CHAPTER VII.

MISCELLANEOUS OBJECTIONS TO THE THEORY OF NATURAL SELECTION.

Longevity—Modifications not necessarily simultaneous—Modifications

apparently of no direct service—Progressive development—Characters of

small functional importance, the most constant—Supposed incompetence of

natural selection to account for the incipient stages of useful

structures—Causes which interfere with the acquisition through natural

selection of useful structures—Gradations of structure with changed

functions—Widely different organs in members of the same class,

developed from one and the same source—Reasons for disbelieving in

great and abrupt modifications.

I will devote this chapter to the consideration of various

miscellaneous objections which have been advanced against my views, as

some of the previous discussions may thus be made clearer; but it would

be useless to discuss all of them, as many have been made by writers

who have not taken the trouble to understand the subject. Thus a

distinguished German naturalist has asserted that the weakest part of

my theory is, that I consider all organic beings as imperfect: what I

have really said is, that all are not as perfect as they might have

been in relation to their conditions; and this is shown to be the case

by so many native forms in many quarters of the world having yielded

their places to intruding foreigners. Nor can organic beings, even if

they were at any one time perfectly adapted to their conditions of

life, have remained so, when their conditions changed, unless they

themselves likewise changed; and no one will dispute that the physical

conditions of each country, as well as the number and kinds of its

inhabitants, have undergone many mutations.

A critic has lately insisted, with some parade of mathematical

accuracy, that longevity is a great advantage to all species, so that

he who believes in natural selection “must arrange his genealogical

tree” in such a manner that all the descendants have longer lives than

their progenitors! Cannot our critics conceive that a biennial plant or

one of the lower animals might range into a cold climate and perish

there every winter; and yet, owing to advantages gained through natural

selection, survive from year to year by means of its seeds or ova? Mr.

E. Ray Lankester has recently discussed this subject, and he concludes,

as far as its extreme complexity allows him to form a judgment, that

longevity is generally related to the standard of each species in the

scale of organisation, as well as to the amount of expenditure in

reproduction and in general activity. And these conditions have, it is

probable, been largely determined through natural selection.

It has been argued that, as none of the animals and plants of Egypt, of

which we know anything, have changed during the last three or four

thousand years, so probably have none in any part of the world. But, as

Mr. G.H. Lewes has remarked, this line of argument proves too much, for

the ancient domestic races figured on the Egyptian monuments, or

embalmed, are closely similar or even identical with those now living;

yet all naturalists admit that such races have been produced through

the modification of their original types. The many animals which have

remained unchanged since the commencement of the glacial period, would

have been an incomparably stronger case, for these have been exposed to

great changes of climate and have migrated over great distances;

whereas, in Egypt, during the last several thousand years, the

conditions of life, as far as we know, have remained absolutely

uniform. The fact of little or no modification having been effected

since the glacial period, would have been of some avail against those

who believe in an innate and necessary law of development, but is

powerless against the doctrine of natural selection or the survival of

the fittest, which implies that when variations or individual

differences of a beneficial nature happen to arise, these will be

preserved; but this will be effected only under certain favourable

circumstances.

The celebrated palæontologist, Bronn, at the close of his German

translation of this work, asks how, on the principle of natural

selection, can a variety live side by side with the parent species? If

both have become fitted for slightly different habits of life or

conditions, they might live together; and if we lay on one side

polymorphic species, in which the variability seems to be of a peculiar

nature, and all mere temporary variations, such as size, albinism, &c.,

the more permanent varieties are generally found, as far as I can

discover, inhabiting distinct stations, such as high land or low land,

dry or moist districts. Moreover, in the case of animals which wander

much about and cross freely, their varieties seem to be generally

confined to distinct regions.

Bronn also insists that distinct species never differ from each other

in single characters, but in many parts; and he asks, how it always

comes that many parts of the organisation should have been modified at

the same time through variation and natural selection? But there is no

necessity for supposing that all the parts of any being have been

simultaneously modified. The most striking modifications, excellently

adapted for some purpose, might, as was formerly remarked, be acquired

by successive variations, if slight, first in one part and then in

another; and as they would be transmitted all together, they would

appear to us as if they had been simultaneously developed. The best

answer, however, to the above objection is afforded by those domestic

races which have been modified, chiefly through man’s power of

selection, for some special purpose. Look at the race and dray-horse,

or at the greyhound and mastiff. Their whole frames, and even their

mental characteristics, have been modified; but if we could trace each

step in the history of their transformation—and the latter steps can be

traced—we should not see great and simultaneous changes, but first one

part and then another slightly modified and improved. Even when

selection has been applied by man to some one character alone—of which

our cultivated plants offer the best instances—it will invariably be

found that although this one part, whether it be the flower, fruit, or

leaves, has been greatly changed, almost all the other parts have been

slightly modified. This may be attributed partly to the principle of

correlated growth, and partly to so-called spontaneous variation.

A much more serious objection has been urged by Bronn, and recently by

Broca, namely, that many characters appear to be of no service whatever

to their possessors, and therefore cannot have been influenced through

natural selection. Bronn adduces the length of the ears and tails in

the different species of hares and mice—the complex folds of enamel in

the teeth of many animals, and a multitude of analogous cases. With

respect to plants, this subject has been discussed by Nägeli in an

admirable essay. He admits that natural selection has effected much,

but he insists that the families of plants differ chiefly from each

other in morphological characters, which appear to be quite unimportant

for the welfare of the species. He consequently believes in an innate

tendency towards progressive and more perfect development. He specifies

the arrangement of the cells in the tissues, and of the leaves on the

axis, as cases in which natural selection could not have acted. To

these may be added the numerical divisions in the parts of the flower,

the position of the ovules, the shape of the seed, when not of any use

for dissemination, &c.

There is much force in the above objection. Nevertheless, we ought, in

the first place, to be extremely cautious in pretending to decide what

structures now are, or have formerly been, of use to each species. In

the second place, it should always be borne in mind that when one part

is modified, so will be other parts, through certain dimly seen causes,

such as an increased or diminished flow of nutriment to a part, mutual

pressure, an early developed part affecting one subsequently developed,

and so forth—as well as through other causes which lead to the many

mysterious cases of correlation, which we do not in the least

understand. These agencies may be all grouped together, for the sake of

brevity, under the expression of the laws of growth. In the third

place, we have to allow for the direct and definite action of changed

conditions of life, and for so-called spontaneous variations, in which

the nature of the conditions apparently plays a quite subordinate part.

Bud-variations, such as the appearance of a moss-rose on a common rose,

or of a nectarine on a peach-tree, offer good instances of spontaneous

variations; but even in these cases, if we bear in mind the power of a

minute drop of poison in producing complex galls, we ought not to feel

too sure that the above variations are not the effect of some local

change in the nature of the sap, due to some change in the conditions.

There must be some efficient cause for each slight individual

difference, as well as for more strongly marked variations which

occasionally arise; and if the unknown cause were to act persistently,

it is almost certain that all the individuals of the species would be

similarly modified.

In the earlier editions of this work I underrated, as it now seems

probable, the frequency and importance of modifications due to

spontaneous variability. But it is impossible to attribute to this

cause the innumerable structures which are so well adapted to the

habits of life of each species. I can no more believe in this than that

the well-adapted form of a race-horse or greyhound, which before the

principle of selection by man was well understood, excited so much

surprise in the minds of the older naturalists, can thus be explained.

It may be worth while to illustrate some of the foregoing remarks. With

respect to the assumed inutility of various parts and organs, it is

hardly necessary to observe that even in the higher and best-known

animals many structures exist, which are so highly developed that no

one doubts that they are of importance, yet their use has not been, or

has only recently been, ascertained. As Bronn gives the length of the

ears and tail in the several species of mice as instances, though

trifling ones, of differences in structure which can be of no special

use, I may mention that, according to Dr. Schöbl, the external ears of

the common mouse are supplied in an extraordinary manner with nerves,

so that they no doubt serve as tactile organs; hence the length of the

ears can hardly be quite unimportant. We shall, also, presently see

that the tail is a highly useful prehensile organ to some of the

species; and its use would be much influence by its length.

With respect to plants, to which on account of Nägeli’s essay I shall

confine myself in the following remarks, it will be admitted that the

flowers of the orchids present a multitude of curious structures, which

a few years ago would have been considered as mere morphological

differences without any special function; but they are now known to be

of the highest importance for the fertilisation of the species through

the aid of insects, and have probably been gained through natural

selection. No one until lately would have imagined that in dimorphic

and trimorphic plants the different lengths of the stamens and pistils,

and their arrangement, could have been of any service, but now we know

this to be the case.

In certain whole groups of plants the ovules stand erect, and in others

they are suspended; and within the same ovarium of some few plants, one

ovule holds the former and a second ovule the latter position. These

positions seem at first purely morphological, or of no physiological

signification; but Dr. Hooker informs me that within the same ovarium

the upper ovules alone in some cases, and in others the lower ones

alone are fertilised; and he suggests that this probably depends on the

direction in which the pollen-tubes enter the ovarium. If so, the

position of the ovules, even when one is erect and the other suspended

within the same ovarium, would follow the selection of any slight

deviations in position which favoured their fertilisation, and the

production of seed.

Several plants belonging to distinct orders habitually produce flowers

of two kinds—the one open, of the ordinary structure, the other closed

and imperfect. These two kinds of flowers sometimes differ wonderfully

in structure, yet may be seen to graduate into each other on the same

plant. The ordinary and open flowers can be intercrossed; and the

benefits which certainly are derived from this process are thus

secured. The closed and imperfect flowers are, however, manifestly of

high importance, as they yield with the utmost safety a large stock of

seed, with the expenditure of wonderfully little pollen. The two kinds

of flowers often differ much, as just stated, in structure. The petals

in the imperfect flowers almost always consist of mere rudiments, and

the pollen-grains are reduced in diameter. In Ononis columnæ five of

the alternate stamens are rudimentary; and in some species of Viola

three stamens are in this state, two retaining their proper function,

but being of very small size. In six out of thirty of the closed

flowers in an Indian violet (name unknown, for the plants have never

produced with me perfect flowers), the sepals are reduced from the

normal number of five to three. In one section of the Malpighiaceæ the

closed flowers, according to A. de Jussieu, are still further modified,

for the five stamens which stand opposite to the sepals are all

aborted, a sixth stamen standing opposite to a petal being alone

developed; and this stamen is not present in the ordinary flowers of

this species; the style is aborted; and the ovaria are reduced from

three to two. Now although natural selection may well have had the

power to prevent some of the flowers from expanding, and to reduce the

amount of pollen, when rendered by the closure of the flowers

superfluous, yet hardly any of the above special modifications can have

been thus determined, but must have followed from the laws of growth,

including the functional inactivity of parts, during the progress of

the reduction of the pollen and the closure of the flowers.

It is so necessary to appreciate the important effects of the laws of

growth, that I will give some additional cases of another kind, namely

of differences in the same part or organ, due to differences in

relative position on the same plant. In the Spanish chestnut, and in

certain fir-trees, the angles of divergence of the leaves differ,

according to Schacht, in the nearly horizontal and in the upright

branches. In the common rue and some other plants, one flower, usually

the central or terminal one, opens first, and has five sepals and

petals, and five divisions to the ovarium; while all the other flowers

on the plant are tetramerous. In the British Adoxa the uppermost flower

generally has two calyx-lobes with the other organs tetramerous, while

the surrounding flowers generally have three calyx-lobes with the other

organs pentamerous. In many Compositæ and Umbelliferæ (and in some

other plants) the circumferential flowers have their corollas much more

developed than those of the centre; and this seems often connected with

the abortion of the reproductive organs. It is a more curious fact,

previously referred to, that the achenes or seeds of the circumference

and centre sometimes differ greatly in form, colour and other

characters. In Carthamus and some other Compositæ the central achenes

alone are furnished with a pappus; and in Hyoseris the same head yields

achenes of three different forms. In certain Umbelliferæ the exterior

seeds, according to Tausch, are orthospermous, and the central one

cœlospermous, and this is a character which was considered by De

Candolle to be in other species of the highest systematic importance.

Professor Braun mentions a Fumariaceous genus, in which the flowers in

the lower part of the spike bear oval, ribbed, one-seeded nutlets; and

in the upper part of the spike, lanceolate, two-valved and two-seeded

siliques. In these several cases, with the exception of that of the

well-developed ray-florets, which are of service in making the flowers

conspicuous to insects, natural selection cannot, as far as we can

judge, have come into play, or only in a quite subordinate manner. All

these modifications follow from the relative position and inter-action

of the parts; and it can hardly be doubted that if all the flowers and

leaves on the same plant had been subjected to the same external and

internal condition, as are the flowers and leaves in certain positions,

all would have been modified in the same manner.

In numerous other cases we find modifications of structure, which are

considered by botanists to be generally of a highly important nature,

affecting only some of the flowers on the same plant, or occurring on

distinct plants, which grow close together under the same conditions.

As these variations seem of no special use to the plants, they cannot

have been influenced by natural selection. Of their cause we are quite

ignorant; we cannot even attribute them, as in the last class of cases,

to any proximate agency, such as relative position. I will give only a

few instances. It is so common to observe on the same plant, flowers

indifferently tetramerous, pentamerous, &c., that I need not give

examples; but as numerical variations are comparatively rare when the

parts are few, I may mention that, according to De Candolle, the

flowers of Papaver bracteatum offer either two sepals with four petals

(which is the common type with poppies), or three sepals with six

petals. The manner in which the petals are folded in the bud is in most

groups a very constant morphological character; but Professor Asa Gray

states that with some species of Mimulus, the æstivation is almost as

frequently that of the Rhinanthideæ as of the Antirrhinideæ, to which

latter tribe the genus belongs. Aug. St. Hilaire gives the following

cases: the genus Zanthoxylon belongs to a division of the Rutaceæ with

a single ovary, but in some species flowers may be found on the same

plant, and even in the same panicle, with either one or two ovaries. In

Helianthemum the capsule has been described as unilocular or

tri-locular; and in H. mutabile, “Une lame _plus ou moins large_,

s’étend entre le pericarpe et le placenta.” In the flowers of Saponaria

officinalis Dr. Masters has observed instances of both marginal and

free central placentation. Lastly, St. Hilaire found towards the

southern extreme of the range of Gomphia oleæformis two forms which he

did not at first doubt were distinct species, but he subsequently saw

them growing on the same bush; and he then adds, “Voilà donc dans un

même individu des loges et un style qui se rattachent tantôt à un axe

verticale et tantôt à un gynobase.”

We thus see that with plants many morphological changes may be

attributed to the laws of growth and the inter-action of parts,

independently of natural selection. But with respect to Nägeli’s

doctrine of an innate tendency towards perfection or progressive

development, can it be said in the case of these strongly pronounced

variations, that the plants have been caught in the act of progressing

towards a higher state of development? On the contrary, I should infer

from the mere fact of the parts in question differing or varying

greatly on the same plant, that such modifications were of extremely

small importance to the plants themselves, of whatever importance they

may generally be to us for our classifications. The acquisition of a

useless part can hardly be said to raise an organism in the natural

scale; and in the case of the imperfect, closed flowers, above

described, if any new principle has to be invoked, it must be one of

retrogression rather than of progression; and so it must be with many

parasitic and degraded animals. We are ignorant of the exciting cause

of the above specified modifications; but if the unknown cause were to

act almost uniformly for a length of time, we may infer that the result

would be almost uniform; and in this case all the individuals of the

species would be modified in the same manner.

From the fact of the above characters being unimportant for the welfare

of the species, any slight variations which occurred in them would not

have been accumulated and augmented through natural selection. A

structure which has been developed through long-continued selection,

when it ceases to be of service to a species, generally becomes

variable, as we see with rudimentary organs; for it will no longer be

regulated by this same power of selection. But when, from the nature of

the organism and of the conditions, modifications have been induced

which are unimportant for the welfare of the species, they may be, and

apparently often have been, transmitted in nearly the same state to

numerous, otherwise modified, descendants. It cannot have been of much

importance to the greater number of mammals, birds, or reptiles,

whether they were clothed with hair, feathers or scales; yet hair has

been transmitted to almost all mammals, feathers to all birds, and

scales to all true reptiles. A structure, whatever it may be, which is

common to many allied forms, is ranked by us as of high systematic

importance, and consequently is often assumed to be of high vital

importance to the species. Thus, as I am inclined to believe,

morphological differences, which we consider as important—such as the

arrangement of the leaves, the divisions of the flower or of the

ovarium, the position of the ovules, &c., first appeared in many cases

as fluctuating variations, which sooner or later became constant

through the nature of the organism and of the surrounding conditions,

as well as through the intercrossing of distinct individuals, but not

through natural selection; for as these morphological characters do not

affect the welfare of the species, any slight deviations in them could

not have been governed or accumulated through this latter agency. It is

a strange result which we thus arrive at, namely, that characters of

slight vital importance to the species, are the most important to the

systematist; but, as we shall hereafter see when we treat of the

genetic principle of classification, this is by no means so paradoxical

as it may at first appear.

Although we have no good evidence of the existence in organic beings of

an innate tendency towards progressive development, yet this

necessarily follows, as I have attempted to show in the fourth chapter,

through the continued action of natural selection. For the best

definition which has ever been given of a high standard of

organisation, is the degree to which the parts have been specialised or

differentiated; and natural selection tends towards this end, inasmuch

as the parts are thus enabled to perform their functions more

efficiently.

A distinguished zoologist, Mr. St. George Mivart, has recently

collected all the objections which have ever been advanced by myself

and others against the theory of natural selection, as propounded by

Mr. Wallace and myself, and has illustrated them with admirable art and

force. When thus marshalled, they make a formidable array; and as it

forms no part of Mr. Mivart’s plan to give the various facts and

considerations opposed to his conclusions, no slight effort of reason

and memory is left to the reader, who may wish to weigh the evidence on

both sides. When discussing special cases, Mr. Mivart passes over the

effects of the increased use and disuse of parts, which I have always

maintained to be highly important, and have treated in my “Variation

under Domestication” at greater length than, as I believe, any other

writer. He likewise often assumes that I attribute nothing to

variation, independently of natural selection, whereas in the work just

referred to I have collected a greater number of well-established cases

than can be found in any other work known to me. My judgment may not be

trustworthy, but after reading with care Mr. Mivart’s book, and

comparing each section with what I have said on the same head, I never

before felt so strongly convinced of the general truth of the

conclusions here arrived at, subject, of course, in so intricate a

subject, to much partial error.

All Mr. Mivart’s objections will be, or have been, considered in the

present volume. The one new point which appears to have struck many

readers is, “That natural selection is incompetent to account for the

incipient stages of useful structures.” This subject is intimately

connected with that of the gradation of the characters, often

accompanied by a change of function, for instance, the conversion of a

swim-bladder into lungs, points which were discussed in the last

chapter under two headings. Nevertheless, I will here consider in some

detail several of the cases advanced by Mr. Mivart, selecting those

which are the most illustrative, as want of space prevents me from

considering all.

The giraffe, by its lofty stature, much elongated neck, fore legs, head

and tongue, has its whole frame beautifully adapted for browsing on the

higher branches of trees. It can thus obtain food beyond the reach of

the other Ungulata or hoofed animals inhabiting the same country; and

this must be a great advantage to it during dearths. The Niata cattle

in South America show us how small a difference in structure may make,

during such periods, a great difference in preserving an animal’s life.

These cattle can browse as well as others on grass, but from the

projection of the lower jaw they cannot, during the often recurrent

droughts, browse on the twigs of trees, reeds, &c., to which food the

common cattle and horses are then driven; so that at these times the

Niatas perish, if not fed by their owners. Before coming to Mr.

Mivart’s objections, it may be well to explain once again how natural

selection will act in all ordinary cases. Man has modified some of his

animals, without necessarily having attended to special points of

structure, by simply preserving and breeding from the fleetest

individuals, as with the race-horse and greyhound, or as with the

game-cock, by breeding from the victorious birds. So under nature with

the nascent giraffe, the individuals which were the highest browsers

and were able during dearths to reach even an inch or two above the

others, will often have been preserved; for they will have roamed over

the whole country in search of food. That the individuals of the same

species often differ slightly in the relative lengths of all their

parts may be seen in many works of natural history, in which careful

measurements are given. These slight proportional differences, due to

the laws of growth and variation, are not of the slightest use or

importance to most species. But it will have been otherwise with the

nascent giraffe, considering its probable habits of life; for those

individuals which had some one part or several parts of their bodies

rather more elongated than usual, would generally have survived. These

will have intercrossed and left offspring, either inheriting the same

bodily peculiarities, or with a tendency to vary again in the same

manner; while the individuals less favoured in the same respects will

have been the most liable to perish.

We here see that there is no need to separate single pairs, as man

does, when he methodically improves a breed: natural selection will

preserve and thus separate all the superior individuals, allowing them

freely to intercross, and will destroy all the inferior individuals. By

this process long-continued, which exactly corresponds with what I have

called unconscious selection by man, combined, no doubt, in a most

important manner with the inherited effects of the increased use of

parts, it seems to me almost certain that an ordinary hoofed quadruped

might be converted into a giraffe.

To this conclusion Mr. Mivart brings forward two objections. One is

that the increased size of the body would obviously require an

increased supply of food, and he considers it as “very problematical

whether the disadvantages thence arising would not, in times of

scarcity, more than counterbalance the advantages.” But as the giraffe

does actually exist in large numbers in Africa, and as some of the

largest antelopes in the world, taller than an ox, abound there, why

should we doubt that, as far as size is concerned, intermediate

gradations could formerly have existed there, subjected as now to

severe dearths. Assuredly the being able to reach, at each stage of

increased size, to a supply of food, left untouched by the other hoofed

quadrupeds of the country, would have been of some advantage to the

nascent giraffe. Nor must we overlook the fact, that increased bulk

would act as a protection against almost all beasts of prey excepting

the lion; and against this animal, its tall neck—and the taller the

better—would, as Mr. Chauncey Wright has remarked, serve as a

watch-tower. It is from this cause, as Sir S. Baker remarks, that no

animal is more difficult to stalk than the giraffe. This animal also

uses its long neck as a means of offence or defence, by violently

swinging its head armed with stump-like horns. The preservation of each

species can rarely be determined by any one advantage, but by the union

of all, great and small.

Mr. Mivart then asks (and this is his second objection), if natural

selection be so potent, and if high browsing be so great an advantage,

why has not any other hoofed quadruped acquired a long neck and lofty

stature, besides the giraffe, and, in a lesser degree, the camel,

guanaco and macrauchenia? Or, again, why has not any member of the

group acquired a long proboscis? With respect to South Africa, which

was formerly inhabited by numerous herds of the giraffe, the answer is

not difficult, and can best be given by an illustration. In every

meadow in England, in which trees grow, we see the lower branches

trimmed or planed to an exact level by the browsing of the horses or

cattle; and what advantage would it be, for instance, to sheep, if kept

there, to acquire slightly longer necks? In every district some one

kind of animal will almost certainly be able to browse higher than the

others; and it is almost equally certain that this one kind alone could

have its neck elongated for this purpose, through natural selection and

the effects of increased use. In South Africa the competition for

browsing on the higher branches of the acacias and other trees must be

between giraffe and giraffe, and not with the other ungulate animals.

Why, in other quarters of the world, various animals belonging to this

same order have not acquired either an elongated neck or a proboscis,

cannot be distinctly answered; but it is as unreasonable to expect a

distinct answer to such a question as why some event in the history of

mankind did not occur in one country while it did in another. We are

ignorant with respect to the conditions which determine the numbers and

range of each species, and we cannot even conjecture what changes of

structure would be favourable to its increase in some new country. We

can, however, see in a general manner that various causes might have

interfered with the development of a long neck or proboscis. To reach

the foliage at a considerable height (without climbing, for which

hoofed animals are singularly ill-constructed) implies greatly

increased bulk of body; and we know that some areas support singularly

few large quadrupeds, for instance South America, though it is so

luxuriant, while South Africa abounds with them to an unparalleled

degree. Why this should be so we do not know; nor why the later

tertiary periods should have been much more favourable for their

existence than the present time. Whatever the causes may have been, we

can see that certain districts and times would have been much more

favourable than others for the development of so large a quadruped as

the giraffe.

In order that an animal should acquire some structure specially and

largely developed, it is almost indispensable that several other parts

should be modified and coadapted. Although every part of the body

varies slightly, it does not follow that the necessary parts should

always vary in the right direction and to the right degree. With the

different species of our domesticated animals we know that the parts

vary in a different manner and degree, and that some species are much

more variable than others. Even if the fitting variations did arise, it

does not follow that natural selection would be able to act on them and

produce a structure which apparently would be beneficial to the

species. For instance, if the number of individuals existing in a

country is determined chiefly through destruction by beasts of prey—by

external or internal parasites, &c.—as seems often to be the case, then

natural selection will be able to do little, or will be greatly

retarded, in modifying any particular structure for obtaining food.

Lastly, natural selection is a slow process, and the same favourable

conditions must long endure in order that any marked effect should thus

be produced. Except by assigning such general and vague reasons, we

cannot explain why, in many quarters of the world, hoofed quadrupeds

have not acquired much elongated necks or other means for browsing on

the higher branches of trees.

Objections of the same nature as the foregoing have been advanced by

many writers. In each case various causes, besides the general ones

just indicated, have probably interfered with the acquisition through

natural selection of structures, which it is thought would be

beneficial to certain species. One writer asks, why has not the ostrich

acquired the power of flight? But a moment’s reflection will show what

an enormous supply of food would be necessary to give to this bird of

the desert force to move its huge body through the air. Oceanic islands

are inhabited by bats and seals, but by no terrestrial mammals; yet as

some of these bats are peculiar species, they must have long inhabited

their present homes. Therefore Sir C. Lyell asks, and assigns certain

reasons in answer, why have not seals and bats given birth on such

islands to forms fitted to live on the land? But seals would

necessarily be first converted into terrestrial carnivorous animals of

considerable size, and bats into terrestrial insectivorous animals; for

the former there would be no prey; for the bats ground-insects would

serve as food, but these would already be largely preyed on by the

reptiles or birds, which first colonise and abound on most oceanic

islands. Gradations of structure, with each stage beneficial to a

changing species, will be favoured only under certain peculiar

conditions. A strictly terrestrial animal, by occasionally hunting for

food in shallow water, then in streams or lakes, might at last be

converted into an animal so thoroughly aquatic as to brave the open

ocean. But seals would not find on oceanic islands the conditions

favourable to their gradual reconversion into a terrestrial form. Bats,

as formerly shown, probably acquired their wings by at first gliding

through the air from tree to tree, like the so-called flying-squirrels,

for the sake of escaping from their enemies, or for avoiding falls; but

when the power of true flight had once been acquired, it would never be

reconverted back, at least for the above purposes, into the less

efficient power of gliding through the air. Bats, might, indeed, like

many birds, have had their wings greatly reduced in size, or completely

lost, through disuse; but in this case it would be necessary that they

should first have acquired the power of running quickly on the ground,

by the aid of their hind legs alone, so as to compete with birds or

other ground animals; and for such a change a bat seems singularly

ill-fitted. These conjectural remarks have been made merely to show

that a transition of structure, with each step beneficial, is a highly

complex affair; and that there is nothing strange in a transition not

having occurred in any particular case.

Lastly, more than one writer has asked why have some animals had their

mental powers more highly developed than others, as such development

would be advantageous to all? Why have not apes acquired the

intellectual powers of man? Various causes could be assigned; but as

they are conjectural, and their relative probability cannot be weighed,

it would be useless to give them. A definite answer to the latter

question ought not to be expected, seeing that no one can solve the

simpler problem, why, of two races of savages, one has risen higher in

the scale of civilisation than the other; and this apparently implies

increased brain power.

We will return to Mr. Mivart’s other objections. Insects often resemble

for the sake of protection various objects, such as green or decayed

leaves, dead twigs, bits of lichen, flowers, spines, excrement of

birds, and living insects; but to this latter point I shall hereafter

recur. The resemblance is often wonderfully close, and is not confined

to colour, but extends to form, and even to the manner in which the

insects hold themselves. The caterpillars which project motionless like

dead twigs from the bushes on which they feed, offer an excellent

instance of a resemblance of this kind. The cases of the imitation of

such objects as the excrement of birds, are rare and exceptional. On

this head, Mr. Mivart remarks, “As, according to Mr. Darwin’s theory,

there is a constant tendency to indefinite variation, and as the minute

incipient variations will be in _all directions_, they must tend to

neutralize each other, and at first to form such unstable modifications

that it is difficult, if not impossible, to see how such indefinite

oscillations of infinitesimal beginnings can ever build up a

sufficiently appreciable resemblance to a leaf, bamboo, or other

object, for natural selection to seize upon and perpetuate.”

But in all the foregoing cases the insects in their original state no

doubt presented some rude and accidental resemblance to an object

commonly found in the stations frequented by them. Nor is this at all

improbable, considering the almost infinite number of surrounding

objects and the diversity in form and colour of the hosts of insects

which exist. As some rude resemblance is necessary for the first start,

we can understand how it is that the larger and higher animals do not

(with the exception, as far as I know, of one fish) resemble for the

sake of protection special objects, but only the surface which commonly

surrounds them, and this chiefly in colour. Assuming that an insect

originally happened to resemble in some degree a dead twig or a decayed

leaf, and that it varied slightly in many ways, then all the variations

which rendered the insect at all more like any such object, and thus

favoured its escape, would be preserved, while other variations would

be neglected and ultimately lost; or, if they rendered the insect at

all less like the imitated object, they would be eliminated. There

would indeed be force in Mr. Mivart’s objection, if we were to attempt

to account for the above resemblances, independently of natural

selection, through mere fluctuating variability; but as the case stands

there is none.

Nor can I see any force in Mr. Mivart’s difficulty with respect to “the

last touches of perfection in the mimicry;” as in the case given by Mr.

Wallace, of a walking-stick insect (Ceroxylus laceratus), which

resembles “a stick grown over by a creeping moss or jungermannia.” So

close was this resemblance, that a native Dyak maintained that the

foliaceous excrescences were really moss. Insects are preyed on by

birds and other enemies whose sight is probably sharper than ours, and

every grade in resemblance which aided an insect to escape notice or

detection, would tend towards its preservation; and the more perfect

the resemblance so much the better for the insect. Considering the

nature of the differences between the species in the group which

includes the above Ceroxylus, there is nothing improbable in this

insect having varied in the irregularities on its surface, and in these

having become more or less green-coloured; for in every group the

characters which differ in the several species are the most apt to

vary, while the generic characters, or those common to all the species,

are the most constant.

The Greenland whale is one of the most wonderful animals in the world,

and the baleen, or whalebone, one of its greatest peculiarities. The

baleen consists of a row, on each side of the upper jaw, of about 300

plates or laminæ, which stand close together transversely to the longer

axis of the mouth. Within the main row there are some subsidiary rows.

The extremities and inner margins of all the plates are frayed into

stiff bristles, which clothe the whole gigantic palate, and serve to

strain or sift the water, and thus to secure the minute prey on which

these great animals subsist. The middle and longest lamina in the

Greenland whale is ten, twelve, or even fifteen feet in length; but in

the different species of Cetaceans there are gradations in length; the

middle lamina being in one species, according to Scoresby, four feet,

in another three, in another eighteen inches, and in the Balænoptera

rostrata only about nine inches in length. The quality of the whalebone

also differs in the different species.

With respect to the baleen, Mr. Mivart remarks that if it “had once

attained such a size and development as to be at all useful, then its

preservation and augmentation within serviceable limits would be

promoted by natural selection alone. But how to obtain the beginning of

such useful development?” In answer, it may be asked, why should not

the early progenitors of the whales with baleen have possessed a mouth

constructed something like the lamellated beak of a duck? Ducks, like

whales, subsist by sifting the mud and water; and the family has

sometimes been called _Criblatores_, or sifters. I hope that I may not

be misconstrued into saying that the progenitors of whales did actually

possess mouths lamellated like the beak of a duck. I wish only to show

that this is not incredible, and that the immense plates of baleen in

the Greenland whale might have been developed from such lamellæ by

finely graduated steps, each of service to its possessor.

The beak of a shoveller-duck (Spatula clypeata) is a more beautiful and

complex structure than the mouth of a whale. The upper mandible is

furnished on each side (in the specimen examined by me) with a row or

comb formed of 188 thin, elastic lamellæ, obliquely bevelled so as to

be pointed, and placed transversely to the longer axis of the mouth.

They arise from the palate, and are attached by flexible membrane to

the sides of the mandible. Those standing towards the middle are the

longest, being about one-third of an inch in length, and they project

fourteen one-hundredths of an inch beneath the edge. At their bases

there is a short subsidiary row of obliquely transverse lamellæ. In

these several respects they resemble the plates of baleen in the mouth

of a whale. But towards the extremity of the beak they differ much, as

they project inward, instead of straight downward. The entire head of

the shoveller, though incomparably less bulky, is about one-eighteenth

of the length of the head of a moderately large Balænoptera rostrata,

in which species the baleen is only nine inches long; so that if we

were to make the head of the shoveller as long as that of the

Balænoptera, the lamellæ would be six inches in length, that is,

two-thirds of the length of the baleen in this species of whale. The

lower mandible of the shoveller-duck is furnished with lamellæ of equal

length with these above, but finer; and in being thus furnished it

differs conspicuously from the lower jaw of a whale, which is destitute

of baleen. On the other hand, the extremities of these lower lamellæ

are frayed into fine bristly points, so that they thus curiously

resemble the plates of baleen. In the genus Prion, a member of the

distinct family of the Petrels, the upper mandible alone is furnished

with lamellæ, which are well developed and project beneath the margin;

so that the beak of this bird resembles in this respect the mouth of a

whale.

From the highly developed structure of the shoveller’s beak we may

proceed (as I have learned from information and specimens sent to me by

Mr. Salvin), without any great break, as far as fitness for sifting is

concerned, through the beak of the Merganetta armata, and in some

respects through that of the Aix sponsa, to the beak of the common

duck. In this latter species the lamellæ are much coarser than in the

shoveller, and are firmly attached to the sides of the mandible; they

are only about fifty in number on each side, and do not project at all

beneath the margin. They are square-topped, and are edged with

translucent, hardish tissue, as if for crushing food. The edges of the

lower mandible are crossed by numerous fine ridges, which project very

little. Although the beak is thus very inferior as a sifter to that of

a shoveller, yet this bird, as every one knows, constantly uses it for

this purpose. There are other species, as I hear from Mr. Salvin, in

which the lamellæ are considerably less developed than in the common

duck; but I do not know whether they use their beaks for sifting the

water.

Turning to another group of the same family. In the Egyptian goose

(Chenalopex) the beak closely resembles that of the common duck; but

the lamellæ are not so numerous, nor so distinct from each other, nor

do they project so much inward; yet this goose, as I am informed by Mr.

E. Bartlett, “uses its bill like a duck by throwing the water out at

the corners.” Its chief food, however, is grass, which it crops like

the common goose. In this latter bird the lamellæ of the upper mandible

are much coarser than in the common duck, almost confluent, about

twenty-seven in number on each side, and terminating upward in

teeth-like knobs. The palate is also covered with hard rounded knobs.

The edges of the lower mandible are serrated with teeth much more

prominent, coarser and sharper than in the duck. The common goose does

not sift the water, but uses its beak exclusively for tearing or

cutting herbage, for which purpose it is so well fitted that it can

crop grass closer than almost any other animal. There are other species

of geese, as I hear from Mr. Bartlett, in which the lamellæ are less

developed than in the common goose.

We thus see that a member of the duck family, with a beak constructed

like that of a common goose and adapted solely for grazing, or even a

member with a beak having less well-developed lamellæ, might be

converted by small changes into a species like the Egyptian goose—this

into one like the common duck—and, lastly, into one like the shoveller,

provided with a beak almost exclusively adapted for sifting the water;

for this bird could hardly use any part of its beak, except the hooked

tip, for seizing or tearing solid food. The beak of a goose, as I may

add, might also be converted by small changes into one provided with

prominent, recurved teeth, like those of the Merganser (a member of the

same family), serving for the widely different purpose of securing live

fish.

Returning to the whales. The Hyperoodon bidens is destitute of true

teeth in an efficient condition, but its palate is roughened, according

to Lacepede, with small unequal, hard points of horn. There is,

therefore, nothing improbable in supposing that some early Cetacean

form was provided with similar points of horn on the palate, but rather

more regularly placed, and which, like the knobs on the beak of the

goose, aided it in seizing or tearing its food. If so, it will hardly

be denied that the points might have been converted through variation

and natural selection into lamellæ as well-developed as those of the

Egyptian goose, in which case they would have been used both for

seizing objects and for sifting the water; then into lamellæ like those

of the domestic duck; and so onward, until they became as well

constructed as those of the shoveller, in which case they would have

served exclusively as a sifting apparatus. From this stage, in which

the lamellæ would be two-thirds of the length of the plates of baleen

in the Balænoptera rostrata, gradations, which may be observed in

still-existing Cetaceans, lead us onward to the enormous plates of

baleen in the Greenland whale. Nor is there the least reason to doubt

that each step in this scale might have been as serviceable to certain

ancient Cetaceans, with the functions of the parts slowly changing

during the progress of development, as are the gradations in the beaks

of the different existing members of the duck-family. We should bear in

mind that each species of duck is subjected to a severe struggle for

existence, and that the structure of every part of its frame must be

well adapted to its conditions of life.

The Pleuronectidæ, or Flat-fish, are remarkable for their asymmetrical

bodies. They rest on one side—in the greater number of species on the

left, but in some on the right side; and occasionally reversed adult

specimens occur. The lower, or resting-surface, resembles at first

sight the ventral surface of an ordinary fish; it is of a white colour,

less developed in many ways than the upper side, with the lateral fins

often of smaller size. But the eyes offer the most remarkable

peculiarity; for they are both placed on the upper side of the head.

During early youth, however, they stand opposite to each other, and the

whole body is then symmetrical, with both sides equally coloured. Soon

the eye proper to the lower side begins to glide slowly round the head

to the upper side; but does not pass right through the skull, as was

formerly thought to be the case. It is obvious that unless the lower

eye did thus travel round, it could not be used by the fish while lying

in its habitual position on one side. The lower eye would, also, have

been liable to be abraded by the sandy bottom. That the Pleuronectidæ

are admirably adapted by their flattened and asymmetrical structure for

their habits of life, is manifest from several species, such as soles,

flounders, &c., being extremely common. The chief advantages thus

gained seem to be protection from their enemies, and facility for

feeding on the ground. The different members, however, of the family

present, as Schiödte remarks, “a long series of forms exhibiting a

gradual transition from Hippoglossus pinguis, which does not in any

considerable degree alter the shape in which it leaves the ovum, to the

soles, which are entirely thrown to one side.”

Mr. Mivart has taken up this case, and remarks that a sudden

spontaneous transformation in the position of the eyes is hardly

conceivable, in which I quite agree with him. He then adds: “If the

transit was gradual, then how such transit of one eye a minute fraction

of the journey towards the other side of the head could benefit the

individual is, indeed, far from clear. It seems, even, that such an

incipient transformation must rather have been injurious.” But he might

have found an answer to this objection in the excellent observations

published in 1867 by Malm. The Pleuronectidæ, while very young and

still symmetrical, with their eyes standing on opposite sides of the

head, cannot long retain a vertical position, owing to the excessive

depth of their bodies, the small size of their lateral fins, and to

their being destitute of a swimbladder. Hence, soon growing tired,

they fall to the bottom on one side. While thus at rest they often

twist, as Malm observed, the lower eye upward, to see above them; and

they do this so vigorously that the eye is pressed hard against the

upper part of the orbit. The forehead between the eyes consequently

becomes, as could be plainly seen, temporarily contracted in breadth.

On one occasion Malm saw a young fish raise and depress the lower eye

through an angular distance of about seventy degrees.

We should remember that the skull at this early age is cartilaginous

and flexible, so that it readily yields to muscular action. It is also

known with the higher animals, even after early youth, that the skull

yields and is altered in shape, if the skin or muscles be permanently

contracted through disease or some accident. With long-eared rabbits,

if one ear flops forward and downward, its weight drags forward all the

bones of the skull on the same side, of which I have given a figure.

Malm states that the newly-hatched young of perches, salmon, and

several other symmetrical fishes, have the habit of occasionally

resting on one side at the bottom; and he has observed that they often

then strain their lower eyes so as to look upward; and their skulls are

thus rendered rather crooked. These fishes, however, are soon able to

hold themselves in a vertical position, and no permanent effect is thus

produced. With the Pleuronectidæ, on the other hand, the older they

grow the more habitually they rest on one side, owing to the increasing

flatness of their bodies, and a permanent effect is thus produced on

the form of the head, and on the position of the eyes. Judging from

analogy, the tendency to distortion would no doubt be increased through

the principle of inheritance. Schiödte believes, in opposition to some

other naturalists, that the Pleuronectidæ are not quite symmetrical

even in the embryo; and if this be so, we could understand how it is

that certain species, while young, habitually fall over and rest on the

left side, and other species on the right side. Malm adds, in

confirmation of the above view, that the adult Trachypterus arcticus,

which is not a member of the Pleuronectidæ, rests on its left side at

the bottom, and swims diagonally through the water; and in this fish,

the two sides of the head are said to be somewhat dissimilar. Our great

authority on Fishes, Dr. Günther, concludes his abstract of Malm’s

paper, by remarking that “the author gives a very simple explanation of

the abnormal condition of the Pleuronectoids.”

We thus see that the first stages of the transit of the eye from one

side of the head to the other, which Mr. Mivart considers would be

injurious, may be attributed to the habit, no doubt beneficial to the

individual and to the species, of endeavouring to look upward with both

eyes, while resting on one side at the bottom. We may also attribute to

the inherited effects of use the fact of the mouth in several kinds of

flat-fish being bent towards the lower surface, with the jaw bones

stronger and more effective on this, the eyeless side of the head, than

on the other, for the sake, as Dr. Traquair supposes, of feeding with

ease on the ground. Disuse, on the other hand, will account for the

less developed condition of the whole inferior half of the body,

including the lateral fins; though Yarrel thinks that the reduced size

of these fins is advantageous to the fish, as “there is so much less

room for their action than with the larger fins above.” Perhaps the

lesser number of teeth in the proportion of four to seven in the upper

halves of the two jaws of the plaice, to twenty-five to thirty in the

lower halves, may likewise be accounted for by disuse. From the

colourless state of the ventral surface of most fishes and of many

other animals, we may reasonably suppose that the absence of colour in

flat-fish on the side, whether it be the right or left, which is

under-most, is due to the exclusion of light. But it cannot be supposed

that the peculiar speckled appearance of the upper side of the sole, so

like the sandy bed of the sea, or the power in some species, as

recently shown by Pouchet, of changing their colour in accordance with

the surrounding surface, or the presence of bony tubercles on the upper

side of the turbot, are due to the action of the light. Here natural

selection has probably come into play, as well as in adapting the

general shape of the body of these fishes, and many other

peculiarities, to their habits of life. We should keep in mind, as I

have before insisted, that the inherited effects of the increased use

of parts, and perhaps of their disuse, will be strengthened by natural

selection. For all spontaneous variations in the right direction will

thus be preserved; as will those individuals which inherit in the

highest degree the effects of the increased and beneficial use of any

part. How much to attribute in each particular case to the effects of

use, and how much to natural selection, it seems impossible to decide.

I may give another instance of a structure which apparently owes its

origin exclusively to use or habit. The extremity of the tail in some

American monkeys has been converted into a wonderfully perfect

prehensile organ, and serves as a fifth hand. A reviewer, who agrees

with Mr. Mivart in every detail, remarks on this structure: “It is

impossible to believe that in any number of ages the first slight

incipient tendency to grasp could preserve the lives of the individuals

possessing it, or favour their chance of having and of rearing

offspring.” But there is no necessity for any such belief. Habit, and

this almost implies that some benefit great or small is thus derived,

would in all probability suffice for the work. Brehm saw the young of

an African monkey (Cercopithecus) clinging to the under surface of

their mother by their hands, and at the same time they hooked their

little tails round that of their mother. Professor Henslow kept in

confinement some harvest mice (Mus messorius) which do not possess a

structurally prehensive tail; but he frequently observed that they

curled their tails round the branches of a bush placed in the cage, and

thus aided themselves in climbing. I have received an analogous account

from Dr. Günther, who has seen a mouse thus suspend itself. If the

harvest mouse had been more strictly arboreal, it would perhaps have

had its tail rendered structurally prehensile, as is the case with some

members of the same order. Why Cercopithecus, considering its habits

while young, has not become thus provided, it would be difficult to

say. It is, however, possible that the long tail of this monkey may be

of more service to it as a balancing organ in making its prodigious

leaps, than as a prehensile organ.

The mammary glands are common to the whole class of mammals, and are

indispensable for their existence; they must, therefore, have been

developed at an extremely remote period, and we can know nothing

positively about their manner of development. Mr. Mivart asks: “Is it

conceivable that the young of any animal was ever saved from

destruction by accidentally sucking a drop of scarcely nutritious fluid

from an accidentally hypertrophied cutaneous gland of its mother? And

even if one was so, what chance was there of the perpetuation of such a

variation?” But the case is not here put fairly. It is admitted by most

evolutionists that mammals are descended from a marsupial form; and if

so, the mammary glands will have been at first developed within the

marsupial sack. In the case of the fish (Hippocampus) the eggs are

hatched, and the young are reared for a time, within a sack of this

nature; and an American naturalist, Mr. Lockwood, believes from what he

has seen of the development of the young, that they are nourished by a

secretion from the cutaneous glands of the sack. Now, with the early

progenitors of mammals, almost before they deserved to be thus

designated, is it not at least possible that the young might have been

similarly nourished? And in this case, the individuals which secreted a

fluid, in some degree or manner the most nutritious, so as to partake

of the nature of milk, would in the long run have reared a larger

number of well-nourished offspring, than would the individuals which

secreted a poorer fluid; and thus the cutaneous glands, which are the

homologues of the mammary glands, would have been improved or rendered

more effective. It accords with the widely extended principle of

specialisation, that the glands over a certain space of the sack should

have become more highly developed than the remainder; and they would

then have formed a breast, but at first without a nipple, as we see in

the Ornithorhyncus, at the base of the mammalian series. Through what

agency the glands over a certain space became more highly specialised

than the others, I will not pretend to decide, whether in part through

compensation of growth, the effects of use, or of natural selection.

The development of the mammary glands would have been of no service,

and could not have been affected through natural selection, unless the

young at the same time were able to partake of the secretion. There is

no greater difficulty in understanding how young mammals have

instinctively learned to suck the breast, than in understanding how

unhatched chickens have learned to break the egg-shell by tapping

against it with their specially adapted beaks; or how a few hours after

leaving the shell they have learned to pick up grains of food. In such

cases the most probable solution seems to be, that the habit was at

first acquired by practice at a more advanced age, and afterwards

transmitted to the offspring at an earlier age. But the young kangaroo

is said not to suck, only to cling to the nipple of its mother, who has

the power of injecting milk into the mouth of her helpless, half-formed

offspring. On this head Mr. Mivart remarks: “Did no special provision

exist, the young one must infallibly be choked by the intrusion of the

milk into the wind-pipe. But there _is_ a special provision. The larynx

is so elongated that it rises up into the posterior end of the nasal

passage, and is thus enabled to give free entrance to the air for the

lungs, while the milk passes harmlessly on each side of this elongated

larynx, and so safely attains the gullet behind it.” Mr. Mivart then

asks how did natural selection remove in the adult kangaroo (and in

most other mammals, on the assumption that they are descended from a

marsupial form), “this at least perfectly innocent and harmless

structure?” It may be suggested in answer that the voice, which is

certainly of high importance to many animals, could hardly have been

used with full force as long as the larynx entered the nasal passage;

and Professor Flower has suggested to me that this structure would have

greatly interfered with an animal swallowing solid food.

We will now turn for a short space to the lower divisions of the animal

kingdom. The Echinodermata (star-fishes, sea-urchins, &c.) are

furnished with remarkable organs, called pedicellariæ, which consist,

when well developed, of a tridactyle forceps—that is, of one formed of

three serrated arms, neatly fitting together and placed on the summit

of a flexible stem, moved by muscles. These forceps can seize firmly

hold of any object; and Alexander Agassiz has seen an Echinus or

sea-urchin rapidly passing particles of excrement from forceps to

forceps down certain lines of its body, in order that its shell should

not be fouled. But there is no doubt that besides removing dirt of all

kinds, they subserve other functions; and one of these apparently is

defence.

With respect to these organs, Mr. Mivart, as on so many previous

occasions, asks: “What would be the utility of the _first rudimentary

beginnings_ of such structures, and how could such insipient buddings

have ever preserved the life of a single Echinus?” He adds, “not even

the _sudden_ development of the snapping action would have been

beneficial without the freely movable stalk, nor could the latter have

been efficient without the snapping jaws, yet no minute, nearly

indefinite variations could simultaneously evolve these complex

co-ordinations of structure; to deny this seems to do no less than to

affirm a startling paradox.” Paradoxical as this may appear to Mr.

Mivart, tridactyle forcepses, immovably fixed at the base, but capable

of a snapping action, certainly exist on some star-fishes; and this is

intelligible if they serve, at least in part, as a means of defence.

Mr. Agassiz, to whose great kindness I am indebted for much information

on the subject, informs me that there are other star-fishes, in which

one of the three arms of the forceps is reduced to a support for the

other two; and again, other genera in which the third arm is completely

lost. In Echinoneus, the shell is described by M. Perrier as bearing

two kinds of pedicellariæ, one resembling those of Echinus, and the

other those of Spatangus; and such cases are always interesting as

affording the means of apparently sudden transitions, through the

abortion of one of the two states of an organ.

With respect to the steps by which these curious organs have been

evolved, Mr. Agassiz infers from his own researches and those of Mr.

Müller, that both in star-fishes and sea-urchins the pedicellariæ must

undoubtedly be looked at as modified spines. This may be inferred from

their manner of development in the individual, as well as from a long

and perfect series of gradations in different species and genera, from

simple granules to ordinary spines, to perfect tridactyle pedicellariæ.

The gradation extends even to the manner in which ordinary spines and

the pedicellariæ, with their supporting calcareous rods, are

articulated to the shell. In certain genera of star-fishes, “the very

combinations needed to show that the pedicellariæ are only modified

branching spines” may be found. Thus we have fixed spines, with three

equi-distant, serrated, movable branches, articulated to near their

bases; and higher up, on the same spine, three other movable branches.

Now when the latter arise from the summit of a spine they form, in

fact, a rude tridactyle pedicellariæ, and such may be seen on the same

spine together with the three lower branches. In this case the identity

in nature between the arms of the pedicellariæ and the movable branches

of a spine, is unmistakable. It is generally admitted that the ordinary

spines serve as a protection; and if so, there can be no reason to

doubt that those furnished with serrated and movable branches likewise

serve for the same purpose; and they would thus serve still more

effectively as soon as by meeting together they acted as a prehensile

or snapping apparatus. Thus every gradation, from an ordinary fixed

spine to a fixed pedicellariæ, would be of service.

In certain genera of star-fishes these organs, instead of being fixed

or borne on an immovable support, are placed on the summit of a

flexible and muscular, though short, stem; and in this case they

probably subserve some additional function besides defence. In the

sea-urchins the steps can be followed by which a fixed spine becomes

articulated to the shell, and is thus rendered movable. I wish I had

space here to give a fuller abstract of Mr. Agassiz’s interesting

observations on the development of the pedicellariæ. All possible

gradations, as he adds, may likewise be found between the pedicellariæ

of the star-fishes and the hooks of the Ophiurians, another group of

the Echinodermata; and again between the pedicellariæ of sea-urchins

and the anchors of the Holothuriæ, also belonging to the same great

class.

Certain compound animals, or zoophytes, as they have been termed,

namely the Polyzoa, are provided with curious organs called avicularia.

These differ much in structure in the different species. In their most

perfect condition they curiously resemble the head and beak of a

vulture in miniature, seated on a neck and capable of movement, as is

likewise the lower jaw or mandible. In one species observed by me, all

the avicularia on the same branch often moved simultaneously backwards

and forwards, with the lower jaw widely open, through an angle of about

90 degrees, in the course of five seconds; and their movement caused

the whole polyzoary to tremble. When the jaws are touched with a needle

they seize it so firmly that the branch can thus be shaken.

Mr. Mivart adduces this case, chiefly on account of the supposed

difficulty of organs, namely the avicularia of the Polyzoa and the

pedicellariæ of the Echinodermata, which he considers as “essentially

similar,” having been developed through natural selection in widely

distinct divisions of the animal kingdom. But, as far as structure is

concerned, I can see no similarity between tridactyle pedicellariæ and

avicularia. The latter resembles somewhat more closely the chelæ or

pincers of Crustaceans; and Mr. Mivart might have adduced with equal

appropriateness this resemblance as a special difficulty, or even their

resemblance to the head and beak of a bird. The avicularia are believed

by Mr. Busk, Dr. Smitt and Dr. Nitsche—naturalists who have carefully

studied this group—to be homologous with the zooids and their cells

which compose the zoophyte, the movable lip or lid of the cell

corresponding with the lower and movable mandible of the avicularium.

Mr. Busk, however, does not know of any gradations now existing between

a zooid and an avicularium. It is therefore impossible to conjecture by

what serviceable gradations the one could have been converted into the

other, but it by no means follows from this that such gradations have

not existed.

As the chelæ of Crustaceans resemble in some degree the avicularia of

Polyzoa, both serving as pincers, it may be worth while to show that

with the former a long series of serviceable gradations still exists.

In the first and simplest stage, the terminal segment of a limb shuts

down either on the square summit of the broad penultimate segment, or

against one whole side, and is thus enabled to catch hold of an object,

but the limb still serves as an organ of locomotion. We next find one

corner of the broad penultimate segment slightly prominent, sometimes

furnished with irregular teeth, and against these the terminal segment

shuts down. By an increase in the size of this projection, with its

shape, as well as that of the terminal segment, slightly modified and

improved, the pincers are rendered more and more perfect, until we have

at last an instrument as efficient as the chelæ of a lobster. And all

these gradations can be actually traced.

Besides the avicularia, the polyzoa possess curious organs called

vibracula. These generally consist of long bristles, capable of

movement and easily excited. In one species examined by me the

vibracula were slightly curved and serrated along the outer margin, and

all of them on the same polyzoary often moved simultaneously; so that,

acting like long oars, they swept a branch rapidly across the

object-glass of my microscope. When a branch was placed on its face,

the vibracula became entangled, and they made violent efforts to free

themselves. They are supposed to serve as a defence, and may be seen,

as Mr. Busk remarks, “to sweep slowly and carefully over the surface of

the polyzoary, removing what might be noxious to the delicate

inhabitants of the cells when their tentacula are protruded.” The

avicularia, like the vibracula, probably serve for defence, but they

also catch and kill small living animals, which, it is believed, are

afterwards swept by the currents within reach of the tentacula of the

zooids. Some species are provided with avicularia and vibracula, some

with avicularia alone and a few with vibracula alone.

It is not easy to imagine two objects more widely different in

appearance than a bristle or vibraculum, and an avicularium like the

head of a bird; yet they are almost certainly homologous and have been

developed from the same common source, namely a zooid with its cell.

Hence, we can understand how it is that these organs graduate in some

cases, as I am informed by Mr. Busk, into each other. Thus, with the

avicularia of several species of Lepralia, the movable mandible is so

much produced and is so like a bristle that the presence of the upper

or fixed beak alone serves to determine its avicularian nature. The

vibracula may have been directly developed from the lips of the cells,

without having passed through the avicularian stage; but it seems more

probable that they have passed through this stage, as during the early

stages of the transformation, the other parts of the cell, with the

included zooid, could hardly have disappeared at once. In many cases

the vibracula have a grooved support at the base, which seems to

represent the fixed beak; though this support in some species is quite

absent. This view of the development of the vibracula, if trustworthy,

is interesting; for supposing that all the species provided with

avicularia had become extinct, no one with the most vivid imagination

would ever have thought that the vibracula had originally existed as

part of an organ, resembling a bird’s head, or an irregular box or

hood. It is interesting to see two such widely different organs

developed from a common origin; and as the movable lip of the cell

serves as a protection to the zooid, there is no difficulty in

believing that all the gradations, by which the lip became converted

first into the lower mandible of an avicularium, and then into an

elongated bristle, likewise served as a protection in different ways

and under different circumstances.

In the vegetable kingdom Mr. Mivart only alludes to two cases, namely

the structure of the flowers of orchids, and the movements of climbing

plants. With respect to the former, he says: “The explanation of their

_origin_ is deemed thoroughly unsatisfactory—utterly insufficient to

explain the incipient, infinitesimal beginnings of structures which are

of utility only when they are considerably developed.” As I have fully

treated this subject in another work, I will here give only a few

details on one alone of the most striking peculiarities of the flowers

of orchids, namely, their pollinia. A pollinium, when highly developed,

consists of a mass of pollen-grains, affixed to an elastic foot-stalk

or caudicle, and this to a little mass of extremely viscid matter. The

pollinia are by this means transported by insects from one flower to

the stigma of another. In some orchids there is no caudicle to the

pollen-masses, and the grains are merely tied together by fine threads;

but as these are not confined to orchids, they need not here be

considered; yet I may mention that at the base of the orchidaceous

series, in Cypripedium, we can see how the threads were probably first

developed. In other orchids the threads cohere at one end of the

pollen-masses; and this forms the first or nascent trace of a caudicle.

That this is the origin of the caudicle, even when of considerable

length and highly developed, we have good evidence in the aborted

pollen-grains which can sometimes be detected embedded within the

central and solid parts.

With respect to the second chief peculiarity, namely, the little mass

of viscid matter attached to the end of the caudicle, a long series of

gradations can be specified, each of plain service to the plant. In

most flowers belonging to other orders the stigma secretes a little

viscid matter. Now, in certain orchids similar viscid matter is

secreted, but in much larger quantities by one alone of the three

stigmas; and this stigma, perhaps in consequence of the copious

secretion, is rendered sterile. When an insect visits a flower of this

kind, it rubs off some of the viscid matter, and thus at the same time

drags away some of the pollen-grains. From this simple condition, which

differs but little from that of a multitude of common flowers, there

are endless gradations—to species in which the pollen-mass terminates

in a very short, free caudicle—to others in which the caudicle becomes

firmly attached to the viscid matter, with the sterile stigma itself

much modified. In this latter case we have a pollinium in its most

highly developed and perfect condition. He who will carefully examine

the flowers of orchids for himself will not deny the existence of the

above series of gradations—from a mass of pollen-grains merely tied

together by threads, with the stigma differing but little from that of

the ordinary flowers, to a highly complex pollinium, admirably adapted

for transportal by insects; nor will he deny that all the gradations in

the several species are admirably adapted in relation to the general

structure of each flower for its fertilisation by different insects. In

this, and in almost every other case, the enquiry may be pushed further

backwards; and it may be asked how did the stigma of an ordinary flower

become viscid, but as we do not know the full history of any one group

of beings, it is as useless to ask, as it is hopeless to attempt

answering, such questions.

We will now turn to climbing plants. These can be arranged in a long

series, from those which simply twine round a support, to those which I

have called leaf-climbers, and to those provided with tendrils. In

these two latter classes the stems have generally, but not always, lost

the power of twining, though they retain the power of revolving, which

the tendrils likewise possess. The gradations from leaf-climbers to

tendril bearers are wonderfully close, and certain plants may be

differently placed in either class. But in ascending the series from

simple twiners to leaf-climbers, an important quality is added, namely

sensitiveness to a touch, by which means the foot-stalks of the leaves

or flowers, or these modified and converted into tendrils, are excited

to bend round and clasp the touching object. He who will read my memoir

on these plants will, I think, admit that all the many gradations in

function and structure between simple twiners and tendril-bearers are

in each case beneficial in a high degree to the species. For instance,

it is clearly a great advantage to a twining plant to become a

leaf-climber; and it is probable that every twiner which possessed

leaves with long foot-stalks would have been developed into a

leaf-climber, if the foot-stalks had possessed in any slight degree the

requisite sensitiveness to a touch.

As twining is the simplest means of ascending a support, and forms the

basis of our series, it may naturally be asked how did plants acquire

this power in an incipient degree, afterwards to be improved and

increased through natural selection. The power of twining depends,

firstly, on the stems while young being extremely flexible (but this is

a character common to many plants which are not climbers); and,

secondly, on their continually bending to all points of the compass,

one after the other in succession, in the same order. By this movement

the stems are inclined to all sides, and are made to move round and

round. As soon as the lower part of a stem strikes against any object

and is stopped, the upper part still goes on bending and revolving, and

thus necessarily twines round and up the support. The revolving

movement ceases after the early growth of each shoot. As in many widely

separated families of plants, single species and single genera possess

the power of revolving, and have thus become twiners, they must have

independently acquired it, and cannot have inherited it from a common

progenitor. Hence, I was led to predict that some slight tendency to a

movement of this kind would be found to be far from uncommon with

plants which did not climb; and that this had afforded the basis for

natural selection to work on and improve. When I made this prediction,

I knew of only one imperfect case, namely, of the young

flower-peduncles of a Maurandia which revolved slightly and

irregularly, like the stems of twining plants, but without making any

use of this habit. Soon afterwards Fritz Müller discovered that the

young stems of an Alisma and of a Linum—plants which do not climb and

are widely separated in the natural system—revolved plainly, though

irregularly, and he states that he has reason to suspect that this

occurs with some other plants. These slight movements appear to be of

no service to the plants in question; anyhow, they are not of the least

use in the way of climbing, which is the point that concerns us.

Nevertheless we can see that if the stems of these plants had been

flexible, and if under the conditions to which they are exposed it had

profited them to ascend to a height, then the habit of slightly and

irregularly revolving might have been increased and utilised through

natural selection, until they had become converted into well-developed

twining species.

With respect to the sensitiveness of the foot-stalks of the leaves and

flowers, and of tendrils, nearly the same remarks are applicable as in

the case of the revolving movements of twining plants. As a vast number

of species, belonging to widely distinct groups, are endowed with this

kind of sensitiveness, it ought to be found in a nascent condition in

many plants which have not become climbers. This is the case: I

observed that the young flower-peduncles of the above Maurandia curved

themselves a little towards the side which was touched. Morren found in

several species of Oxalis that the leaves and their foot-stalks moved,

especially after exposure to a hot sun, when they were gently and

repeatedly touched, or when the plant was shaken. I repeated these

observations on some other species of Oxalis with the same result; in

some of them the movement was distinct, but was best seen in the young

leaves; in others it was extremely slight. It is a more important fact

that according to the high authority of Hofmeister, the young shoots

and leaves of all plants move after being shaken; and with climbing

plants it is, as we know, only during the early stages of growth that

the foot-stalks and tendrils are sensitive.

It is scarcely possible that the above slight movements, due to a touch

or shake, in the young and growing organs of plants, can be of any

functional importance to them. But plants possess, in obedience to

various stimuli, powers of movement, which are of manifest importance

to them; for instance, towards and more rarely from the light—in

opposition to, and more rarely in the direction of, the attraction of

gravity. When the nerves and muscles of an animal are excited by

galvanism or by the absorption of strychnine, the consequent movements

may be called an incidental result, for the nerves and muscles have not

been rendered specially sensitive to these stimuli. So with plants it

appears that, from having the power of movement in obedience to certain

stimuli, they are excited in an incidental manner by a touch, or by

being shaken. Hence there is no great difficulty in admitting that in

the case of leaf-climbers and tendril-bearers, it is this tendency

which has been taken advantage of and increased through natural

selection. It is, however, probable, from reasons which I have assigned

in my memoir, that this will have occurred only with plants which had

already acquired the power of revolving, and had thus become twiners.

I have already endeavoured to explain how plants became twiners,

namely, by the increase of a tendency to slight and irregular revolving

movements, which were at first of no use to them; this movement, as

well as that due to a touch or shake, being the incidental result of

the power of moving, gained for other and beneficial purposes. Whether,

during the gradual development of climbing plants, natural selection

has been aided by the inherited effects of use, I will not pretend to

decide; but we know that certain periodical movements, for instance the

so-called sleep of plants, are governed by habit.

I have now considered enough, perhaps more than enough, of the cases,

selected with care by a skilful naturalist, to prove that natural

selection is incompetent to account for the incipient stages of useful

structures; and I have shown, as I hope, that there is no great

difficulty on this head. A good opportunity has thus been afforded for

enlarging a little on gradations of structure, often associated with

strange functions—an important subject, which was not treated at

sufficient length in the former editions of this work. I will now

briefly recapitulate the foregoing cases.

With the giraffe, the continued preservation of the individuals of some

extinct high-reaching ruminant, which had the longest necks, legs, &c.,

and could browse a little above the average height, and the continued

destruction of those which could not browse so high, would have

sufficed for the production of this remarkable quadruped; but the

prolonged use of all the parts, together with inheritance, will have

aided in an important manner in their co-ordination. With the many

insects which imitate various objects, there is no improbability in the

belief that an accidental resemblance to some common object was in each

case the foundation for the work of natural selection, since perfected

through the occasional preservation of slight variations which made the

resemblance at all closer; and this will have been carried on as long

as the insect continued to vary, and as long as a more and more perfect

resemblance led to its escape from sharp-sighted enemies. In certain

species of whales there is a tendency to the formation of irregular

little points of horn on the palate; and it seems to be quite within

the scope of natural selection to preserve all favourable variations,

until the points were converted, first into lamellated knobs or teeth,

like those on the beak of a goose—then into short lamellæ, like those

of the domestic ducks—and then into lamellæ, as perfect as those of the

shoveller-duck—and finally into the gigantic plates of baleen, as in

the mouth of the Greenland whale. In the family of the ducks, the

lamellæ are first used as teeth, then partly as teeth and partly as a

sifting apparatus, and at last almost exclusively for this latter

purpose.

With such structures as the above lamellæ of horn or whalebone, habit

or use can have done little or nothing, as far as we can judge, towards

their development. On the other hand, the transportal of the lower eye

of a flat-fish to the upper side of the head, and the formation of a

prehensile tail, may be attributed almost wholly to continued use,

together with inheritance. With respect to the mammæ of the higher

animals, the most probable conjecture is that primordially the

cutaneous glands over the whole surface of a marsupial sack secreted a

nutritious fluid; and that these glands were improved in function

through natural selection, and concentrated into a confined area, in

which case they would have formed a mamma. There is no more difficulty

in understanding how the branched spines of some ancient Echinoderm,

which served as a defence, became developed through natural selection

into tridactyle pedicellariæ, than in understanding the development of

the pincers of crustaceans, through slight, serviceable modifications

in the ultimate and penultimate segments of a limb, which was at first

used solely for locomotion. In the avicularia and vibracula of the

Polyzoa we have organs widely different in appearance developed from

the same source; and with the vibracula we can understand how the

successive gradations might have been of service. With the pollinia of

orchids, the threads which originally served to tie together the

pollen-grains, can be traced cohering into caudicles; and the steps can

likewise be followed by which viscid matter, such as that secreted by

the stigmas of ordinary flowers, and still subserving nearly but not

quite the same purpose, became attached to the free ends of the

caudicles—all these gradations being of manifest benefit to the plants

in question. With respect to climbing plants, I need not repeat what

has been so lately said.

It has often been asked, if natural selection be so potent, why has not

this or that structure been gained by certain species, to which it

would apparently have been advantageous? But it is unreasonable to

expect a precise answer to such questions, considering our ignorance of

the past history of each species, and of the conditions which at the

present day determine its numbers and range. In most cases only general

reasons, but in some few cases special reasons, can be assigned. Thus

to adapt a species to new habits of life, many co-ordinated

modifications are almost indispensable, and it may often have happened

that the requisite parts did not vary in the right manner or to the

right degree. Many species must have been prevented from increasing in

numbers through destructive agencies, which stood in no relation to

certain structures, which we imagine would have been gained through

natural selection from appearing to us advantageous to the species. In

this case, as the struggle for life did not depend on such structures,

they could not have been acquired through natural selection. In many

cases complex and long-enduring conditions, often of a peculiar nature,

are necessary for the development of a structure; and the requisite

conditions may seldom have concurred. The belief that any given

structure, which we think, often erroneously, would have been

beneficial to a species, would have been gained under all circumstances

through natural selection, is opposed to what we can understand of its

manner of action. Mr. Mivart does not deny that natural selection has

effected something; but he considers it as “demonstrably insufficient”

to account for the phenomena which I explain by its agency. His chief

arguments have now been considered, and the others will hereafter be

considered. They seem to me to partake little of the character of

demonstration, and to have little weight in comparison with those in

favour of the power of natural selection, aided by the other agencies

often specified. I am bound to add, that some of the facts and

arguments here used by me, have been advanced for the same purpose in

an able article lately published in the “Medico-Chirurgical Review.”

At the present day almost all naturalists admit evolution under some

form. Mr. Mivart believes that species change through “an internal

force or tendency,” about which it is not pretended that anything is

known. That species have a capacity for change will be admitted by all

evolutionists; but there is no need, as it seems to me, to invoke any

internal force beyond the tendency to ordinary variability, which

through the aid of selection, by man has given rise to many

well-adapted domestic races, and which, through the aid of natural

selection, would equally well give rise by graduated steps to natural

races or species. The final result will generally have been, as already

explained, an advance, but in some few cases a retrogression, in

organisation.

Mr. Mivart is further inclined to believe, and some naturalists agree

with him, that new species manifest themselves “with suddenness and by

modifications appearing at once.” For instance, he supposes that the

differences between the extinct three-toed Hipparion and the horse

arose suddenly. He thinks it difficult to believe that the wing of a

bird “was developed in any other way than by a comparatively sudden

modification of a marked and important kind;” and apparently he would

extend the same view to the wings of bats and pterodactyles. This

conclusion, which implies great breaks or discontinuity in the series,

appears to me improbable in the highest degree.

Everyone who believes in slow and gradual evolution, will of course

admit that specific changes may have been as abrupt and as great as any

single variation which we meet with under nature, or even under

domestication. But as species are more variable when domesticated or

cultivated than under their natural conditions, it is not probable that

such great and abrupt variations have often occurred under nature, as

are known occasionally to arise under domestication. Of these latter

variations several may be attributed to reversion; and the characters

which thus reappear were, it is probable, in many cases at first gained

in a gradual manner. A still greater number must be called

monstrosities, such as six-fingered men, porcupine men, Ancon sheep,

Niata cattle, &c.; and as they are widely different in character from

natural species, they throw very little light on our subject. Excluding

such cases of abrupt variations, the few which remain would at best

constitute, if found in a state of nature, doubtful species, closely

related to their parental types.

My reasons for doubting whether natural species have changed as

abruptly as have occasionally domestic races, and for entirely

disbelieving that they have changed in the wonderful manner indicated

by Mr. Mivart, are as follows. According to our experience, abrupt and

strongly marked variations occur in our domesticated productions,

singly and at rather long intervals of time. If such occurred under

nature, they would be liable, as formerly explained, to be lost by

accidental causes of destruction and by subsequent intercrossing; and

so it is known to be under domestication, unless abrupt variations of

this kind are specially preserved and separated by the care of man.

Hence, in order that a new species should suddenly appear in the manner

supposed by Mr. Mivart, it is almost necessary to believe, in

opposition to all analogy, that several wonderfully changed individuals

appeared simultaneously within the same district. This difficulty, as

in the case of unconscious selection by man, is avoided on the theory

of gradual evolution, through the preservation of a large number of

individuals, which varied more or less in any favourable direction, and

of the destruction of a large number which varied in an opposite

manner.

That many species have been evolved in an extremely gradual manner,

there can hardly be a doubt. The species and even the genera of many

large natural families are so closely allied together that it is

difficult to distinguish not a few of them. On every continent, in

proceeding from north to south, from lowland to upland, &c., we meet

with a host of closely related or representative species; as we

likewise do on certain distinct continents, which we have reason to

believe were formerly connected. But in making these and the following

remarks, I am compelled to allude to subjects hereafter to be

discussed. Look at the many outlying islands round a continent, and see

how many of their inhabitants can be raised only to the rank of

doubtful species. So it is if we look to past times, and compare the

species which have just passed away with those still living within the

same areas; or if we compare the fossil species embedded in the

sub-stages of the same geological formation. It is indeed manifest that

multitudes of species are related in the closest manner to other

species that still exist, or have lately existed; and it will hardly be

maintained that such species have been developed in an abrupt or sudden

manner. Nor should it be forgotten, when we look to the special parts

of allied species, instead of to distinct species, that numerous and

wonderfully fine gradations can be traced, connecting together widely

different structures.

Many large groups of facts are intelligible only on the principle that

species have been evolved by very small steps. For instance, the fact

that the species included in the larger genera are more closely related

to each other, and present a greater number of varieties than do the

species in the smaller genera. The former are also grouped in little

clusters, like varieties round species; and they present other

analogies with varieties, as was shown in our second chapter. On this

same principle we can understand how it is that specific characters are

more variable than generic characters; and how the parts which are

developed in an extraordinary degree or manner are more variable than

other parts of the same species. Many analogous facts, all pointing in

the same direction, could be added.

Although very many species have almost certainly been produced by steps

not greater than those separating fine varieties; yet it may be

maintained that some have been developed in a different and abrupt

manner. Such an admission, however, ought not to be made without strong

evidence being assigned. The vague and in some respects false

analogies, as they have been shown to be by Mr. Chauncey Wright, which

have been advanced in favour of this view, such as the sudden

crystallisation of inorganic substances, or the falling of a facetted

spheroid from one facet to another, hardly deserve consideration. One

class of facts, however, namely, the sudden appearance of new and

distinct forms of life in our geological formations supports at first

sight the belief in abrupt development. But the value of this evidence

depends entirely on the perfection of the geological record, in

relation to periods remote in the history of the world. If the record

is as fragmentary as many geologists strenuously assert, there is

nothing strange in new forms appearing as if suddenly developed.

Unless we admit transformations as prodigious as those advocated by Mr.

Mivart, such as the sudden development of the wings of birds or bats,

or the sudden conversion of a Hipparion into a horse, hardly any light

is thrown by the belief in abrupt modifications on the deficiency of

connecting links in our geological formations. But against the belief

in such abrupt changes, embryology enters a strong protest. It is

notorious that the wings of birds and bats, and the legs of horses or

other quadrupeds, are undistinguishable at an early embryonic period,

and that they become differentiated by insensibly fine steps.

Embryological resemblances of all kinds can be accounted for, as we

shall hereafter see, by the progenitors of our existing species having

varied after early youth, and having transmitted their newly-acquired

characters to their offspring, at a corresponding age. The embryo is

thus left almost unaffected, and serves as a record of the past

condition of the species. Hence it is that existing species during the

early stages of their development so often resemble ancient and extinct

forms belonging to the same class. On this view of the meaning of

embryological resemblances, and indeed on any view, it is incredible

that an animal should have undergone such momentous and abrupt

transformations as those above indicated, and yet should not bear even

a trace in its embryonic condition of any sudden modification, every

detail in its structure being developed by insensibly fine steps.

He who believes that some ancient form was transformed suddenly through

an internal force or tendency into, for instance, one furnished with

wings, will be almost compelled to assume, in opposition to all

analogy, that many individuals varied simultaneously. It cannot be

denied that such abrupt and great changes of structure are widely

different from those which most species apparently have undergone. He

will further be compelled to believe that many structures beautifully

adapted to all the other parts of the same creature and to the

surrounding conditions, have been suddenly produced; and of such

complex and wonderful co-adaptations, he will not be able to assign a

shadow of an explanation. He will be forced to admit that these great

and sudden transformations have left no trace of their action on the

embryo. To admit all this is, as it seems to me, to enter into the

realms of miracle, and to leave those of science.