"Under changed conditions of life, it is at least possible that slight modifications of instinct might be profitable to a species. If it can be shown that instincts do vary ever so little, then I can see no difficulty in natural selection preserving and continually accumulating variations of instinct to any extent that was profitable.

"It is thus, as I believe, that all the most complex and wonderful instincts have originated. As modifications of corporeal structure arise from, and are increased by, use or habit -- and are diminished or lost by disuse -- so I do not doubt it has been with instincts.

"But I believe that the effects of habit are in many cases of subordinate importance to the effects of the natural selection of what may be called spontaneous variations of instincts -- that is of variations produced by the same unknown causes which produce slight deviations of bodily structure.

"No complex instinct can possibly be produced through natural selection, except by the slow and gradual accumulation of numerous slight, yet profitable, variations.

"Hence, as in the case of corporeal structures, we ought to find in nature, not the actual transitional gradations by which each complex instinct has been acquired -- for these could be found only in the lineal ancestors of each species -- but we ought to find in the collateral lines of descent some evidence of such gradations.

"We ought at least to be able to show that gradations of some kind are possible. This we certainly can do.

"I have been surprised to find -- making allowance for the instincts of animals having been but little observed except in Europe and North America, and for no instinct being known amongst extinct species -- how very generally gradations, leading to the most complex instincts, can be discovered.

"Changes of instinct may sometimes be facilitated by the same species having different instincts at different periods of life -- or at different seasons of the year -- or when placed under different circumstances -- in which case either the one or the other instinct might be preserved by natural selection.

"One of the strongest instances of an animal apparently performing an action for the sole good of another, with which I am acquainted, is that of aphides voluntarily yielding, as was first observed by Huber, their sweet excretion to ants. That they do so voluntarily, the following facts show.

"I removed all the ants from a group of about a dozen aphides on a dock-plant, and prevented their attendance during several hours. After this interval, I felt sure that the aphides would want to excrete. I watched them for some time through a lens, but not one excreted; I then tickled and stroked them with a hair in the same manner, as well as I could, as the ants do with their antennae; but not one excreted.

"Afterwards I allowed an ant to visit them, and it immediately seemed, by its eager way of running about, to be well aware what a rich flock it had discovered. It then began to play with its antennae on the abdomen first of one aphis and then of another. Each, as soon as it felt the antennae, immediately lifted up its abdomen and excreted a limpid drop of sweet juice, which was eagerly devoured by the ant.

"Even the quite young aphides behaved in this manner, showing that the action was instinctive, and not the result of experience.

"It is certain, from the observations of Huber, that the aphides show no dislike to the ants: if the latter be not present they are at last compelled to eject their excretion. But as the excretion is extremely viscid, it is no doubt a convenience to the aphides to have it removed. Therefore probably they do not excrete solely for the good of the ants.

"Although there is no evidence that any animal performs an action for the exclusive good of another species, yet each tries to take advantage of the instincts of others, as each takes advantage of the weaker bodily structure of other species. So again instincts cannot be considered as absolutely perfect. As details on this and other such points are not indispensable, they may be here passed over.

"As some degree of variation in instincts under a state of nature -- and the inheritance of such variations -- are indispensable for the action of natural selection, as many instances as possible ought to be given. Want of space prevents me.

"I can only assert that instincts certainly do vary -- for instance, the migratory instinct, both in extent and direction, and in its total loss.

"So it is with the nests of birds -- which vary partly in dependence on the situations chosen, and on the nature and temperature of the country inhabited -- but often from causes wholly unknown to us. Audubon has given several remarkable cases of differences in the nests of the same species in the northern and southern United States.

"Why, it has been asked, if instinct be variable, has it not granted to the bee "the ability to use some other material when wax was deficient"? But what other natural material could bees use? They will work, as I have seen, with wax hardened with vermilion or softened with lard.

"Andrew Knight observed that his bees, instead of laboriously collecting propolis, used a cement of wax and turpentine, with which he had covered decorticated trees. It has lately been shown that bees, instead of searching for pollen, will gladly use a very different substance, namely oatmeal.

"Fear of any particular enemy is certainly an instinctive quality, as may be seen in nestling birds, though it is strengthened by experience, and by the sight of fear of the same enemy in other animals.

"The fear of man is slowly acquired, as I have elsewhere shown, by the various animals which inhabit desert islands. We see an instance of this even in England, in the greater wildness of all our large birds in comparison with our small birds.

"We shall thus be enabled to see the part which habit and the selection of so-called spontaneous variations have played in modifying the mental qualities of our domestic animals.

"It is notorious how much domestic animals vary in their mental qualities. With cats, for instance, one naturally takes to catching rats, and another mice, and these tendencies are known to be inherited. One cat, according to Mr. St. John, always brought home gamebirds, another hares or rabbits, and another hunted on marshy ground and almost nightly caught woodcocks or snipes.

"A number of curious and authentic instances could be given of various shades of disposition and of taste, and likewise of the oddest tricks, associated with certain frames of mind or periods of time, being inherited.

"But let us look to the familiar case of the breeds of the dogs. It cannot be doubted that young pointers (I have myself seen a striking instance) will sometimes point and even back other dogs the very first time that they are taken out.

"Retrieving is certainly in some degree inherited by retrievers -- and a tendency to run round, instead of at, a flock of sheep, by shepherd dogs. I cannot see that these actions, performed without experience by the young, and in nearly the same manner by each individual, performed with eager delight by each breed, and without the end being known- for the young pointer can no more know that he points to aid his master, than the white butterfly knows why she lays her eggs on the leaf of the cabbage-

"I cannot see that these actions differ essentially from true instincts. If we were to behold one kind of wolf -- when young and without any training, as soon as it scented its prey -- stand motionless like a statue -- and then slowly crawl forward with a peculiar gait -- and another kind of wolf rushing round, instead of at, a herd of deer, and driving them to a distant point -- we should assuredly call these actions instinctive.

"Domestic instincts, as they may be called, are certainly far less fixed than natural instincts. But they have been acted on by far less rigorous selection, and have been transmitted for an incomparably shorter period, under less fixed conditions of life.

"How strongly these domestic instincts, habits, and dispositions are inherited, and how curiously they become mingled, is well shown when different breeds of dogs are crossed.

"Thus it is known that a cross with a bull-dog has affected for many generations the courage and obstinacy of greyhounds. A cross with a greyhound has given to a whole family of shepherd-dogs a tendency to hunt hares.

"These domestic instincts, when thus tested by crossing, resemble natural instincts, which in a like manner become curiously blended together, and for a long period exhibit traces of the instincts of either parent.

"No one would ever have thought of teaching, or probably could have taught, the tumbler-pigeon to tumble,- an action which, as I have witnessed, is performed by young birds, that have never seen a pigeon tumble. We may believe that some one pigeon showed a slight tendency to this strange habit, and that the long-continued selection of the best individuals in successive generations made tumblers what they now are.

"Near Glasgow there are house-tumblers, as I hear from Mr. Brent, which cannot fly eighteen inches high without going head over heels.

"It may be doubted whether any one would have thought of training a dog to point, had not some one dog naturally shown a tendency in this line; and this is known occasionally to happen, as I once saw, in a pure terrier. The act of pointing is probably, as many have thought, only the exaggerated pause of an animal preparing to spring on its prey.

"When the first tendency to point was once displayed, methodical selection and the inherited effects of compulsory training in each successive generation would soon complete the work. Unconscious selection is still in progress, as each man tries to procure, without intending to improve the breed, dogs which stand and hunt best.

"On the other hand, habit alone in some cases has sufficed. Hardly any animal is more difficult to tame than the young of the wild rabbit. Scarcely any animal is tamer than the young of the tame rabbit. But I can hardly suppose that domestic rabbits have often been selected for tameness alone. We must attribute at least the greater part of the inherited change from extreme wildness to extreme tameness, to habit and long-continued close confinement.

"Natural instincts are lost under domestication.

"A remarkable instance of this is seen in those breeds of fowls which very rarely or never become "broody," that is, never wish to sit on their eggs.

"Familiarity alone prevents our seeing how largely and how permanently the minds of our domestic animals have been modified. It is scarcely possible to doubt that the love of man has become instinctive in the dog. All wolves, foxes, jackals, and species of the cat genus, when kept tame, are most eager to attack poultry, sheep, and pigs; and this tendency has been found incurable in dogs which have been brought home as puppies from countries such as Tierra del Fuego and Australia, where the savages do not keep these domestic animals.

"How rarely, on the other hand, do our civilised dogs, even when quite young, require to be taught not to attack poultry, sheep, and pigs! No doubt they occasionally do make an attack, and are then beaten; and if not cured, they are destroyed; so that habit and some degree of selection have probably concurred in civilising by inheritance our dogs.

"On the other hand, young chickens have lost, wholly by habit, that fear of the dog and cat which no doubt was originally instinctive with them; for I am informed by Captain Hutton that the young chickens of the parent-stock, the Gallus bankiva, when reared in India under a hen, are at first excessively wild.

"So it is with young pheasants reared in England under a hen. It is not that chickens have lost all fear, but fear only of dogs and cats, for if the hen gives the danger-chuckle, they will run (more especially young turkeys) from under her, and conceal themselves in the surrounding grass or thickets; and this is evidently done for the instinctive purpose of allowing as we see in wild ground-birds, their mother to fly away.

"I will select only three -- namely, the instinct which leads the cuckoo to lay her eggs in other birds' nests -- the slave-making instinct of certain ants -- and the cell-making power of the hive-bee. These two latter instincts have generally and justly been ranked by naturalists as the most wonderful of all known instincts.

"Instincts of the Cuckoo. It is supposed by some naturalists that the more immediate cause of the instinct of the cuckoo is, that she lays her eggs, not daily, but at intervals of two or three days -- so that, if she were to make her own nest and sit on her own eggs those first laid would have to be left for some time unincubated -- or there would be eggs and young birds of different ages in the same nest.

"If this were the case, the process of laying and hatching might be inconveniently long, more especially as she migrates at a very early period. The first hatched young would probably have to be fed by the male alone.

"But the American cuckoo is in this predicament. She makes her own nest, and has eggs and young successively hatched, all at the same time. It has been both asserted and denied that the American cuckoo occasionally lays her eggs in other birds' nests.

"I have lately heard from Dr. Merrell, of Iowa, that he once found in Illinois a young cuckoo together with a young jay in the nest of a blue jay (Garrulus cristatus). As both were nearly full feathered, there could be no mistake in their identification.

"I could also give several instances of various birds which have been known occasionally to lay their eggs in other birds' nests.

"Now let us suppose that the ancient progenitor of our European cuckoo had the habits of the American cuckoo, and that she occasionally laid an egg in another bird's nest. If the old bird profited by this occasional habit through being enabled to migrate earlier or through any other cause -- or if the young were made more vigorous by advantage being taken of the mistaken instinct of another species than when reared by their own mother -- encumbered as she could hardly fail to be by having eggs and young of different ages at the same time -- then the old birds or the fostered young would gain an advantage.

"And analogy would lead us to believe, that the young thus reared would be apt to follow by inheritance the occasional and aberrant habit of their mother, and in their turn would be apt to lay their eggs in other birds' nests --and thus be more successful in rearing their young.

"By a continued process of this nature, I believe that the strange instinct of our cuckoo has been generated.

"But in all cases, speculation on an instinct known to us only in a single species, is useless. We have hitherto had no facts to guide us.

"Until recently the instincts of the European and of the nonparasitic American cuckoo alone were known. Now, owing to Mr. Ramsay's observations, we have learnt something about three Australian species, which lay their eggs in other birds' nests.

"The chief points to be referred to are three. First, that the common cuckoo, with rare exceptions, lays only one egg in a nest, so that the large and voracious young bird receives ample food.

"Secondly, that the eggs are remarkably small, not exceeding those of the skylark -- a bird about one-fourth as large as the cuckoo. That the small size of the egg is a real cause of adaptation we may infer from the fact of the non-parasitic American cuckoo laying full-sized eggs.

"Thirdly, that the young cuckoo, soon after birth, has the instinct, the strength, and a properly shaped back for ejecting its foster-brothers, which then perish from cold and hunger.

"This has been boldly called a beneficent arrangement, in order that the young cuckoo may get sufficient food, and that its foster-brothers may perish before they had acquired much feeling!

"Turning now to the Australian species.

"Though these birds generally lay only one egg in a nest, it is not rare to find two or even three eggs in the same nest. In the bronze cuckoo the eggs vary greatly in size, from eight to ten times in length.

"Now if it had been of an advantage to this species to have laid eggs even smaller than those now laid -- so as to have deceived certain foster-parents -- or, as is more probable, to have been hatched within a shorter period -- for it is asserted that there is a relation between the size of eggs and the period of their incubation -- then there is no difficulty in believing that a race or species might have been formed which would have laid smaller and smaller eggs.

"For these would have been more safely hatched and reared.

"Mr. Ramsay remarks that two of the Australian cuckoos, when they lay their eggs in an open nest, manifest a decided preference for nests containing eggs similar in colour to their own. The European species apparently manifests some tendency towards a similar instinct, but not rarely departs from it -- as is shown by her laying her dull and pale-coloured eggs in the nest of the Hedge-warbler with bright greenish-blue eggs.

"Had our cuckoo invariably displayed the above instinct, it would assuredly have been added to those which it is assumed must all have been acquired together.

"This case is more remarkable than that of the cuckoo. These bees have not only had their instincts but their structure modified in accordance with their parasitic habits. They do not possess the pollen-collecting apparatus which would have been indispensable if they had stored up food for their own young.

"Some species of Sphegidea (wasp-like insects) are likewise parasitic. M. Fabre has lately shown good reason for believing that -- although the Tachytes nigra generally makes its own burrow and stores it with paralysed prey for its own larvae -- yet that, when this insect finds a burrow already made and stored by another species, it takes advantage of the prize and becomes for the occasion parasitic.

"In this case, as with that of the Molothrus or cuckoo, I can see no difficulty in natural selection making an occasional habit permanent, if of advantage to the species, and if the insect whose nest and stored food are feloniously appropriated, be not thus exterminated.

"Slave-making instinct.-

"This remarkable instinct was first discovered in the Formica (Polyerges) rufescens by Pierre Huber, a better observer even than his celebrated father.

"This ant is absolutely dependent on its slaves. Without their aid, the species would certainly become extinct in a single year.

"The males and fertile female do no work of any kind, and the workers or sterile females, though most energetic and courageous in capturing slaves, do no other work.

"They are incapable of making their own nests, or of feeding their own larvae. When the old nest is found inconvenient, and they have to migrate, it is the slaves which determine the migration, and actually carry their masters in their jaws.

"So utterly helpless are the masters, that when Huber shut up thirty of them without a slave, but with plenty of the food which they like best -- and with their own larvae and pupae to stimulate them to work -- they did nothing. They could not even feed themselves, and many perished of hunger.

"This species is found in the southern parts of England, and its habits have been attended to by Mr. F. Smith, of the British Museum, to whom I am much indebted for information on this and other subjects. Although fully trusting to the statements of Huber and Mr. Smith, I tried to approach the subject in a sceptical frame of mind, as any one may well be excused for doubting the existence of so extraordinary an instinct as that of making slaves.

"Hence, I will give the observations which I made in some little detail. I opened fourteen nests of F. sanguinea, and found a few slaves in all. Males and fertile females of the slave species (F. fusca) are found only in their own proper communities, and have never been observed in the nests of F. sanguinea.

"The slaves are black and not above half the size of their red masters, so that the contrast in their appearance is great. When the nest is slightly disturbed, the slaves occasionally come out, and like their masters are much agitated and defend the nest. When the nest is much disturbed, and the larvae and pupae are exposed, the slaves work energetically together with their masters in carrying them away to a place of safety.

"Hence, it is clear, that the slaves feel quite at home.

"During the months of June and July, on three successive years, I watched for many hours several nests in Surrey and Sussex, and never saw a slave either leave or enter a nest. As, during these months, the slaves are very few in number, I thought that they might behave differently when more numerous; but Mr. Smith informs me that he has watched the nests at various hours during May, June, and August, both in Surrey and Hampshire, and has never seen the slaves, though present in large numbers in August, either leave or enter the nest.

"Hence he considers them as strictly household slaves. The masters, on the other hand, may be constantly seen bringing in materials for the nest, and food of all kinds.

"During the year 1860, however, in the month of July, I came across a community with an unusually large stock of slaves, and I observed a few slaves mingled with their masters leaving the nest, and marching along the same road to a tall Scotch-fir-tree, twenty-five yards distant, which they ascended together, probably in search of aphides or cocci.

"Still more briefly I have attempted to show that instincts vary slightly in a state of nature.

"No one will dispute that instincts are of the highest importance to each animal. Therefore there is no real difficulty -- under changing conditions of life -- in natural selection accumulating to any extent slight modifications of instinct which are in any way useful. In many cases habit or use and disuse have probably come into play.

"I do not pretend that the facts given in this chapter strengthen in any great degree my theory. But none of the cases of difficulty, to the best of my judgment, annihilate it.

"On the other hand, the fact that instincts are not always absolutely perfect and are liable to mistakes -- that no instinct can be shown to have been produced for the good of other animals, though animals take advantage of the instincts of others -- that the canon in natural history, of "Natura non facit saltum," is applicable to instincts as well as to corporeal structure, and is plainly explicable on the foregoing views, but is otherwise inexplicable, all tend to corroborate the theory of natural selection.

"This theory is also strengthened by some few other facts in regard to instincts -- as by that common case of closely allied, but distinct species -- when inhabiting distant parts of the world and living under considerably different conditions of life, yet often retaining nearly the same instincts.

"For instance, we can understand, on the principle of inheritance, how it is that the thrush of tropical South America lines its nest with mud, in the same peculiar manner as does our British thrush. How it is that the hornbills of Africa and India have the same extraordinary instinct of plastering up and imprisoning the females in a hole in a tree, with only a small hole left in the plaster through which the males feed them and their young when hatched. How it is that the male wrens (Troglodytes) of North America build "cocknests," to roost in, like the males of our kittywrens,- a habit wholly unlike that of any other known bird.

"The view commonly entertained by naturalists is that species, when intercrossed, have been specially endowed with sterility, in order to prevent their confusion.

"This view certainly seems at first highly probable, for species living together could hardly have been kept distinct had they been capable of freely crossing.

"The subject is in many ways important for us, more especially as the sterility of species when first crossed -- and that of their hybrid offspring -- cannot have been acquired, as I shall show, by the preservation of successive profitable degrees of sterility.

"It is an incidental result of differences in the reproductive systems of the parent-species.

"In treating this subject, two classes of facts, to a large extent fundamentally different, have generally been confounded. Namely, the sterility of species when first crossed, and the sterility of the hybrids produced from them.

"Pure species have of course their organs of reproduction in a perfect condition. Yet when intercrossed they produce either few or no offspring.

"Hybrids, on the other hand, have their reproductive organs functionally impotent -- as may be clearly seen in the state of the male element in both plants and animals -- though the formative organs themselves are perfect in structure, as far as the microscope reveals.

"In the first case the two sexual elements which go to form the embryo are perfect. In the second case they are either not at all developed, or are imperfectly developed.

"It is impossible to study the several memoirs and works of those two conscientious and admirable observers, Kolreuter and Gartner, who almost devoted their lives to this subject, without being deeply impressed with the high generality of some degree of sterility.

"Kolreuter makes the rule universal. Then he cuts the knot, for in ten cases in which he found two forms -- considered by most authors as distinct species, quite fertile together -- he unhesitatingly ranks them as varieties.

"Gartner, also, makes the rule equally universal. He disputes the entire fertility of Kolreuter's ten cases.

"But in these and in many other cases, Gartner is obliged carefully to count the seeds, in order to show that there is any degree of sterility.

"He always compares the maximum number of seeds produced by two species when first crossed -- and the maximum produced by their hybrid offspring -- with the average number produced by both pure parent-species in a state of nature.

"But causes of serious error here intervene. A plant, to be hybridised, must be castrated -- and, what is often more important -- must be secluded in order to prevent pollen being brought to it by insects from other plants.

"Nearly all the plants experimented on by Gartner were potted, and were kept in a chamber in his house. That these processes are often injurious to the fertility of a plant cannot be doubted. For Gartner gives in his table about a score of cases of plants which he castrated, and artificially fertilised with their own pollen -- and (excluding all cases such as the Leguminosae, in which there is an acknowledged difficulty in the manipulation) -- half of these twenty plants had their fertility in some degree impaired.

"I think no better evidence of this can be required than that the two most experienced observers who have ever lived, namely Kolreuter and Gartner, arrived at diametrically opposite conclusions in regard to some of the very same forms.

"It is also most instructive to compare -- but I have not space here to enter on details -- the evidence advanced by our best botanists on the question whether certain doubtful forms should be ranked as species or varieties -- with the evidence from fertility adduced by different hybridisers -- or by the same observer from experiments made during different years.

"It can thus be shown that neither sterility nor fertility affords any certain distinction between species and varieties. The evidence from this source graduates away, and is doubtful in the same degree as is the evidence derived from other constitutional and structural differences.

"In regard to the sterility of hybrids in successive generations:-- though Gartner was enabled to rear some hybrids -- carefully guarding them from a cross with either pure parent -- for six or seven, and in one case for ten generations.

"Yet he asserts positively that their fertility never increases, but generally decreases greatly and suddenly.

"With respect to this decrease, it may first be noticed that when any deviation in structure or constitution is common to both parents, this is often transmitted in an augmented degree to the offspring. Both sexual elements in hybrid plants are already affected in some degree.

"But I believe that their fertility has been diminished in nearly all these cases by an independent cause, namely, by too close interbreeding.

"I have made so many experiments and collected so many facts -- showing on the one hand that an occasional cross with a distinct individual or variety increases the vigour and fertility of the offspring -- and on the other hand that very close interbreeding lessens their vigour and fertility -- that I cannot doubt the correctness of this conclusion.

"Hybrids are seldom raised by experimentalists in great numbers. As the parent-species, or other allied hybrids, generally grow in the same garden, the visits of insects must be carefully prevented during the flowering season. Hence hybrids, if left to themselves, will generally be fertilised during each generation by pollen from the same flower. This would probably be injurious to their fertility, already lessened by their hybrid origin.

"I am strengthened in this conviction by a remarkable statement repeatedly made by Gartner -- namely, that if even the less fertile hybrids be artificially fertilised with hybrid pollen of the same kind, their fertility -- notwithstanding the frequent ill effects from manipulation -- sometimes decidedly increases, and goes on increasing.

"Now, in the process of artificial fertilisation, pollen is as often taken by chance (as I know from my own experience) from the anthers of another flower -- as from the anthers of the flower itself which is to be fertilised. A cross between two flowers, though probably often on the same plant, would be thus effected.

"Moreover, whenever complicated experiments are in progress, so careful an observer as Gartner would have castrated his hybrids. This would have ensured in each generation a cross with pollen from a distinct flower -- either from the same plant or from another plant of the same hybrid nature.

"Most of them have now been discussed. One -- namely the distinctness of specific forms -- and their not being blended together by innumerable transitional links, is a very obvious difficulty.

"I assigned reasons why such links do not commonly occur at the present day under the circumstances apparently most favourable for their presence -- namely, on an extensive and continuous area with graduated physical conditions.

"I endeavoured to show, that the life of each species depends in a more important manner on the presence of other already defined organic forms, than on climate. Therefore, that the really governing conditions of life do not graduate away quite insensibly like heat or moisture.

"I endeavoured, also, to show that intermediate varieties -- from existing in lesser numbers than the forms which they connect -- will generally be beaten out and exterminated during the course of further modification and improvement.

"The main cause, however, of innumerable intermediate links not now occurring everywhere throughout nature, depends on the very process of natural selection, through which new varieties continually take the places of and supplant their parent-forms.

"But just in proportion as this process of extermination has acted on an enormous scale, so must the number of intermediate varieties, which have formerly existed, be truly enormous.

"Why then is not every geological formation and every stratum full of such intermediate links? Geology assuredly does not reveal any such finely-graduated organic chain.

"I have found it difficult, when looking at any two species, to avoid picturing to myself forms directly intermediate between them.

"But this is a wholly false view. We should always look for forms intermediate between each species and a common but unknown progenitor. And the progenitor will generally have differed in some respects from all its modified descendants.

"To give a simple illustration -- the fantail and pouter pigeons are both descended from the rock-pigeon. If we possessed all the intermediate varieties which have ever existed, we should have an extremely close series between both and the rock-pigeon.

"But we should have no varieties directly intermediate between the fantail and pouter. None, for instance, combining a tail somewhat expanded with a crop somewhat enlarged, the characteristic features of these two breeds.

"These two breeds, moreover, have become so much modified -- that, if we had no historical or indirect evidence regarding their origin -- it would not have been possible to have determined -- from a mere comparison of their structure with that of the rock-pigeon, C. livia -- whether they had descended from this species or from some allied form, such as C. aenas.

"So, with natural species, if we look to forms very distinct -- for instance to the horse and tapir -- we have no reason to suppose that links directly intermediate between them ever existed, but between each and an unknown common parent.

"The common parent will have had in its whole organisation much general resemblance to the tapir and to the horse -- but in some points of structure may have differed considerably from both, even perhaps more than they differ from each other.

"For instance, a horse from a tapir. In this case direct intermediate links will have existed between them.

"But such a case would imply that one form had remained for a very long period unaltered, whilst its descendants had undergone a vast amount of change. The principle of competition between organism and organism, between child and parent, will render this a very rare event. In all cases the new and improved forms of life tend to supplant the old and unimproved forms.

"By the theory of natural selection all living species have been connected with the parent-species of each genus -- by differences not greater than we see between the natural and domestic varieties of the same species at the present day.

"These parent-species, now generally extinct, have in their turn been similarly connected with more ancient forms -- and so on backwards, always converging to the common ancestor of each great class. So that the number of intermediate and transitional links -- between all living and extinct species -- must have been inconceivably great.

"It is hardly possible for me to recall to the reader who is not a practical geologist, the facts leading the mind feebly to comprehend the lapse of time.

"He who can read Sir Charles Lyell's grand work on the Principles of Geology -- which the future historian will recognise as having produced a revolution in natural science, and yet does not admit how vast have been the past periods of time -- may at once close this volume.

"Not that it suffices to study the Principles of Geology -- or to read special treatises by different observers on separate formations, and to mark how each author attempts -- to give an inadequate idea of the duration of each formation, or even of each stratum.

"We can best gain some idea of past time by knowing the agencies at work, and learning how deeply the surface of the land has been denuded, and how much sediment has been deposited.

"The tides in most cases reach the cliffs only for a short time twice a day, and the waves eat into them only when they are charged with sand or pebbles; for there is good evidence that pure water effects nothing in wearing away rock.

"At last the base of the cliff is undermined, huge fragments fall down, and these, remaining fixed, have to be worn away atom by atom, until after being reduced in size they can be rolled about by the waves, and then they are more quickly ground into pebbles, sand, or mud.

"But how often do we see along the bases of retreating cliffs rounded boulders, all thickly clothed by marine productions, showing how little they are abraded and how seldom they are rolled about! Moreover, if we follow for a few miles any line of rocky cliff, which is undergoing degradation, we find that it is only here and there, along a short length or round a promontory, that the cliffs are at the present time suffering.

"The appearance of the surface and the vegetation show that elsewhere years have elapsed since the waters washed their base.

"We have, however, recently learnt from the observations of Ramsay, in the van of many excellent observers- of Jukes, Geikie, Croll, and others, that subaerial degradation is a much more important agency than coast-action, or the power of the waves.

"The whole surface of the land is exposed to the chemical action of the air and of the rain-water with its dissolved carbolic acid, and in colder countries to frost. The disintegrated matter is carried down even gentle slopes during heavy rain, and to a greater extent than might be supposed, especially in arid districts, by the wind.

"It is then transported by the streams and rivers, which when rapid deepen their channels, and triturate the fragments. On a rainy day, even in a gently undulating country, we see the effects of subaerial degradation in the muddy rills which flow down every slope.

"Messrs. Ramsay and Whitaker have shown, and the observation is a most striking one, that the great lines of escarpment in the Wealden district and those ranging across England, which formerly were looked at as ancient sea-coasts, cannot have been thus formed, for each line is composed of one and the same formation, whilst our sea-cliffs are everywhere formed by the intersection of various formations.

"This being the case, we are compelled to admit that the escarpments owe their origin in chief part to the rocks of which they are composed having resisted subaerial denudation better than the surrounding surface; this surface consequently has been gradually lowered, with the lines of harder rock left projecting.

"Nothing impresses the mind with the vast duration of time, according to our ideas of time, more forcibly than the conviction thus gained that subaerial agencies which apparently have so little power, and which seem to work so slowly, have produced great results."

Time - time - time. Atom by atom by atom. Aren't you beginning to feel very small? Does 5,000 years ago seem historical?

"I remember having been much struck when viewing volcanic islands, which have been worn by the waves and pared all round into perpendicular cliffs of one or two thousand feet in height. The gentle slope of the lava-streams, due to their formerly liquid state, showed at a glance how far the hard, rocky beds had once extended into the open ocean.

"The same story is told still more plainly by faults -- those great cracks along which the strata have been upheaved on one side, or thrown down on the other, to the height or depth of thousands of feet. For since the crust cracked, and it makes no great difference whether the upheaval was sudden, or, as most geologists now believe, was slow and effected by many starts, the surface of the land has been so completely planed down that no trace of these vast dislocations is externally visible.

"The Craven fault, for instance, extends for upwards of 30 miles, and along this line the vertical displacement of the strata varies from 600 to 3000 feet.

"Professor Ramsay has published an account of a downthrow in Anglesea of 2300 feet. And he informs me that he fully believes that there is one in Merionethshire of 12,000 feet.

"In the Cordillera I estimated one mass of conglomerate at ten thousand feet; and although conglomerates have probably been accumulated at a quicker rate than finer sediments, yet from being formed of worn and rounded pebbles, each of which bears the stamp of time, they are good to show how slowly the mass must have been heaped together.

"Professor Ramsay has given me the maximum thickness, from actual measurement in most cases, of the successive formations in different parts of Great Britain; and this is the result:-

Palaeozoic strata (not including igneous beds): 57,154 feet Secondary strata: 13,190 feet Tertiary strata: 2,249 feet

-making altogether 72,584 feet; that is, very nearly thirteen and three-quarters British miles.

"Some of the formations, which are represented in England by thin beds, are thousands of feet in thickness on the Continent. Moreover, between each successive formation, we have, in the opinion of most geologists, blank periods of enormous length.

"That our collections are imperfect is admitted by every one. The remark of that admirable palaeontologist, Edward Forbes, should never be forgotten -- namely, that very many fossil species are known and named from single and often broken specimens, or from a few specimens collected on some one spot.

"Only a small portion of the surface of the earth has been geologically explored, and no part with sufficient care, as the important discoveries made every year in Europe prove.

"No organism wholly soft can be preserved. Shells and bones decay and disappear when left on the bottom of the sea, where sediment is not accumulating.

"We probably take a quite erroneous view, when we assume that sediment is being deposited over nearly the whole bed of the sea, at a rate sufficiently quick to embed and preserve fossil remains. Throughout an enormously large proportion of the ocean, the bright blue tint of the water bespeaks its purity.

"The many cases on record of a formation conformably covered -- after an immense interval of time -- by another and later formation, without the underlying bed having suffered in the interval any wear and tear, seem explicable only on the view of the bottom of the sea not rarely lying for ages in an unaltered condition.

"The remains which do become embedded -- if in sand or gravel -- will, when the beds are upraised, generally be dissolved by the percolation of rain-water charged with carbolic acid.

"Some of the many kinds of animals which live on the beach between high and low water mark seem to be rarely preserved. For instance, the several species of the Chthamalinae (a sub-family of sessile cirripedes) coat the rocks all over the world in infinite numbers. They are all strictly littoral, with the exception of a single Mediterranean species, which inhabits deep water, and this has been found fossil in Sicily.

"Not one other species has hitherto been found in any tertiary formation. Yet it is known that the genus Chthamalus existed during the Chalk period.

"Lastly, many great deposits requiring a vast length of time for their accumulation, are entirely destitute of organic remains, without our being able to assign any reason.

"One of the most striking instances is that of the Flysch formation, which consists of shale and sandstone -- several thousand, occasionally even six thousand feet in thickness -- and extending for at least 300 miles from Vienna to Switzerland.