre, jaws and legs, &c., as
having been metamorphosed, not one from the other, as
they now exist, but from some common and simpler
element. Most naturalists, however, use such language
only in a metaphorical sense ; they are far from meaning
that during a long course of descent, primordial organs
of any kind—vertebre in the one case and legs in the
other—have actually been converted into skulls or jaws.
Yet so strong is the appearance of this having occurred,
that naturalists can hardly avoid employing language
having this plain signification. According to the views
here maintained, such language may be used literally ;
and the wonderful fact of the jaws, for instance, of a
crab retaining numerous characters. which they probably
Cuar. XIV.] DEVELOPMENT AND EMBRYOLOGY. 239
would have retained through inheritance, if they had
really been metamorphosed from true though extremely
simple legs, is in part explained.
Development and Embryology.
This is one of the most important subjects in the
whole round of natural history. ‘The metamorphoses of
insects, with which every one is familiar, are generally
effected abruptly by a few stages; but the transforma-
tions are in reality numerous and gradual, though
concealed. A certain ephemerous insect (Chléeon)
during its development, moults, as shown by Sir J.
Lubbock, above twenty times, and each time undergoes
a certain amount of change; and in this case we see
the act of metamorphosis performed in a primary and
gradual manner. Many insects, and especially certain
crustaceans, show us what wonderful changes of
structure can be effected during development. Such
changes, however, reach their acme in the so-called
alternate generations of some of the lower animals. It
is, for instance, an astonishing fact that a delicate
branching coralline, studded with polypi and attached
to a submarine rock, should produce, first by budding
and then by transverse division, a host of huge floating
jelly-fishes; and that these should produce eggs, from
which are hatched swimming animalcules, which attach
themselves to rocks and become developed into branch-
ing corallines; and so on in an endless cycle. The
belief in the essential identity of the process of
alternate generation and of ordinary metamorphosis
has been greatly strengthened by Wagner’s discovery
of the larva or maggot of a fly, namely the Cecidomyia,
producing asexually other larvee, and these others, which
240 DEVELOPMENT AND EMBRYOLOGY. ([Cnar. XIV.
finally are developed into mature males and females,
propagating their kind in the ordinary manner by eggs.
It may be worth notice that when Wagner’s remark-
able discovery was first announced, I was asked how
was it possible to account for the larve of this fly
having acquired the power of asexualreproduction. As
long as the case remained ‘unique no answer could be
given. But already Grimm has shown that another fly,
a Chironomus, reproduces itself in nearly the same
manner, and he believes that this occurs frequently in
the Order. It is the pupa, and not the larva, of the
Chironomus which has this power; and Grimm further
shows that this case, to a certain extent, “ unites that
of the Cecidomyia with the parthenogenesis of the
Coccide ;”—the term parthenogenesis implying that
the mature females of the Coccide are capable of
producing fertile eggs without the concourse of the
male. Certain animals belonging to several classes are
now known to have the power of ordinary reproduction
at an unusually early age; and we have only to acceler-
ate parthenogenetic reproduction by gradual steps to an
earlier and earlier age,—Chironomus showing us an
almost exactly intermediate stage, viz., that of the pupa
and we can perhaps account for the marvellous case
of the Cecidomyia.
It has already been stated that various parts in
the same individual which are exactly alike dur-
ing an early embryonic period, become widely dif-
ferent and serve for widely different purposes in
the adult state. So again it has been shown that
generally the embryos of the most distinct species
belonging to the same class are closely similar, but
become, when fully developed, widely dissimilar. A
Cuap. XIV.] DEVELOPMENT AND EMBRYOLOGY. 241
better proof of this latter fact cannot be given than the
statement by Von Baer that “the embryos of mammalia,
“of birds, lizards, and snakes, probably also of chelonia,
“are in their earliest states exceedingly like one another.
“both as a whole and in the mode of development of
“their parts; so much so, in fact, that we can often
“distinguish the embryos only by their size. In my
“possession are two little embryos in spirit, whose
“names I have omitted to attach, and at present I am
“quite unable to say to what class they belong. They
“may be lizards or small birds, or very young mam-
“malia, so complete is the similarity in the mode
“of formation of the head and trunk in these animals.
“The extremities, however, are still absent in these
“embryos. But even if they had existed in the earliest
“stage of their development we should learn nothing, for
“the feet of lizards and mammals, the wings and feet of
“birds, no less than the hands and feet of man, all arise
“from the same fundamental form.” The larve of most
crustaceans, at corresponding stages of development,
closely resemble each other, however different the
adults may become; and so it is with very many other
animals. A trace of the law of embryonic resemblance
occasionally lasts till a rather late age: thus birds of
the same genus, and of allied genera, often resemble
each other in their immature plumage; as we see in the
spotted feathers in the young of the thrush group. In
the cat tribe, most of the species when adult are striped
or spotted in lines; and stripes or spots can be plainly
distinguished in the whelp of the lion and the puma.
We occasionally though rarely see something of the
same kind in plants; thus the first leaves of the ulex or
furze, and the first leaves of the phyllodineous acacias,
242. DEVELOPMENT AND EMBRYOLOGY. ([Cuap. XIV.
are pinnate or divided like the ordinary leaves of the
lesuminose. | .
The points of structure, in which the embryos of
widely different animals within the same class resemble
each other, often have no direct relation to their
conditions of existence. We cannot, for instance,
suppose that in the embryos of the vertebrata the
peculiar loop-like courses of the arteries near the
branchial slits are related to similar conditions,—in the
young mammal which is nourished in the womb of its
mother, in the egg of the bird which is hatched in a
nest, and in the spawn of a frog under water. We have
no more reason to believe in such a relation, than we
have to believe that the similar bones in the hand of a
man, wing of a bat, and fin of a porpoise, are related to
similar conditions of life. No one supposes that the
stripes on the whelp of a lion, or the spots on the
young blackbird, are of any use to these animals.
The case, however, is different when an animal during
any part of its embryonic career is active, and has to
provide for itself. The period of activity may come on
earlier or later in life; but whenever it comes on, the
adaptation of the larva to its conditions of life is just as
perfect and as beautiful as in the adult animal. In how
important a manner this has acted, has recently been
well shown by Sir J. Lubbock in his remarks on the
close similarity of the larvee of some insects belonging to
very different orders, and on the dissimilarity of the
larve of other insects within the same order, according
to their habits of life. Owing to such adaptations, the
similarity of the larve of allied animals is sometimes
greatly obscured ; especially when there is a division of
labour during the different stages of development. as
Cuar. XIV.] DEVELOPMENT AND EMBRYOLOGY. 243
when the same larva has during one stage to search for
food, and during another stage has to search for a place
of attachment. Cases can even be given of the larve of
allied species, or groups of species, differing more from
each other than do the adults. In most cases, however,
the larvee, though active, still obey, more or less closely,
the law of common embryonic resemblance. Curripedes
afford a good instance of this; even the illustrious
Cuvier did not perceive that a barnacle was a crustacean :
but a glance at the larva shows this in an unmistakable
manner. So again the two main divisions of cirripedes,
the pedunculated and sessile, though differimg widely in
external appearance, have larve in all their stages
barely distinguishable.
The embryo in the course of development generally
rises in organisation; I use this expression, though I am
aware that it is hardly possible to define clearly what is
meant by the organisation being higher or lower. But
no one probably will dispute that the butterfly is
higher than the caterpillar. In some cases, however, the
mature animal must be considered as lower in the scale
than the larva, as with certain parasitic crustaceans.
To refer once again to cirripedes: the larve in the first
stage have three pairs of locomotive organs, a simple
single eye, and a probosciformed mouth, with which
they feed largely, for they increase much in size. In
the second stage, answering to the chrysalis stage of
butterflies, they have six pairs of beautifully constructed
natatory legs, a pair of magnificent compound eyes, and
extremely complex antenne; but they have a closed
and imperfect mouth, and cannot feed: their function at
this stage is, to search out by their well-developed
organs of sense, and to reach by their active powers of
244 DEVELOPMENT AND EMBRYOLOGY. ([Cuar. XIV
swimming, a proper place on which to become attached
and to undergo their final metamorphosis. When this
is completed they are fixed for life: their legs are now
converted into prehensile organs; they again obtain a
well-constructed mouth; but they have no antenne, and
their two eyes are now reconverted into a minute, single,
simple eye-spot. In this last and complete state, cirri-
pedes may be considered as either more highly or more
lowly organised than they were in the larval condition.
But in some genera the larve become developed into
hermaphrodites having the ordinary structure, and into
what I have called complemental males; and in the
latter the development has assuredly been retrograde, for
the male is a mere sack, which lives for a short time
and is destitute of mouth, stomach, and every other
organ of importance, excepting those for reproduction.
We are so much accustomed to see a difference in
structure between the embryo and the adult, that we are
tempted to look at this difference as in some necessary
manner contingent on growth. But there is no reason
why, for instance, the wing of a bat, or the fin of a por-
poise, should not have been sketched out with all their
parts in proper proportion, as soon as any part became
visible. In some whole groups of animals and in
certain members of other groups this is the case, and
the embryo does not at any period differ widely from
the adult: thus Owen has remarked in regard to cuttle-
fish, “there is no metamorphosis; the cephalopodic
character is manifested long before the parts of the
embryo are completed.” lLand-shells and fresh-water
crustaceans are born having their proper forms, whilst
the marine members of the same two great classes pass
through considerable and often great changes during
Cuar. XIV.] DEVELOPMENT AND EMBRYOLOGY. 245
their development. Spiders, again, barely undergo any
metamorphosis. The larvee of most insects pass through
a worm-like stage, whether they are active and adapted
to diversified habits, or are inactive from being placed
in the midst of proper nutriment or from being fed by
their parents; but in some few cases, as in that of
Aphis, if we look to the admirable drawings of the
development of this insect, by Professor Huxley, we see
hardly any trace of the vermiform stage.
Sometimes it is only the earlier developmental stages
which fail. Thus Fritz Miller has made the remarkable
discovery that certain shrimp-like crustaceans (allied to
Penceus) first appear under the simple nauplius-form,
and after passing through two or more zvea-stages, and
then through the mysis-stage, finally acquire their
mature structure: now in the whole great malacostracan
order, to which these crustaceans belong, no other
member is as yet known to be first developed under the
nauplius-form, though many appear as zoeas; neverthe- —
less Miller assigns reasons for his belief, that if there
had been no suppression of development, all these
crustaceans would have appeared as nauplii.
How, then, can we explain these several facts in
embryology,—namely, the very general, though not
universal, difference in structure between the embryo
and the adult;—the various parts in the same in-
dividual embryo, which ultimately become very unlike
and serve for diverse purposes, being at an early period.
of growth alike;—the common, but not invariable,
resemblance between the embryos or larve of the most
distinct species in the same class;—the embryo often
retaining whilst within the egg or womb, structures
which are of no service to it, either at that or at a later
246 DEVELOPMENT AND EMBRYOLOGY. ([Caap. XIV.
period of life; on the other hand larve, which have to
provide for their own wants, being perfectly adapted
to the surrounding conditions ;—and lastly the fact of
certain larvee standing higher in the scale of organisation
than the mature animal into which they are developed ?
I believe that all these facts can be explained, as follows.
It is commonly assumed, perhaps from monstrosities
affecting the embryo at a very early period, that slight
variations or individual differences necessarily appear
at an equally early period. We have little evidence on
this head, but what we have certainly points the other
way; for it is notorious that breeders of cattle, horses,
and various fancy animals, cannot positively tell, until
some time after birth, what will be the merits or
demerits of their young animals. We see this plainly
in our own children; we cannot tell whether a child
will be tall or short, or what its precise features will be.
The question is not, at what period of life each variation
may have been caused, but at what period the effects
are displayed. The cause may have acted, and I believe
often has acted, on one or both parents before the act of
generation. It deserves notice that it is of no import-
ance to a very young animal, as long as it remains in
its mother’s womb or in the egg, or as long as it is
nourished and protected by its parent, whether most of
its characters are acquired a little earlier or later in life.
It would not signify, for instance, to a bird which
obtained its food by having a much-curved beak
whether or not whilst young it possessed a beak of this
shape, as long as it was fed by its parents.
I have stated in the first chapter, that at whatever
age a variation first appears in the parent, it tends to
re-appear at a corresponding age in the offspring.
Cuar. XIV.] DEVELOPMENT AND EMBRYOLOGY. 247
Certain variations can only appear at corresponding
ages; for instance, peculiarities in the caterpillar,
cocoon, or imago states of the silk-moth: or, again, in
the full-grown horns of cattle. But variations, which,
for all that we can see might have first appeared either
earler or later in life, likewise tend to reappear at a
corresponding age in the offspring and parent. I am
far from meaning that this is invariably the case, and
I could give several exceptional cases of variations
(taking the word in the largest sense) which have
supervened at an earlier age in the child than in the
parent.
_ These two principles, namely, that slight variations
generally appear at a not very early period of life, and
are inherited at a corresponding not early period,
explain, as I believe, all the above specified leading
facts in embryology. But first let us look to a few
analogous cases in our domestic varieties. Some
authors who have written on Dogs, maintain that the
greyhound and bulldog, though so different, are really
closely allied varieties, descended from the same wild
stock; hence I was curious to see how far their puppies
differed from each other: I was told by breeders that
they differed just as much as their parents, and this,
judging by the eye, seemed almost to be the case; but
on actually measuring the old dogs and their six-days-
old puppies, I found that the puppies had not acquired
nearly their full amount of proportional difference. So,
again, I was told that the foals of cart and race-horses
—hbreeds which have been almost wholly formed by
selection under domestication—differed as much as the
full-grown animals; but having had careful measure-
ments made of the dams and of three-days-old colts of
39
248 DEVELOPMENT AND EMBRYOLOGY. (Cnar. XIV.
race and heavy cart-horses, I find that this is by no
means the case.
As we have conclusive evidence that the breeds of
the Pigeon are descended from a single wild species, I
compared the young within twelve hours after being
hatched; I carefully measured the proportions (but
will not here give the details) of the beak, width of
mouth, length of nostril and of eyelid, size of feet and
leneth of leg, in the wild parent-species, in pouters,
fantails, runts, barbs, dragons, carriers, and tumblers.
Now some of these birds, when mature, differ in so
extraordinary a manner in the length and form of beak,
and in other characters, that they would certainly have
been ranked as distinct genera if found in a state of
nature. But when the nestling birds of these several
breeds were placed in a row, though most of them could
just be distinguished, the proportional differences in
the above specified points were incomparably less than
in the full-grown birds. Some characteristic points of
difference—for instance, that of the width of mouth—
could hardly be detected in the young. But there was
one remarkable exception to this rule, for the young of
the short-faced tumbler differed from the young of the
wild rock-pigeon and of the other breeds, in almost
exactly the same proportions as in the adult state.
These facts are explained by the above two principles.
Fanciers select their dogs, horses, pigeons, &c., for
breeding, when nearly grown up: they are indifferent
whether the desired qualities are acquired earlier or
later in life, if the full-grown animal possesses them.
And the cases just given, more especially that of the
pigeons, show that the characteristic differences which
have been accumulated by man’s selection, and which
Cuap. XIV.| DEVELOPMENT AND EMBRYOLOGY. 249
give value to his breeds, do not generally appear at a
very early period of life, and are inherited at a corre-
sponding not early period. But the case of the short-
faced tumbler, which when twelve hours old possessed
its proper characters, proves that this is not the
universal rule; for here the characteristic differences
must either have appeared at an earlier period than
usual, or, if not so, the differences must have been
inherited, not at a corresponding, but at an earlier age.
Now let us apply these two principles to species in a
state of nature. Let us take a group of birds, descended
from some ancient form and modified through natural
selection for different habits. Then, from the many
slight successive variations having supervened in the
several species at a not early age, and having been
inherited at a corresponding age, the young will have
been but little modified, and they will still resemble
each other much more closely than do the adults,—just
as we have seen with the breeds of the pigeon. We
may extend this view to widely distinct structures and
to whole classes. The fore-limbs, for instance, which
once served as legs to a remote progenitor, may have
become, through a long course of modification, adapted
in one descendant to act as hands, in another as paddles,
in another as wings; but on the above two principles
the fore-limbs will not have been much modified in the
embryos of these several forms; although in each form
the fore-limb will differ greatly in the adult state,
Whatever influence long-continued use or disuse may
have had in modifying the hmbs or other parts of any
species, this will chiefly or solely have affected it when
nearly mature, when it was compelled to use its full
powers to gain its own living; and the effects thus
950 DEVELOPMENT AND EMBRYOLOGY. ([Cuap. XIV.
produced will have been transmitted to the offspring at
a corresponding nearly mature age. Thus the young
will not be modified, or will be modified only in a slight
degree, through the effects of the increased use or
disuse of parts.
With some animals the successive variations may
have supervened at a very early period of life, or the
steps may have been inherited at an earlier age than
that at which they first occurred. In either of these
cases, the young or embryo will closely resemble the
mature parent-form, as we have seen with the short-
faced tumbler. And this is the rule of development in
certain whole groups, or in certain sub-groups alone,
as with cuttle-fish, land-shells, fresh-water crustaceans,
spiders, and some members of the great class of insects.
With respect to the final cause of the young in such
groups not passing through any metamorphosis, we can
see that this would follow from the following contin-
gences; namely, from the young having to provide at a
very early age for their own wants, and from their
following the same habits of life with their parents; for
in this case, it would be indispensable for their existence
that they should be modified in the same manner as
their parents. Again, with respect to the singular fact
that many terrestrial and fresh-water animals do not
undergo any metamorphosis, whilst marine members of
the same groups pass through various transformations,
Fritz Miller has suggested that the process of slowly
modifying and adapting an animal to live on the land
or in fresh water, instead of in the sea, would be greatly
simplified by its not passing through any larval stage;
for it is not probable that places well adapted for both
the larval and mature stages, under such new and
Cuar. XIV.] DEVELOPMENT AND EMBRYOLOGY. 201
greatly changed habits of life, would commonly be found
unoccupied or ill-occupied by other organisms. In this
case the gradual acquirement at an earlier and earlier
age of the adult structure would be favoured by natural
selection; and all traces of former metamorphoses would
finally be lost.
If, on the other hand, it profited the young of an
animal to follow habits of hfe slightly different from
those of the parent-form, and consequently to be con-
structed on a slightly different plan, or if it profited a
larva already different from its parent to change still
further, then, on the principle of inheritance at corre-
sponding ages, the young or the larve might be rendered
by natural selection more and more different from their
parents to any conceivable extent. Differences in the
larva might, also, become correlated with successive
stages of its development; so that the larva, in the first
stage, might come to differ greatly from the larva in the
second stage, as 1s the case with many animals. The
adult might also become fitted for sites or habits, in
which organs of locomotion or of the senses, &c., would
be useless; and in this case the metamorphosis would
be retrograde.
From the remarks just made we can see how by
changes of structure in the young, in conformity with
changed habits of life, together with inheritance at corres-
ponding ages, animals might come to pass through stages
of development, perfectly distinct from the primordial
condition of their adult progenitors. Most of our best
authorities are now convinced that the various larval
and pupal stages of insects have thus been acquired
through adaptation, and not through inheritance from
some ancient form, The curious case of Sitaris—a
252 DEVELOPMENT AND EMBRYOLOGY. ([Cuapr. XIV.
beetle which passes through certain unusual stages of
development—will illustrate how this might occur.
The first larval form is described by M. Fabre, as an
active, minute insect, furnished with six legs, two long
antenne, and four eyes. These larve are hatched in
the nests of bees; and when the male-bees emerge from
their burrows, in the spring, which they do before the
females, the larve spring on them, and afterwards crawl
on to the females whilst paired with the males. As
soon as the female bee deposits her eggs on the surface
of the honey stored in the cells, the larve of the Sitaris
leap on the eggs and devour them. Afterwards they
undergo a complete change; their eyes disappear; their
legs and antenne become rudimentary, and they feed on
honey; so that they now more closely resemble the
ordinary larve of insects; ultimately they undergo a
further transformation, and finally emerge as the perfect
beetle. Now, if an insect, undergoing transformations
like those of the Sitaris, were to become the progenitor
of a whole new class of insects, the course of develop-
ment of the new class would be widely different from
that of our existing insects; and the first larval stage
certainly would not represent the former condition of
any adult and ancient form.
On the other hand it is highly probable that with
many animals the embryonic or larval stages show us,
more or less completely, the condition of the progenitor
of the whole group in its adult state. In the great class
of the Crustacea, forms wonderfully distinct from each
other, namely, suctorial parasites, cirripedes, entomo-
straca, and even the malacostraca, appear at first as
- larvee under the nauplius-form ; and as these larve live
and feed in the open sea, and are not adapted for any
Cuar. XIV.] DEVELOPMENT AND EMBRYOLOGY. 2538
peculiar habits of life, and from other reasons assigned
by Fritz Miller, it is probable that at some very remote
period an independent adult animal, resembling the
Nauplius, existed, and subsequently produced, along
several divergent lines of descent, the above-named
great Crustacean groups. . So again it is probable, from
what we know of the embryos of mammals, birds, fishes,
and reptiles, that these animals are the modified descen-
dants of some ancient progenitor, which was furnished
in its adult state with branchie, a swim-bladder, four
fin-like limbs, and a long tail, all fitted for an aquatic
life.
As all the organic beings, extinct and recent, which
have ever lived, can be arranged within a few great
classes; and as all within each class have, according to
our theory, been connected together by fine gradations,
the best, and, if our collections were nearly perfect,
the only possible arrangement, would be genealogical ;
descent being the hidden bond of connexion which
naturalists have been seeking under the term of the
Natural System. On this view we can understand how
it is that, in the eyes of most naturalists, the structure
of the embryo is even more important for classification
than that of the adult. In two or more groups of
animals, however much they may differ from each other
in structure and habits in their adult condition, if they
pass through closely similar embryonic stages, we may
feel assured that they all are descended from one
parent-form, and are therefore closely related. Thus,
community in embryonic structure reveals community
of descent ; but dissimilarity in embryonic development
does not prove discommunity of descent, for in one of
two groups the developmental stages may have been
254 DEVELOPMENT AND EMBRYOLOGY. ([Cuapr. XIV.
suppressed, or may have been so greatly modified
through adaptation to new habits of life, as to be no
longer recognisable. Even in groups, in which the
adults have been modified to an extreme degree, com-
munity of origin is often revealed by the structure of
the larve; we have seen, for instance, that cirripedes,
though externally so like shell-fish, are at once known
by their larve to belong to the great class of crustaceans.
As the embryo often shows us more or less plainly the
structure of the less modified and ancient progenitor of
the group, we can see why ancient and extinct forms so
often resemble in their adult state the embryos of
existing species of the same class. Agassiz believes this
to be a universal law of nature; and we may hope
hereafter to see the law proved true. It can, however,
be proved true only in those cases in which the ancient
state of the progenitor of the group has not been wholly’
obliterated, either by successive variations having super-
vened at a very early period of growth, or by such
variations having been inherited at an earlier age than
that at which they first appeared. It should also be
borne in mind, that the law may be true, but yet, owing
to the geological record not extending far enough back
in time, may remain for a long period, or for ever,
incapable of demonstration. The law will not strictly
hold good in those cases in which an ancient form
became adapted in its larve state to some special line
of life, and transmitted the same larval state to a whole
group of descendants; for such larval will not resemble
any still more ancient form in its adult state.
Thus, as it seems to me, the leading facts in
embryology, which are second to none in importance,
are explained on the principle of variations in the
Cuap. XIV.] RUDIMENTARY ORGANS. DATS,
many descendants from some one ancient progenitor,
having appeared at a not very early period of life, and
having been inherited at a corresponding period. Em-
bryology rises greatly in interest, when we look at the
embryo as a picture, more or less obscured, of the
progenitor, either in its adult or larval state, of all the
members of the same great class.
Rudimentary, Atrophied, and Aborted Organs.
Organs or parts in this strange condition, bearing the
plain stamp of inutility, are extremely common, or even
general, throughout nature. It would be impossible to
name one of the higher animals in which some part or
other is not in a rudimentary condition. In the mam-
malia, for instance, the males possess rudimentary
mamme ; in snakes one lobe of the lungs is rudimen-
tary; in birds the “bastard-wing” may safely be
considered as a rudimentary digit, and in some species
the whole wing is so far rudimentary that it cannot be
used for flight. What can be more curious than the
presence of teeth in foetal whales, which when grown
up have not a tooth in their heads ; or the teeth, which
never cut through the gums, in the upper jaws of .
unborn calves ?
Rudimentary organs plainly declare their origin and
meaning in various ways. There are beetles belonging
to closely allied species, or even to the same identical
species, which have either full-sized and perfect wings,
or mere rudiments of membrane, which not rarely lie
under wing-covers firmly soldered together; and in
these cases it is impossible to doubt, that the rudiments
represent wings. Rudimentary organs sometimes retain
their potentiality: this occasionally occurs with the
256 RUDIMENTARY, ATROPHIED, ([Cxar. XIV
mamme of male mammals, which have been known to
become well 4leveloped and to secrete milk. So again
in the udders in the genus Bos, there are normally four
developed and two rudimentary teats; but the latter in
our domestic cows sometimes become well developed
and yield milk. In regard to plants the petals are
sometimes rudimentary, and sometimes well-developed
in the individuals of the same species. In certain
plants having separated sexes Kolreuter found that by
crossing a species, in which the male flowers included a
rudiment of a pistil, with an hermaphrodite species,
having of course a well-developed pistil, the rudiment
in the hybrid offspring was much increased in size;
and this clearly shows that the rudimentary and perfect
pistils are essentially alike in nature. An animal may
possess various parts in a perfect state, and yet they
may in one sense be rudimentary, for they are useless:
thus the tadpole of the common Salamander or Water-
newt, as Mr. G. H. Lewes remarks, “has gills, and
“passes its existence in the water; but the Salamandra
“atra, which lives high up among the mountains, brings
“forth its young full-formed. This animal never lives
“in the water. Yet if we open a gravid female, we
“find tadpoles inside her with exquisitely feathered
“oills; and when placed in water they swim about
“like the tadpoles of the water-newt. Obviously this
“aquatic organisation has no reference to the future
“life of the animal, nor has it any adaptation to its
“embryonic condition ; it has solely reference to ances-
“tral adaptations, it repeats a phase in the development
“of its progenitors.”
An organ, serving for two purposes, may become
rudimentary or utterly aborted for one, even the more
Cuap. XIV.] AND ABORTED ORGANS. AST
important purpose, and remain perfectly efficient for
the other. Thus in plants, the office of the pistil is to
allow the pollen-tubes to reach the ovules within the
ovarium. The pistil consists‘ of a stigma supported
on a style; but in some Composite, the male florets,
which of course cannot be fecundated, have a rudimen-
tary pistil, for it is not crowned with a stigma; but the
style remains well developed and is clothed in the usual
manner with hairs, which serve to brush the pollen out
of the surrounding and conjoined anthers. Again, an
organ may become rudimentary for its proper purpose,
and be used for a distinct one: in certain fishes the
swim-bladder seems to be rudimentary for its proper
function of giving buoyancy, but has become converted
into a nascent breathing organ or lung. Many similar
instances could be given.
Useful organs, however little they may be developed,
unless we have reason to suppose that they were
formerly more highly developed, ought not to be con-
sidered as rudimentary. They may be in a nascent
condition, and in progress towards further development.
Rudimentary organs, on the other hand, are either quite
useless, such as teeth which never cut through the
gums, or almost useless, such as the wings of an ostrich,
which serve merely as sails. As organs in this con-
dition would formerly, when still less developed, have
been of even less use than at present, they cannot
formerly have been produced through variation and
natural selection, which acts solely by the preservation
of useful modifications. They have been partially
retained by the power of inheritance, and relate to a
former state of things. It is, however, often difficult to
distinguish between rudimentary and nascent organs ;
258 - RUDIMENTARY, ATROPHIED, ([C#%>. XIV.
for we can judge only by analogy whether a part is
capable of further development, in which case alone it
deserves to be called nascent. Organs in this condition
will always be somewhat rare; for beings thus provided
will commonly have been supplanted by their successors
with the same organ in a more perfect state, and conse-
quently will have become long ago extinct. The wing
of the penguin is of high service, acting as a fin; it
may, therefore, represent the nascent state of the wing:
not that I believe this to be the case; it is more pro-
bably a reduced organ, modified for a new function: the
wing of the Apteryx, on the other hand, is quite useless,
and is truly rudimentary. Owen considers the simple
filamentary limbs of the Lepidosiren as the “ beginnings
of organs which attain full functional development in
higher vertebrates ;” but, according to the view lately
advocated by Dr. Giinther, they are probably remnants,
consisting of the persistent axis of a fin, with the lateral
rays or branches aborted. The mammary glands of the
Ornithorhynchus may be considered, in comparison
with the udders of a cow, as in a nascent condition.
The ovigerous frena of certain cirripedes, which have
ceased to give attachment to the ova and are feebly
developed, are nascent branchie.
Rudimentary organs in the individuals of the same
species are very liable to vary in the degree of their
development and in other respects. In closely allied
species, also, the extent to which the same organ has
been reduced occasionally differs much. This latter fact
is well exemplified in the state of the wings of female
moths belonging to the same family. Rudimentary
organs may be utterly aborted; and this implies, that
in certain animals or plants, parts are entirely absent
Cuap. XIV.] AND ABORTED ORGANS. 259
which analogy would lead us to expect to find in them,
and which are occasionally found in monstrous indivi-
duals. Thus in most of the Scrophulariacee the fifth
stamen is utterly aborted; yet we may conclude that a
fifth stamen once existed, for a rudiment of it is found
in many species of the family, and this rudiment
occasionally becomes perfectly developed, as may some-
times be seen in the common snap-dragon. In tracing
the homologies of any part in different members of the
same class, nothing is more common, or, in order fully
to understand the relations of the parts, more useful
than the discovery of rudiments. This is well shown
in the drawings given by Owen of the leg-bones of the
horse, ox, and rhinoceros.
It is an important fact that rudimentary organs, such
as teeth in the upper jaws of whales and ruminants, can
often be detected in the embryo, but afterwards wholly
disappear. It is also, I believe, a universal rule, that
a rudimentary part is of greater size in the embryo
relatively to the adjoining parts, than in the adult; so
that the organ at this early age is less rudimentary, or
even cannot be said to be in any degree rudimentary.
Hence rudimentary organs in the adult are often said
to have retained their embryonic condition.
I have now given the leading facts with respect
to rudimentary organs. In reflecting on them, every
one must be struck with astonishment; for the same
reasoning power which tells us that most parts and
organs are exquisitely adapted for certain purposes, tells
us with equal plainness that these rudimentary or
atrophied organs are imperfect and useless. In works
on natural history, rudimentary organs are generally
sald to have been created “for the sake of symmetry,”
40
260 _ RUDIMENTARY, ATROPHIED, (Car. XIV
or in order “to complete the scheme of nature.” But
this is not an explanation, merely a re-statement of the
fact. Nor is it consistent with itself: thus the boa-
constrictor has rudiments of hind-limbs and of a pelvis,
and if it be said that these bones have been retained
“to complete the scheme of nature,” why, as Professor
Weismann asks, have they not been retained by other
snakes, which do not possess even a vestige of these
same bones? What would be thought of an astronomer
who maintained that the satellites revolve in elliptic
courses round their planets “for the sake of symmetry,”
because the planets thus revolve round the sun? An
eminent physiologist accounts for the presence of rudi-
mentary organs, by supposing that they serve to excrete
matter in excess, or matter injurious to the system; but
can we suppose that the minute papilla, which often
represents the pistil in male flowers, and which is
formed of mere cellular tissue, can thus act? Can we
suppose that rudimentary teeth, which are subsequently
absorbed, are beneficial to the rapidly growing embryonic
calf by removing matter so precious as phosphate of
lime? When a man’s fingers have been amputated,
imperfect nails have been known to appear on the
stumps, and I could as soon believe that these vestiges
of nails are developed in order to excrete horny matter,
as that the rudimentary nails on the fin of the manatee
have been developed for this same purpose.
On the view of descent with modification, the origin
of rudimentary organs is comparatively simple; and we
can understand to a large extent the laws governing
their imperfect development. We have plenty of cases
of rudimentary organs in our domestic productions,—as
the stump of a tail in tailless breeds,—the vestige of an
Cuap. XIV.] AND ABORTED ORGANS. 261
ear in earless breeds of sheep,—the reappearance of
minute dangling horns in hornless breeds of cattle,
more especially, according ta Youatt, in young animals,
—and the state of the whole flower in the cauliflower.
We often see rudiments of various parts In monsters ;
but I doubt whether any of these cases throw light on
the origin of rudimentary organs in a state of nature,
further than by showing that rudiments can be pro-
duced ; for the balance of evidence clearly indicates that
species under nature do not undergo great and abrupt
changes. But we learn from the study of our domestic
productions that the disuse of parts leads to their
reduced size; and that the result is inherited.
It appears probable that disuse has been the main
agent in rendering organs rudimentary. It would at
first lead by slow steps to the more and more complete
reduction of a part, until at last it became rudimentary,
—as in the case of the eyes of animals inhabiting dark
caverns, and of the wings of birds inhabiting oceanic
islands, which have seldom been forced by beasts of prey
to take flight, and have ultimately lost the power of
flying. Again, an organ, useful under certain conditions,
might become injurious under others, as with the wings
of beetles living on small and exposed islands; and in
this case natural selection will have aided in reducing
the organ, until it was rendered harmless and rudi-
mentary.
Any change in structure and function, which can be
effected by small stages, is within the power of natural
selection; so that an organ rendered, through changed
habits of life, useless or injurious for one purpose, might
be modified and used for another purpose. An organ
might, also, be retained for one alone of its former func-
262 - RUDIMENTARY, ATROPHIED, ([Caar. XIV.
tions. Organs, originally formed by the aid of natural
selection, when rendered useless may well be variable,
for their variations can no longer be checked by natural
selection. All this agrees well with what we see under
nature. Moreover, at whatever period of life either disuse
or selection reduces an organ, and this will generally
be when the being has come to maturity and has to
exert its full powers of action, the principle of inherit-
ance at corresponding ages will tend to reproduce the
organ in its reduced state at the same mature age, but
will seldom affect 1t in the embryo. Thus we can
understand the greater size of rudimentary organs in
the embryo relatively to the adjoining parts, and their
lesser relative size in the adult. If, for instance, the
digit of an adult animal was used less and less during
many generations, owing to some change of habits, or if
an organ or gland was less and less functionally exercised,
we may infer that it would become reduced im size in the
adult descendants of this animal, but would retain nearly
its original standard of development in the embryo.
There remains, however, this difficulty. After an
organ has ceased being used,and has become in con-
sequence much reduced, how can it be still further
reduced in size until the merest vestige is left; and
how can it be finally quite obliterated? It is scarcely
possible that disuse can go on producing any further
effect after the organ has once been rendered functionless.
Some additional explanation is here requisite which I
cannot give. If, for instance, it could be proved that
every part of the organisation tends to vary in a greater
degree towards diminution than towards augmentation
of size, then we should be able to understand how an
organ which has become useless would be rendered, in-
Cuar. XIV.] AND ABORTED ORGANS. 263
dependently of the effects of disuse, rudimentary and
would at last be wholly suppressed; for the variations
towards diminished size would no longer be checked by
natural selection. The principle of the economy of
growth, explained in a former chapter, by which the
materials forming any part, if not useful to the pos-
sessor, are saved as far as is possible, will perhaps come
into play in rendering a useless part rudimentary. But
this principle will almost necessarily be confined to the
earlier stages of the process of reduction; for we cannot
suppose that a minute papilla, for instance, representing
in a male flower the pistil of the female flower, and
formed merely of cellular tissue, could be further reduced
or absorbed for the sake of economising nutriment.
Finally, as rudimentary organs, by whatever steps
they may have been degraded into their present useless
condition, are the record of a former state of things, and
have been retained solely through the power of inherit-
ance,—we can understand, on the genealogical view of
classification, how it is that systematists, in placing
organisms in their proper places in the natural system,
have often found rudimentary parts as useful as, or even
sometimes more useful than, parts of high physiological
importance. Rudimentary organs may be compared
with the letters in a word, still retained in the spelling,
but become useless in the pronunciation, but which serve
as a clue for its derivation. On the view of descent
with modification, we may conclude that the existence
of organs in a rudimentary, imperfect, and useless con-
dition, or quite aborted, far from presenting a strange
difficulty, as they assuredly do on the old doctrine of
creation, might even have been anticipated in accordance
with the views here explained.
264 | SUMMARY. [Cuar, XIV.
Summary.
In this chapter I have attempted to show, that the
arrangement of all organic beings throughout all time
in groups under groups—that the nature of the relation-
ships by which all living and extinct organisms are
united by complex, radiating, and circuitous lines of
affinities into a few grand classes,—the rules followed
and the difficulties encountered by naturalists in their
classifications,—the value set upon characters, if constant
and prevalent, whether of high or of the most trifling
importance, or, aS with rudimentary organs, of no
importance,—the wide opposition in value between
analogical or adaptive characters, and characters of true
affinity ; and other such rules ;—all naturally follow if
we admit the common parentage of allied forms, together
with their modification through variation and natural
selection, with the contingencies of extinction and di-
vergence of character. In considering this view of classifi-
cation, it should be borne in mind that the element of
descent has been universally used in ranking together.
the sexes, ages, dimorphic forms, and acknowledged
varieties of the same species, however much they may
differ from each other in structure. If we extend the
use of this element of descent,—the one certainly
known cause of similarity in organic beings,—we shall
understand what is meant by the Natural System:
it is genealogical in its attempted arrangement,
with the grades of acquired difference marked by
the terms, varieties, species, genera, families, orders,
and classes.
On this same view of descent with modification, most
Cuap. XIV.] SUMMARY. 265
of the great factsin Morphology become intelligible,—
whether we look to the same pattern displayed by the
different species of the same class in their homologous
organs, to whatever purpose applied; or to the serial
and lateral homologies in each individual animal and
plant.
On the principle of successive slight variations, not
necessarily or generally supervening at a very early
period of life, and being inherited at a corresponding
period, we can understand the leading facts in Embry-
ology ; namely, the close resemblance in the individual
embryo of the parts which are homologous, and which
when matured become widely different in structure and
function; and the resemblance of the homologous parts
or organs in allied though distinct species, though fitted
in the adult state for habits as different as is possible.
Larvee are active embryos, which have been specially
modified in a greater or less degree in relation to their
habits of life, with their modifications inherited at a
corresponding early age. On these same principles,—
and bearing in mind that when organs are reduced in
size, either from disuse or through natural selection, it
will generally be at that period of life when the being
has to provide for its own wants, and bearing in mind
how strong is the force of inheritance—the occurrence
of rudimentary organs might even have been anticipated.
The importance of embryological characters and of rudi-
mentary organs in classification is intelligible, on the
view that a natural arrangement must be genealogical.
Finally, the several classes of facts which have been
considered in this chapter, seem to me to proclaim go
plainly, that the innumerable species, genera and
families, with which this world is peopled, are all
266 SUMMARY. [Cuap. XIV.
descended, each within its own class or group, from
common parents, and have all been modified in the
course of descent, that I should without hesitation adopt
this view, even if it were unsupported by other facts or
arguments.
Cuar. XV.] RECAPITULATION. 267
CHAPTER XV.
RECAPITULATION AND CONCLUSION.
Recapitulation of the objections to the theory of Natural Selection
—Recapitulation of the general and special circumstances in its
favour—Causes of the general belief in the immutability of
species — How far the theory of Natural Selection may be
extended — Effects of its adoption on the study of Natural
History—Concluding remarks.
As this whole volume is one long argument, it may
be convenient to the reader to have the leading facts
and inferences briefly recapitulated.
That many and serious objections may be advanced
against the theory of descent with modification through
variation and natural selection, I do not deny. I have
endeavoured to give to them their full force. Nothing
at first can appear more ditficult to believe than that
the more complex organs and instincts have been per-
fected, not by means superior to, though analogous with,
human reason, but by the accumulation of innumerable
slight variations, each good for the individual possessor.
Nevertheless, this difficulty, though appearing to our
imagination insuperably great, cannot be considered
real if we admit the following propositions, namely,
that all parts of the organisation and instincts offer, at
least, individual differences—that there is a struggle for
existence leading to the preservation of profitable devia-
tions of structure or instinct—and, lastly, that gradations
268 RECAPITULATION. (Cuar. XV.
in the state of perfection of each organ may have existed,
each good of its kind. The truth of these propositions
cannot, I think, be disputed. ;
It is, no doubt, extremely difficult even to conjecture
by what gradations many structures have been perfected,
more especially amongst broken and failing groups of
organic beings, which have suffered much extinction;
but we see so many strange gradations in nature, that
we ought to be extremely cautious in saying that any
organ or instinct, or any whole structure, could not have
arrived at its present state by many graduated steps.
There are, it must be admitted, cases of special difficulty
opposed to the theory of natural selection; and one of
the most curious of these is the existence in the same
community of two or three defined castes of workers or
sterile female ants; but I have attempted to show how
these difficulties can be mastered.
With respect to the almost universal sterility of
species when first crossed, which forms so remarkable a
contrast with the almost universal fertility of varieties
when crossed, I must refer the reader to the recapitula-
tion of the facts given at the end of the ninth chapter,
which seem to me conclusively to show that this sterility
is no more a special endowment than is the incapacity of
two distinct kinds of trees to be grafted together; but
that it is incidental on differences confined to the repro-
ductive systems of the intercrossed species. We see the
truth of this conclusion in the vast difference in the
results of crossing the same two species reciprocally,—
that is, when one species is first used as the father and
then as the mother. Analogy from the consideration of
dimorphic and trimorphic plants clearly leads to the
same conclusion, for when the forms are illegitimately
Cuar. XV] RECAPITULATION. 969
united, they yield few or no seed, and their offspring are
more or less sterile; and these forms belong to the same
undoubted species, and differ from each other in no respect
except in their reproductive organs and functions.
Although the fertility of varieties when intercrossed
and of their mongrel offspring has been asserted by so
many authors to be universal, this cannot be considered
as quite correct after the facts given on the high
authority of Gartner and Kélreuter. Most of the varieties
which have been experimented on have been produced
under domestication; and as domestication (I do not
mean mere confinement) almost certainly tends to elimi-
nate that sterility which, judging from analogy, would
have affected the parent-species if intercrossed, we ought
not to expect that domestication would lkewise induce
sterility in their modified descendants when crossed.
This elimination of sterility apparently follows from
the same cause which allows our domestic animals to
breed freely under diversified circumstances; and this
again apparently follows from their having been gradu-
ally accustomed to frequent changes in their conditions
of life.
A double and parallel series of facts seems to throw
much light on the sterility of species, when first crossed,
and of their hybrid offspring. On the one side, there is
good reason to believe that slight changes in the con-
ditions of life give vigour and fertility to all organic
beings. We know also that across between the distinct
individuals of the same variety, and between distinct
varieties, increases the number of their offspring, and
certainly gives to them increased size and vigour. This
is chiefly owing to the forms which are crossed having
been exposed to somewhat different conditions of life;
270 RECAPITULATION. [Cuap. XV.
for I have ascertained by a laborious series of experi-
ments that if all the individuals of the same variety
be subjected during several generations to the same
conditions, the good derived from crossing is often much
diminished or wholly disappears. This is one side of
the case. On the other side, we know that species
which have long been exposed to nearly uniform condi-
tions, when they are subjected under confinement to
new and greatly changed conditions, either perish, or
if they survive, are rendered sterile, though retaining
perfect health. This does not occur, or only in a very
shght degree, with our domesticated productions, which
have long been exposed to fluctuating conditions. Hence
when we find that hybrids produced by a cross between
two distinct species are few in number, owing to their
perishing soon after conception or at a very early age,
or if surviving that they are rendered more or less sterile,
it seems highly probable that this result is due to their
having been in fact subjected to a great change in their
conditions of life, from being compounded of two distinct
organisations. He who will explain in a definite manner
why, for instance, an elephant or a fox will not breed
under confinement in its native country, whilst the
domestic pig or dog will breed freely under the most
diversified conditions, will at the same time be able to
give a definite answer to the question why two distinct
species, when crossed, as well as their hybrid offspring,
are generally rendered more or less sterile, whilst two
domesticated varieties when crossed and their mongrel
offspring are perfectly fertile.
Turning to geographical distribution, the difficulties
encountered on the theory of descent with modification
are serious enough. All the individuals of the same
Cuar. XV.]J RECAPITULATION. 271
species, and all the species of the same genus, or even
higher group, are descended from common parents; and
therefore, in however distant and isolated parts of the
world they may now be found, they must in the course
of successive generations have travelled from some one
point to all the others. We are often wholly unable even
to conjecture how this could have been effected. Yet,
as we have reason to believe that some species have
retained the same specific form for very long periods of
time, immensely long as measured by years, too much
stress ought not to be laid on the occasional wide diffu-
sion of the same species; for during very long periods
there will always have been a good chance for wide
migration by many means. A broken or interrupted
range may often be accounted for by the extinction of
the species in the intermediate regions. It cannot be
denied that we are as yet very ignorant as to the full
extent of the various climatal and geographical changes
which have affected the earth during modern periods ;
and such changes will often have facilitated migration.
As an example, I have attempted to show how potent
has been the influence of the Glacial period on the dis-
tribution of the same and of allied species throughout
the world. Weare as yet profoundly ignorant of the
many occasional means of transport. With respect to
distinct species of the same genus inhabiting distant
and isolated regions, as the process of modification has
necessarily been slow, all the means of migration will
have been possible during a very long period; and
consequently the difficulty of the wide diffusion of the
species of the same genus is in some degree lessened.
As according to the theory of natural selection an
interminable number of intermediate forms must have
41
272 RECAPITULATION. [Cuar. XV.
existed, linking together all the species in each group by
gradations as fine as are our existing varieties, it may be
asked, Why do we not see these linking forms all around
us? Why are not all organic beings blended together
in an inextricable chaos? With respect to existing forms,
we should remember that we have no right to expect
(excepting in rare cases) to discover directly connecting
links between them, but only between each and some
extinct and supplanted form. Even on a wide area,
which has during a long period remained continuous,
and of which the climatic and other conditions of life
change insensibly in proceeding from a district occupied
by one species into another district occupied by a closely
allied species, we have no just right to expect often to
find intermediate varieties In the intermediate zones.
For we have reason to believe that only a few species
of a genus ever undergo change; the other species
becoming utterly extinct and leaving no modified
progeny. Of the species which do change, only a few
within the same country change at the same time; and
all modifications are slowly effected. I have also shown
that the intermediate varieties which probably at first
existed in the intermediate zones, would be lable to be
supplanted by the allied forms on either hand; for the
latter, from existing in greater numbers, would generally
be modified and improved at a quicker rate than the
intermediate varieties, which existed in lesser numbers ;
so that the intermediate varieties would, in the long
run, be supplanted and exterminated.
On this doctrine of the extermination of an infinitude
of connecting links, between the living and extinct in-
habitants of the world, and at each successive period
between the extinct and still older species, why is not
6
Cuap. XV.) RECAPITULATION. 273
every geological formation charged with such links?
Why does not every collection of fossil remains afford
plain evidence of the gradation and mutation of the forms
of life? Although geological research has undoubtedly
revealed the former existence of many links, bringing
numerous forms of life much closer together, it does not
yield the infinitely many fine gradations between past
and present species required on the theory; and this is
the most obvious of the many objections which may be
urged against it. Why, again, do whole groups of allied
species appear, though this appearance is often false, to
have come in suddenly on the successive geological
stages? Although we now know that organic beings
appeared on this globe, at a period incalculably remote,
long kefore the lowest bed of the Cambrian system
was deposited, why do we not find beneath this system
great piles of strata stored with the remains of the pro-
genitors of the Cambrian fossils? For on the theory, |
such strata must somewhere have been deposited at
these ancient and utterly unknown epochs of the world’s
history.
I can answer these questions and objections only on
the supposition that the geological record is far more im-
perfect than most geologists believe. The number of
specimens in all our museums is absolutely as nothing
compared with the countless generations of countless
species which have certainly existed. The parent-form
of any two or more species would not be in all its char-
acters directly intermediate between its modified off-
spring, any more than the rock-pigeon is directly inter-
mediate in crop and tail between its descendants, the
pouter and fantail pigeons. We should not be able
to recognise a species as the parent of another and
274. | RECAPITULATION. (Car. XV.
modified species, if we were to examine the two ever so
closely, unless we possessed most of the intermediate
links; and owing to the imperfection of the geological
record, we have no just right to expect to find so many
links. If two or three, or even more linking forms were
discovered, they would simply be ranked by many
naturalists as so many new species, more especially if
found in different geological sub-stages, let their dif-
ferences be ever so slight. Numerous existing doubtful
forms could be named which are probably varieties;
but who will pretend that in future ages so many fossil
links will be discovered, that naturalists will be able to
decide whether or not these doubtful forms ought to be
called varieties? Only a small portion of the world
has been geologically explored. Only organic beings of
certain classes can be preserved in a fossil condition, at
least In any great number. Many species when once
formed never undergo any further change but become
extinct without leaving modified descendants; and the
periods, during which species have undergone modifica-
tion, though long as measured by years, have probably
been short in comparison with the periods during which
they retained the same form. It is the dominant and
widely ranging species which vary most frequently and
vary most, and varieties are often at first local—both
causes rendering the discovery of intermediate links in
any one formation less likely. Local varieties will
not spread into other and distant regions until they are
considerably modified and improved; and when they
have spread, and are discovered in a geological formation,
they appear as if suddenly created there, and will be
simply classed as new species. Most formations have
been intermittent in their accumulation; and their
Cuapr. XV.] RECAPITULATION. 275
duration has probably been shorter than the average
duration of specific forms. Successive formations are in
most cases separated from each other by blank intervals
of time of great length; for fossiliferous formations thick
enough to resist future degradation can as a general rule
_be accumulated only where much sediment is deposited
on the subsiding bed of the sea. During the alternate
periods of elevation and of stationary level the record
will generally be blank. During these latter periods
there will probably be more variability in the forms of
life; during periods of subsidence, more extinction.
With respect to the absence of strata rich in fossils
beneath the Cambrian formation, I can recur only to
the hypothesis given in the tenth chapter; namely, that
though our continents and oceans have endured for an
enormous period in nearly their present relative positions,
we have no reason to assume that this has always been
the case; consequently formations much older than any
now known may he buried beneath the great oceans.
With respect to the lapse of time not having been suffi-
cient since our planet was consolidated for the assumed
amount of organic change, and this objection, as urged
by Sir William Thompson, is probably one of the gravest
as yet advanced, I can only say, firstly, that we do not
know at what rate species change as measured by years,
and secondly, that many philosophers are not as yet
willing to admit that we know enough of the constitu-
tion of the universe and of the interior of our globe to
speculate with safety on its past duration.
That the geological record is imperfect all will admit ;
but that it is imperfect to the degree required by our
theory, few will be inclined to admit. If we look to
long enough intervals of time, geology plainly declares
= ne
276 RECAPITULATION. [Cuar. XV
that species have all changed; and they have changed
in the manner required by the theory, for they have
changed slowly and in a graduated manner. We clear!
see this in the fossil remains from consecutive formations
invariably being much more closely related to each other,
than are the fossils from widely separated formations.
Such is the sum of the several chief objections and
difficulties which may be justly urged against the
theory; and I have now briefly recapitulated the
answers and explanations which, as far as I can see,
may be given. I have felt these difficulties far too
heavily during many years to doubt their weight. But
it deserves especial notice that the more important
objections relate to questions on which we are con-
fessedly ignorant; nor do we know how ignorant we
are. We do not know all the possible transitional
gradations between the simplest and the most perfect
organs; it cannot be pretended that we know all the
varied means of Distribution during the long lapse of
years, or that we know how imperfect is the Geological
Record. Serious as these several objections are, in my
judgment they are by no means sufficient to overthrow
the theory of descent with subsequent modification.
Now let us turn to the other side of the argument.
Under domestication we see much variability, caused, or
at least excited, by changed conditions of life; but often
in so obscure a manner, that we are tempted to consider
the variations as spontaneous. Variability is governed
by many complex laws,—by correlated growth, compen-
sation, the increased use and disuse of parts, and the
definite action of the surrounding conditions. There is
much difficulty in ascertaining how largely our domestic
Cuar. XV.] RECAPITULATION. 2
productions have been modified; but we may safely
infer that the amount has been large, and that modifica-
tions can be inherited for long periods. As long as the
conditions of life remain the same, we have reason to
believe that a modification, which has already been
inherited for many generations, may continue to be
inherited for an almost infinite number of generations.
On the other hand, we have evidence that variability
when it has once come into play, does not cease under
domestication for a very long period; nor do we know
that it ever ceases, for new varieties are still occasionally
produced by our oldest domesticated productions. 3
Variability is not actually caused by man; he only
unintentionally exposes organic beings to new condi-
tions of life, and then nature acts on the organisation
and causes it to vary. But man can and does select the
variations given to him by nature, and thus accumulates
them in any desired manner. He thus adapts animals
and plants for his own benefit or pleasure. He may
do this methodically, or he may do it unconsciously by
preserving the individuals most useful or pleasing to
him without any intention of altering the breed. It is
certain that he can largely influence the character of a
breed by selecting, in each successive generation, indi-
vidual differences so slight as to be inappreciable except
by an educated eye. This unconscious process of selec-
tion has been the great agency in the formation of the
most distinct and useful domestic breeds. That many
breeds produced by man have to a large extent the
character of natural species, is shown by the inextric-
able doubts whether many of them are varieties or
aboriginally distinct species.
There ig no reason why the principles which have
278 RECAPITULATION. (Cuar. XV.
acted so efficiently under domestication should not have
acted under nature. In the survival of favoured
individuals and races, during the constantly-recurrent
Struggle for Existence, we see a powerful and ever-
acting form of Selection. The struggle for existence
inevitably follows from the high geometrical ratio of
increase which is common to all organic beings. This
high rate of increase is proved by calculation—by the
rapid increase of many animals and plants during a
succession of peculiar seasons, and when naturalised in
new countries. More individuals are born than can
possibly survive. A grain in the balance may determine
which individuals shall hve and which shall die —which
variety or species shall increase in number, and which
shall decrease, or finally become extinct. As the indi-
viduals of the same species come in all respects into the
closest competition with each other, the struggle will
generally be most severe between them; it will be
almost equally severe between the varieties of the same
species, and next in severity between the species of the
same genus. On the other hand the struggle will often
be severe between beings remote in the scale of nature.
The slightest advantage in certain individuals, at any
age or during any season, over those with which they
come into competition, or better adaptation in however
slight a degree to the surrounding physical conditions,
will, in the long run, turn the balance.
With animals having separated sexes, there will be
in most cases a struggle between the males for the posses-
sion of the females. The most vigorous males, or those
which have most successfully struggled with their con-
ditions of life, will generally leave most progeny. But
success will often depend on the males having special
Cuap. XV.] RECAPITULATION. 279
weapons, or means of defence, or charms; and a slight
advantage will lead to victory.
As geology plainly proclaims that each land has
undergone great physical changes, we might have ex-
pected to find that organic beings have varied under
nature, in the same way as they have varied under
domestication. And if there has been any variability
under nature, 1t would be an unaccountable fact if natural
selection had not come into play. It has often been
asserted, but the assertion is incapable of proof, that the
amount of variation under nature is a strictly limited
quantity. Man, though acting on external characters
alone and often capriciously, can produce within a short
period a great result by adding up mere individual
differences in his domestic productions; and every one
admits that species present individual differences. But,
besides such differences, all naturalists admit that natural
varieties exist, which are considered sufficiently distinct
to be worthy of record in systematic works. No one
has drawn any clear distinction between individual
differences and slight varieties; or between more plainly
marked varieties and sub-species, and species. On
separate continents, and on different parts of the same
continent when divided by barriers of any kind, and on
outlying islands, what a multitude of forms exist, which
some experienced naturalists rank as varieties, others as
' geographical races or sub-species, and others as distinct,
though closely allied species !
If then, animals and plants do vary, let it be ever so
slightly or slowly, why should not variations or indi-
vidual differences, which are in any way beneficial, be
preserved and accumulated through natural selection, or
the survival of the fittest? If man can by patience
280 RECAPITULATION. (Cuar. XV.
select variations useful to him, why, under changing
and complex conditions of life, should not variations
useful to nature’s living products often arise, and be
preserved or selected? What limit can be put to this
power, acting during long ages and rigidly scrutinising
the whole constitution, structure, and habits of each
creature,—favouring the good and rejecting the bad? I
can see no limit to this power, in slowly and beautifully |
adapting each form to the most complex relations of life.
The theory of natural selection, even if we look no farther
than this, seems to be in the highest degree probable.
I have already recapitulated, as fairly as I could, the
opposed ditiiculties and objections: now let us turn to
the special facts and arguments in favour of the theory.
On the view that species are only strongly marked
and permanent varieties, and that each species first
existed as a variety, we can see why it is that no line
of demarcation can be drawn between species, commonly
supposed to have been produced by special acts of crea-
tion, and varieties which are acknowledged to have been
produced by secondary laws. On this same view we can
understand how it is that in a region where many species
of a genus have been produced, and where they now
flourish, these same species should present many varieties;
for where the manufactory of species has been active, we
might expect, as a general rule, to find it still in action;
and this is the case if varieties be incipient species.
Moreover, the species of the larger genera, which afford
the greater number of varieties or incipient species,
retain to a certain degree the character of varieties; for
they differ from each other by a less amount of difference
than do the species of smaller genera. The closely allied
Cuap. XV] RECAPITULATION. 281
species also of the larger genera apparently have re-
stricted ranges, and in their affinities they are clustered
in little groups round other species—in both respects
resembling varieties. These are strange relations on
the view that each species was independently created,
but are intelligible if each existed first as a variety.
As each species tends by its geometrical rate of repro-
duction to increase inordinately in number; and as the
modified descendants of each species will be enabled to
increase by as much as they become more diversified in
habits and structure, so as to be able to seize on many
and widely different places in the economy of nature,
there will be a constant tendency in natural selection
to preserve the most divergent offspring of any one
species. Hence, during a long-continued course of
modification, the slight differences characteristic of
varieties of the same species, tend to be augmented into
the greater differences characteristic of the species of the
same genus. New and improved varieties will inevitably
supplant and exterminate the older, less improved, and
intermediate varieties; and thus species are rendered to
a large extent defined and distinct objects. Dominant
species belonging to the larger groups within each class
tend to give birth to new and dominant forms; so that
each large group tends to become still larger, and at the
same time more divergent in character. But as all
groups cannot thus go on increasing in size, for the
world would not hold them, the more dominant groups
beat the less dominant. This tendency in the large
groups to go on increasing in size and diverging in char-
acter, together with the inevitable contingency of much
extinction, explains the arrangement of all the forms of
life in groups subordinate to groups, all within a few great
282 RECAPITULATION. (Cuap. XV.
classes, which has prevailed throughout all time. This
grand fact of the grouping of all organic beings under
what is called the Natural System, is utterly inexplic-
able on the theory of creation.
As natural selection acts solely by accumulating slight,
successive, favourable variations, it can produce no great
or sudden modifications; it can act only by short and
slow steps. Hence, the canon of “Natura non facit
saltum,’ which every fresh addition to our knowledge
tends to confirm, is on this theory intelligible. We can
see why throughout nature the same general end is
gained by an almost infinite diversity of means, for every
peculiarity when once acquired is long inherited, and
structures already modified in many different ways have
to be adapted for the same general purpose. We can,
in short, see why nature is prodigal in variety, though
niggard in innovation. But why this should be a law
of nature if each species has been independently created
no man can explain.
Many other facts are, as it seems to me, explicable on
this theory. How strange it is that a bird, under the
form of a woodpecker, should prey on insects on the
ground; that upland geese which rarely or never swim,
should possess webbed feet; that a thrush-like bird
should dive and feed on sub-aquatic insects; and thata
petrel should have the habits and structure fitting it for
the life of an auk! and so in endless other cases. But
on the view of each species constantly trying to increase
in number, with natural selection always ready to adapt
the slowly varying descendants of each to any un-
occupied or ill-occupied place in nature, these facts cease
to be strange, or might even have been anticipated.
We can to acertain extent understand how it is that
Cuar. XV.] RECAPITULATION. 283
there is so much beauty throughout nature; for this
may be largely attributed to the agency of selection.
That beauty, according to our sense of it, is not universal,
must be admitted by every one who will look at some
venomous snakes, at some fishes, and at certain hideous
bats with a distorted resemblance to the human face.
Sexual selection has given the most brillant colours,
elegant patterns, and other ornaments to the males, and
sometimes to both sexes of many birds, butterflies, and
other animals. With birds it has often rendered the
voice of the male musical to the female, as well as to
our ears. Flowers and fruit have been rendered con-
spicuous by brilliant colours in contrast with the green
foliage, in order that the flowers may be easily seen,
visited, and fertilised by insects, and the seeds dis-
seminated by birds. How it comes that certain colours,
-gounds, and forms should give pleasure to man and the
lower animals,—that is, how the sense of beauty in its
simplest form was first acquired,—we do not know any
more than how certain odours and flavours were first
rendered agreeable. |
As natural selection acts by competition, it adapts
and improves the inhabitants of each country only in
relation to their co-inhabitants; so that we need feel no
surprise at the species of any one country, although on
the ordinary view supposed to have been created and
specially adapted for that country, being beaten and
supplanted by the naturalised productions trom another
land. Nor ought we to marvel if all the contrivances
in nature be not, as far as we can judge, absolutely
perfect, as in the case even of the human eye; or if
some of them be abhorrent to our ideas of fitness. We
need not marvel at the sting of the bee, when used
42
284 RECAPITULATION. (Cuar. XV.
against an enemy, causing the bee’s own death; at
drones being produced in such great numbers for one
single act, and being then slaughtered by their sterile
sisters; at the astonishing waste of pollen by our fir-
trees; at the instinctive hatred of the queen-bee for her
own fertile daughters; at ichneumonide feeding within
the living bodies of caterpillars; or at other such cases.
The wonder indeed is, on the theory of natural selection,
that more cases of the want of absolute perfection have
not been detected.
The complex and little known laws governing the
production of varieties are the same, as far as we can
judge, with the laws which have governed the production
of distinct species. In both cases physical conditions
seem to have produced some direct and definite effect,
but how much we cannot say. Thus, when varieties
enter any new station, they occasionally assume some
of the characters proper to the species of that station.
With both varieties and species, use and disuse seem to
have produced a considerable effect ; for it is impossible
to resist this conclusion when we look, for instance, at
the logger-headed duck, which has wings incapable of
flight, in nearly the same condition as in the domestic
duck; or when we look at the burrowing tucu-tucu,
which is occasionally blind, and then at certain moles,
which are habitually blind and have their eyes covered
with skin; or when we look at the blind animals in-
habiting the dark caves of America and Europe. With
varieties and species, correlated variation seems to have
played an important part, so that when one part has
been modified other parts have been necessarily modified.
With both varieties and species, reversions to long-lost
characters occasionally occur. How inexplicable on the
Cuap. XV.] RECAPITULATION. 285
theory of creation is the occasional appearance of stripes
on the shoulders and legs of the several species of the
horse-genus and of their hybrids! How simply is this
fact explained if we believe that these species are all
descended from a striped progenitor, in the same manner
as the several domestic breeds of the pigeon are descended
from the blue and barred rock-pigeon !
On the ordinary view of each species having been
independently created, why should specific characters,
or those by which the species of the same genus
differ from each other, be more variable than generic
characters in which they all agree? Why, for instance,
should the colour of a flower be more likely to vary in
any one species of a genus, if the other species possess
differently coloured flowers, than if all possessed the
same coloured flowers? If species are only well-marked
varieties, of which the characters have become in a high
degree permanent, we can understand this fact; for they
have already varied since they branched off from a
common progenitor in certain characters, by which they
have come to be specifically distinct from each other;
therefore these same characters would be more likely
again to vary than the generic characters which have
been inherited without change for an immense period.
It is inexplicable on the theory of creation why a part
developed in a very unusual manner in one species
alone of a genus, and therefore, as we may naturally infer,
of great importance to that species, should be eminently
liable to variation ; but, on our view, this part has under-
gone, since the several species branched off from a
common progenitor, an unusual amount of variability
and modification, and therefore we might expect the
part generally to be still variable. But a part may be
286 RECAPITULATION. ([Cuap. XV.
developed in the most unusual manner, hke the wing
of a bat, and yet not be more variable than any other
structure, if the part be common to many subordinate
forms, that is, if it has been inherited for a very long
period ; for in this case it will have been rendered con-
stant by long-continued natural selection.
Glancing at instincts, marvellous as some are, they
offer no greater difficulty than do corporeal structures
on the theory of the natural selection of successive, slight,
but profitable modifications. We can thus understand
why nature moves by graduated steps in endowing
different animals of the same class with their several
instincts. Ihave attempted to show how much lheht
the principle of gradation throws on the admirable arehi-
tectural powers of the hive-bee. Habit no doubt often
comes into play in modifying instincts ; but it certainly
is not indispensable, as we see in the case of neuter
insects, which leave no progeny to inherit the effects of
long-continued habit. On the view of all the species of
the same genus having descended from a common parent,
and having inherited much in common, we can under-
stand how it is that allied species, when placed under
widely different conditions of life, yet follow nearly the
same instincts; why the thrushesof tropicaland temperate
South America, for instance, line their nests with mud
like our British species. On the view of instincts having
been slowly acquired through natural selection, we need
not marvel at some instincts being not perfect and lable
to mistakes, and at many instincts causing other animals
to sufier.
If species be only well-marked and permanent varie-
ties, we can at once see why their crossed offspring
should follow the same complex laws in their degrees
Cuar. XV.] RECAPITULATION. 287
and kinds of resemblance to their parents,—in being
absorbed into each other by successive crosses, and in
other such points,—as do the crossed offspring of ac-
knowledged varieties. This similarity would be a strange
fact, if species had been independently created and
varieties had been produced through secondary laws.
If we admit that the geological record is imperfect
to an extreme degree, then the facts, which the record
does give, strongly support the theory of descent with
- modification. New species have come on the stage slowly
and at successive intervals; and the amount of change,
after equal intervals of time,is widely different in dif-
ferent groups. The extinction of species and of whole
groups of species, which has played so conspicuous a
part in the history of the organic world, almost inevitably
follows from the principle of natural selection; for old
forms are supplanted by new and improved forms.
Neither single species nor groups of species reappear
when the chain of ordinary generation is once broken.
The gradual diffusion of dominant forms, with the slow
modification of their descendants, causes the forms of
life, after long intervals of time, to appear as if they had
changed simultaneously throughout the world. The fact
of the fossil remains of each formation being in some
degree intermediate in character between the fossils in
the formations above and below, is simply explained by
their intermediate position in the chain of descent. The
grand fact that all extinct beings can be classed with
all recent beings, naturally follows from the living and
the extinct being the offspring of common parents. As
species have generally diverged in character during their
long course of descent and modification, we can under-
stand why it is that the more ancient forms, or early
288 RECAPITULATION. [Cuar. XV.
progenitors of each group, so often occupy a position
in some degree intermediate between existing groups.
Recent forms are generally looked upon as being, on the
whole, higher in the scale of organisation than ancient
forms; and they must be higher, in so far as the later
and more improved forms have conquered the older and
less improved forms in the struggle for hfe; they have
also generally had their organs more specialised for dif-
ferent functions. This fact is perfectly compatible with
numerous beings still retaining simple and but little
improved structures, fitted for simple conditions of life ;
it is likewise compatible with some forms having retro-
graded in organisation, by having become at each stage
of descent better fitted for new and degraded habits of
life. Lastly, the wonderful law of the long endurance
of allied forms on the samé continent,—of marsupials
in Australia, of edentata in America, and other such
cases,—is intelligible, for within the same country the
existing and the extinct will be closely allied by descent.
Looking to geographical distribution, if we admit that
there has been during the long course of ages much migra-
tion from one part of the world to another, owing to
former climatal and geographical changes and to the
many occasional and unknown means of dispersal, then
we can understand, on the theory of descent with modi-
fication, most of the great leading facts in Distribution.
We can see why there should be so striking a parallelism
in the distribution of organic beings throughout space,
and in their geological succession throughout time; for
in both cases the beings have been connected by the
bond of ordinary generation, and the means of modifica-
tion have been the same. We see the full meaning of
the wonderful fact, which has struck every traveller
a
Cuap. XV.] RECAPITULATION. 289
namely, that on the same continent, under the most
diverse conditions, under heat and cold, on mountain
and lowland, on deserts and marshes, most of the inhabit-
ants within each great class are plainly related; for they
are the descendants of the same progenitors and early
colonists. On this same principle of former migration,
combined in most cases with modification, we can under-
stand, by the aid of the Glacial period, the identity of
some few plants, and the close alliance of many others,
on the most distant mountains, and in the northern and
southern temperate zones ; and likewise the close alliance
of some of the inhabitants of the sea in the northern and
southern temperate latitudes, though separated by the
whole intertropical ocean. Although two countries may
present physical conditions as closely similar as the
same species ever require, we need feel no surprise at
their inhabitants being widely different, if they have
been for a long period completely sundered from each
other; for as the relation of organism to organism is the
most important of all relations, and as the two countries
will have received colonists at various periods and in
different proportions, from some other country or from
each other, the course of modification in the two areas
will inevitably have been different.
On this view of migration, with subsequent modifica-
tion, we see why oceanic islands are inhabited by only
few species, but of these, why many are peculiar or
endemic forms. We clearly see why species belonging
to those groups of animals which cannot cross wide
spaces of the ocean, as frogs and terrestrial mammals, do
not inhabit oceanic islands ; and why, on the other hand,
new and peculiar species of bats, animals which can
traverse the ocean, are often found on islands far distant
290 RECAPITULATION. (Cuap. XV.
from any continent. Such cases as the presence of
peculiar species of bats on oceanic islands and the
absence of all other terrestrial mammals, are facts utterly
inexplicable on the theory of independent acts of
creation.
The existence of closely allied or representative species
in any two areas, implies, on the theory of descent with
modification, that the same parent-forms formerly in-
habited both areas: and we almost invariably find that
wherever many closely allied species inhabit two areas,
some identical species are still common toboth. Wherever
many closely allied yet distinct species occur, doubtful
forms and varieties belonging to the same groups like-
wise occur. It is arule of high generality that the in-
habitants of each area are related to the inhabitants of
the nearest source whence immigrants might have been
derived. We see this in the striking relation of nearly
all the plants and animals of the Galapagos archipelago,
of Juan Fernandez, and of the other American islands,
to the plants and animals of the neighbouring American
mainland; and of those of the Cape de Verde archi-
pelago, and of the other African islands to the African
mainland. It must be admitted that these facts receive
no explanation on the theory of creation.
The fact, as we have seen, that all past and present
organic beings ean be arranged within a few great classes,
in groups subordinate to groups, and with the extinct
groups often falling in between the recent groups, is
intelligible on the theory of natural selection with its
contingencies of extinction and divergence of character.
On these same principles we see how it is, that the
mutual affinities of the forms within each class are so
complex and circuitous. We see why certain characters
.
Car. XV.]. RECAPITULATION. 291
are far more serviceable than others for classification ;—
why adaptive characters, though of paramount import-
ance to the beings, are of hardly any importance in
classification ; why characters derived from rudimentary
parts, though of no service to the beings, are often of
high classificatory value; and why embryological char-
acters are often the most valuable of all. The real
affinities of all organic beings, in contradistinction to
their adaptive resemblances, are due to inheritance or
community of descent. The Natural System is a gene-
alogical arrangement, with the acquired grades of dif-
ference, marked by the terms, varieties, species, genera,
families, &c.; and we have to discover the lines of
descent by the most permanent characters: whatever
they may be and of however slight vital importance.
The similar framework of bones in the hand of a man,
wing of a bat, fin of the porpoise, and leg of the horse,
—the same number of vertebree forming the neck of the
giraffe and of the elephant,—and innumerable other such
facts, at once explain themselves on the theory of descent
with slow and slight successive modifications. The simi-
larity of pattern in the wing and in the leg of a bat,
though used for such different purpose,—in the jaws
and legs of a crab,—in the petals, stamens, and pistils
of a flower, is likewise, to a large extent, intelligible on
the view of the gradual modification of parts or organs,
which were aboriginally alike in an early progenitor in
each of these classes. On the principle of successive
variations not always supervening at an early age, and
being inherited at a corresponding not early period of
life, we clearly see why the embryos of mammals, birds,
reptiles, and fishes should be so closely similar, and so
unlike the adult forms. We may cease marvelling at
292 RECAPITULATION. _[CHar. XV.
the embryo of an air-breathing mammal or bird having
branchial slits and arteries running in loops, like those
of a fish which has to breathe the air dissolved in water
by the aid of well-developed branchie.
Disuse, aided sometimes by natural selection, will
often have reduced organs when rendered useless under
changed habits or conditions of life; and we can under-
stand on this view the meaning of rudimentary organs.
But disuse and selection will generally act on each
creature, when it has come to maturity and has to play
its full part in the struggle for existence, and will thus
have little power on an organ during early life; hence
the organ will not be reduced or rendered rudimentary
at this early age. The calf, for instance, has inherited
teeth, which never cut through the gums of the upper
jaw, from an early progenitor having well-developed
teeth; and we may believe, that the teeth in the mature
animal were formerly reduced by disuse, owing to the
tongue and palate, or lps, having become excellently
fitted through natural selection to browse without their
aid; whereas in the calf, the teeth have been left un-
affected, and on the principle of inheritance at corre-
sponding ages have been inherited from a remote period
to the present day. On the view of each organism with
all its separate parts having been specially created, how
utterly inexplicable is it that organs bearing the plain
stamp of inutility, such as the teeth in the embryonic
calf or the shrivelled wings under the soldered wing-
covers of many beetles, should so frequently occur.
Nature may be said to have taken pains to reveal her
scheme of modification, by means of rudimentary organs,
of embryological and homologous structures, but we are
too blind to understand her meaning.
Cuap. XV.] CONCLUSION. 293
I have now recapitulated the facts and considerations
which have thorouchly convinced me that species have
been modified, during a long course of descent. This
has been effected chiefly through the natural selection
of numerous successive, slight, favourable variations ;
aided in an important manner by the inherited effects
of the use and disuse of parts; and in an unimportant
manner, that is in relation to adaptive structures, whether
past or present, by the direct action of external condi-
tions, and by variations which seem to us in our ignor-
ance to arise spontaneously. It appears that I formerly
underrated the frequency and value of these latter forms
of variation, as leading to permanent modifications of
structure independently of natural selection. But as my
conclusions have lately been much misrepresented, and
it has been stated that I attribute the modification of
species exclusively to natural selection, I may be per-
mitted to remark that in the first edition of this work,
and subsequently, I placed ina most conspicuous posi-—
tion—namely, at the close of the Introduction—the
following words: “ I am convinced that natural selection
has been the main but not the exclusive means of modi-
fication.” This has been of no avail. Great is the power
of steady misrepresentation; but the history of science
shows that fortunately this power does not long endure.
It can hardly be supposed that a false theory would
explain, in so satisfactory a manner as does the theory
of natural selection, the several large classes of facts
above specified. It has recently been objected that this
is an unsafe method of arguing; but it is a method used
in judging of the common events of life, and has often
been used by the greatest natural philosophers. The
undulatory theory of light has thus been arrived at; and
294 | CONCLUSION. [Cuar. XV.
the belief in the revolution of the earth on its own axis
was until lately supported by hardly any direct evidence.
It is no valid objection that science as yet throws no
light on the far higher problem of the essence or origin
of life. Who can explain what is the essence of the
attraction of gravity ? No one now objects to following
out the results consequent on this unknown element
of attraction; notwithstanding that Leibnitz formerly
accused Newton of introducing “occult qualities and
miracles into philosophy.”
I see no good reason why the views given in this volume
should shock the religious feelings of any one. It is
satisfactory, as showing how transient such impressions
are, to remember that the greatest discovery ever made
by man, namely, the law of the attraction of gravity,
was also attacked by Leibnitz, “as subversive of natural,
and inferentially of revealed, religion.” A celebrated
author and divine has written to me that “he has gradu-
“ally learnt to see that it is just as noble a conception
“of the Deity to believe that He created a few original
“forms capable of self-development into other and need-
“ful forms, as to believe that He required a fresh act of
“creation to supply the voids caused by the action of
“ His laws.”
Why, it may be asked, until recently did nearly all
the most eminent living naturalists and geologists dis-
believe in the mutability of species. It cannot. be
asserted that organic beings in a state of nature are
subject to no variation; it cannot be proved that the
amount of variation in the course of long ages is a limited
quantity ; no clear distinction has been, or can be, drawn
between species and well-marked varieties. It cannot
be maintained that species when intercrossed are invarie
Cuap, XV.] CONCLUSION. 295
ably sterile, and varieties invariably fertile; or that
sterility is a special endowment and sign of creation.
The belief that species were immutable productions was
almost unavoidable as long as the history of the world
was thought to be of short duration; and now that we
have acquired some idea of the lapse of time, we are too
apt to assume, without proof, that the geological record
is so perfect that it would have afforded us plain evidence
of the mutation of species, if they had undergone
mutation.
But the chief cause of our natural unwillingness to
admit that one species has given birth to other and
distinct species, is that we are always slow in admitting
great changes of which we do not see the steps. The
difficulty is the same as that felt by so many geologists,
when Lyell first insisted that long lines of inland cliffs
had been formed, and great valleys excavated, by the
agencies which we see still at work. The mind cannot
possibly grasp the full meaning of the term of even a
million years; it cannot add up and perceive the full
effects of many slight variations, accumulated during an
almost infinite number of generations.
Although I am fully convinced of the truth of the
views given in this volume under the form of an abstract,
I by no means expect to convince experienced naturalists
whose minds are stocked with a multitude of facts all
viewed, during a long course of years, from a point of
view directly opposite to mine. It is so easy to hide
our ignorance under such expressions as the “plan of
creation,” “unity of design,’ &c., and to think that we
give an explanation when we only re-state a fact. Any
one whose disposition leads him to attach more weight
to unexplained difficulties than to the explanation of a
43
296 CONCLUSION. [Cuap. XV
certain number of facts will certainly reject the theory.
A few naturalists, endowed with much flexibility of
mind, and who have already begun to doubt the immu-
tability of species, may be influenced by this volume;
but I look with confidence to the future,—to young and
rising naturalists, who will be able to view both sides of
the question with impartiality. Whoever is led to believe
that species are mutable will do good service by con-
scientiously expressing his conviction ; for thus only can
the load of prejudice by which this subject is over-
whelmed be removed.
Several eminent naturalists have of late published
their belief that a multitude of reputed species in each
genus are not real species; but that other species are
real, that is, have been independently created. This
seems to me a strange conclusion to arrive at. They
admit that a multitude of forms, which till lately they
themselves thought were special creations, and which
are stil] thus looked at by the majority of naturalists,
and which consequently have all the external character
istic features of true species,—they admit that these
have been produced by variation, but they refuse to
extend the same view to other and slightly different
forms. Nevertheless they do not pretend that they can
define, or even conjecture, which are the created forms
of life, and which are those produced by secondary laws.
They admit variation as a vera causa in one case, they
arbitrarily reject it in another, without assigning any
distinction in the two cases. The day will come when
this will be given as a curious illustration of the blind-
ness of preconceived opinion. These authors seem no
more startled at a miraculous act of creation than at an
erdinary birth. But do they really believe that at innu-
Cuap. XV.] CONCLUSION. 297
merable periods in the earth’s history certain elemental
atoms have been commanded suddenly to flash into
living tissues? Do they believe that at each supposed
act of creation one individual or many were produced ?
Were ali the infinitely numerous kinds of animals and
plants created as eggs or seed, or as full grown? and in
the case of mammals, were they created bearing the
false marks of nourishment from the mother’s womb ?
Undoubtedly some of these same questions cannot be
answered by those who believe in the appearance or
creation of only a few forms of life, or of some one form
alone. It has been maintained by several authors that
it is as easy to believe in the creation of a million beings
as of one; but Maupertuis’ philosophical axiom “ of least
action” leads the mind more willingly to admit the
smaller number; and certainly we ought not to believe
that innumerable beings within each great class have
been created with plain, but deceptive, marks of descent
from a single parent.
As arecord of a former state of things, I have retained
in the foregoing paragraphs, and elsewhere, several
sentences which imply that naturalists believe in the
separate creation of each species ; and I have been much
censured for having thus expressed myself. But un-
doubtedly this was the general belief when the first -
edition of the present work appeared. I formerly spoke
to very many naturalists on the subject of evolution,
and never once met with any sympathetic agreement.
It is probable that some did then believe in evolution,
but they were either silent, or expressed themselves so
ambiguously that it was not easy to understand their
meaning. Now things are wholly changed, and almost
every naturalist admits the great principle of evolution.
298 CONCLUSION. [Cuar. XV.
There are, however, some who still think that species
have suddenly given birth, through quite unexplained
means, to new and totally different forms: but, as I
have attempted to show, weighty evidence can be op-
posed to the admission of great and abrupt modifications.
Under a scientific point of view, and as leading to further
investigation, but little advantage is gained by believing
that new forms are suddenly developed in an inexplic-
able manner from old and widely different forms, over
the old belief in the creation of species from the dust of
the earth.
It may be asked how far I extend the doctrine of the
modification of species. The question is difficult to
answer, because the more distinct the forms are which
we consider, by so much the arguments in favour of
community of descent become fewer in number and
less in force. But some arguments of the greatest
weight extend very far. All the members of whole
classes are connected together by a chain of affinities,
and all can be classed on the same principle, in
groups subordinate to groups. Fossil remains some-
times tend to fill up very wide intervals between
existing orders.
Organs in a rudimentary condition plainly show that
an early progenitor had the organ in a fully developed
condition; and this in some cases implies an enormous -
amount of modification in the descendants. Throughout
whole classes various structures are formed on the same
pattern, and at a very early age the embryos closely
resemble each other. Therefore I cannot doubt that the
theory of descent with modification embraces all the
members of the same great class or kingdom. I believe
that animals are descended from at most only four or
ah ae
Cuap. XV.J CONCLUSION. 299
five progenitors, and plants from an equal or lesser
number.
Analogy would lead me one step farther, namely, to
the belief that all animals and plants are descended from
some one prototype. But analogy may be a deceitful
guide. Nevertheless all living things have much in
-common, in their chemical composition, their cellular
structure, their laws of growth, and their liability to in-
jurious influences. We see this even in so trifling a
fact as that the same poison often similarly affects
plants and animals; or that the poison secreted by the
gall-fly produces monstrous growths on the wild rose or
oak-tree. With all organic beings, excepting perhaps
some of the very lowest, sexual reproduction seems to
be essentially similar. With all, as far as is at present
known, the germinal vesicle is the same; so that all
organisms start from a common origin. If we look even
to the two main divisions—namely, to the animal and
vegetable kingdoms—certain low forms are so far inter-
mediate in character that naturalists have disputed to
which kingdom they should be referred. As Professor
Asa Gray has remarked, “the spores and other repro-
“ductive bodies of many of the lower alge may claim
“to have first a characteristically animal, and then an
“unequivocally vegetable existence.” Therefore, on the
principle of natural selection with divergence of char-
acter, it does not seem incredible that, from some such
low and intermediate form, both animals and plants
may have been developed; and, if we admit this, we
must likewise admit that all the organic beings which
have ever lived on this earth may be descended from
some one primordial form. But this inference is chiefly
grounded on analogy, and it is immaterial whether or
— 300 CONCLUSION. [Cuap. XV.
not it be accepted. No doubt it is possible, as Mr. G.
H. Lewes has urged, that at the first commencement of
life many different forms were evolved; but if so, we
may conclude that only a very few have left modified
descendants. For, as I have recently remarked in regard
to the members of each great kingdom, such as the Ver-
tebrata, Articulata, &c., we have distinct evidence in
their embryological, homologous, and rudimentary struc-
tures, that within each kingdom all the. members are
descended from a single progenitor.
When the views advanced by me in this volume, and
by Mr. Wallace, or when analogous views on the origin
of species are generally admitted, we can dimly foresee
that there will be a considerable revolution in natural
history. Systematists will be able to pursue their labours
as at present; but they will not be incessantly haunted
by the shadowy doubt whether this or that form be a
true species. This, I feel sure and I speak after ex-
perience, will be no slight relief. The endless disputes
whether or not some fifty species of British brambles
are good species will cease. Systematists will have only
to decide (not that this will be easy) whether any form
be sufficiently constant and distinct from other forms,
to be capable of definition; and if definable, whether
the differences be sufficiently important to deserve a
specific name. This latter point will become a far more
essential consideration than it is at present; for differ-
ences, however slight, between any two forms, if not
blended by intermediate gradations, are looked at by
most naturalists as sufficient to raise both forms to the
rank of species.
Hereafter we shall be compelled to acknowledge that
the only distinction between species and well-marked
Cuap. XV] CONCLUSION. 301
varieties is, that the latter are known, or believed, to be
connected at the present day by intermediate gradations
whereas species were formerly thus connected. Hence,
without rejecting the consideration of the present exist-
ence of intermediate gradations between any two forms,
we shall be led to weigh more carefully and to value
higher the actual amount of difference between them.
It is quite possible that forms now generally acknow-
ledged to be merely varieties may hereafter be thought
worthy of specific names ; and in this case scientific and
common language will come into accordance. In short,
we shall have to treat species In the same manner as
those naturalists treat genera, who admit that genera
are merely artificial combinations made for convenience.
This may not be a cheering prospect; but we shall at
least be freed from the vain search for the undiscovered
and undiscoverable essence of the term species.
The other and more general departments of natural
history will rise greatly in interest. The terms used
by naturalists, of affinity, relationship, community of
type, paternity, morphology, adaptive characters, rudi-
mentary and aborted organs, é&c., will cease to be meta-
phorical, and will have a plain signification. When we
no longer look at an organic being as a savage looks at
a ship, as something wholly beyond his comprehension ;
when we regard every production of nature as one
which has had a long history; when we contemplate
every complex structure and instinct as the summing
up of many contrivances, each useful to the possessor,
in the same way as any great mechanical invention is
the summing up of the labour, the experience, the reason,
and even the blunders of numerous workmen; when we
thus view each organic being, how far more interesting
302 CONCLUSION. (Car. XV
—I speak from experience—does the study of natural
history become! .
A grand and almost untrodden field of inquiry will
be opened, on the causes and laws of variation, on cor-
relation, on the effects of use and disuse, on the direct
action of external conditions, and so forth. The study
of domestic productions will rise immensely in value.
A new variety raised by man will be a more important
and interesting subject for study than one more species
added to the infinitude of already recorded species.
Our classifications will come to be, as far as they can
be so made, genealogies; and will then truly give what
may be called the plan of creation. The rules for classi-
fying will no doubt become simpler when we have a defi-
nite object in view. We possess no pedigrees or armorial
bearings; and we have to discover and trace the many
diverging lines of descent in our natural genealogies, by
characters of any kind which have long been inherited.
Rudimentary organs will speak infallibly with respect
to the nature of long-lost structures. Species and
groups of species which are called aberrant, and which
may fancifully be called living fossils, will aid us in
forming a picture of the ancient forms of life. Embry-
ology will often reveal to us the structure, in some
degree obscured, of the prototypes of each great class.
When we can feel assured that all the individuals
of the same species, and all the closely allied species
of most genera, have within a not very remote period
descended from one parent, and have migrated from
some one birth-place; and when we better know the
many means of migration, then, by the light which
geology now throws, and will continue to throw, on
former changes’ of climate and of the level of the land,
Cuap. XV.) ~ CONCLUSION. 803
we shall surely be enabled to trace in an admirable
manner the former migrations of the inhabitants of the
whole world. Even at present, by comparing the
differences between the inhabitants of the sea on the
opposite sides of a continent, and the nature of the
various inhabitants on that continent in relation to their
apparent means of immigration, some lght can be thrown
on ancient geography.
The noble science of Geology loses glory from the
extreme imperfection of the record. The crust of the
earth with its imbedded remains must not be looked at
as a well-filled museum, but as a poor collection made at
hazard and at rare intervals. The accumulation of each
great fossiliferous formation will be recognised as having
depended on an unusual concurrence of favourable cir-
cumstances, and the blank intervals between the suc-
cessive stages as having been of vast duration. But we
shall be able to gauge with some security the duration
of these intervals by a comparison of the preceding
and succeeding organic forms. We must be cautious in
attempting to correlate as strictly contemporaneous two
formations, which do not include many identical species,
by the general succession of the forms of life. As
species are produced and exterminated by slowly acting
and still existing causes, and not by miraculous acts of
creation; and as the most important of all causes of
organic changeis one which is almost independent of
altered and perhaps suddenly altered physical conditions,
namely, the mutual relation of organism to organism,—
the improvement of one organism entailing the improve-
ment or the extermination of others; it follows, that the
amount of organic change in the fossils of consecutive
formations probably serves as a fair measure of the
304 CONCLUSION. (Caar. XV.
relative, though not actual lapse of time. A number
of species, however, keeping in a body might remain for
a long period unchanged, whilst within the same period
several of these species by migrating Into new countries
and coming into competition with foreign associates,
might become modified; so that we must not overrate
the accuracy of organic change as a measure of time.
In the future I see open fields for far more important
researches. Psychology will be securely based on the
foundation already well laid by Mr. Herbert Spencer,
that of the necessary acquirement of each mental power
and capacity by gradation. Much light will be thrown
on the origin of man and his history.
Authors of the highest eminence seem to be fully
satisfied with the view that each species has been
independently created. To my mind it accords better
with what we know of the laws impressed on matter by
the Creator, that the production and extinction of the
past and present inhabitants of the world should have
been due to secondary causes, like those determining the
birth and death of the individual. When I view all
beings not as special creations, but as the lineal descend-
ants of some few beings which lived long before the first
bed of the Cambrian system was deposited, they seem
to me to become ennobled. Judging from the past, we
may safely infer that not one living species will transmit
its unaltered likeness to a distant futurity. And of the
species now living very few will transmit progeny of
any kind to a far distant futurity; for the manner in
which all organic beings are grouped, shows that the
greater number of species in each genus, and all the
species in many genera, have left no descendants, but
have become utterly extinct. We can so far take a
Cuap. XV.] CONCLUSION. 305
prophetic glance into futurity as to foretell that it will
be the common and widely-spread species, belonging to
the larger and dominant groups within each class, which
will ultimately prevail and procreate new and dominant
species. As all the living forms of life are the lineal
descendants of those which lived long before tie Cam-
brian epoch, we may feel certain that the ordinary
succession by generation has never once been broken,
and that no cataclysm has desolated the whole world.
Hence we may look with some confidence to a secure
future of great length. And as natural selection works
solely by and for the good of each being, all corporeal and
mental endowments will tend to progress towards
perfection.
It is interesting to contemplate a tangled bank,
clothed with many plants of many kinds, with birds
singing on the bushes, with various insects flitting about,
and with worms crawling through the damp earth, and
to reflect that these elaborately constructed forms, so
different from each other, and dependent upon each
other in so complex a manner, have all been produced
by laws acting around us. These laws, taken in the
largest sense, being Growth with Reproduction; In-
heritance which is almost implied by reproduction;
Variability from the indirect and direct action of the
conditions of life, and from use and disuse: a Ratio of
Increase so high as to lead to a Struggle for Life, and as
a consequence to Natural Selection, entailing Divergence
of Character and the Extinction of less-improved forms.
Thus, from the war of- nature, from famine and death,
the most exalted object which we are capable of con-
ceiving, namely, the production of the higher animals,
directly follows. There is grandeur in this view of life,
3806 CONCLUSION. (Cuap. XV.
with its several powers, having been originally breathed
by the Creator into a few forms or into one; and that,
whilst tois planet has gone cycling on according to the
fixed law of gravity, from so simple a beginning endless
forms most beautiful and most wonderful have been, and
are being evolved.
GLOSSARY
OF THE
PRINCIPAL SCIENTIFIC TERMS USED IN THE
PRESENT VOLUME.*
== O0= =
ABERRANT.—Forms or groups of animals or plants which deviate
in important characters from their nearest allies, so as not to be
easily included in the same group with them, are said to be
aberrant.
ABERRATION (in Optics).—In the refraction of light by a convex lens
the rays passing through different parts of the lens are brought
to a focus at slightly different distances,—this is called spherical
aberration ; at the same time the coloured rays are separated by
the prismatic action of the lens and likewise brought to a focus
at different distances,—this is chromatic aberration.
ABNORMAL.—Contrary to the general rule.
AgorTED.—An organ is said to be aborted, when its development
has been arrested at a very early stage.
Azixism.—Albinos are animals in which the usual colouring
matters characteristic of the species have not been produced in
the skin and its appendages. Albinism is the state of being an
albino.
Aucz.—A class of plants including the ordinary sea-weeds and the
filamentous fresh-water weeds.
* T am indebted to the kindness of Mr. W. S. Dallas for this
Glossary, which has been given because several readers have com-
plained to me that some of the terms used were unintelligible to them.
Mr. Dallas has endeavoured to give the explanations of the terms in
as popular a form as possible,
44
308 GLOSSARY.
ALTERNATION OF GENERATIONS.—This term is applied to a peculiar
~ mode of reproduction which prevails among many of the lower
animals, in which the egg produces a living form quite different
from its parent, but from which the parent-form is reproduced
by a process of budding, or by the division of the substance
of the first product of the egg.
AmmonitTEs.—A group of fossil, spiral, chambered shells, ailied to
the existing pearly Nautilus, but having the partitions between
the chambers waved in complicated patterns at their junction
with the outer wall of the shell.
AwaLocy.—That resemblance of structures which depends upon
similarity of function, as in the wings of insects and birds.
Such structures are said to be analogous, and to be analogues of
each other.
ANIMALCULE.—A minute animal: generally applied to those visible
only by the microscope.
ANNELIDs.—A class of worms in which the surface of the body
exhibits a more or less distinct division into rings or segments,
generally provided with appendages for locomotion and with
gills. It includes the ordinary marine worms, the earthworms,
and the leeches.
ANTENN#.—Jointed organs appended to the head in Insects,
Crustacea and Centipedes, and not belonging to the mouth.
ANTHERS.—The summits of the stamens of flowers, in which the
pollen or fertilising dust is produced.
APLACENTALIA, APLACENTATA or Aplacental Mammals. See Mam-
malia.
ARCHETYPAL.—Of or belonging to the Archetype, or ideal primi-
tive form upon which all the beings of a group seem to be
organised.
ARTICULATA.—A great division of the Animal Kingdom character-
ised generally by having the surface of the body divided into
rings called segments, a greater or less number of which are
furnished with jointed legs (such as Insects, Crustaceans and
Centipedes).
ASYMMETRICAL.—Having the two sides unlike.
ATROPHIED.—Arrested in development at a very early stage.
Batanus.—The genus including the common Acorn-shells which
live in abundance on the rocks of the sea-coast.
Batracuians.—A class of animals allied to the Reptiles, but
GLOSSARY. 309
undergoing a peculiar metamorphosis, in which the young
animal is generally aquatic and breathes by gills. (Hxamples,
Frogs, Toads, and Newts.)
Bovtprers.—Large transported blocks of stone generally imbedded
in clays or gravels.
Bracuropopa.—A class of marine Mollusca, or rofborliel animals,
furnished with a bivalve shell, attached to submarine objects
by a stalk which passes through an aperture in one of the
valves, and furnished with fringed arms, by the action of which
food is carried to the mouth.
Brancuiz.—Gills or organs for respiration in water.
Brancurau.—Pertaining to gills or branchiz.
CamprIAN System.—A Series of very ancient Paleozoic rocks,.
between the Laurentian and the Silurian. Until recently these
were regarded as the oldest fossiliferous rocks.
Canipz.—The Dog-family, including the Dog, Wolf, Fox, Jackal,
&e.
Carapace.—tThe shell enveloping the anterior part of the body in
Crustaceans generally; applied also to the hard shelly pieces of
the Cirripedes.
CARBONIFEROUS.—This term is applied to the great formation which
includes, among other rocks, the coal-measures. It belongs to
the oldest, or Paleozoic, system of formations:
CaupaL.—Of or belonging to the tail.
CrpHALOPops.—The highest class of the Mollusca, or soft-bodied
animals, characterised by having the mouth surrounded by a
greater or less number of fleshy arms or tentacles, which, in
most living species, are furnished with sucking-cups. (Ha-
amples, Cuttle-fish, Nautilus.)
Creracea.—An order of Mammalia, including the Whales, Dolphins,
&c., having the form of the body fish-like, the skin naked, and
only the fore-limbs developed.
CuEeLonta.—An order of Reptiles including the Turtles, Tortoises, &c.
CirripepEs.—An order of Crustaceans including the Barnacles and
Acorn-shells. Their young resemble those of many other
Crustaceans inform; but when mature they are always attached
to other objects, either directly or by means of a stalk, and their
bodies are enclosed by a calcareous shell composed of several
pieces, two of which can open to give issue to a bunch of curled,
juinted tentacles, which represent the limbs.
310 i GLOSSARY.
Coccus.—The genus of Insects including the Cochineal. In these
the male is a minute, winged fly, and the female generally a
motionless, berry-like mass.
Cocoon.—A case usually of silky material, in which insects are
frequently enveloped during the second or resting-stage (pupa)
of their existence. The term “cocoon-stage” is here used as
equivalent to “‘ pupa-stage.”
CcaLosPERMoUsS.—A term applied to those fruits of the Umbelliferze
which have the seed hollowed on the inner face.
CoLEopTERA.—Beetles, an order of Insects, having a biting mouth
and the first pair of wings more or less horny, forming sheaths
for the second pair, and usually meeting in a straight line down
the middle of the back.
CoLumn.—A peculiar organ in the flowers of Orchids, in which
the stamens, style and stigma (or the reproductive parts) are
united.
Compositz or Compositous Prants.—Plants in which the inflores-
cence consists of numerous small flowers (florets) brought
together into a dense head, the base of which is enclosed by a
common envelope. (Laamples, the Daisy, Dandelion, &c.)
ConFERVZ.—The filamentous weeds of fresh water.
CoNGLOMERATE.—A rock made up of fragments of rock or pebbles,
cemented together by some other material.
CorotLta.—The second envelope of a flower usually composed of
coloured, leaf-like organs (petals), which may be united by their
edges either in tbe basal part or throughout.
CoRRELATION.—The normal coincidence of one phenomenon,
character, &c., with another.
Coryms.—A bunch of flowers in which those springing from the
lower part of the flower stalk are supported on long stalks so as
to be nearly on a level with the upper ones.
CoryLEepons.—The first or seed-leaves of plants.
CrusTAcEans.—A class of articulated animals, having the skin of
the body generally more or less hardened by the depésition of
calcareous matter, breathing by means of gills. (Hxamples,
Crab, Lobster, Shrimp, &c.)
CurcuLio.—The old generic term for the Beetles known as Weevils,
characterised by their four-jointed feet, and by the head being
produced into a sort of beak, upon the sides of which the
antenne are inserted.
CuranrEous.—Of or belonging to the skin.
GLOSSARY. 311
DrGRADATION.—The wearing down of land by the action of the sea
or of meteoric agencies.
DEnuDATION.—The wearing away of the surface of the land by water.
Drvontan System or formation.—A series of Palxozoic rocks,
including the Old Red Sandstone.
DicortyLepons or DtcoTyLeponous Puants.—A class of plants
characterised by having two seed-leaves, by the formation of
new wood between the bark and the old wood (exogenous
growth) and by the reticulation of the veins of the leaves. The
parts of the flowers are generally in multiples of five.
DIFFERENTIATION.—The separation or discrimination of parts or
organs which in simpler forms of life are more or less united.
DrimorpPHic.—Having two distinct forms.—Dimorphism is the con-
dition of the appearance of the same species under two dissimilar
forms.
Diacious.—Having the organs of the sexes upon distinct indi-
viduals.
Diorirs.—A peculiar form of Greenstone.
Dorsat.—Of or belonging to the back.
Epentata.—A peculiar order of Quadrupeds, characterised by the
absence of at least the middle incisor (front) teeth in both jaws.
(Examples, the Sloths and Armadillos.)
E.ytra.—The hardened fore-wings of Beetles, serving as sheaths
for the membranous hind-wings, which constitute the true
organs of flight.
Empryo.—The young animal undergoing development within the
egg or womb.
EmpryoLtocy.—The study of the development of the embryo.
Enpemic.—Peculiar to a given locality.
Entomostraca.—A division of the class Crustacea, having all the
segments of the body usually distinct, gills attached to the feet
or organs of the mouth, and the feet fringed with fine hairs.
They are generally of small size.
Eocene.—The earliest of the three divisions of the Tertiary epoch
of geologists. Rocks of this age contain a small proportion of
shells identical with species now living.
Epruemerous Insrcts.—Insects allied to the May-fly.
Fauna.—tThe totality of the animals naturally inhabiting a certain
country or region, or which have lived during a given geological
period.
312 GLOSSARY.
Fe.ip#£.—The Cat-family. —
FrraL.—Having become wild from a state of cultivation or domes-
tication.
Frora.—tThe totality of the plants growing naturally in a country,
or during a given geological period.
Fiorets.—Flowers imperfectly developed in some respects, and
collected into a dense spike or head, as in the Grasses, the
Dandelion, &c.
Fartaut.—Of or belonging to the fetus, or embryo in course of
development.
FoRAMINIFERA.—A class of animals of very low organisation, and
generally of small size, having a jelly-like body, from the surface
of which delicate filaments can be given off and retracted for the
prehension of external objects, and having a calcareous or sandy
shell, usually divided into chambers, and perforated with small -
apertures. :
FossiILIFERous.—Containing fossils.
Fossor1aL.—Having a faculty of digging. - The Fossorial Hymen-
optera are a group of Wasp-like Insects, which burrow in sandy
soil to make nests for their young.
FRENUM (pl. Frena).—A small band or fold of skin.
Funai (sing. Funevus).—A class of cellular plants, of which Mush-
rooms, Toadstools, and Moulds, are familiar examples.
Furcuta.—The forked bone formed by the union of the collar-bones
in many birds, such as the common Fowl.
GALLINAcEous Brirps.—<An order of Birds of which the common
Fowl, Turkey, and Pheasant, are well-known examples.
GaL Us.— lhe genus of birds wh'ch includes the common Fowl.
GaNGLioN.—A swelling or Knot from which nerves are given off as
from a centre.
Gano Fisnes.—Fishes covered with peculiar enamelled bony
scales. Most of them are extinct.
GERMINAL VESICLE.—A minute vesicle in the eggs of animals, from
which the development of the embryo proceeds.
GuacraL Perwop.—A period of great cold and of enormous extension
of ice upon the surface of the earth. It is believed that glacial
periods have occurred repeatedly during the geological history of
the earth, but the term is generally applied to the close of the
Tertiary e;och, when nearly the whole of Europe was subjected
to an arctic climate.
Scag
GLOSSARY. 313
Guanp.—An organ which secretes or separates some peculiar
product from the blood or sap of animals or plants.
Guorris.—The opening of the windpipe into the cesophagus or gullet.
Gyeiss.—A rock approaching granite in composition, but more or
less laminated, and really produced by the alteration of a
sedimentary deposit after its consolidation.
GRALLATORES.— The so-called Wading-birds (Storks, Cranes, Snipes,
&c.), which are generally furnished with long legs, bare of
feathers above the heel, and have no membranes between the
toes.
GraniTE.—A rock consisting essentially of crystals of felspar and
mica in a mass of quartz.
Hasitat.—The locality in which a plant or animal naturally lives.
HemipTera.—An order or sub-order of Insects, characterised by the
possession of a jointed beak or rostrum, and by having the fore-
wings horny in the basal portion and membranous at the
extremity, where they cross each other. This group includes
the various species of Bugs.
HERMAPHRODITE.— Possessing the organs of both sexes.
Homotoey.—That relation between parts which results from their
development from corresponding embryonic parts, either in
different animals, as in the case of the arm of man, the fore-leg
of a quadruped, and the wing of a bird; or in the same in-
dividual, as in the case of the fore and hind legs in quadrupeds,
and the segments or rings and their appendages of which the
body of a worm, a centipede, &c., is composed. The latter is
called serial homology. 'The parts which stand in such a relation
to each other are said to be homologous, and one such part or
organ is called the homologue of the other. In different plants
the parts of the flower are homologous, and in general these
parts are regarded as homologous with leaves.
Homorrera.—An order or sub-order of Insects having (like the
Hemiptera) a jointed beak, but in which the fore-wings are
either wholly membranous or wholly leathery. The Cicada,
Frog-hoppers, and Aphides, are well-known examples,
Hysrip.—the offspring of the union of two distinct species.
Hymenoptera.—An order of Insects possessing biting jaws and
usually four membranous wings in which there are a few veins.
Bees and Wasps are familiar examples of this group.
HyprrTROPHIED.—Excessively developed.
314 GLOSSARY.
IcHNEUMONID£.—A family of Hymenopterous insects, the members
of which lay their eggs in the bodies or eggs of other insects.
Imaco.—The periect (generally winged) reproductive state of an
insect.
Ixpicgens. — The aboriginal animal or vegetable inhabitants of a
country or region.
INFLORESCENCE.—The mode of arrangement of the flowers of plants.
Inruson14.—A class of microscopic Animalcules, so called from
their having originally been observed in infusions of vegetable
matters. They consist of a gelatinous material enclosed in a
delicate membrane, the whole or part of which is furnished with
short vibrating hairs (called cilia), by means of which the
animalcules swim through the water or convey the minute
particles of their food to the orifice of the mouth.
Insectivorous.—Feeding on Insects.
INVERTEBRATA, Or INVERTEBRATE ANIMALS.—Those animals which
do not possess a backbone or spinal column.
Lacunz.—Spaces left among the tissues in some of the lower
animals, and serving in place of vessels for the circulation of the
fluids of the body.
LAMELLATED.—Furnished with lamelle or little plates.
Larva (pl. Larvz).—The first condition of an insect at its issuing
from the egg, when it is usually in the form of a grub, caterpillar,
or maggot.
LaryNx.—The upper part of the windpipe opening into the gullet.
LAURENTIAN.—A group of greatly altered and very ancient rocks,
which is greatly developed along the course of the St. Laurence,
whence the name. It is in these that the earliest known traces
of organic bodies have been found.
LEGuMINos=.—An order of plants represented by the common Peas
and Beans, having an irregular flower in which one petal stands
up like a wing, and the stamens and pistil are enclosed in a
sheath formed by two other petals. The fruit is a pod (or
legume).
Lemuripz.—A group of four-handed animals, distinct from the
Monkeys and approaching the Insectivorous Quadrupeds in some
of their characters and habits. Its members have the nostrils
curved or twisted, and a claw instead of a nail upon the first
finger of the hind hands.
LepipopTers.—An order of Insects, characterised by the possession
GLOSSARY. old
of a spiral proboscis, and of four large more or less scaly wings.
It includes the well-known Butterflies and Moths.
Lirrorau.—Inhabiting the seashore.
Lorss.—A marly deposit of recent (Post-Tertiary) date which
occupies a great part of the valley of the Rhine.
Maxacostraca.—The higher division of the Crustacea, including
the ordinary Crabs, Lobsters, Shrimps, &c., together with the
Woodlice and Sand-hoppers.
Mammatia.—tThe highest class of animals, including the ordinary
hairy quadrupeds, the Whales, and Man, and characterised by
the production of living young which are nourished after birth
by milk from the teats WMammez, Mammary glands) of the
mother. A striking difference in embryonic development has
led to the division of this class into two great groups; in one of
these, when the embryo has attained a certain stage, a vascular
connection, called the placenta, is formed between the embryo
and the mother; in the other this is wanting, and the young are
produced in a very incomplete state. The former, including the
greater part of the class, are called Placental mammals; the
latter, or Aplacental mammals, include the Marsupials and
Monotremes (Ornithorhynchus).
Mammuirerous. Having mammze or teats (see Mammatta).
Manpis.es, in Insects.—The first or uppermost pair of jaws, which
are generally solid, horny, biting organs. In Birds the term is
applied to both jaws with their horny coverings. In Quadrupeds
the mandible is properly the lower jaw.
Marsupiats.—An order of Mammalia in which the young are born
in a very incomplete state of development, and carried by the
mother, while sucking, in a ventral pouch (marsupium), such as
the Kangaroos, Opossums, &c. (see MAMMALIA),
MaxiLua, in Insects.—The second or lower pair of jaws, which are
composed of several joints and furnished with peculiar jointed
appendages called palpi, or feelers.
Mexanism.—The opposite of albinism; an undue development of
colouring material in the skin and its appendages.
Metamorpuic Rocxs.—Sedimentary rocks which have undergone
alieration, generally by the action of heat, subsequently to their
deposition and consolidation.
Mo.uusca.—One of the great divisions of the Animal Kingdom,
including those animals which have a soft body, usually
316 GLOSSARY.
furnished with a shell, and in which the nervous ganglia, or
centres, present no definite general arrangement. They are
generally known under the denomination of “ shell-fish ;” the
cuttle-fish, and the common snails, whelks, oysters, mussels, and
cockles, may serve as examples of them.
MonocoryLepons, or MonocoryLeponous PLants.— Plants in
which the seed sends up only a single seed-leaf (or cotyledon) ;
characterised by the absence of consecutive layers of wood in
the stem (endogenous growth), by the veins of the leaves being
generally straight, and by the parts of the flowers being generally
in multiples of three. (Hxamples, Grasses, Lilies, Orchids,
Palms, &c.)
Moratnes.—The accumulations of fragments of rock brought down
by glaciers.
Morrnotocy.—The law of form or structure independent of
function.
Mysis-stace.—A stage in the development of certain Crustaceans
(Prawns), in which they closely resemble the adults of a genus
(Mysis) belonging to a slightly lower group.
Nascent.—Commencing development.
Natatory.—Adap‘ed for the purpose of swimming.
Navp.ius-ForM.—The earliest stage in the development of many
Crustacea, especially belonging to the lower groups. In this
stage the animal has a short body, with indistinct indications of
a division into segments, and three pairs of tringed limbs. This
form of the common fresh-water Cyclops was described as a
distinct genus under the name of Naupiius.
NervurATION.—The arrangement of the veins or nervures in the
wings of Insects.
Nevurers.—Imperfectly developed females of certain social insects
(such as Ants and Bees), which perform all the labours of the
community. Hence they are also called workers.
Nictiratincg MemBRANE.—A semi-transparent membrane, which
can be drawn across the eye in Birds and Reptiles, either to
moderate the effects of a strong light or to sweep particles of
dust, &c., from the surface of the eye.
OcELLI.—The simple eyes or stemmata of Insects, usually situated
on the crown of the head between the great compound eyes.
@isopHacus.—The gullet.
GLOSSARY. 317
Oo1itic.—A great series of secondary rocks, so called. from the
texture of some of its members, which appear to be made up of
a mass of small egg-like calcareous bodies.
OpeRcuLUM.—A calcareous plate employed by many Mollusca to
close the aperture of their shell. The opercular valves of
Cirripedes are those which close the aperture of the shell.
Orpit.—The bony cavity for the reception of the eye.
OrGanism.—An organised being, whether plant or animal.
OrTHOSPERMOUS.—A term applied to those fruits of the Umbelliferze
which have the seed straight.
OscuLant.—Forms or groups apparently intermediate between and
connecting other groups are said to be osculant.
Ova.— Eggs.
Ovarium or Ovary (in plants).— The lower part of the pistil or
female organ of the flower, containing the ovules or incipient
seeds; by growth after the other organs of the flower have
fallen, it usually becomes converted into the fruit.
OvicrRous.—EKge¢g-bearing.
Ovu zs (of plants).—The seeds in the earliest condition.
PacHYDERMS.—A group of Mammalia, so called from their thick
skins, and including the Elephant, Rhinoceros, Hippopotamus,
&e.
Patmozorc.—The oldest system of fossiliferous rocks.
Parpr.—Jointed appendages to some of the organs of the mouth in
Insects and Crustacea.
PapILIONAcEm.—An order of Plants (see Lecuminos®).—The
flowers of these plants are called papilionaceous, or butterfly-
like, from the fancied resemblance of the expanded superior
petals to the wings of a butterfly.
ParasiteE.—An animal or plant living upon or in, and at the
expense of, another organism.
PARTHENOGENESIS.—The production of living organisms from
unimpregnated eggs or seeds.
PEDUNCULATED.—Supported upon a stem or stalk. The peduncu-
lated oak has its acorns borne upon a, footstool.
Peoria or PELoRIsM.—The appearance of regularity of structure in
the flowers of plants which normally bear irregular flowers.
Petyis.—The bony arch to which the hind limbs of vertebrate
animals are articulated.
Pztats.—The leaves of the corolla, or second circle of organs in a
ae
318 GLOSSARY.
flower. They are usually of delicate texture and brightly
coloured.
PHYLLODINEOUS.—Having flattened, leaf-like twigs or leafstalks
instead of true leaves.
PiemMent.—The colouring material produced generally in the super-
ficial partsof animals, The cells secreting it are called pigment-
cells.
PInnaTE.—Bearing leaflets on each side of a central stalk.
Pistiis.—The female organs of a flower, which occupy a position
in the centre of the other floral organs. The pistil is generally
divisible into the ovary or germen, the style and the
stigma.
PLACENTALIA, PLACENTATA, or Placental Mammals.—See Mam-
MALIA.
PLANTIGRADES.—Quadrupeds which walk upon the whole sole of
the foot, like the Bears.
Piastic.—Readily capable of change. .
PLEISTOCENE Prertop.—The latest portion of the Tertiary epoch.
PLUMULE (in plants).—The minute bud between the seed-leaves of
newly-germinated plants.
Piutonic Rocxs.—Rocks supposed to have been produced by
igneous action in the depths of the earth.
PoLLtEN.—The male element in flowering plants; usually a fine dust
produced by the anthers, which, by contact with the stigma
effects the fecundation of the seeds. This impregnation is
brought about by means of tubes (pollen-tubes) which issue
from the pollen-grains adhering to the stigma, and penetrate
through the tissues until they reach the ovary.
PoLtyanprovus (flowers).—F lowers having many stamens,
Potycamous PLants.—Plants in which some flowers are unisexual
and others hermaphrodite. The unisexual (male and female)
flowers, may be on the same or on different plants.
PoLtyMorPHIc.—Presenting many forms.
Potyzoary.—The common structure formed by the cells of the
Polyzoa, such as the well-known Sea-mats.
PREHENSILE.—Capable of grasping.
PREPOTENT.—Having a superiority of power.
Priwaries.—The feathers forming the tip of the wing of a bird, and
inserted upon that part which represents the hand of man.
Processes.—Projecting portions of bones, usually for the attach
ment of muscles, ligaments, &c.
GLOSSARY. 319
Propotis.—A resinous material collected by the Hive-Bees from the
opening buds of various trees.
PROTEAN.—Exceedingly variable.
Protozoa.—The lowest great division of the Animal Kingdom.
These animals are composed of a gelatinous material, and show
scarcely any trace of distinct organs. The Infusoria, Foramini-
fera, and Sponges, with some other forms, belong to this
division.
Pura (pl. Pupm).—The second stage in the development of an
Insect, from which it emerges in the perfect (winged) reproduc-
tive form. In most insects the pupal stage is passed in perfect
repose. The chrysalis is the pupal state of butterflies.
RapDIcLE.—The minute root of an embryo plant.
Ramus.—One half of the lower jaw in the Mammalia. The portion
which rises to articulate with the skull is called the ascending
ramus.
Rance.—The extent of country over which a plant or animal is
naturally spread. ange in time expresses the distribution of a
species or group through the fossiliferous beds of the earth’s
crust.
Retrna.—The delicate inner coat of the eye, formed by nervous
filaments spreading from the optic nerve, and serving for the
perception of the impressions produced by light.
RETROGRESSION.—Backward development. When an animal, as it
approaches maturity, becomes less perfectly organised than
might be expected from its early stages and known relation-
ships, it is said to undergo a retrogrude development or meta-
mor phosis.
Ruizorops.—A class of lowly organised animals (Protozoa), having a
gelatinous body, the surface of which can be protruded in the
form of root-like processes or filaments, which serve for loco-
motion and the prehension of food. The most important order
is that of the Foraminifera.
RopEents.—The gnawing Mammalia, such as the Rats, Rabbits, and
Squirrels. They are especially characterised by the possession
of a single pair of chisel-like cutting teeth in each jaw, between
which and the grinding teeth there is a great gap.
Rusus.—The Bramble Genus.
RUDIMENTARY.—Very imperfectly developed.
Ruminants.—The group of Quadrupeds which ruminate or chew
45
*
320 ve GLOSSARY.
the cud, eae as oxen, sheep, and deer. They have divided
hoofs, and are destitute of front teeth in the upper jaw.
Sacrat.—Belonging to the sacrum, or the bone composed usually
of two or more united vertebree to which the sides of the pelvis
in vertebrate animals are attached.
SarcopE.—The gelatinous material of which the bodies of the
lowest animals (Protozoa) are composed.
ScuTELL#.—The horny plates with which the feet of birds are
generally more or less covered, especially in front.
SEDIMENTARY FoRMATIONS.—Rocks deposited as sediments from
water.
SreGMENTs.—The transverse rings of which the body of an articulate
animal or Annelid is composed. .
Sepats.—The leaves or segments of the calyx, or outermost envelope
of an ordinary flower. They are usually screen, but sometimes
brightly coloured.
SERRATURES.—Teeth like those of a saw.
SEssILE.—Not supported on a stem or footstalk.
SILURIAN SysteM.—A very ancient system of fossiliferous rocks
belonging to the earlier part of the Palzozoic series.
SPECIALISATION.—The setting apart of a particular organ for the
performance of a particular function.
Sprnat Cuoorp.—The central portion of the nervous system in the
Vertebrata, which descends from the brain through the arches
of the vertebra, and gives off nearly all the nerves to the various
organs of the body.
Stamens.—The male organs of flowering plants, standing in a circle
within the petals. They usually consist of a filament and an
anther, the anther being the essential part in which the pollen,
or fecundating dust, is formed.
SterNuM.—The breast-bone.
Stieéma.—The apical portion of the pistil in flowering plants.
SripuLes.—Small leafy organs placed at the base of the footstalks
of the leaves in many plants.
StyLe.—The middle portion of the perfect pistil, which rises like a
column from the ovary and supports the stigma at its summit.
SuBcuTANEOUS.—Situated beneath the skin.
Sucror1at.—Adapted for sucking.
Suroures (in the skull).—The lines of junction of the bones of which
the skull is composed.
GLOSSARY. 321
Tarsus (pl. Tarsi).—The jointed feet of articulate animals, such as
Insects.
TELEOSTEAN FisHrs.—Fishes of the kind familiar to us in the
present day, having the skeleton usually comnletely ossified and
the scales horny.
TENTACULA or TENTACLES.—Delicate fleshy organs of prehension or
touch possessed by many of the lower animals.
Tertiary.—The latest geological epoch, immediately preceding the
establishment of the present order of things.
TracHEA.—The windpipe or passage for the admission of air to the
lungs.
TripactyLe.—Three-fingered, or composed of three movable parts
attached to a common base.
TRILOBITES.—A_ peculiar group of extinct Crustaceans, somewhat
resembling the Woodlice in external form, and, like some of
them, capable of rolling themselves up into a ball. Their
remains are found only in the Paleozoic rocks, and most abun-
dantly in those of Silurian age.
TRiImoRPHICc.—Presenting three distinct forms.
UMBELLIFERZ.—An order of plants in which the flowers, which
contain five stamens and a pistil with two styles, are supported
upon footstalks which spring from the top of the flower stem
and spread out like the wires of an umbrella, so as to bring all
the flowers in the same head (wmbel) nearly to the same level.
(Examples, Parsley and Carrot.)
Uneunata.—Hoofed quadrupeds.
UnIcELLULAR.—Consisting of a single cell,
VascuLar.—Containing blood-vessels,
VermMirorM.—Like a worm.
VERTEBRATA: OF VERTEBRATE ANIMALS.—The highest division of
the animal kingdom, so called from the presence in most
cases of a backbone composed of numerous joints or vertebra,
which constitutes the centre of the skeleton and at the same
time supports and protects the central parts of the nervous
system. :
Wuorts.—The circles or spiral lines in which the parts of plants are
arranged upon the axis of growth.
Worxers.—See Neuters.
322 GLOSSARY.
ZoEA-STAGE.—The earliest stage in the development of many of
the higher Crustacea, so called from the name of Zoéa applied to
these young animals when they were supposed to constitute a
peculiar genus.
Zoorps.—In many of the lower animals (such as the Corals, Meduse,
&c.) reproduction takes place in two ways, namely, by means of
eggs and by a process of budding with or without separation
from the parent of the product of the latter, which is often very
different from that of the egg. The individuality of the species
is represented by the whole of the form produced between two
sexual reproductions; and these forms, which are apparently
individual animals, have been called zooids,
INDEX.
ABERRANT.
AZORES.
A.
ABERRANT groups, li. 227.
Abyssinia, plants of, ii. 167.
Acciimatisation, i. 173.
Adoxa, i. 270
Affinities of extinct species, ii. 106.
of organic beings, i. 225.
Agassiz, on Amblyopsis, i. 173.
, on groups of species suddenly
appearing, i. 88.
, on prophetic forms, ii. 107.
, on embryological succession,
li. 120.
, on the Glacial period, ii. 151.
, on embryological characters,
ii. 210.
, on the latest tertiary forms,
Vt: 71.
, on parallelism of embryologi-
cal development and geological
succession, li. 254.
, Alex., on pedicellarie, i. 297.
Ales of New Zealand, ii. 164.
Alligators, males, fighting, i. 108.
Alternate generations, 11. 239.
Amblyopsis, blind fish, i. 173.
America, North, productions allied
to those of Europe, ii. 156.
; , boulders and glaciers of,
li. 159.
, South, no modern formations
on west coast, il. 61.
Ammonites, sudden extinction of,
a. OD.
Anagallis, sterility of, ii. 4.
Analogy of variations, i. 197.
Ancylus, ii. 174.
Andaman Islands inhabited by a
toad, ii. 182.
Animals, not domesticated from
being variable, i. 19.
, domestic, descended from seve-
ral stocks, i, 21.
—, , acclimatisation of, L
175.
Animals of Australia, i. 140.
with thicker fur in cold eli-
mates, 1. 166.
, blind, in caves, i. 172.
extinct, of Australia, ii. 121.
Aromma, i. 361.
Antarctic islands, ancient flora of,
li. 190.
Antechinus, ti. 219.
Ants attending aphides, i. 323.
, Slave-making instinct, i.
336.
, heuters, structure of, i. 359.
Apes, not having acquired intel-
lectual powers, 1. 282.
Aphides, attended by ants, i. 323
Aphis, development of, ii. 245,
Apteryx, 1. 218.
Arab horses, i. 40.
Aralo-Caspian Sea, ii. 121.
Archeopteryx, ii. 80.
Archiac, M. de, on the succession of
species, ii. 103.
Artichoke, Jerusalem, i. 176.
Ascension, plants of, ii. 178.
Asclepias, pollen of, i. 236.
Asparagus, il. 143.
Aspicarpa, ii. 209.
Asses, striped, 1. 198.
, improved by selection, i. 48,
Ateuchus, i. 168.
Aucapitaine, on land-shells, ii.
187
Audubon, on habits of frigate-bird,
1. 222.
, on variation in birds’ nests, i.
4
, on heron eating seeds, ii. 176.
Australia, animals of, 1. 140.
, dogs of, 1. 328.
—,, extinct animals of, ii. 121.
——, European plants in, ii. 163.
» glaciers of, ii. 159.
Azara, on flies destroying cattle, iL
89
Azores, flora of, ii. 149.
324 BABINGTON. INDEX. BUZAREINGUES.
B. Birds acquiring fear, i. 325.
Babington, Mr., on British plants,
1. 58.
Baer, Von, standard of Highness, i.
151.
, comparison of bee and fish,
ii. 118.
, embryonic similarity of the
Vertebrata, ii. 241. ,
Baker, Sir S., on the giraffe, i. 278.
Balancement of growth, i. 182.
Baleen, i. 285.
Barberry, flowers of, i. 121.
Barrande, M., on Silurian colonies,
li. 90.
——, on the succession of species,
ii. 103.
, on parallelism of palzozoic
formations, ii. 106.
, on affinities of ancient species,
li. 108.
Barriers, importance of, ii. 130.
Bates, Mr., on mimetic butterflies,
li. 222, 223, 224.
Batrachians on islands, ii. 182.
Bats, how structure acquired, L
218.
, distribution of, ii. 184.
Bear, catching water-insects, i. 220.
Beauty, how acquired, i. 249; ii.
283.
Bee, sting of, i. 255.
, queen, killing rivals, i. 256.
—, Australian, extermination of,
a, OS:
Bees fertilising flowers, i. 90.
, hive, not sucking the red
clover, te Ri 8
, Ligurian, i. 117.
, hive, cell-making instinct, i
342.
, variation in habits, i. 324.
» parasitic, 1. 336.
, humble, cells of, i. 343.
Beetles, wingless, in Madeira, i. 169.
with deficient tarsi, i. 168.
Bentham, Mr., on British plants,
1. 58.
, on classification, ii. 211.
Berkeley, Mr., on seeds in salt
water, li. 142.
Bermuda, birds of, ii. 180,
, beauty of, i. 252.
annually cross the Atlantic,
ii. 150. ;
, colour of, on continents, i.
165.
, footsteps, and remains of, in
secondary rocks, ii. 79.
, fossil, in caves of Brazil, ii.
121.
, of Madeira, Bermuda, and
Galapagos, ii. 179, 180.
, song of males, i. 109.
transporting seeds, ii. 148,
——, waders, ii. 175.
, Wingless, i. 167, 218.
Bizcacha, ii. 133.
, affinities of, ii. 227.
g, in fish, i
Bladder for swimming
230.
Blindness of cave animals, i. 170.
Blyth, Mr., on distinctness of Indian -
cattle, i. 21.
, on striped hemionus, i. 199.
, on crossed geese, ii. 10.
Borrow, Mr.,on the Spanish pointer,
i. 40.
Bory St. Vincent, on Batrachians,
ii. 182.
Bosquet, M., on fossil Chthamalus,
ii. 80.
Boulders, erratic, on the Azores, ii,
149.
Brauchia, i. 231, 232.
of crustaceans, i. 238.
Braun, Prof., on the seeds of Fuma-
riacee, 1. 271.
Brent,Mr., on house-tumblers, i. 326.
Britain, mammals of, ii. 185.
Broca, Prof., on Natural Selection,
1. 265.
Bronu, Prof.,on duration of specific
forms, ii. 66.
, various objections by, i. 265.
Brown, Robert, on classification, ii.
207.
, Séquard, on inherited muti-
lations, i. 168.
Busk, Mr., on the Polyzoa, i. 301.
Butterflies, mimetic, ii. 222, 223,
224.
Buzareingues, on sterility of varie-
CABBAGE.
INDEX.
325
COPE.
C.
Cabbage, varieties of, crossed, iL
Calceolaria, ii. 7, 8.
Canary-birds, sterility of hybrids,
Thee
Cape de Verde islands, productions
of, ii. 189.
, plants of, on mountains, ii.
162.
Cape of Good Hope, plants of, i.
158; ii. 178.
Carpenter, Dr., on foraminifera, ii
ie
Carthamus, i. 271.
Catasetum, i. 243; ii. 216.
Cats, with blue eyes, deaf, i. 13.
, Variation in habits of, 1. 325.
curling tail when going to
spring, 1. 204.
Cattle destroying fir-trees, i. 88.
destroyed by flies in Paraguay,
i. 89.
—— breeds of, locally extinct, i.
134
, fertility of Indian and Euro-
pe.n breeds, ii. 10.
, Indian, i. 21; i. 10.
Cave. inhabitants of, blind, i. 170.
Cecidomyia, li. 259.
Celts, proving antiquity of man,
i. 21.
Centres of Creation, ii. 135.
Cephalopode, structures of eyes,
i. 236.
, development of, ii. 244.
Cercopithecus, tail of, 1. 294.
Ceroxyius laceratus, i. 284.
Cervulus, ii. 9.
Cetacea, tceth and hair, i. 179.
, development of the whale-
bone. i. 285.
Cetaceans, 1. 285.
Ceylon. plants of, ii. 164.
Chalk formation, ii. 100.
Characters, divergence of, i. 134.
, sexual, variable, i. 185, 191.
, adaptive or analogical, ii. 218.
Charlock, i. 94.
Checks to increase, i. 83.
, mutual, i. 86.
Chelz of Cr ustaceans, i. 300.
————
Chickens, instinctive tameness of,
Ta320-
Chironomus, its asexual reproduc-
tion, ii. 240.
Chthamaline, ii. 59.
Chthamalus, eretacean species of,
die ole
Circumstances favourable to selec-
tion of domestic products, i. 46.
tonatural selection, i. 124.
Cirripedes capable of crossing, i. 124.
, carapace aborted, i. 184.
—,, their ovigerous frena, i Ti 232.
, fossil, ii. ”80.
* larvae of, ii. 243.
Claparede, Prof., on the haiolee:
pers of the Ac arid, j 1s 230:
Clarke, Rev. W. B., on old glaciers
in Australia, ii. 159.
Classification, ii. 202.
Clift, Mr., on the succession of
types, 11. 121.
Climate, effects of, in checking in-
crease of beings, i. 84.
, adaptation of, to organisms,
1. 174.
Climbing plants, i. 230.
——, development of, i. 305.
Clover visited by bees, i. 117.
Cobites, intestine of, i. 229.
Cockroach, i. 93.
Collections, paleontological, poor,
li. 58.
Colour, influenced by climate, i. 165.
, in relation to attack by flies,
i. 248.
Columba livia, parent of domestic
pigeons, i. 26.
Colymbetes, ii. 174.
Compensation of growth, i. 182.
Composite, flowers and seeds of,
HALAS)
, outer and inner florets of,
1270:
, male flowers of, ii. 257,
Conclusion, general, ii. 2:3.
Conditions, slight changes in,
favoura)le to fertility, i ii. 27,
Convergence of genera, i. 156.
Coot, i. 222.
Cope, Prof., on the acceleration or
retardation of the period of re-
production, i. 232,
326
CORAL-ISLANDS.
INDEX.
DOUBLE.
Coral-islands, seeds drifted to,
ii. 145.
reefs, indicating movements
of earth, ii. 145.
Corn-crake, i. 223.
Correlated variation in domestic
productions, i. 13.
Coryanthes, i. 241.
Creation, single centres of, i. 135.
Crinum, ii. 6.
Croll, Mr., on subaerial denuda-
tion, ii. 53, 56.
, on the age of our oldest for-
mations, ii. 83.
, on alternate Glacial periods
in the North and South, ii. 160.
Crosses, reciprocal, ii. 14.
Crossing of domestic animals, im-
portance in altering breeds, i. 23.
, advantages of, i. 119, 120.
, unfavourable to selection,
ai ase
Criiger, Dr., on Coryanthes, i. 241.
Crustacea of New Zealand, ii. 164.
Crustacean, blind, i. 171.
air-breathers, i. 238.
Crustaceans, their chelz, i. 300.
Cryptocerus, i. 359.
Ctenomys, blind, i. 170.
Cuckoo, instinct of, i. 319, 330.
Cunningham, Mr., on the flight of
the logger-headed duck, i. 167.
Currants, grafts of, ii. 19.
Currents of sea, rate of, il. 144.
Cuvier, on conditions of existence,
i. 320.
Cuvier, on fossil monkeys, ii. 79.
, Fred., on instinet, i 320.
Cyclostoma, resisting salt water,
ii. 187.
D.
Dana, Prof., on blind cave-animals,
i. 172.
, on relations of crustaceans of
Japan, li. 158.
,on crustaceans of New Zea-
land, ii. 164.
Dawson, Dr., on eozoon, li. 85.
De Candolle, Aug. Pyr., on struggle
for existence, i. 77.
»on umbcellifere, i. 181.
—, on general affinities, ii. 228.
De Candolle, Alph., on the varia-
bility of oaks, i. 62. ©
,on low plants, widely dis-
persed, ii. 196.
, on widely-ranging plants
being variable, i. 67.
, on naturalisation, i. 139.
, on winged seeds, i. 181.
, on Alpine species suddenly
becoming rare, i. 210.
, on distribution of plants with
large seeds, ii. 145.
,on vegetation of Australia,
ii. 167.
, on fresh-water plants, ii. 174.
, on insular plants, ii. 178.
Degradation of rocks, ii. 52.
Denudation, rate of, ii. 54.
of oldest rocks, ii. 85.
of granitic areas, li. 64.
Development of ancient forms,
ui. 116.
Devonian system, ii. 113.
Dianthus, fertility of crosses, ii.
13.
Dimorphism in plants, i. 55; ii, 29.
Dirt on feet of birds, ii. 148.
Dispersal, means of, ii. 140.
during Glacial period, ii. 151.
Distribution, geograpical, ii. 129.
, means of, 11. 140.
Disuse, effect of, under nature,
i. 167.
Divergence of character, i. 134.
Diversification of means for same
general purpose, i. 240.
Division, physiological, of labour,
i. 13
Dog, resemblance of jaw to that of
the Thylacinus, ii. 220.
Dogs, hairless, with imperfect teeth,
1. 14.
descended from several wild
stocks, i. 22.
, domestic instincts of, i. 827.
, inl|.erited civilisation of, i. 327.
——., fertility of breeds together,
ii. 10.
—., of crosses, ii. 35.
» proportions of body in differs
ent breeds, when young, ii. 247.
Domestication, variation under, i.7.
| Double flowers, i. 358.
DOWNING.
T)owning, Mr., on fruit-trees in Ame-
rica, 1. 104.
Dragon flies, intestines of, i. 229.
Drift-timber, i. 145.
Driver-ant, i. 361.
Drones killed by other bees, i. 256.
Duck, domestic, wings of, reduced,
i. 12.
, beak of, i. 285.
, logger-headed, i. 218.
Duckweed, ii. 173.
Dugong, atiinities of, ii. 206.
Dung-beetles with deficient tarsi,
i. 168.
Dytiscus, ii. 174.
E.
Earl, Mr. W., on the Malay Archi-
pelago, ii. 185.
Ears, drooping, in domestic animals,
E13.
, rudimentary, i. 261.
Earth, seeds in roots of trees, ii. 145.
charged with seeds, ii. 148.
Echinodermata, their pedicellarie,
i. 297.
Eciton, i. 359.
Economy of organisation, i. 182.
Edentata, teeth and hair, i. 179.
, fossil species of, 11. 288.
Edwards, Milne, on physiological
division of labour, i. 139.
, on: gradations of structure,
i. 244.
,on embryological characters,
ii. 210.
Eggs, young birds escaping from,
i. 106.
Egypt, productions of, not modified.
i. 263.
Electric organs, i. 234.
Elephant, rate of increase, i. 80.
, of Glacial period, i. 176.
Embryology, ii. 239.
Eozoon Canadense, ii. 84.
Epilepsy inherited, i. 167.
Existence, struggle for, 1. 75.
, condition of, i. 261.
Extinction, as bearing on natural
selection, i. 150.
of domestic varieties, i. 145.
» ii. 94.
Eye, structure of, i. 225.
INDEX.
327
FLOWER.
Eye, correction for aberration, i.
255.
Eyes, reduced in moles, i. 170.
E;
Fabre, M., on hymenoptera fight:
ing, i. 108.
, on parasitic sphex, i. 336.
, on Sitaris, ii. 252. :
Falconer, Dr., on naturalisation of
plants in India, i. 80.
on elephants and mastodons,
ie ES
— and Cautley, on mammals of
sub-Himalayan beds, ii. 122.
Falkland Islands, wolf of, ii. 183.
Faults, ii. 34.
Faunas, marine, ti. 131.
Fear, instinctive, in birds, i. 329.
Feet of birds, young molluscs ad-
hering to, ti. 174.
Fertilisation variously effected, 1.
241, 252.
Fertility of hybrids, ii. 6.
, from slight changes in con-
ditions, ii. 28.
of crossed varieties, ii. 34.
Fir-trees destroyed by cattle, i. 88.
, pollen of, i. 257.
Fish, flying, i. 218.
, teleostean, sudden appear-
ance of, ii. 81.
, eating seeds, ii. 146, 175.
, iresh-water, distribution of,
li. 172.
Fishes, ganoid, now confined to fresh
water, i. 180.
, electric organs of, 1. 234.
, ganoid, living in fresh water,
11 99}
—, of southern hemisphere, ii.
Flat-fish, their structure, i. 290.
Flight, powers of, how acquired,
i. 218.
Flint-tools, proving antiquity of
man, i. 21.
Flower, Prof.,on the Larnyx, i. 297.
, on Halitherium, ii. 108.
, on the resemblance between
the jaws of the dog and Thyla-
cinus, ii. 220.
FLOWER.
328
INDEX.
GMELIN.
Flower, Prof., on the homology of the
feet of certain marsupials, ti . 2382.
Flowers, structure of, in relation to
crossing, 1. 114.
, of composite and umbelli-
fer, i. 179, 270.
, beauty of, 1. 252.
, double, i. 358.
Flysch formation, destitute of or-
ganic remains, li. 59.
Forbes, Mr. D., on glacial action in
the Andes, ii. 160.
, E., on colours of shells, i
165.
,on abrupt range of shells in
depth, i. 210.
, on poorness of paleontological
collections, ii. 58.
, on continuous succession of
genera, li. 93.
, on continental extensions, ii.
140, 141.
, on distribution during Glacial
period, ii. 152.
—, on parallelism in time and
space, 11. 200.
Forests, changes in, in America,
i: oe
Formation, Devonian, ii. 113.
Cambrian, il. 84.
ones thickness of, in Britain,
ii. 55.
, intermittent, i. 69.
Formica, rufescens, 1. 336.
, sanguinea, 1. 338.
, flava, neuter of, i. 360.
Forms, lowly organised, long en-
during, i. 154.
Frena, ovigerous, of cirripedes, i
232.
Fresh-water productions, dispersal
of, 1. 171.
Fries, on species in large genera
being closely allied to other
species, 1. 71.
Frigate-bird, i. 222.
Frogs on islands, ii. 182.
Fruit-trees, gradual improvement
of, i. 42.
in United States, i. 104.
, varieties of, acclimatised in
United States, i. 176.
Fuci, crossed, ii. 15, 23.
Fur, thicker in cold climates, i. 166.
Furze, ii. 241.
G.
Galapagos Archipelago, birds of,
Hi: 478:
productions of, ii. 188, 190.
Ga'axias, its wide range, ii. 172.
Galeopithecus, i. 217.
Game, increase of, checked by ver-
min, i. 86.
Gartner, on sterility of hybads ii.
3, 4, 11.
, on reciprocal crosses, ii. 15.
, on crossed maize and verbas-
cum, ii. 37.
—, on comparison of hybrids and
mongrels, ii. 40, 41, 42.
Gaudry, Prof., on intermediate ge-
nera of fossil mammals in Attica,
ii. 107.
Geese, fertility when crossed, ii.
9, 10.
, upland, i. 222.
Geikie, Mr., on subaerial denuda-
tion, li. 53.
Genealogy, important in classifica-
tion, ii. 212.
Generations, alternate, ii. 239.
Geoffroy St. Hilaire, on balance-
ment, i. 182.
, on homologous organs, ii. 233.
——,, Isidore, on variability of re-
peated parts, i. 184.
, or correlation, in monstroci-
ties, i. 13.
, on correlation, i. 179.
, on variable parts being often
monstrous, i. 190.
Geograpliical distribution, ii. 129.
Geography, ancient, ii. 303.
Geology, future progress of, ii. 302.
, imperfection of the record,
ii. 303.
Gervais, Prof., on Typotherium, ii.
108.
Giraffe, tail of, i. 245.
, structure of, i. 276,
Glacial period, ii. 151.
, affecting the Northand South,
ii. 158.
Glands, mammary, i. 295.
Gmelin, on distribution, ii. 151.
a
GODWIN-AUSTEN.
INDEX.
329
HOOKER.
Godwin-Austen, Mr., on the Malay
Archipelazo, i. 74.
Goethe, on compensation of growth,
i. 182.
Gomphia, i. 272.
Gooseberry, grafts of, ii. 19.
Gould, Dr. Aug. A. on land-shells,
ii. 186.
, Mr., on colours of birds, i. 165.
, on instincts of cuckoo, i. 333.
, on distribution of genera of
birds, ii. 195.
Gourds, crossed, ii. 38.
Graha, on the Uria lacrymas, i. 113.
Grafting, capacity of, ii. 18, 19, 20.
Granite, areas of denuded, ii. 64.
Grasses, varieties of, i. 137.
Gray, Dr. Asa, on the variability of
oaks, i. 62.
, on man not causing varia-
bility, i. 98.
, on sexes of the holly, i. 116.
, on trees of the United States,
i. 128.
——, on naturalised plants in the
United States, i. 139.
, on estivation, i. 272.
, on Alpine plants, ii. 151.
, on rarity of intermediate va-
rieties, i. 212.
, Dr. J. E., on striped mule,
£099.
Grebe, i. 221.
Grimm, on asexual reproduction,
ii. 240.
Groups, aberrant, ii. 227.
Grouse, colours of, i. 104.
, red, a doubtful species, i. 59.
Growth, compensation of, i. 182.
Giinther, Dr., on flat-fish, i. 292.
, on prelensile tails, 1. 294.
, on the fishes of Panama, ii. 131.
, on the rauge of fresh-water
fishes, ii. 172.
——,on the limbs of Lepidosiren,
li. 258.
H.
Haast, Dr., on glaciers of New Zea-
land, ii. 159.
Habit, effect of, under domestica-
tion, i. 12.
—, effect of, under nature, i. 168.
Habit, diversified, of same species,
i. 219.
Hiackel, Prof., on classification and
the lines of descent, ii. 231.
Hiir and teeth, correlated, i. 179.
Halitherium, ii. 108.
Harcourt, Mr. E. V., on the birds of
Madeira, ii. 180.
Hariung, M., on boulders in the
Azores, ii. 149.
Hazel-uuts, ii. 143.
Hearne, on habits of bears, i. 220.
Heath, changes in vegetation, i,
87.
Hector, Dr., on glaciers of New Zea-
land, ii. 159.
Heer, Oswald, on ancient cultivated
plants, i. 20.
, on plants of Madeira, i. 130.
Helianthemum, i. 272.
Helix pomatia, ii. 187.
, resisting salt water, ii. 187.
Helmholtz, M.,on the imperfection
of the human eye, i. 255.
Helosciadium, ii. 143.
Hemionus, striped, i. 202.
Hensen, Dr., on the eyes of Cepha-
lopods, i. 237.
Herbert, W., on struggle for exist-
ence, 1. 77.
——., on sterility of hybrids, ii. 6.
Hermaphrodites crossing, i. 119.
Heron eating seed, ii. 176.
Heron, Sir R., on peacocks, i. 109.
Heusinger, on white animals poi-
soned by certain plants, i. 13.
Hewitt, Mr., on sterility of first
crosses, li. 23.
Hildebrand, Prof., on the self-ste-
rility of Cory:alis, ii. 7.
Hilgendorf, on intermediate varie-
ties, ii. 66.
Himalaya, glaciers of, ii. 159.
, plants of, ii. 162.
Hippeastrum, ii. 7.
Hippocampus, i. 295.
Hofmeister, Prof., on the move-
ments of plants, i. 308.
Holly-trees, sexes of, i. 115.
Hooker, Dr., on trees of New Zea-
land, i. 123.
, on acclimatisation of Hima-
layan trees, i. 174.
330
HOOKER
Hooker, Dr., on flowers of umbel-
lifere, i. 180.
,on the position of ovules, i.
268.
, on glaciers of Himalaya, ii.
159.
, on alge of New Zealand, ii.
164.
, on vegetation at the base of
the Himalaya, ii. 164.
, on plants of Tierra del Fuego,
ii. 161.
on Australian plants, ii. 163,
190.
, on relations of flora of Ame-
rica, ii. 167.
, on flora of the Antarctic lands,
ii. 169, 189.
, on the plants of the Gala-
pagos, li. 181, 188.
,on glaciers of the Lebanon,
ii. 159,
. on man not causing varia-
bility, i. 97.
, on plants of mountains of
Fernando Po, ii. 162.
Hooks on palms, i. 247.
on seeds, on islands, ii. 181.
Hopkins, Mr., on denudation, ii. 63.
Hornbill, remarkable instinct of, 1.
364.
Horns, rudimentary, i. 261.
Horse, fossil, in La Plata, ii. 96.
, proportions of, when young,
ii. 247.
Horses destroyed by flies in Para-
guay, 1. 89.
, striped, i. 199,
Horticulturists, selection applied by,
i, 37.
Huber, on cells of bees, i. 349.
. P., on reason blended with
instinct, 1. 520.
.on habitual nature of instincts,
i. 320.
, on slave-making auts, i. 336.
, on Melipona domestica, i. 343.
Hudson, Mr., on the Ground-Wood-
pecker of La Plata, i. 221.
, on the Molothrus, i. 334.
Humble-bees, cells, of, i. 343.
Hunter, J., on secondary sexual]
characters, i. 185.
INDEX.
JAVA
Hutton, Captain, on crossed geese,
11, 10:
Huxley, Prof., on structure of her-
maphrodites, i. 124.
, on the affinities of the Sirenia,
ii. 108.
,on forms connecting birds and
reptiles, ii. 108.
, on homologous organs, ii. 238.
. on the development of apbis,
li. 245.
Hybrids and mongrels compared,
ii. 39,
Hybridism, ii. 1.
Hydra, structure of, i. 229.
Hymenoptera, fighting, i. 108.
Hymenopterous insect, diving, i.
222.
Hyoseris, i. 271.
I,
Ibla, i. 183.
Icebergs transporting seeds, ii. 148.
Increase, rate of, i. 79.
Individuals, numbers favourable to
selection, i. 124.
, many, whether simultaneously
created, li. 139.
Inheritance, laws of, i. 15.
, at corresponding ages, i. 15,
105.
Insects, colour of, fitted for their
stations, i. 103.
, sea-side, colours of, i. 165.
, blind, in caves, i. 171.
. luminous, 1. 236.
——, their resemblance to certain
objects, i. 283.
, neuter, i, 359.
Instinct, i. 319.
, not varying simultaneously *
with structure, i. 357.
Instincts, domestic, i. 325.
Intercrossing, advantages of, i. 119,
ii. 27.
Islands, oceanic, ii. 177.
Isolation favourable to selection, L
127.
Je
Japan, productions of, ii. 158.
Java, piunts of, ii. 162.
JONES.
INDEX.
331
‘LYELL.
Jones, Mr. J. M., on the birds of
Bermuda, ii. 180.
Jourdain, M., on the eye-spots of
star-fishes, i. 225.
Jukes, Prof., on subaerial denuda-
tion, li. 53.
Jussieu, on classification, ii. 209.
K,
Kentucky, caves of, i. 172.
Kerguelen-land, flora of, ii. 169, 18S.
Kidney-bean, acclimatisation of, i.
ALL.
Kidneys of birds, i. 178.
Kirby, on tarsi deficient in beetles,
i. 168.
Knight, Andrew, on cause of varia-
tion, i. 8.
Kolreuter, on Intercrossing, i. 119.
, on the barberry, 1. 121.
, on sterility of hybrids, ii. 3, 4.
——, on reciprocal crosses, ii. 15,
, on crossed varieties of nico-
tiana, li. 38.
, on crossing male and herma-
phrodite flowers, ii. 256.
L.
Lamarck, on adaptive characters, ii.
218
Lancelet, i. 154.
» eyes of, 1. 227.
Landois, on the development of the
wings of insects, 1. 231.
Land-shells, distribution of, ii. 186.
, of Madeira, naturalised, ii.
193.
, resisting salt water, ii. 187.
Languages, classification of, ii. 214.
Lankester, Mr. E,. Ray, on Longe-
vity, i. 263.
, on homologies, il. 237.
Lapse, great, of time, ii. 51.
Larve, ii. 241, 242, 243.
Laurel, nectar secreted by the leaves,
i. 114.
Laurentian formation, ii. 84,
Laws of variation, i. 164.
Leech, varieties of, i. 93.
Leguminose, nectar secreted by
glands, i. 114.
46
Leibnitz’ attack on Newton, ii. 294.
Lepidosiren, i. 130 ; ii. 109.
, limbs in a nascent condition,
li. 258.
Lewes, Mr. G. H., on species not
having changed in Egypt, i. 263.
,on the Salamandra atra, 11.
256.
—, on many forms of life having
been at first evolved, ii. 300.
Life, struggle for, i. 77.
Lingula, Silurian, ii. 83.
Linneus, aphorism of, ii. 205.
Lion, mane of, i. 109.
, young of, striped, ii. 241.
Lobelia fulgens, i. 90, 121.
, sterility of crosses, ii. 7.
Lockwood, Mr., on the ova of the
Hippocampus, i. 295.
Locusts transporting seeds, ii. 147.
Logan, Sir W.,on Laurentian forma-
tion, ji. 84.
Lowe, Rey. R. T., on locusts visiting
Madeira, ii. 147.
Lowness of structure connected
with variability, i. 184.
, related to wide distribution,
ig UBYS:
Lubbock, Sir J., on the nerves of
coccus, 1. 04.
,on secondary sexual charac-
ters, 1. 193.
, on a diving hymenopterous
insect, i. 222.
, on affinities, ii, 73.
, on metamorphoses, ii, 239,
242,
Lucas, Dr. P., on inheritance, i. 14.
» on resemblance of child to
parent, il. 43.
Lund and Clausen, on fossils of
Brazil, js 12
Lyell, Sir C., on the struggle for
existence, i. 77.
, on modern changes of the
earth, i. 118.
, on terrestrial animals not
having been developed on islands,
i. 281.
, on a carboniferous land-shell,
ii. 59.
, on strata beneath Silurian
system, ii. 84.
332
LYELL.
INDEX.
MOTHS
Lyell, Sir C., on the imperfection of
the geological record, ii. 88.
, on the appearance of species,
ii. 88
, on Barrande’s colonies, ii. 90.
, on tertiary formations of
Europe and North America, il.
101.
, on parallelism of tertiary for-
mations, i. 106.
, on transport of seeds by ice-
bergs, ii. 148.
, on great alterations of cli-
mate, 11. 170.
, on the distribution of fresh-
water shells, ii. 174.
, on land-shells of Madeira,
ii. 193.
Lyell and Dawson, on fossilized trees
in Nova Scotia, i. 70.
Lythrum salicaria, trimorphic, ii.
32.
M.
Macleay, on analogical characters,
ii. 218.
Macrauchenia, li. 107.
M‘Donnell, Dr., on electric organs,
i. 234.
Madeira, plants of, i. 130.
, beetles of, wingless, i. 169.
, fossil land-shells of, ii. 121.
, birds of, 11. 180.
Magpie time in Norway, i. 325.
Males fighting, 1. 108.
Maize, crossed, ii. 37.
Malay Archipelago compared with
Europe, ii. 74.
, mammals of, 11. 185.
Malm, on flat-fish, i. 291.
Malpighiacez, small
flowers of, 1. 269.
, ii. 209.
Mamme, their development, i. 295.
, rudimentary, ii. 255.
Mammals, fossil, in secondary for-
mation, ii. 79.
—, insular, 1i. 183.
Man, origin of, ii. 304.
Manatee, rudimentary nails of, ii.
260.
Marsupials of Australia, i. 140.
——,, structure of their feet, Li. 232
imperfect
'
Marsupials, fossil species of, ii. 121.
Martens, M., experiment on seeds,
ri. 144.
Martin, Mr. W. C., on striped mules,
i. 201.
Masters, Dr., on Saponaria, i. 272.
Matteucci, on the electric organs of
rays, 1. 234.
Matthiola, reciprocal crosses of, ii.
15.
Maurandia, i. 307.
Means of dispersal, ii. 140.
Melipona domestica, i. 343.
Merrell, Dr., on the American
cuckoo, i. 330.
Metamorphism of oldest rocks, ii. 85.
«Mice destroying bees, i. 90.
, acclimatisation of, i. 175.
, tails of, 1. 294.
Miller, Prof., on the cells of bees,
1. 344, 350.
Mirabilis, crosses of, ii. 15.
Missel-thrush, i. 93.
Mistletoe, complex relations of, i. 3.
Mivart, Mr., on the relation of hair
and teeth, i. 179.
, on the eyes of cephalopods,
i. 237.
, various objections to Natural
Selection, i. 275.
, on abrupt modifications, i. 313.
, on the resemblance of the
mouse and antecliinus, ii. 218.
Mocking-thrush of the Galapagos
ii. 193.
Modification of species not abrupt,
li. 298.
Moles, blind, i. 170.
Molothrus, habits of, i. 334.
Mongrels, fertility and sterility of,
li. 34.
and hybrids compared, ii. 39.
Monkeys, fossil, ii. 79.
Monachanthus, ii. 216.
Mons, Van, on the origin of fruit-
trees, 1. 33.
Monstrosities, i. 51.
Mogquin-Tandon, on sea-side plants,
i. 166.
Morphology, ii. 231.
Morren, on the leaves of Oxalis,
i. 308.
| Moths, hybrid, ii, 9.
MOZART.
Mozart, musical powers of, i. 321.
Mud, seeds in, ii. 175.
Mules, striped, i. 201.
Miiller, Adolf, on the instincts of the
cuckoo, i. 331.
Miiller, Dr. Ferdinand, on Alpine
Australian plants, ii. 163.
Miiller, Fritz, on dimorphic crus-
taceans, i. 55, 362.
, on the lancelet, i. 154.
, on air-breathing crustaceans,
1. 238.
, on climbing plants, i. 307.
—, on the self-sterility of orchids,
te
, on embryology in relation to
classification, ii. 210.
, on the metamorphoses of crus-
taceans, ii. 245, 253.
, on terrestrial and fresh-water
organisms not undergoing any
metamorplosis, ii. 250.
Multiplication of species not indefi-
nite, i. 157.
Murchison, Sir R., on the forma-
tions of Russia, ii. 60.
, on azoic formations, li. 84.
—,, on extinction, li. 94.
Murie, Dr., on the modification of
the skull in old age, i. 233.
Murray, Mr. A., on cave-insects,
is:
Mustela vison, i. 216.
Myanthus, ii. 216.
Myrmecocy stus, i. 359.
Myrmica, eyes of, i. 361.
N.
Nageli,on morphological characters,
i. 266
Nails, rudimentary, H. 260.
Nathusius, Von, on pigs, i. 249.
Natural history, future progress of,
ii. 301.
— selection, i. 97.
system, il. 204.
Naturalisation of forms distinct from
the indigenous species, i. 138.
Naturalisation in New Zealand, i.
255.
Naudin, on analogous variations in
gourds, i. 195.
, on hybrid gourds, ii. 38.
INDEX.
399
OSTRICH.
Naudin, on reversion, ii. 41.
Nautilus, Silurian, ii. 83.
Nectar of plants, i. 114.
Nectaries, how formed, i. 114.
Nelumbium luteum, ii. 176.
Nests, variations in, i. 324, 355, 364.
Neuter insects, i. 359, 360.
Newman, Col.; on humble-beesg, i. 90.
New Zealand, productions of, not
perfect, i. 255.
, baturalised products of, ii. 119.
» fossil birds of, ii. 121.
——, ; glaciers of, ii. 159.
, crustaceans of, ii. 164.
» alge of, ii. 164.
; number of plants of, ii. 178.
» flora of, ii. 189.
ie Sir IL, attacked for irre-
ligion, ii. 294.
, Prof., on earth attached toa
partridge’s foot, ii. 148.
Nicotiana, crossed varieties of, ii. 39.
; certain species very sterile,
ii. 14.
Nitsche, Dr., on the Polyzoa, i. 801.
Noble, Mr., on fertility of Rhodo-
dendron, ii. 8.
Nodules, phosphatic, in azoic rocks,
li. 84.
0.
Oaks, variability of, i. 62.
Onites, appelles, i. 168.
Ononis, small imperfect flowers of,
1. 269.
Orchids, fertilisation of, i. 241.
: the development of their
flowers, i. 303.
, forms of, ii. 216.
Orchis, pollen of, i. 236.
Organisation, tendency to advance,
Tole
Organs of extreme perfection, i, 223.
, electric, of fishes, i. 234.
—— of little importance, i. 245.
» homologous, ii. 233.
, rudiments of, and nascent
li. 255.
Ornithorhynchus, i. 130; ii. 208.
, mamme of, i. 296.
Ostrich not capable of flight, i. 281.
, habit of laying eggs together,
i, 335,
3
dot
OSTRICH.
INDEX.
PLANTS
Ostrich, American, two species of,
ree sy >
Otter, habits of, how acquired, i.
216.
Ouzel, water, i. 222.
Owen, Prof., on birds not flying, i.
167.
——,on vegetative repetition, 1.
184.
—, on variability of unusually
developed parts, 1. 185.
, on the eyes of fishes, i. 227.
.on the swim-bladder of fishes,
231.
, on fossil horse of La Plata, ii.
96.
——, on generalized form, ii. 107.
, on relation of ruminants and
pachyderms, 11. 107.
, on fossil birds of New Zea-
land, ii. 121.
, on succession of types, 11.121.
, on affinities of the dugong,
ii. 206.
, on homologous organs, ii. 233.
,on the metamorphosis of ce-
phalopods, ii. 244.
P.
Pacific Ocean, faunas of, ii. 131.
Pacini, on electric organs, i. 235.
Paley, on no organ formed to give
pain, 1. 254.
Pullas, on the fertility of the domes-
ticated descendants of wild stocks,
ii. 10.
Palm with hooks, i. 247.
Papaper bracteatum, 1. 272.
Paraguay, cattle destroyed by flies,
i. 89.
Parasites, i. 334.
Partridge, with ball of earth at-
tached to foot, ii. 148.
Parts greatly developed, variable,
1. 185.
Parus major, i. 220.
Passiflora, ii. 7.
Peaches in United States, i. 104.
Pear, grafts of, ii. 18.
Pedicellariz, i. 298.
Pelagornium, flowers of, i. 180.
, Sterility of, iL. 7.
Pelvis of women, i. 173.
Peloria, i. 180.
Period, glacial, ii. 151.
Petrels, habits of, i. 221.
Phasianus, fertility of hybrids, ii. 9.
Pheasant, young, wild, i. 329.
Pictet, Prof., on groups of species
suddenly appearing, ii. 77.
, on rate of organic change, il.
90.
, ON continuous succession of
genera, li. 93.
, on change in latest tertiary
forms, ii. 71.
—, on close alliance of fossils in
consecutive formations, ii. 114.
78. :
Pierce, Mr., on varieties of wolves,
1nd Lt Bi
Pigeons with feathered feet and skin
between toes, i. 14.
, breeds described, and origin
of, i. 23.
, breeds of, how produced, i. 44,
47.
, tumbler, not being able to get
out of egg, i. 106.
, reverting to blue colour, i. 197.
——,, instinct of tumbling, i. 327.
, young of, ii. 248.
Pigs, black, not affected by the
paint-root, i. 13.
, modified by want of exercise,
i. 249.
Pistil, rudimentary, ii. 256.
Plants, poisonous, not affectiny cer-
tain coloured animals, i. 13.
, selection, applied to, i. 41
, gradual improvement of, i 42.
, not improved in barbarous
countries, i. 43.
, dimorphic, i. 55; ii. 29.
——, destroyed by insects, i. 83.
, in midst of range, have to
struggle with otlier plants, i. 95.
, nectar of, i. 114.
, fleshy, on sea-sliores, i. 166.
, climbing, 1. 250, 305.
, fresh-water, distribution of, ii.
174.
—, low in seale, widely distri-
buted, ii. 196.
, on early transitional links, ii.
baci Se
PLEURONECTIDA.
Pleuronectide, their structure, i,
290.
Plumage, laws of change in sexes
of birds, i. 109.
Plums in the United States, i. 104.
Pointer dog, origin of, i. 40.
, habits of, i. 327.
Poison not affecting certain coloured
animals, i. 13.
, similar effect of, on animals
and plants, ii. 299.
Pollen of fir-trees, i. 257.
transported by various means,
1. 241, 252:
Poilinia, their development, i. 304.
Polyzoa, their avicularia, i. 301.
Poole, Col., on striped hemionus,
1. 202.
Potemogeton, ii. 175.
Pouchet, on the colours of flat-fish,
4, 298.
Prestwich, Mr., on English and
Frene!: eocene formations, ii. 105.
Pro totrupes, 1. 222.
P:oteolepas, i. 183.
Proteus, i. 178.
Psychology, future progress of, ii.
304.
Pyrgoma, found in the chalk, ii. 81.
Q.
Quagza, striped, i. 201.
Quatrefages, M., on hybrid moths,
reap
Quercus, variability of, i. 62.
Quince, grafts of, ii. 18.
R.
Rabbits, disposition of young, i
28
oa
ol0.
Races, domestic, characters of, i. 18.
Race-horses, Arab, i. 40.
, English, ii. 140.
Radcliffe, Dr., the electrical organs
of the torpedo, i. 234.
Ramond, on plants of Pyrenees, ii.
iAP
Ramsay, Prof., on subacrial denu-
dation, ii. 53.
, on thickness of the British
formations, ii. 55, 56.
—, on faults, ii. 0d.
INDEX.
O00
SAUROPHAGUS,
Ramsay, Mr., on instincts of cuckoo,
1. 333.
Ratio of increase, i. 79.
Rats supplanting each other, i. 93.
, acclimatisation of, 1. 175.
——, blind, in cave, i. 171.
Rattle-snake, i. 254.
Reason and instinct, i. 319.
Recapitulation, general, ii. 267.
Reciprocity of crosses, ii. 14.
Record, geological, imperfect, ii. 48.
Rengger, on flies destroying cattle,
Ty fh
Reproduction, rate of, i. 79.
Resemblance, protective, of insects,
i. 283.
to parents in mongrels and
hybrids, ii. 41.
Reversion, law of inheritance, i.
16.
——, in pigeons, to blue colour, i.
8
Rhododendron, sterility of, ii. 7, 8.
Richard, Prof.,on Aspicarps, ii. 209.
Richardson, Sir J., on structure of
squirrels, i. 216.
, on fishes of the southern hemi-
sphere, ii. 164.
Robinia, grafts of, ii. 19.
Rodents, blind, i. 170.
Rogers, Prof., Map of N. America,
li. 65.
Rudimentary organs, ii. 255.
Rudiments important for classifica-
tion, ii. 207.
Riitimeyer, on Indian cattle, i. 21;
ii. 10
Salamandra atra, ii. 256.
Saliva used in nests, i. 355.
Salvin, Mr., on the beaks of ducks,
1252
Sageret, on grafts, ii. 18.
Saimons, males fighting,and hooked
jaws of, i. 108.
Salt water, how far injurious te
seeds, ii. 142.
— not destructive to land-shells,
ii. 187.
Salter, Mr., on early death of hybrid
empryos, li. 23.
Saurophagus sulphuratus, i. 220.
336
SCHACHT.
Schacht, Prof., on Phyllotaxy, i
270.
Schiddte, on blind insects, i. 172.
, on flat-fish, 1. 290.
Schlegel, on snakes, i i. 178.
Schobl, Dr., on the ears of mice, i.
268.
Scott, J.. Mr., on the self-sterility
of orchids, ili. 7.
, on the crossing of varieties of
verbascum, ii, 38.
Sea-water, how far injurious to
secds, ii. 142.
—— not destructive to land-shells,
li. 187.
Sebright, Sir J., on crossed animals,
ioe:
Sedgwick, Prof., on groups of spe-
cies suddenly appearing, ey Pe
Seedlings destroyed by insects, i
83.
Seeds, nutriment in, i. 94.
, winged, i. 181.
—, means of dissemination, i,
240, 252; ii. 146.
, power of resisting salt water,
li, 143.
, in crops and intestines of
birds, ij. 146.
, eaten by fish, ii. 146, 176.
,in mud, ii. 175.
* hooked, on islands, il. 181.
Selection of domestic products, 1.
34.
, principle not of recent origin,
1. 3Y.
pores tadp i 39.
, natural, 1.
— * sexual, i. 107.
, objections to term, 1. 99.
natural, has not induced steri-
lity, ii. 20.
Sexes, relations of, i. 108.
Sexual characters variable, i. 191.
selection, 1. 107.
Sheep, Merino, their selection, i. 36.
, two sub-breeds, unintention-
ally produced, i. 41.
, mountain varieties of, i. 93.
Shells, colours of, i. 165.
, hinges of, i. 240.
——., littoral, seldom embedded, ii.
58.
INDEX.
SQUALODON.
Shells, fresh-water, long retain the
same forms, ii. 117.
—., fresh-water, oe of, ii,
173.
, of Madeira, ii. 180.
, land, distribution of, ii. 180.
, land, resisting salt water, ii.
187.
Shrew-mouse, ii. 218.
Silene, infertility of crosses, ii. 14.
Silliman, Prof., on blind rat, i. 171.
Sirenia, their affinities, ii. 108.
Sitaris, metamorphosis of, ii. 252.
Skulls of young mammals, i. 248;
11235:
Slave-making instinet, i. 336.
Smith, Col. Hamilton, on striped
horses, 1. 200.
, Mr. Fred., on slave-making
ants, 1. 337.
, on neuter ants, i. 360.
Smitt, Dr., on the Polyzoa, i. 301.
Snake with tooth forcutting through
egg-shell, 1. 334.
Somerville, Lord, on selection of
sheep, i. 35.
Sorbus, gratts of, ii. 19.
Sorex, ii. 218.
Spaniel, King Charles’s breed, i. 40.
Specialisation of organs, i. 152.
Species, polymorpliic, i. 54.
, dominant, 1. 67.
, common, variable, i. 66.
—— in large genera variable, i. 69.
groups of, suddenly appear-
ing, ii. 77, 82.
beneath Silurian formations,
li. 84.
successively appearing, ii. 89. *
changing simultaneously
throug:.out the world, ii. 100.
Spencer, Lord, on inerease in size of
cattle, 1. 40.
. Herbert, Mr., on the first steps
in differentiation, i. 155.
, on the tendency to an equili-
brium in all forces, ii. 29.
Sphex, parasitic, i. 336.
Spiders, development of, ii. 245.
Sports in plants, i. 11.
Sprengel, C. C., on crossing, i. 119.
, on ray-fiorets, i. 180.
Squalvdon, ii. 108.
SQUIRRELS.
Squirrels, gradations in structure, i.
216.
Staifordshire, heath, changes in, i,
87.
Stag-beetles, fighting, i. 108.
Star-fishes, eyes of, i. 225.
, their pedicellariz, i. 299.
Sterility from changed conditions of
life, i. 10.
of hybrids, ii. 3.
, laws of, ii. 11.
, causes of, ii. 20.
, from unfavourable conditions,
26:
—— not induced through natural
selection, ii. 21.
St. Helena, productions of, ii, 178.
St. Hilaire, Aug., on variability of
certain plants, i. 272.
, on classification, ii. 209.
St. John, Mr., on habits of cats, i.
325.
Sting of bee, i. 256.
Stocks, aboriginal, of domestic ani-
mals, i. 22.
Strata, thickness of, in Britain, il.
55.
Stripes on horses, i. 199.
Structure, degrees of utility of, i.
249.
Struggle for existence, i. 75.
Succession, geological, ii. 89.
of types in same areas, ii. 121.
Swallow, one species supplanting
another, i. 93.
Swaysland, Mr., on earth adhering
to the feet of migratory birds, ii.
148.
Swifts, nests of, i. 355.
Swim-bladder, i. 230.
Switzerland, lake habitations of, i.
20.
System, natural, ii, 204,
TT
Tail of giraffe, i. 245.
of aquatic anima!s, i. 246,
, prehensile, 1. 294.
, rudimentary, ii. 260.
Tanais, dimorphic, i. 59d.
Tarsi, deficient, i. 168.
Tausch, Dr., on umbellifere, i. 271.
INDEX.
Bot
TUMBLER.
Teeth and hair correlated, i. 179.
, rudimentary, in embryonic,
calf, li. 255, 292.
Tegetmeier, Mr., on cells of bees, i.
346, 392.
Temminck, on distribution aiding
classification, ii. 211.
Tendrils, their development, i,
305.
Thompson, Sir W., on the age of
the habitable world, ii. 83.
, on the consolidation of the
crust of the earth, ii. 275.
Thouin, on grafts, ii. 19.
Thrush, aquatic species of, i. 222.
» mocking, of the Galapagos, ii.
192.
» young of, spotted, ii. 241,
, nest of, 1. 364.
Thuret, M., on crossed fuci, ii. 15.
Thwaites, Mr., on acclimatisation,
i. 174.
Thylacinus, ii. 220.
Tierra del Fuego, dogs of, i. 328.
, plants of, ii. 169,
Timber-drift, ii. 145.
Time, lapse of, ii. 51.
by itself not causing modifica-
tion, 1. 126.
Titmouse, i. 220.
Toads on islands, ii. 182.
Tobacco, crossed varieties of, ii, 38.
Tomes, Mr., on the distribution of
bats, 11. 184.
Transitions in varieties rare, i. 208.
Traquair, Dr., on flat-fish, i. 293.
Trautschold, on intermediate varie-
ties, il. 66.
Trees on islands belong to peculiar
orders, ii. 182.
with separated sexes, i. 123,
Trifolium pratense, i. 90, 117.
incarnatum, i. 117,
Trigonia, ii. 99.
Trilobites, ii. 83.
, sudden extinction of, 99,
Trimen, Mr., on imitating-insects,
ii. 224.
Trimorphism in plants, i. 55; ii. 29,
Troglodytes, i. 364.
Tuco-tuco, blind, i. 170.
Tumbler pigeons, habits of, heredi-
tary, 1. 327.
338
TUMBLER.
INDEX.
WATERHOUSE.
Tumbler, young of, ii. 248.
Turkey-cock, tuft of hair on breast,
i. 110.
, vaked skin on head, i. 248.
——, young of, instinctively wild,
i. 329.
Turnip and cabbage, analogous
variations of, i. 195.
Type, unity of, i. 260, 261.
Types, succession of, in same areas,
121,
Typotherium, ii. 108.
Uv.
Udders enlarged by use, i. 12.
, rudimentary, ii. 256.
Ulex, young leaves of, ii. 241.
Umbellifere, flowers and seeds of,
i. 180.
——, outer and inner florets of, i.
270.
Unity of type, i. 260, 261.
Uria lacrymans, i. 113.
Use, effects of, under domestication,
eb
, effects of, in a state of nature,
i. 167.
Utility, how far important in the
construction of each part, i. 249.
Wy,
Valenciennes, on fresh-water fish,
ii. 173.
Variability of mongrels and hybrids,
ii. 39.
Variation under domestication, i. 8.
—— caused by reproductive system
being atiected by conditions of
life, i. 10.
—— under nature, i. 51.
— , laws of, i. 164.
, correlated, i. 13, 177, 248.
Variations appear at corresponding
ages, 1. 16, 1U5.
analogous in distinet species,
i. 193.
Varieties, natural, i. 50.
, struggle between, 1. 93.
, domestic, extinction of, i. 134.
——., transitional, rarity of, i. 208.
——, when crossed, fertile, ii. 34.
Varieties, when crossed, sterile, ii. 37
, classification of, ii. 215.
Verbascum, sterility of, ii. 7.
. varieties of crossed, ii. 38.
Verlot, M., on double stocks, i. 358.
Verneuil, M. de, on the succession
of species, ii. 103.
Vibracula of the Polyzoa, i. 301.
Viola, small imperfect flowers of, i.
269.
—, tricolor, i. 90.
Virchow, on the structure of the
crystalline lens, i. 227.
Virginia, pigs of, i. 104.
Volcanic islands, denudation of, ii.
54.
Vulture, naked skin on head, i. 247.
WwW
Wading-birds, ii. 175.
Wagner, Dr., on Cecidomyia, ii
239.
Wagner, Moritz, on the importance
of isolation, i. 127.
Wallace, Mr., on origin of species,
i. 2.
, on the limit of variation under
domestication, i. 48.
» on dimorphic lepidoptera, i.
D9, 362.
, on races in the Malay Archi-
pelago, i. 58.
, on the improvement of the
eye, 1. 227.
, on the walking-stick insect, i
284.
, on laws of geographical dis-
tribution, li. 139.
, on the Malay Archipelago, ii
185.
, on mimetic animals, ii. 224.
Walsh, Mr. B. D., on phytophagie
forms, i. 60.
, on equal variability, i. 195.
Water, fresh, productions of, ii. 171.
Water-hen, 1, 222.
Waterhouse, Mr.,
marsupials, i. 140.
, on greatly developed parts
being variable, i. 185.
, on the cells of bees, i. 343.
, on general affinities, i. 227.
on Australian
WATER-OUZEL.
INDEX.
539
ZEUGLODON.
Water-ouzel, i. 222.
W:itson, Mr. H. C., on range of
varieties of British plants, 1. 57,
73.
—.,, on acclimatisation, i. 134.
——, on flora of Azores, ii. 149.
——, on Alpine plants, ii. 153.
, on rarity of intermediate va-
rieties, i. 212.
, on convergence, i. 156.
, on the indefinite multiplica-
tion of species, i. 157.
Weaile, Mr., on locusts transporting
seeds, ii, 147.
Web of feet in water-birds, i. 223.
Weismann, Prof., on the causes of
variability, i. 8.
, on rudimentary organs, ii. 260.
West Indian Islands, mammals of,
ii. 185. ;
Westwood, on species in large genera
being closely allied to others, i.
TA.
, on the tarsi of Engide, i. 192.
, on the entenne of hymeno-
pterous insects, ii. 207,
Whales, i. 285.
Wheat, varicties of, i. 137.
White Mountains, flora of, ii. 151.
Whittaker, Mr., on lines of escarp-
ment, il. 53.
Wichura, Max, on hybrids, ii. 24,
27, 41.
Wings, reduction of size, i. 169.
of insects homologous with
branchis, i. 231.
, rudimentary, in insects, ii.
255.
Wolf crossed with dog, i. 327.
of Falkland Isles, ii. 183.
Wollasten, Mr., on varieties of in-
sects, 1. 59.
, on fossil varieties of shells in
Madeira. i. 65,
|
Wollaston, Mr., on colours of insects
on sea-shore, 1. 165.
, on wingless beetles, i. 169.
, on rarity of intermediate va-
rieties, 1. 212.
, on insular insects, ii, 178.
, on land-shells of Madeira
naturalised, ii. 193.
Wolves, varieties of, i. 111.
Woodcock with earth attached to
leg, ii. 148.
Woodpecker, habits of, i. 220.
, green colour of, i. 247.
Woodward. Mr., on the duzation of
specific forms, ii. 66.
——, on Pyrgoma, ii. 81.
, on the continuous succession
of genera, ii. 93.
, on the succession of types, ii.
121.
World, species changing simultane-
ously throughout, ii. 100.
Wrens, nest of, i. 364.
Wright, Mr. Chauncey, on the
giraffe, i. 278.
, on abrupt modifications, i,
316.
Wyman, Prof., on correlation of
colour and effects of poison, i.
ley
——, on the cells of the bee, i. 345
YG
Youatt, Mr., on selection, i. 35.
, on sub-breeds of sheep, i. 41.
, on rudimentary horns in
young cattle, ii. 261.
Z.
Zanthoxylon, i. 272.
Zebra, stripes on, i. 199,
Zeuglodon, ii. 108,
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