CHAPTER XIV._On the Origin of Species by Means of Natural Selection or the Preservation of Favoured Races in the Struggle for Life. (2nd edition)

RECAPITULATION AND CONCLUSION.

Recapitulation of the difficulties on 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 natural selection, I do not deny. I have

endeavoured to give to them their full force. Nothing at first can appear

more difficult to believe than that the more complex organs and instincts

should have been perfected, 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

gradations in the perfection of any organ or instinct which we may

consider, either do now exist or could have existed, each good of its

kind,--that all organs and instincts are, in ever so slight a degree,

variable,--and, lastly, that there is a struggle for existence leading to

the preservation of each profitable deviation of structure or instinct. The

truth of these propositions cannot, I think, be disputed. {460}

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; 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 being, could not have arrived at its present state

by many graduated steps. There are, it must be admitted, cases of special

difficulty on the theory of natural selection; and one of the most curious

of these is the existence of two or three defined castes of workers or

sterile females in the same community of ants; but I have attempted to show

how this difficulty 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

recapitulation of the facts given at the end of the eighth chapter, which

seem to me conclusively to show that this sterility is no more a special

endowment than is the incapacity of two trees to be grafted together; but

that it is incidental on constitutional differences in the reproductive

systems of the intercrossed species. We see the truth of this conclusion in

the vast difference in the result, when the same two species are crossed

reciprocally; that is, when one species is first used as the father and

then as the mother.

The fertility of varieties when intercrossed and of their mongrel offspring

cannot be considered as universal; nor is their very general fertility

surprising when we remember that it is not likely that either their

constitutions or their reproductive systems should have been profoundly

modified. Moreover, most of the varieties which have been experimentised on

have been {461} produced under domestication; and as domestication (I do

not mean mere confinement) apparently tends to eliminate sterility, we

ought not to expect it also to produce sterility.

The sterility of hybrids is a very different case from that of first

crosses, for their reproductive organs are more or less functionally

impotent; whereas in first crosses the organs on both sides are in a

perfect condition. As we continually see that organisms of all kinds are

rendered in some degree sterile from their constitutions having been

disturbed by slightly different and new conditions of life, we need not

feel surprise at hybrids being in some degree sterile, for their

constitutions can hardly fail to have been disturbed from being compounded

of two distinct organisations. This parallelism is supported by another

parallel, but directly opposite, class of facts; namely, that the vigour

and fertility of all organic beings are increased by slight changes in

their conditions of life, and that the offspring of slightly modified forms

or varieties acquire from being crossed increased vigour and fertility. So

that, on the one hand, considerable changes in the conditions of life and

crosses between greatly modified forms, lessen fertility; and on the other

hand, lesser changes in the conditions of life and crosses between less

modified forms, increase fertility.

Turning to geographical distribution, the difficulties encountered on the

theory of descent with modification are grave enough. All the individuals

of the same species, and all the species of the same genus, or even higher

group, must have descended from common parents; and therefore, in however

distant and isolated parts of the world they are now found, they must in

the course of successive generations have passed from some one part to the

others. We are often wholly unable {462} 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, enormously long

as measured by years, too much stress ought not to be laid on the

occasional wide diffusion of the same species; for during very long periods

of time 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 of the full extent of the various climatal

and geographical changes which have affected the earth during modern

periods; and such changes will obviously have greatly facilitated

migration. As an example, I have attempted to show how potent has been the

influence of the Glacial period on the distribution both of the same and of

representative species throughout the world. We are as yet profoundly

ignorant of the many occasional means of transport. With respect to

distinct species of the same genus inhabiting very 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 species of the same

genus is in some degree lessened.

As on the theory of natural selection an interminable number of

intermediate forms must have existed, linking together all the species in

each group by gradations as fine as our present 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 {463} 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 climate and other conditions of life change insensibly in

going 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 zone. For we have reason

to believe that only a few species are undergoing change at any one period;

and all changes are slowly effected. I have also shown that the

intermediate varieties which will at first probably exist in the

intermediate zones, will be liable to be supplanted by the allied forms on

either hand; and the latter, from existing in greater numbers, will

generally be modified and improved at a quicker rate than the intermediate

varieties, which exist in lesser numbers; so that the intermediate

varieties will, 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 inhabitants of the world, and at each

successive period between the extinct and still older species, why is not

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? We meet with no such evidence, and this is

the most obvious and forcible of the many objections which may be urged

against my theory. Why, again, do whole groups of allied species appear,

though certainly they often falsely appear, to have come in suddenly on the

several geological stages? Why do we not find great piles of strata beneath

the Silurian system, stored with the remains of the progenitors of the

Silurian groups of fossils? For certainly on my theory such {464} strata

must somewhere have been deposited at these ancient and utterly unknown

epochs in the world's history.

I can answer these questions and grave objections only on the supposition

that the geological record is far more imperfect than most geologists

believe. It cannot be objected that there has not been time sufficient for

any amount of organic change; for the lapse of time has been so great as to

be utterly inappreciable by the human intellect. The number of specimens in

all our museums is absolutely as nothing compared with the countless

generations of countless species which certainly have existed. We should

not be able to recognise a species as the parent of any one or more species

if we were to examine them ever so closely, unless we likewise possessed

many of the intermediate links between their past or parent and present

states; and these many links we could hardly ever expect to discover, owing

to the imperfection of the geological record. 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, on the common view, whether or not

these doubtful forms are varieties? As long as most of the links between

any two species are unknown, if any one link or intermediate variety be

discovered, it will simply be classed as another and distinct species. 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. Widely ranging species vary most, and varieties are

often at first local,--both causes rendering the discovery of intermediate

links less likely. Local varieties will not spread into other and distant

regions until they are considerably modified and {465} improved; and when

they do spread, if discovered in a geological formation, they will appear

as if suddenly created there, and will be simply classed as new species.

Most formations have been intermittent in their accumulation; and their

duration, I am inclined to believe, has been shorter than the average

duration of specific forms. Successive formations are separated from each

other by enormous blank intervals of time; for fossiliferous formations,

thick enough to resist future degradation, can 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 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 fossiliferous formations beneath the lowest

Silurian strata, I can only recur to the hypothesis given in the ninth

chapter. That the geological record is imperfect all will admit; but that

it is imperfect to the degree which I require, few will be inclined to

admit. If we look to long enough intervals of time, geology plainly

declares that all species have changed; and they have changed in the manner

which my theory requires, for they have changed slowly and in a graduated

manner. We clearly see this in the fossil remains from consecutive

formations invariably being much more closely related to each other, than

are the fossils from formations distant from each other in time.

Such is the sum of the several chief objections and difficulties which may

justly be urged against my theory; and I have now briefly recapitulated the

answers and explanations which can be given to them. I have felt these

difficulties far too heavily during many years to {466} doubt their weight.

But it deserves especial notice that the more important objections relate

to questions on which we are confessedly 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 the Geological Record is. Grave as

these several difficulties are, in my judgment they do not overthrow the

theory of descent from a few created forms with subsequent modification.

Now let us turn to the other side of the argument. Under domestication we

see much variability. This seems to be mainly due to the reproductive

system being eminently susceptible to changes in the conditions of life; so

that this system, when not rendered impotent, fails to reproduce offspring

exactly like the parent-form. Variability is governed by many complex

laws,--by correlation of growth, by use and disuse, and by the direct

action of the physical conditions of life. There is much difficulty in

ascertaining how much modification our domestic productions have undergone;

but we may safely infer that the amount has been large, and that

modifications 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 wholly cease; for new varieties are still occasionally produced by our

most anciently domesticated productions. {467}

Man does not actually produce variability; he only unintentionally exposes

organic beings to new conditions of life, and then nature acts on the

organisation, and causes variability. But man can and does select the

variations given to him by nature, and thus accumulate 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 to him at the time, without any thought of

altering the breed. It is certain that he can largely influence the

character of a breed by selecting, in each successive generation,

individual differences so slight as to be quite inappreciable by an

uneducated eye. This process of selection has been the great agency in the

production of the most distinct and useful domestic breeds. That many of

the breeds produced by man have to a large extent the character of natural

species, is shown by the inextricable doubts whether very many of them are

varieties or aboriginal species.

There is no obvious reason why the principles which have acted so

efficiently under domestication should not have acted under nature. In the

preservation of favoured individuals and races, during the

constantly-recurrent Struggle for Existence, we see the most powerful and

ever-acting means 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, or when naturalised in a new country. More individuals

are born than can possibly survive. A grain in the balance will determine

which individual shall live and which shall die,--which variety or species

shall increase in number, and which {468} shall decrease, or finally become

extinct. As the individuals 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. But the struggle will often be very severe between beings

most remote in the scale of nature. The slightest advantage in one being,

at any age or during any season, over those with which it comes into

competition, or better adaptation in however slight a degree to the

surrounding physical conditions, will turn the balance.

With animals having separated sexes there will in most cases be a struggle

between the males for possession of the females. The most vigorous

individuals, or those which have most successfully struggled with their

conditions of life, will generally leave most progeny. But success will

often depend on having special weapons or means of defence, or on the

charms of the males; and the slightest advantage will lead to victory.

As geology plainly proclaims that each land has undergone great physical

changes, we might have expected that organic beings would have varied under

nature, in the same way as they generally have varied under the changed

conditions of domestication. And if there be any variability under nature,

it would be an unaccountable fact if natural selection had not come into

play. It has often been asserted, but the assertion is quite 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 there are at least individual differences in species under

{469} nature. But, besides such differences, all naturalists have admitted

the existence of varieties, which they think sufficiently distinct to be

worthy of record in systematic works. No one can draw any clear distinction

between individual differences and slight varieties; or between more

plainly marked varieties and sub-species, and species. Let it be observed

how naturalists differ in the rank which they assign to the many

representative forms in Europe and North America.

If then we have under nature variability and a powerful agent always ready

to act and select, why should we doubt that variations in any way useful to

beings, under their excessively complex relations of life, would be

preserved, accumulated, and inherited? Why, if man can by patience select

variations most useful to himself, should nature fail in selecting

variations useful, under changing conditions of life, to her living

products? 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

looked no further than this, seems to me to be in itself probable. I have

already recapitulated, as fairly as I could, the opposed difficulties 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 creation, and varieties which are

acknowledged to have been produced by secondary laws. On this same {470}

view we can understand how it is that in each 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 species also of

the larger genera apparently have restricted ranges, and in their

affinities they are clustered in little groups round other species--in

which respects they resemble varieties. These are strange relations on the

view of each species having been independently created, but are

intelligible if all species first existed as varieties.

As each species tends by its geometrical ratio of reproduction to increase

inordinately in number; and as the modified descendants of each species

will be enabled to increase by so much the more as they become diversified

in habits and structure, so as to be enabled 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 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 {471} larger groups 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 succeed in 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 character,

together with the almost inevitable contingency of much extinction,

explains the arrangement of all the forms of life, in groups subordinate to

groups, all within a few great classes, which we now see everywhere around

us, and which has prevailed throughout all time. This grand fact of the

grouping of all organic beings seems to me utterly inexplicable on the

theory of creation.

As natural selection acts solely by accumulating slight, successive,

favourable variations, it can produce no great or sudden modification; it

can act only by very short and slow steps. Hence the canon of "Natura non

facit saltum," which every fresh addition to our knowledge tends to make

truer, is on this theory simply intelligible. We can plainly 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 woodpecker, should have been

created to prey on insects on the ground; that upland geese, which never or

rarely swim, should have been created with webbed feet; that a thrush

should have been created to dive and feed on sub-aquatic insects; and that

a petrel should have been created with habits and structure fitting it for

the life of an auk or grebe! and so on in endless other cases. But on the

view of each {472} species constantly trying to increase in number, with

natural selection always ready to adapt the slowly varying descendants of

each to any unoccupied or ill-occupied place in nature, these facts cease

to be strange, or perhaps might even have been anticipated.

As natural selection acts by competition, it adapts the inhabitants of each

country only in relation to the degree of perfection of their associates;

so that we need feel no surprise at the inhabitants of any one country,

although on the ordinary view supposed to have been specially created and

adapted for that country, being beaten and supplanted by the naturalised

productions from another land. Nor ought we to marvel if all the

contrivances in nature be not, as far as we can judge, absolutely perfect;

and if some of them be abhorrent to our ideas of fitness. We need not

marvel at the sting of the bee causing the bee's own death; at drones being

produced in such vast numbers for one single act, with the great majority

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 ichneumonidæ feeding within the live bodies of

caterpillars; and 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 observed.

The complex and little known laws governing variation are the same, as far

as we can see, with the laws which have governed the production of

so-called specific forms. In both cases physical conditions seem to have

produced but little direct effect; yet when varieties enter any zone, they

occasionally assume some of the characters of the species proper to that

zone. In both varieties and species, use and disuse seem to have produced

some effect; for it is difficult to resist this {473} 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 tucutucu, 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 inhabiting the dark caves of

America and Europe. In both varieties and species correlation of growth

seems to have played a most important part, so that when one part has been

modified other parts are necessarily modified. In both varieties and

species reversions to long-lost characters occur. How inexplicable on the

theory of creation is the occasional appearance of stripes on the shoulder

and legs of the several species of the horse-genus and in their hybrids!

How simply is this fact explained if we believe that these species have

descended from a striped progenitor, in the same manner as the several

domestic breeds of pigeon have descended from the blue and barred

rock-pigeon!

On the ordinary view of each species having been independently created, why

should the specific characters, or those by which the species of the same

genus differ from each other, be more variable than the 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,

supposed to have been created independently, have differently coloured

flowers, than if all the species of the genus have 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; {474} and therefore these same characters would be more

likely still to be variable than the generic characters which have been

inherited without change for an enormous period. It is inexplicable on the

theory of creation why a part developed in a very unusual manner in any one

species of a genus, and therefore, as we may naturally infer, of great

importance to the species, should be eminently liable to variation; but, on

my view, this part has undergone, since the several species branched off

from a common progenitor, an unusual amount of variability and

modification, and therefore we might expect this part generally to be still

variable. But a part may be developed in the most unusual manner, like 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 constant by long-continued natural selection.

Glancing at instincts, marvellous as some are, they offer no greater

difficulty than does corporeal structure 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. I have attempted to

show how much light the principle of gradation throws on the admirable

architectural powers of the hive-bee. Habit no doubt sometimes 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 understand how it is that allied species, when placed under

considerably different conditions of life, {475} yet should follow nearly

the same instincts; why the thrush of South America, for instance, lines

her nest 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 apparently not perfect and liable to mistakes, and at many

instincts causing other animals to suffer.

If species be only well-marked and permanent varieties, we can at once see

why their crossed offspring should follow the same complex laws in their

degrees 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 acknowledged varieties. On the other hand, these would

be strange facts if species have been independently created, and varieties

have been produced by secondary laws.

If we admit that the geological record is imperfect in an extreme degree,

then such facts as the record gives, 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 different 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 on the principle of

natural selection; for old forms will be supplanted by new and improved

forms. Neither single species nor groups of species reappear when the chain

of ordinary generation has once been 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 {476} 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 organic beings belong to the same system with recent beings,

falling either into the same or into intermediate groups, follows from the

living and the extinct being the offspring of common parents. As the groups

which have descended from an ancient progenitor have generally diverged in

character, the progenitor with its early descendants will often be

intermediate in character in comparison with its later descendants; and

thus we can see why the more ancient a fossil is, the oftener it stands in

some degree intermediate between existing and allied groups. Recent forms

are generally looked at as being, in some vague sense, higher than ancient

and extinct forms; and they are in so far higher as the later and more

improved forms have conquered the older and less improved organic beings in

the struggle for life. Lastly, the law of the long endurance of allied

forms on the same continent,--of marsupials in Australia, of edentata in

America, and other such cases,--is intelligible, for within a confined

country, the recent and the extinct will naturally be allied by descent.

Looking to geographical distribution, if we admit that there has been

during the long course of ages much migration 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 modification, 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 {477}

modification have been the same. We see the full meaning of the wonderful

fact, which must have struck every traveller, 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 inhabitants

within each great class are plainly related; for they will generally be

descendants of the same progenitors and early colonists. On this same

principle of former migration, combined in most cases with modification, we

can understand, 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, under the most different climates; and likewise the close

alliance of some of the inhabitants of the sea in the northern and southern

temperate zones, though separated by the whole intertropical ocean.

Although two areas may present the same physical conditions of life, we

need feel no surprise at their inhabitants being widely different, if they

have been for a long period completely separated from each other; for as

the relation of organism to organism is the most important of all

relations, and as the two areas will have received colonists from some

third source or from each other, at various periods and in different

proportions, the course of modification in the two areas will inevitably be

different.

On this view of migration, with subsequent modification, we can see why

oceanic islands should be inhabited by few species, but of these, that many

should be peculiar. We can clearly see why those animals which cannot cross

wide spaces of ocean, as frogs and terrestrial mammals, should not inhabit

oceanic islands; and why, on the other hand, new and peculiar species of

bats, which can traverse the ocean, should so often be found on islands far

distant from any continent. Such facts {478} as the presence of peculiar

species of bats, and the absence of all other mammals, on oceanic islands,

are 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 parents

formerly inhabited both areas; and we almost invariably find that wherever

many closely allied species inhabit two areas, some identical species

common to both still exist. Wherever many closely allied yet distinct

species occur, many doubtful forms and varieties of the same species

likewise occur. It is a rule of high generality that the inhabitants of

each area are related to the inhabitants of the nearest source whence

immigrants might have been derived. We see this in nearly all the plants

and animals of the Galapagos archipelago, of Juan Fernandez, and of the

other American islands being related in the most striking manner to the

plants and animals of the neighbouring American mainland; and those of the

Cape de Verde archipelago and 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

constitute one grand natural system, with group subordinate to group, and

with extinct groups often falling in between 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 species and genera within each class are so

complex and circuitous. We see why certain characters are far more

serviceable than others for classification;--why adaptive characters,

though of paramount importance to the being, are of hardly any {479}

importance in classification; why characters derived from rudimentary

parts, though of no service to the being, are often of high classificatory

value; and why embryological characters are the most valuable of all. The

real affinities of all organic beings are due to inheritance or community

of descent. The natural system is a genealogical arrangement, in which we

have to discover the lines of descent by the most permanent characters,

however slight their vital importance may be.

The framework of bones being the same in the hand of a man, wing of a bat,

fin of the porpoise, and leg of the horse,--the same number of vertebræ

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 similarity of pattern in the wing

and 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 intelligible on the view of the gradual modification of parts or

organs, which were alike in the early progenitor of each class. 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 can

clearly see why the embryos of mammals, birds, reptiles, and fishes should

be so closely alike, and should be so unlike the adult forms. We may cease

marvelling at the embryo of an air-breathing mammal or bird having

branchial slits and arteries running in loops, like those in a fish which

has to breathe the air dissolved in water, by the aid of well-developed

branchiæ.

Disuse, aided sometimes by natural selection, will often tend to reduce an

organ, when it has become useless by changed habits or under changed

conditions {480} of life; and we can clearly understand 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 of

acting on an organ during early life; hence the organ will not be much

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 reduced, during successive

generations, by disuse or by the tongue and palate having been better

fitted by natural selection to browse without their aid; whereas in the

calf, the teeth have been left untouched by selection or disuse, and on the

principle of inheritance at corresponding ages have been inherited from a

remote period to the present day. On the view of each organic being and

each separate organ having been specially created, how utterly inexplicable

it is that parts, like the teeth in the embryonic calf or like the

shrivelled wings under the soldered wing-covers of some beetles, should

thus so frequently bear the plain stamp of inutility! Nature may be said to

have taken pains to reveal, by rudimentary organs and by homologous

structures, her scheme of modification, which it seems that we wilfully

will not understand.

I have now recapitulated the chief facts and considerations which have

thoroughly convinced me that species have been modified, during a long

course of descent, by the preservation or the natural selection of many

successive slight favourable variations. I cannot believe that a false

theory would explain, as it seems to me that the theory of natural

selection does explain, {481} the several large classes of facts above

specified. I see no good reason why the views given in this volume should

shock the religious feelings of any one. A celebrated author and divine has

written to me that "he has gradually 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 needful 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, have all the most eminent living naturalists and

geologists rejected this view of 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 invariably 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 any great change of which we do not see the intermediate

steps. The difficulty is the same as that felt by so many geologists, when

Lyell first insisted that long {482} lines of inland cliffs had been

formed, and great valleys excavated, by the slow action of the coast-waves.

The mind cannot possibly grasp the full meaning of the term of a hundred

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 restate a fact. Any one whose

disposition leads him to attach more weight to unexplained difficulties

than to the explanation of a certain number of facts will certainly reject

my theory. A few naturalists, endowed with much flexibility of mind, and

who have already begun to doubt on the immutability 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 conscientiously expressing his conviction;

for only thus can the load of prejudice by which this subject is

overwhelmed 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 {483} they themselves thought were special

creations, and which are still thus looked at by the majority of

naturalists, and which consequently have every external characteristic

feature of true species,--they admit that these have been produced by

variation, but they refuse to extend the same view to other and very

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 blindness of preconceived

opinion. These authors seem no more startled at a miraculous act of

creation than at an ordinary birth. But do they really believe that at

innumerable 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

all 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? Although

naturalists very properly demand a full explanation of every difficulty

from those who believe in the mutability of species, on their own side they

ignore the whole subject of the first appearance of species in what they

consider reverent silence.

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 may consider, by so much the arguments fall away in

force. But some arguments of the greatest weight {484} extend very far. All

the members of whole classes can be connected together by chains of

affinities, and all can be classified on the same principle, in groups

subordinate to groups. Fossil remains sometimes 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

state; and this in some instances necessarily implies an enormous amount of

modification in the descendants. Throughout whole classes various

structures are formed on the same pattern, and at an embryonic age the

species closely resemble each other. Therefore I cannot doubt that the

theory of descent with modification embraces all the members of the same

class. I believe that animals have descended from at most only four or five

progenitors, and plants from an equal or lesser number.

Analogy would lead me one step further, namely, to the belief that all

animals and plants have 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 germinal vesicles, their cellular

structure, and their laws of growth and reproduction. We see this even in

so trifling a circumstance 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. Therefore I should infer

from analogy that probably all the organic beings which have ever lived on

this earth have descended from some one primordial form, into which life

was first breathed by the Creator.

When the views advanced by me in this volume, and by Mr. Wallace in the

Linnean Journal, or when analogous views on the origin of species are

generally {485} 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 in essence a

species. This I feel sure, and I speak after experience, will be no slight

relief. The endless disputes whether or not some fifty species of British

brambles are true 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 differences, 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 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 existence 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 acknowledged to be merely varieties may hereafter be

thought worthy of specific names, as with the primrose and cowslip; 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 {486} 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, rudimentary

and aborted organs, &c., will cease to be metaphorical, and will have a

plain signification. When we no longer look at an organic being as a savage

looks at a ship, as at something wholly beyond his comprehension; when we

regard every production of nature as one which has had a history; when we

contemplate every complex structure and instinct as the summing up of many

contrivances, each useful to the possessor, nearly in the same way as when

we look at any great mechanical invention as 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, I speak from

experience, will 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 correlation of growth, 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 classifying will no doubt become simpler when we

have a definite object in view. We possess no {487} 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. Embryology

will 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

birthplace; 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, 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 of the

inhabitants of the sea on the opposite sides of a continent, and the nature

of the various inhabitants of that continent in relation to their apparent

means of immigration, some light 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 embedded 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 circumstances, and the blank intervals between the successive stages as

having been of vast duration. But we shall {488} 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 include few

identical species, by the general succession of their forms of life. As

species are produced and exterminated by slowly acting and still existing

causes, and not by miraculous acts of creation and by catastrophes; and as

the most important of all causes of organic change is 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 being entailing the improvement 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 lapse of actual time. A

number of species, however, keeping in a body might remain for a long

period unchanged, whilst within this 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. During early periods of

the earth's history, when the forms of life were probably fewer and

simpler, the rate of change was probably slower; and at the first dawn of

life, when very few forms of the simplest structure existed, the rate of

change may have been slow in an extreme degree. The whole history of the

world, as at present known, although of a length quite incomprehensible by

us, will hereafter be recognised as a mere fragment of time, compared with

the ages which have elapsed since the first creature, the progenitor of

innumerable extinct and living descendants, was created.

In the distant future I see open fields for far more {489} important

researches. Psychology will be based on a new foundation, that of the

necessary acquirement of each mental power and capacity by gradation. 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 descendants of some few beings which

lived long before the first bed of the Silurian 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 of

each genus, and all the species of many genera, have left no descendants,

but have become utterly extinct. We can so far take a prophetic glance into

futurity as to foretel that it will be the common and widely-spread

species, belonging to the larger and dominant groups, 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 the

Silurian 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 equally inappreciable length. And as natural selection works {490}

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 an entangled 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 on 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; Inheritance which is almost implied by

reproduction; Variability from the indirect and direct action of the

external 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 conceiving, namely, the

production of the higher animals, directly follows. There is grandeur in

this view of life, with its several powers, having been originally breathed

by the Creator into a few forms or into one; and that, whilst this 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.

* * * * *

{491}

INDEX.

Aberrant groups, 429.

Abyssinia, plants of, 375.

Acclimatisation, 139.

Affinities of extinct species, 329.

---- of organic beings, 411.

Agassiz on Amblyopsis, 139.

---- on groups of species suddenly appearing, 302, 305.

---- on embryological succession, 338.

---- on the glacial period, 366.

---- on embryological characters, 418.

---- on the embryos of vertebrata, 439.

---- on parallelism of embryological development and geological

succession, 449.

Algæ of New Zealand, 376.

Alligators, males, fighting, 88.

Amblyopsis, blind fish, 139.

America, North, productions allied to those of Europe, 371.

--------, boulders and glaciers of, 373.

----, South, no modern formations on west coast, 290.

Ammonites, sudden extinction of, 321.

Anagallis, sterility of, 247.

Analogy of variations, 159.

Ancylus, 386.

Animals, not domesticated from being variable, 17.

----, domestic, descended from several stocks, 19.

--------, acclimatisation of, 141.

---- of Australia, 116.

---- with thicker fur in cold climates, 133.

----, blind, in caves, 137.

----, extinct, of Australia, 339.

Anomma, 240.

Antarctic islands, ancient flora of, 399.

Antirrhinum, 161.

Ants attending aphides, 210.

----, slave-making instinct, 219.

----, neuter, structure of, 236.

Aphides, attended by ants, 210.

Aphis, development of, 442.

Apteryx, 182.

Arab horses, 35.

Aralo-Caspian Sea, 339.

Archaic, M. de, on the succession of species, 325.

Artichoke, Jerusalem, 142.

Ascension, plants of, 389.

Asclepias, pollen of, 193.

Asparagus, 359.

Aspicarpa, 417.

Asses, striped, 163.

Ateuchus, 135.

Audubon on habits of frigate-bird, 185.

---- on variation in birds'-nests, 212.

---- on heron eating seeds, 387.

Australia, animals of, 116.

----. dogs of, 215.

----, extinct animals of, 339.

----, European plants in, 375.

Azara on flies destroying cattle, 72.

Azores, flora of, 363.

Babington, Mr., on British plants, 48.

Balancement of growth, 147.

Bamboo with hooks, 197.

Barberry, flowers of, 98.

Barrande, M., on Silurian colonies, 313.

---- on the succession of species, 325.

---- on parallelism of palæozoic formations, 328.

---- on affinities of ancient species, 330.

Barriers, importance of, 347.

Batrachians on islands, 393.

Bats, how structure acquired, 180.

----, distribution of, 394.

Bear, catching water-insects, 184.

Bee, sting of, 202.

----, queen, killing rivals, 202.

Bees fertilising flowers, 73.

----, hive, not sucking the red clover, 95.

{492}

--------, cell-making instinct, 224.

----, humble, cells of, 225.

----, parasitic, 218.

Beetles, wingless, in Madeira, 135.

---- with deficient tarsi, 135.

Bentham, Mr., on British plants, 48.

----, on classification, 419.

Berkeley, Mr., on seeds in salt-water, 358.

Bermuda, birds of, 391.

Birds acquiring fear, 212.

---- annually cross the Atlantic, 364.

----, colour of, on continents, 132.

----, footsteps and remains of, in secondary rocks, 304.

----, fossil, in caves of Brazil, 339.

---- of Madeira, Bermuda, and Galapagos, 391.

----, song of males, 89.

---- transporting seeds, 361.

----, waders, 385.

----, wingless, 134, 182.

----, with traces of embryonic teeth, 450.

Bizcacha, 349.

----, affinities of, 429.

Bladder for swimming in fish, 190.

Blindness of cave animals, 137.

Blyth, Mr., on distinctness of Indian cattle, 18.

----, on striped Hemionus, 163.

----, on crossed geese, 254.

Boar, shoulder-pad of, 88.

Borrow, Mr., on the Spanish pointer, 35.

Bory St. Vincent on Batrachians, 393.

Bosquet, M., on fossil Chthamalus, 305.

Boulders, erratic, on the Azores, 363.

Branchiæ, 190.

Brent, Mr., on house-tumblers, 214.

----, on hawks killing pigeons, 362.

Brewer, Dr., on American cuckoo, 217.

Britain, mammals of, 396.

Bronn on duration of specific forms, 294.

Brown, Robert, on classification, 415.

Buckman on variation in plants, 10.

Buzareingues on sterility of varieties, 270.

Cabbage, varieties of, crossed, 99.

Calceolaria, 251.

Canary-birds, sterility of hybrids, 252.

Cape de Verde islands, 398.

Cape of Good Hope, plants of, 110, 375.

Carrier-pigeons killed by hawks, 362.

Cassini on flowers of compositæ, 145.

Catasetum, 424.

Cats, with blue eyes, deaf, 12.

----, variation in habits of, 91.

---- curling tail when going to spring, 201.

Cattle destroying fir-trees, 72.

---- destroyed by flies in La Plata, 72.

----, breeds of, locally extinct, 111.

----, fertility of Indian and European breeds, 254.

Cave, inhabitants of, blind, 137.

Centres of creation, 352.

Cephalopodæ, development of, 442.

Cervulus, 253.

Cetacea, teeth and hair, 144.

Ceylon, plants of, 375.

Chalk formation, 322.

Characters, divergence of, 111.

----, sexual, variable, 156.

----, adaptive or analogical, 426.

Charlock, 76.

Checks to increase, 67.

---- ----, mutual, 71.

Chickens, instinctive tameness of, 216.

Chthamalinæ, 289.

Chthamalus, cretacean species of, 305.

Circumstances favourable to selection of domestic products, 40.

---- ---- to natural selection, 102.

Cirripedes capable of crossing, 101.

----, carapace aborted, 148.

----, their ovigerous frena, 192.

----, fossil, 304.

----, larvæ of, 440.

Classification, 413.

Clift, Mr., on the succession of types, 339.

Climate, effects of, in checking increase of beings, 68.

----, adaptation of, to organisms, 139.

{493}

Cobites, intestine of, 190.

Cockroach, 76.

Collections, palæontological, poor, 288.

Colour, influenced by climate, 132.

----, in relation to attacks by flies, 198.

Columba livia, parent of domestic pigeons, 23.

Colymbetes, 386.

Compensation of growth, 147.

Compositæ, outer and inner florets of, 144.

----, male flowers of, 451.

Conclusion, general, 480.

Conditions, slight changes in, favourable to fertility, 267.

Coot, 185.

Coral-islands, seeds drifted to, 361.

---- reefs, indicating movements of earth, 310.

Corn-crake, 186.

Correlation of growth in domestic productions, 11.

---- of growth, 143, 198.

Cowslip, 49.

Creation, single centres of, 352.

Crinum, 250.

Crosses, reciprocal, 258.

Crossing of domestic animals, importance in altering breeds, 20.

----, advantages of, 96.

---- unfavourable to selection, 102.

Crustacea of New Zealand, 376.

Crustacean, blind, 137.

Cryptocerus, 239.

Ctenomys, blind, 137.

Cuckoo, instinct of, 216.

Currants, grafts of, 262.

Currents of sea, rate of, 360.

Cuvier on conditions of existence, 206.

---- on fossil monkeys, 304.

----, Fred., on instinct, 208.

Dana, Prof., on blind cave-animals, 139.

----, on relations of crustaceans of Japan, 372.

----, on crustaceans of New Zealand, 376.

De Candolle on struggle for existence, 62.

---- on umbelliferæ, 146.

---- on general affinities, 430.

----, Alph., on low plants, widely dispersed, 406.

----, ----, on widely-ranging plants being variable, 53.

----, ----, on naturalisation, 115.

----, ----, on winged seeds, 146.

----, ----, on Alpine species suddenly becoming rare, 175.

----, ----, on distribution of plants with large seeds, 360.

----, ----, on vegetation of Australia, 379.

----, ----, on fresh-water plants, 386.

----, ----, on insular plants, 389.

Degradation of coast-rocks, 282.

Denudation, rate of, 285.

---- of oldest rocks, 308.

Development of ancient forms, 336.

Devonian system, 334.

Dianthus, fertility of crosses, 256.

Dirt on feet of birds, 362.

Dispersal, means of, 356.

---- during glacial period, 365.

Distribution, geographical, 346.

----, means of, 356.

Disuse, effects of, under nature, 134.

Divergence of character, 111.

Division, physiological, of labour, 115.

Dogs, hairless, with imperfect teeth, 12.

---- descended from several wild stocks, 18.

----, domestic instincts of, 213.

----, inherited civilisation of, 215.

----, fertility of breeds together, 254.

----, ---- of crosses, 268.

----, proportions of, when young, 444.

Domestication, variation under, 7.

Downing, Mr., on fruit-trees in America, 85.

Downs, North and South, 286.

Dragon-flies, intestines of, 190.

Drift-timber, 360.

Driver-ant, 240.

Drones killed by other bees, 202.

Duck, domestic, wings of, reduced, 11.

----, logger-headed, 182.

{494}

Duckweed, 385.

Dugong, affinities of, 414.

Dung-beetles with deficient tarsi, 135.

Dyticus, 386.

Earl, Mr. W., on the Malay Archipelago, 395.

Ears, drooping, in domestic animals, 11.

----, rudimentary, 454.

Earth, seeds in roots of trees, 361.

Eciton, 238.

Economy of organisation, 147.

Edentata, teeth and hair, 144.

----, fossil species of, 339.

Edwards, Milne, on physiological divisions of labour, 115.

----, on gradations of structure, 194.

----, on embryonical characters, 418.

Eggs, young birds escaping from, 87.

Electric organs, 192.

Elephant, rate of increase, 64.

---- of glacial period, 141.

Embryology, 438.

Existence, struggle for, 60.

----, conditions of, 206.

Extinction, as bearing on natural selection, 109.

---- of domestic varieties, 111,

----, 317.

Eye, structure of, 187.

----, correction for aberration, 202.

Eyes reduced in moles, 137.

Fabre, M. on parasitic sphex, 218.

Falconer, Dr., on naturalisation of plants in India, 65.

---- on fossil crocodile, 313.

---- on elephants and mastodons, 334.

---- and Cautley on mammals of sub-Himalayan beds, 340.

Falkland Island, wolf of, 394.

Faults, 285.

Faunas, marine, 348.

Fear, instinctive, in birds, 212.

Feet of bird, young molluscs adhering to, 385.

Fertility of hybrids, 249.

---- from slight changes in conditions, 267.

---- of crossed varieties, 268.

Fir-trees destroyed by cattle, 72.

---- ----, pollen of, 203.

Fish, flying, 182.

----, teleostean, sudden appearance of, 305.

---- eating seeds, 362, 387.

----, fresh-water, distribution of, 384.

Fishes, ganoid, now confined to fresh water, 107.

----, electric organs of, 192.

----, ganoid, living in fresh water, 321.

---- of southern hemisphere, 376.

Flight, powers of, how acquired, 182.

Flowers, structure of, in relation to crossing, 97.

---- of compositæ and umbelliferæ, 144.

Forbes, E., on colours of shells, 132.

---- on abrupt range of shells in depth, 175.

---- on poorness of palæontological collections, 288.

---- on continuous succession of genera, 316.

---- on continental extensions, 357.

---- on distribution during glacial period, 366.

---- on parallelism in time and space, 409.

Forests, changes in, in America, 74.

Formation, Devonian, 334.

Formations, thickness of, in Britain, 284.

----, intermittent, 290.

Formica rufescens, 219.

---- sanguinea, 219.

---- flava, neuter of, 240.

Frena, ovigerous, of cirripedes, 192.

Fresh-water productions, dispersal of, 383.

Fries on species in large genera being closely allied to other species,

57.

Frigate-bird, 185.

Frogs on islands, 393.

Fruit-trees, gradual improvement of, 37.

---- ---- in United States, 85.

---- ----, varieties of, acclimatised in United States, 142.

{495}

Fuci, crossed, 258.

Fur, thicker in cold climates, 133.

Furze, 439.

Galapagos Archipelago, birds of, 390.

----, productions of, 398, 400.

Galeopithecus, 181.

Game, increase of, checked by vermin, 68.

Gärtner on sterility of hybrids, 247, 255.

----, on reciprocal crosses, 258.

----, on crossed maize and verbascum, 270.

----, on comparison of hybrids and mongrels, 272.

Geese, fertility when crossed, 253.

----, upland, 185.

Genealogy important in classification, 425.

Geoffroy St. Hilaire on balancement, 147.

---- ---- on homologous organs, 434.

---- ----, Isidore, on variability of repeated parts, 149.

---- ----, on correlation in monstrosities, 11.

---- ----, on correlation, 144.

---- ----, on variable parts being often monstrous, 155.

Geographical distribution, 346.

Geography, ancient, 487.

Geology, future progress of, 487.

----, imperfection of the record, 279.

Giraffe, tail of, 195.

Glacial period, 365.

Gmelin on distribution, 365.

Gnathodon, fossil, 368.

Godwin-Austen, Mr., on the Malay Archipelago, 300.

Goethe on compensation of growth, 147.

Gooseberry, grafts of, 262.

Gould, Dr. A., on land-shells, 397.

----, Mr., on colours of birds, 132.

----, on birds of the Galapagos, 398.

----, on distribution of genera of birds, 404.

Gourds, crossed, 270.

Grafts, capacity of, 261.

Grasses, varieties of, 113.

Gray, Dr. Asa, on trees of United States, 100.

----, on naturalised plants in the United States, 115.

----, on rarity of intermediate varieties, 176.

----, on Alpine plants, 365.

----, Dr. J. E., on striped mule, 165.

Grebe, 185.

Groups, aberrant, 429.

Grouse, colours of, 84.

----, red, a doubtful species, 49.

Growth, compensation of, 147.

----, correlation of, in domestic products, 11.

----, correlation of, 143.

Habit, effect of, under domestication, 11.

----, effect of, under nature, 134.

----, diversified, of same species, 183.

Hair and teeth, correlated, 144.

Harcourt, Mr. E. V., on the birds of Madeira, 391.

Hartung, M. on boulders in the Azores, 363.

Hazel-nuts, 359.

Hearne on habits of bears, 184.

Heath, changes in vegetation, 72.

Heer, O., on plants of Madeira, 107.

Helix pomatia, 397.

Helosciadium, 359.

Hemionus, striped, 163.

Herbert, W., on struggle for existence, 62.

----, on sterility of hybrids, 249.

Hermaphrodites crossing, 96.

Heron eating seed, 387.

Heron, Sir R., on peacocks, 89.

Heusinger on white animals not poisoned by certain plants, 12.

Hewitt, Mr., on sterility of first crosses, 264.

Himalaya, glaciers of, 373.

----, plants of, 375.

Hippeastrum, 250.

Holly-trees, sexes of, 93.

Hollyhock, varieties of, crossed, 271.

Hooker, Dr., on trees of New Zealand, 100.

{496}

----, on acclimatisation of Himalayan trees, 140.

----, on flowers of umbelliferæ, 145.

----, on glaciers of Himalaya, 373.

----, on algæ of New Zealand, 376.

----, on vegetation at the base of the Himalaya, 378.

----, on plants of Tierra del Fuego, 374, 378.

----, on Australian plants, 375, 399.

----, on relations of flora of South America, 379.

----, on flora of the Antarctic lands, 381, 399.

----, on the plants of the Galapagos, 392, 398.

Hooks on bamboos, 197.

---- to seeds on islands, 392.

Horner, Mr., on the antiquity of Egyptians, 18.

Horns, rudimentary, 454.

Horse, fossil, in La Plata, 318.

Horses destroyed by flies in La Plata, 72.

----, striped, 163.

----, proportions of, when young, 444.

Horticulturists, selection applied by, 32.

Huber on cells of bees, 230.

----, P., on reason blended with instinct, 208.

----, on habitual nature of instincts, 208.

----, on slave-making ants, 219.

----, on Melipona domestica, 225.

Humble-bees, cells of, 225.

Hunter, J., on secondary sexual characters, 150.

Hutton, Captain, on crossed geese, 254.

Huxley, Prof., on structure of hermaphrodites, 101.

----, on embryological succession, 338.

----, on homologous organs, 438.

----, on the development of aphis, 442.

Hybrids and mongrels compared, 272.

Hybridism, 245.

Hydra, structure of, 190.

Ibla, 148.

Icebergs transporting seeds, 363.

Increase, rate of, 63.

Individuals, numbers favourable to selection, 102.

----, many, whether simultaneously created, 355.

Inheritance, laws of, 12.

---- at corresponding ages, 14, 86.

Insects, colour of, fitted for habitations, 84.

----, sea-side, colours of, 132.

----, blind, in caves, 138.

----, luminous, 193.

----, neuter, 236.

Instinct, 207.

Instincts, domestic, 213.

Intercrossing, advantages of, 96.

Islands, oceanic, 388.

Isolation favourable to selection, 104.

Japan, productions of, 372.

Java, plants of, 375.

Jones, Mr. J. M., on the birds of Bermuda, 391.

Jussieu on classification, 417.

Kentucky, caves of, 137.

Kerguelen-land, flora of, 381, 399.

Kidney-bean, acclimatisation of, 142.

Kidneys of birds, 144.

Kirby on tarsi deficient in beetles, 135.

Knight, Andrew, on cause of variation, 7.

Kölreuter on the barberry, 98.

---- on sterility of hybrids, 246.

---- on reciprocal crosses, 258.

---- on crossed varieties of nicotiana, 271.

---- on crossing male and hermaphrodite flowers, 451.

Lamarck on adaptive characters, 426.

Land-shells, distribution of, 397.

---- of Madeira, naturalised, 403.

Languages, classification of, 422.

Lapse, great, of time, 282.

{497}

Larvæ, 440.

Laurel, nectar secreted by the leaves,

Laws of variation, 131.

Leech, varieties of, 76.

Leguminosæ, nectar secreted by glands, 92.

Lepidosiren, 107, 330.

Life, struggle for, 60.

Lingula, Silurian, 307.

Linnæus, aphorism of, 413.

Lion, mane of, 88.

----, young of, striped, 439.

Lobelia fulgens, 73, 98.

Lobelia, sterility of crosses, 250.

Loess of the Rhine, 384.

Lowness of structure connected with variability, 149.

Lowness, related to wide distribution, 406.

Lubbock, Mr., on the nerves of coccus, 46.

Lucas, Dr. P., on inheritance, 12.

----, on resemblance of child to parent, 275.

Lund and Clausen on fossils of Brazil, 339.

Lyell, Sir C, on the struggle for existence, 62.

----, on modern changes of the earth, 95.

----, on measure of denudation, 284.

----, on a carboniferous land-shell, 289.

----, on strata beneath Silurian system, 308.

----, on the imperfection of the geological record, 311.

----, on the appearance of species, 312.

----, on Barrande's colonies, 313.

----, on tertiary formations of Europe and North America, 323.

----, on parallelism of tertiary formations, 328.

----, on transport of seeds by icebergs, 363.

----, on great alternations of climate, 382.

----, on the distribution of fresh-water shells, 385.

----, on land-shells of Madeira, 402.

Lyell and Dawson on fossilized trees in Nova Scotia, 297.

Macleay on analogical characters, 426.

Madeira, plants of, 107.

----, beetles of, wingless, 135.

----, fossil land-shells of, 339.

----, birds of, 390.

Magpie tame in Norway, 212.

Maize, crossed, 270.

Malay Archipelago compared with Europe, 300.

----, mammals of, 395.

Malpighiaceæ, 417.

Mammæ, rudimentary, 451.

Mammals, fossil, in secondary formation, 304.

----, insular, 394.

Man, origin of races of, 199.

Manatee, rudimentary nails of, 454.

Marsupials of Australia, 116.

----, fossil species of, 339.

Martens, M., experiment on seeds, 360.

Martin, Mr. W. C., on striped mules, 165.

Matteucci on the electric organs of rays, 193.

Matthiola, reciprocal crosses of, 258.

Means of dispersal, 356.

Melipona domestica, 225.

Metamorphism of oldest rocks, 308.

Mice destroying bees, 74.

----, acclimatisation of, 141.

Migration, bears on first appearance of fossils, 297.

Miller, Prof., on the cells of bees, 226.

Mirabilis, crosses of, 258.

Missel-thrush, 76.

Misseltoe, complex relations of, 3.

Mississippi, rate of deposition at mouth, 284.

Mocking-thrush of the Galapagos, 402.

Modification of species, how far applicable, 483.

Moles, blind, 137.

Mongrels, fertility and sterility of, 268.

---- and hybrids compared, 272.

{498}

Monkeys, fossil, 304.

Monocanthus, 424.

Mons, Van, on the origin of fruit-trees, 29.

Moquin-Tandon on sea-side plants, 132.

Morphology, 433.

Mozart, musical powers of, 209.

Mud, seeds in, 386.

Mules, striped, 165.

Müller, Dr. F., on Alpine Australian plants, 375.

Murchison, Sir R., on the formations of Russia, 290.

----, on azoic formations, 308.

----, on extinction, 317.

Mustela vison, 179.

Myanthus, 424.

Myrmecocystus, 239.

Myrmica, eyes of, 240.

Nails, rudimentary, 454.

Natural history, future progress of, 485.

---- selection, 80.

---- system, 413.

Naturalisation of forms distinct from the indigenous species, 115.

---- in New Zealand, 201.

Nautilus, Silurian, 307.

Nectar of plants, 92.

Nectaries, how formed, 92.

Nelumbium luteum, 387.

Nests, variation in, 211.

Neuter insects, 236.

Newman, Mr., on humble-bees, 74.

New Zealand, productions of, not perfect, 201.

----, naturalised products of, 337.

----, fossil birds of, 339.

----, glacial action in, 373.

----, crustaceans of, 376.

----, algæ of, 376.

----, number of plants of, 389.

----, flora of, 399.

Nicotiana, crossed varieties of, 271.

----, certain species very sterile, 257.

Noble, Mr., on fertility of Rhododendron, 252.

Nodules, phosphatic, in azoic rocks, 308.

Oak, varieties of, 50.

Onites apelles, 135.

Orchis, pollen of, 193.

Organs of extreme perfection, 186.

----, electric, of fishes, 192.

---- of little importance, 194.

----, homologous, 434.

----, rudiments of, and nascent, 450.

Ornithorhynchus, 107, 416.

Ostrich not capable of flight, 134.

----, habit of laying eggs together, 218.

----, American, two species of, 349.

Otter, habits of, how acquired, 179.

Ouzel, water, 185.

Owen, Prof., on birds not flying, 134.

----, on vegetative repetition, 149.

----, on variable length of arms in ourang-outang, 150.

----, on the swim-bladder of fishes, 191.

----, on electric organs, 192.

----, on fossil horse of La Plata, 319.

----, on relations of ruminants and pachyderms, 329.

----, on fossil birds of New Zealand, 339.

----, on succession of types, 339.

----, on affinities of the dugong, 414.

----, on homologous organs, 434.

----, on the metamorphosis of cephalopods and spiders, 442.

Pacific Ocean, faunas of, 348.

Paley on no organ formed to give pain, 201.

Pallas on the fertility of the wild stocks of domestic animals, 254.

Paraguay, cattle destroyed by flies, 72.

Parasites, 217.

Partridge, dirt on feet, 363.

Parts greatly developed, variable, 150.

----, degrees of utility of, 201.

Parus major, 184.

Passiflora, 251.

Peaches in United States, 85.

Pear, grafts of, 262.

{499}

Pelargonium, flowers of, 145.

----, sterility of, 251.

Pelvis of women, 144.

Peloria, 145.

Period, glacial, 365.

Petrels, habits of, 184.

Phasianus, fertility of hybrids, 253.

Pheasant, young, wild, 216.

Philippi on tertiary species in Sicily, 312.

Pictet, Prof., on groups of species suddenly appearing, 302, 305.

----, on rate of organic change, 313.

----, on continuous succession of genera, 316.

----, on close alliance of fossils in consecutive formations, 335.

----, on embryological succession, 338.

Pierce, Mr., on varieties of wolves, 91.

Pigeons with feathered feet and skin between toes, 12.

----, breeds described, and origin of, 20.

----, breeds of, how produced, 39, 42.

----, tumbler, not being able to get out of egg, 87.

----, reverting to blue colour, 160.

----, instinct of tumbling, 214.

----, carriers, killed by hawks, 362.

----, young of, 445.

Pistil, rudimentary, 451.

Plants, poisonous, not affecting certain coloured animals, 12.

----, selection applied to, 32.

----, gradual improvement of, 37.

---- not improved in barbarous countries, 38.

---- destroyed by insects, 67.

----, in midst of range, have to struggle with other plants, 77.

----, nectar of, 92.

----, fleshy, on sea-shores, 132.

----, fresh-water, distribution of, 386.

----, low in scale, widely distributed, 406.

Plumage, laws of change in sexes of birds, 89.

Plums in the United States, 85.

Pointer dog, origin of, 35.

----, habits of, 213.

Poison not affecting certain coloured animals, 12.

----, similar effect of, on animals and plants, 484.

Pollen of fir-trees, 203.

Poole, Col., on striped hemionus, 163.

Potamogeton, 387.

Prestwich, Mr., on English and French eocene formations, 328.

Primrose, 49.

----, sterility of, 247.

Primula, varieties of, 49.

Proteolepas, 148.

Proteus, 139.

Psychology, future progress of, 489.

Quagga, striped, 165.

Quince, grafts of, 262.

Rabbit, disposition of young, 215.

Races, domestic, characters of, 16.

Race-horses, Arab, 35.

----, English, 356.

Ramond on plants of Pyrenees, 368.

Ramsay, Prof., on thickness of the British formations, 284.

----, on faults, 285.

Ratio of increase, 63.

Rats, supplanting each other, 76.

----, acclimatisation of, 141.

----, blind in cave, 137.

Rattle-snake, 201.

Reason and instinct, 208.

Recapitulation, general, 459.

Reciprocity of crosses, 258.

Record, geological, imperfect, 279.

Rengger on flies destroying cattle, 72.

Reproduction, rate of, 63.

Resemblance to parents in mongrels and hybrids, 273.

Reversion, law of inheritance, 14.

---- in pigeons to blue colour, 160.

Rhododendron, sterility of, 251.

Richard, Prof., on Aspicarpa, 417.

Richardson, Sir J., on structure of squirrels, 180.

----, on fishes of the southern hemisphere, 376.

Robinia, grafts of, 262.

{500}

Rodents, blind, 137.

Rudimentary organs, 450.

Rudiments important for classification, 416.

Sagaret on grafts, 262.

Salmons, males fighting, and hooked jaws of, 88.

Salt-water, how far injurious to seeds, 358.

Saurophagus sulphuratus, 183.

Schiödte on blind insects, 138.

Schlegel on snakes, 144.

Sea-water, how far injurious to seeds, 358.

Sebright, Sir J., on crossed animals, 20.

----, on selection of pigeons, 31.

Sedgwick, Prof., on groups of species suddenly appearing, 302.

Seedlings destroyed by insects, 67.

Seeds, nutriment in, 77.

----, winged, 146.

----, power of resisting salt-water, 358.

---- in crops and intestines of birds, 361.

---- eaten by fish, 362, 387.

---- in mud, 386.

----, hooked, on islands, 392.

Selection of domestic products, 29.

----, principle not of recent origin, 33.

----, unconscious, 34.

----, natural, 80.

----, sexual, 87.

----, natural, circumstances favourable to, 102.

Sexes, relations of, 87.

Sexual characters variable, 156.

---- selection, 87.

Sheep, Merino, their selection, 31.

----, two sub-breeds unintentionally produced, 36.

----, mountain, varieties of, 76.

Shells, colours of, 132.

----, littoral, seldom embedded, 288.

----, fresh-water, dispersal of, 385

---- of Madeira, 391.

----, land, distribution of, 397.

Silene, fertility of crosses, 257.

Silliman, Prof., on blind rat, 137.

Skulls of young mammals, 197, 436.

Slave-making instinct, 219.

Smith, Col. Hamilton, on striped horses, 164.

----, Mr. Fred., on slave-making ants, 219.

----, on neuter ants, 239.

----, Mr., of Jordan Hill, on the degradation of coast-rocks, 283.

Snap-dragon, 161.

Somerville, Lord, on selection of sheep, 31.

Sorbus, grafts of, 262.

Spaniel, King Charles's breed, 35.

Species, polymorphic, 46.

----, common, variable, 53.

---- in large genera variable, 54.

----, groups of, suddenly appearing, 302, 307.

---- beneath Silurian formations, 307.

---- successively appearing, 312.

---- changing simultaneously throughout the world, 322.

Spencer, Lord, on increase in size of cattle, 35.

Sphex, parasitic, 218.

Spiders, development of, 442.

Spitz-dog crossed with fox, 268.

Sports in plants, 9.

Sprengel, C. C, on crossing, 98.

----, on ray-florets, 145.

Squirrels, gradations in structure, 180.

Staffordshire, heath, changes in, 71.

Stag-beetles, fighting, 88.

Sterility from changed conditions of life, 9.

---- of hybrids, 246.

---- ----, laws of, 255.

---- ----, causes of, 263.

---- from unfavourable conditions, 265.

---- of certain varieties, 269.

St. Helena, productions of, 390.

St. Hilaire, Aug., on classification, 418.

St. John, Mr., on habits of cats, 91.

Sting of bee, 202.

Stocks, aboriginal, of domestic animals, 18.

Strata, thickness of, in Britain, 284.

Stripes on horses, 163.

{501}

Structure, degrees of utility of, 201.

Struggle for existence, 60.

Succession, geological, 312.

Succession of types in same areas, 338.

Swallow, one species supplanting another, 76.

Swim-bladder, 190.

System, natural, 413.

Tail of giraffe, 195.

---- of aquatic animals, 196.

----, rudimentary, 454.

Tarsi deficient, 135.

Tausch on umbelliferous flowers, 146.

Teeth and hair correlated, 144.

----, embryonic, traces of, in birds, 450.

----, rudimentary, in embryonic calf, 450, 480.

Tegetmeier, Mr., on cells of bees, 228, 233.

Temminck on distribution aiding classification, 419.

Thouin on grafts, 262.

Thrush, aquatic species of, 185.

----, mocking, of the Galapagos, 402.

----, young of, spotted, 439.

----, nest of, 243.

Thuret, M., on crossed fuci, 258.

Thwaites, Mr., on acclimatisation, 140.

Tierra del Fuego, dogs of, 215.

----, plants of, 374, 378.

Timber-drift, 360.

Time, lapse of, 282.

Titmouse, 184.

Toads on islands, 393.

Tobacco, crossed varieties of, 271.

Tomes, Mr., on the distribution of bats, 395.

Transitions in varieties rare, 172.

Trees on islands belong to peculiar orders, 392.

---- with separated sexes, 99.

Trifolium pratense, 73, 94.

---- incarnatum, 94.

Trigonia, 321.

Trilobites, 307.

----, sudden extinction of, 321.

Troglodytes, 243.

Tucutucu, blind, 137.

Tumbler pigeons, habits of, hereditary, 214.

----, young of, 446.

Turkey-cock, brush of hair on breast, 90.

Turkey, naked skin on head, 197.

----, young, wild, 216.

Turnip and cabbage, analogous variations of, 159.

Type, unity of, 206.

Types, succession of, in same areas, 339.

Udders enlarged by use, 11.

----, rudimentary, 451.

Ulex, young leaves of, 439.

Umbelliferæ, outer and inner florets of, 144.

Unity of type, 206.

Use, effects of, under domestication, 11.

----, effects of, in a state of nature, 134.

Utility, how far important in the construction of each part, 199.

Valenciennes on fresh-water fish, 384.

Variability of mongrels and hybrids, 274.

Variation under domestication, 7.

---- caused by reproductive system being affected by conditions of life,

---- under nature, 44.

----, laws of, 131.

Variations appear at corresponding ages, 14, 86.

----, analogous in distinct species, 159.

Varieties, natural, 44.

----, struggle between, 75.

----, domestic, extinction of, 111.

----, transitional, rarity of, 172.

----, when crossed, fertile, 268.

----, when crossed, sterile, 269.

----, classification of, 423.

Verbascum, sterility of, 251.

----, varieties of, crossed, 271.

Verneuil, M. de, on the succession of species, 325.

Viola tricolor, 73.

{502}

Volcanic islands, denudation of, 285.

Vulture, naked skin on head, 197.

Wading-birds, 386.

Wallace, Mr., on origin of species, 2.

----, on law of geographical distribution, 355.

----, on the Malay Archipelago, 395.

Wasp, sting of, 202.

Water, fresh, productions of, 383.

Water-hen, 185.

Waterhouse, Mr., on Australian marsupials, 116.

----, on greatly developed parts being variable, 150.

----, on the cells of bees, 225.

----, on general affinities, 429.

Water-ouzel, 185.

Watson, Mr. H. C, on range of varieties of British plants, 58.

----, on acclimatisation, 140.

----, on flora of Azores, 363.

----, on Alpine plants, 368, 376.

----, on rarity of intermediate varieties, 176.

Weald, denudation of, 285.

Web of feet in water-birds, 185.

West Indian islands, mammals of, 396.

Westwood on species in large genera being closely allied to others, 57.

---- on the tarsi of Engidæ, 157.

---- on the antennæ of hymenopterous insects, 415.

Wheat, varieties of, 113.

White Mountains, flora of, 365.

Wings, reduction of size, 134.

---- of insects homologous with branchiæ, 191.

----, rudimentary, in insects, 450.

Wolf crossed with dog, 214.

---- of Falkland Isles, 394.

Wollaston, Mr., on varieties of insects, 48.

----, on fossil varieties of land-shells in Madeira, 52.

----, on colours of insects on sea-shore, 132.

----, on wingless beetles, 135.

----, on rarity of intermediate varieties, 176.

----, on insular insects, 389.

----, on land-shells of Madeira, naturalised, 402.

Wolves, varieties of, 90.

Woodpecker, habits of, 184.

----, green colour of, 197.

Woodward, Mr., on the duration of specific forms, 294.

----, on the continuous succession of genera, 316.

----, on the succession of types, 339.

World, species changing simultaneously throughout, 322.

Wrens, nest of, 243.

Youatt, Mr., on selection, 31.

----, on sub-breeds of sheep, 36.

----, on rudimentary horns in young cattle, 454.

Zebra, stripes on, 163.

THE END.

* * * * *

LONDON: PRINTED BY WILLIAM CLOWES AND SONS, STAMFORD STREET, AND CHARING

CROSS.

* * * * *

Corrections made to printed original.

p. 133. "the slightest use to a being": 'slighest' in original.

p. 193. "as Matteucci asserts": 'Matteucei' in original (the index

correctly has Matteucci).

p. 201. "deposited in the living bodies of other insects": 'depo-sisted'

(across page break) in original.

p. 315. "the newly-formed fantail": 'faintail' in original.

p. 398. "the volcanic nature of the soil": 'volanic' in original.

p. 403. "Madeira and the adjoining islet": 'Maderia' in original; and so in

"from Porto Santo to Madeira".

p. 442. "the same individual embryo": 'indivividual' in original.

p. 458. "innumerable species, genera, and families": 'inumerable' in

original.

p. 490. "Inheritance which is almost implied by reproduction":

'Inheritrnce' in original.

On the Origin of Species by Means of Natural Selection or the Preservation of Favoured Races in the Struggle for Life. (2nd edition) · 第 14 / 14 章