"Behold in our stout and clumsy horses, habituated to draw heavy loads, and which constitute a special race by always being kept together—behold, I say, the difference in their form compared with those of English horses, which are all slender, with long necks, because for a long period they have been trained to run swiftly: behold in them the influence of a difference of habit, and judge for yourselves. You find them, then, such as they are in some degree in nature. You find there our cock and our hen in the condition we have [made] them, as also the mixed races that we have formed by mixed breeding between the varieties produced in different countries, or where they were so in the state of domesticity. You find there likewise our different races of domestic pigeons, our different dogs, etc. What are our cultivated fruits, our wheat, our cabbage, our lettuce, etc., etc., if they are not the result of changes which we ourselves have effected in these plants, in changing by our culture the conditions of their situation? Are they now found in this condition in nature? To these incontestable facts add the considerations which I have discussed in my Recherches sur les Corps vivans (p. 56 et suiv.), and decide for yourselves.

"Thus, among living bodies, nature, as I have already said, offers only in an absolute way individuals which succeed each other genetically, and which descend one from the other. So the species among them are only relative, and only temporary.

"Nevertheless, to facilitate the study and the knowledge of so many different bodies it is useful to give the name of species to the entire collection of individuals which are alike, which reproduction perpetuates in the same condition as long as the conditions of their situation do not change enough to make their habits, their character, and their form vary.

"Such is, citizens, the exact sketch of that which goes on in nature since she has existed, and of that which the observation of her acts has alone enabled us to discover. I have fulfilled my object if, in presenting to you the results of my researches and of my experience, I have been able to disclose to you that which in your studies of this kind deserves your special attention.

"You now doubtless conceive how important are the considerations which I have just exposed to you, and how wrong you would be if, in devoting yourself to the study of animals or of plants, you should seek to see among them only the multiplied distinctions that we have been obliged to establish; in a word, if you should confine yourselves to fixing in your memory the variable and indefinite nomenclature which is applied to so many different bodies, instead of studying Nature herself—her course, her means, and the constant results that she knows how to attain."

On the next fly page are the following words: Esquisse d'une Philosophie zoologique.

IV. Lamarck's Views as published in 1806.[177]

"Those who have observed much and have consulted the great collections, have been able to convince themselves that as gradually as the circumstances of their habitat, of exposure to their surroundings, of climate, food, mode of living, etc., have changed, the characters of size, form, of proportion between the parts, of color, of consistence, of duration, of agility, and of industry have proportionately changed.

"They have been able to see, as regards the animals, that the more frequent and longer sustained use of any organ gradually strengthens this organ, develops it, enlarges it, and gives it a power proportional to the length of time it has been used; while the constant lack of use of such an organ insensibly weakens it, causes it to deteriorate, progressively diminishes its faculties, and tends to make it waste away.[178]

"Finally, it has been remarked that all that nature has made individuals to acquire or lose by the sustained influence of circumstances where their race has existed for a long time, she has preserved by heredity in the new individuals which have originated from them (elle le conserve par la generation aux nouveaux individus qui en proviennent). These verities are firmly grounded, and can only be misunderstood by those who have never observed and followed nature in her operations.

"Thus we are assured that that which is taken for species among living bodies, and that all the specific differences which distinguish these natural productions, have no absolute stability, but that they enjoy only a relative stability; which it is very important to consider in order to fix the limits which we must establish in the determination of that which we must call species.

"It is known that different places change in nature and character by reason of their position, their 'composition' [we should say geological structure or features], and their climate; that which is easily perceived in passing over different places distinguished by special characteristics; behold already a cause of variation for the natural productions which inhabit these different places. But that which is not sufficiently known, and even that which people refuse to believe, is that each place itself changes after a time, in exposure, in climate, in nature, and in character, although with a slowness so great in relation to our period of time that we attribute to it a perfect stability.

"Now, in either case, these changed places proportionately change the circumstances relative to the living bodies which inhabit them, and these produce again other influences on those same bodies.

"We see from this that if there are extremes in these changes there are also gradations (nuances), that is to say, steps which are intermediate, and which fill up the interval; consequently there are also gradations in the differences which distinguish that which we call species.

"Indeed, as we constantly meet with such shades (or intermediate steps) between these so-called species, we find ourselves forced to descend to the minutest details to find any distinctions; the slightest peculiarities of form, of color, of size, and often even of differences only perceived in the aspect of the individual compared with other individuals which are related to it the more by their relations, are seized upon by naturalists to establish specific differences; so that, the slightest varieties being reckoned as species, our catalogues of species grow infinitely great, and the name of the productions of nature of the most interest to us are, so to speak, buried in these enormous lists, become very difficult to find, because now the objects are mostly only determined by characters which our senses can scarcely enable us to perceive.

"Meanwhile we should remember that nothing of all this exists in nature; that she knows neither classes, orders, genera, nor species, in spite of all the foundation which the portion of the natural series which our collection contains has seemed to afford them; and that of organic or living bodies there are, in reality, only individuals, and among different races which gradually pass (nuancent) into all degrees of organization" (p. 14).

On p. 70 he speaks of the animal chain from monad to man, ascending from the most simple to the most complex. The monad is the most simple, the most like a germ of living bodies, and from its nature passes to the volvoces, proteus, vibrios; from them nature arrives at the production of "polypes rotiferes"—and then at "Radiaires," worms, Arachnida, Crustacea, and Cirrhipedes.

FOOTNOTES:

[162] Discours d'ouverture du Cours de Zoologie donne dans le Museum national d'Histoire naturelle, le 21 floreal, an 8 de la Republique (1800). Floreal is the name adopted by the National Convention for the eighth month of the year. In the years of the Republic 1 to 7 it extended from April 20 to May 19 inclusive, and in the years 8 to 13 from April 21 to May 20 (Century Cyclopedia of Names). The lecture, then, in which Lamarck first presented his views was delivered on some day between April 21 and May 20, 1800.

[163] Lamarck by the word generation implies heredity. He nowhere uses the word heredite.

[164] "L'oiseau que le besoin attire sur l'eau pour y trouver la proie qui le fait vivre, ecarte les doigts de ses pieds lorsqu'il veut frapper l'eau et se mouvoir a sa surface" (p. 13). If the word veut has suggested the doctrine of appetency in meaning has been pushed too far by the critics of Lamarck.

[165] This he already touched upon in his Memoires de Physique et d'Histoire naturelle (p. 342).

[166] Systeme des Animaux sans Vertebres, pp. 16 and 17.

[167] I have cited the incontestable proofs in my Hydrogeologie, and I have the conviction that one day all will be compelled to accept these great truths.

[168] Ranunculus aquaticus capillaceus (Tournef., p. 291).

[169] Ranunculus aquaticus (folio rotundo et capillaceo, Tournef., p. 291).

[170] Gramen junceum, etc. (Moris, hist. 3, sec. 8, t. 9, f. 4).

[171] Discours d'ouverture d'un Cours de Zoologie, prononce en prairial, an XI, au Museum d'Histoire naturelle, sur la question, Qu'est-ce que l'espece parmi les corps vivans? (1803).

[172] Recherches sur l'Organisation des Corps vivans, p. 9.

[173] "See at the end of this discourse the sketch of a Philosophie zoologique relative to this subject." [This sketch was not added—only the title at the end of the book.]

[174] See the Annales du Museum d'Hist. nat., IV^e cahier. 1., 1802, pp. 302, 303: Memoires sur les Fossiles des Environs de Paris, etc. He repeats in his Discours what he wrote in 1802 in the Annales.

[175] Ibid. This is repeated from the article in the Annales.

[176] Ibid. "See my Recherches sur les Corps vivans" (Appendix, p. 141).

[177] Discours d'Ouverture du Cours des Animaux sans Vertebres, prononce dans le Museum d'Histoire naturelle en mai 1806. (No imprint. 8^o, pp. 108.) Only the most important passages are here translated.

[178] "We know that all the forms of organs compared to the uses of these same organs are always perfectly adapted. But there is a common error in this connection, since it is thought that the forms of organs have caused their functions (en ont amene l'emploi), whereas it is easy to demonstrate by observation that it is the uses (usages) which have given origin to the forms of organs."



CHAPTER XVII

THE "PHILOSOPHIE ZOOLOGIQUE"

Lamarck's mature views on the theory of descent comprise a portion of his celebrated Philosophie zoologique. We will let him tell the story of creation by natural causes so far as possible in his own words.

In the avertissement, or preface, he says that his experience has led him to realize that a body of precepts and of principles relating to the study of animals and even applicable to other parts of the natural sciences would now be useful, our knowledge of zooelogical facts having, for about thirty years, made considerable progress.

After referring to the differences in structure and faculties characterizing animals of different groups, he proceeds to outline his theory, and begins by asking:

"How, indeed, can I consider the singular modification in the structure of animals, as we glance over the series from the most perfect to the least perfect, without asking how we can account for a fact so positive and so remarkable—a fact attested to me by so many proofs? Should I not think that nature has successively produced the different living beings by proceeding from the most simple to the most compound; because in ascending the animal scale from the most imperfect up to the most perfect, the organization perfects itself and becomes gradually complicated in a most remarkable way?"

This leads him to consider what is life, and he remarks (p. xv.) that it does not exist without external stimuli. The conditions necessary for the existence of life are found completely developed in the simplest organization. We are then led to inquire how this organization, by reason of certain changes, can give rise to other organisms less simple, and finally originate creatures becoming gradually more complicated, as we see in ascending the animal scale. Then employing the two following considerations, he believes he perceives the solution of the problem which has occupied his thoughts.

He then cites as factors (1) use and disuse; (2) the movement of internal fluids by which passages are opened through the cellular tissue in which they move, and finally create different organs. Hence the movement of fluids in the interior of animals, and the influence of new circumstances as animals gradually expose themselves to them in spreading into every inhabitable place, are the two general causes which have produced the different animals in the condition we now see them. Meanwhile he perceived the importance of the preservation by heredity, though he nowhere uses that word, in the new individuals reproduced of everything which the results of the life and influencing circumstances had caused to be acquired in the organization of those which have transmitted existence to them.

In the Discours preliminaire, referring to the progression in organization of animals from the simplest to man, as also to the successive acquisition of different special organs, and consequently of as many faculties as new organs obtained, he remarks:

"Then we can perceive how needs (besoins), at the outset reduced to nullity, and of which the number gradually increases, have produced the inclination (penchant) to actions fitted to satisfy it; how the actions, becoming habitual and energetic, have caused the development of the organs which execute them; how the force which excites the organic movements may, in the simplest animals, be outside of them and yet animate them; how, then, this force has been transported and fixed in the animal itself; finally, how it then has become the source of sensibility, and in the end that of acts of intelligence.

"I shall add that if this method had been followed, then sensation would not have been regarded as the general and immediate cause of organic movements, and it would not have been said that life is a series of movements which are executed in virtue of sensations received by different organs; or, in other words, that all the vital movements are the product of impressions received by the sensitive parts.[179]

"This cause seems, up to a certain point, established as regards the most perfect animals; but had it been so relatively to all living beings, they should all be endowed with the power of sensation. But it cannot be proved that this is the case with plants, and it cannot likewise be proved that it is so with all the animals known.

"But nature in creating her organisms has not begun by suddenly establishing a faculty so eminent as that of sensation: she has had the means of producing this faculty in the imperfect animals of the first classes of the animal kingdom," referring to the Protozoa. But she has accomplished this gradually and successively. "Nature has progressively created the different special organs, also the faculties which animals enjoy."

He remarks that though it is indispensable to classify living forms, yet that our classifications are all artificial; that species, genera, families, orders, and classes do not exist in nature—only the individuals really exist. In the third chapter he gives the old definition of species, that they are fixed and immutable, and then speaks of the animal series, saying:

"I do not mean by this to say that the existing animals form a very simple series, and especially evenly graduated; but I claim that they form a branched series,[180] irregularly graduated, and which has no discontinuity in its parts, or which, at least, has not always had, if it is true that, owing to the extinction of some species, there are some breaks. It follows that the species which terminates each branch of the general series is connected at least on one side with other species which intergrade with it" (p. 59).

He then points out the difficulty of determining what are species in certain large genera, such as Papilio, Ichneumon, etc. How new species arise is shown by observation.

"A number of facts teaches us that in proportion as the individuals of one of our species are subjected to changes in situation, climate, mode of life or habits, they thereby receive influences which gradually change the consistence and the proportions of their parts, their form, their faculties, even their structure; so that it follows that all of them after a time participate in the changes to which they have been subjected.

"In the same climate very different situations and exposures cause simple variations in the individuals occurring there; but, after the lapse of time, the continual differences of situation of the individuals of which I speak, which live and successively reproduce under the same circumstances, produce differences in them which become, in some degree, essential to their existence, so that at the end of many successive generations these individuals, which originally belonged to another species, became finally transformed into a new species distinct from the other.

"For example, should the seeds of a grass or of any other plant natural to a moist field be carried by any means at first to the slope of a neighboring hill, where the soil, although more elevated, will yet be sufficiently moist to allow the plant to live there, and if it results, after having lived there and having passed through several generations, that it gradually reaches the dry and almost arid soil of a mountain side; if the plant succeeds in living there, and perpetuates itself there during a series of generations, it will then be so changed that any botanists who should find it there would make a distinct species of it.

"The same thing happens in the case of animals which circumstances have forced to change in climate, mode of life, and habits; but in their case the influences of the causes which I have just cited need still more time than the plants to bring about notable changes in the individuals.

"The idea of embracing, under the name of species, a collection of like individuals which are perpetuated by generation, and which have remained the same as long as nature has endured, implies the necessity that the individuals of one and the same species should not cross with individuals of a different species.

"Unfortunately observation has proved, and still proves every day, that this consideration is unfounded; for hybrids, very common among plants, and the pairings which we often observe between the individuals of very different species of animals, have led us to see that the limits between these supposed constant species are not so fixed as has been imagined.

"In truth, nothing often results from these singular unions, especially if they are very ill-assorted, and then the individuals which do result from them are usually infertile; but also, when the disparities are less great, we know that the default in question does not occur.

"But this cause only suffices to create, step by step, varieties which finally become races, and which, with time, constitute what we call species.

"To decide whether the idea which is formed of the species has any real foundation, let us return to the considerations which I have already explained; they lead us to see:

"1. That all the organized bodies of our globe are true productions of Nature, which she has successively formed after the lapse of much time;

"2. That, in her course. Nature has begun, and begins over again every day, to form the simplest organisms, and that she directly creates only those, namely, which are the first germs (ebauches) of organization, which are designated by the expression of spontaneous generations;

"3. That the first germs of the animal and plant having been formed in appropriate places and circumstances, the faculties of a beginning life and of an organic movement established, have necessarily gradually developed the organs, and that with time they have diversified them, as also the parts;

"4. That the power of growth in each part of the organized body being inherent in the first created forms of life, it has given rise to different modes of multiplication and of regeneration of individuals; and that consequently the progress acquired in the composition of the organization and in the shape and diversity of the parts has been preserved;

"5. That with the aid of sufficient time, of circumstances which have been necessarily favorable, of changes of condition that every part of the earth's surface has successively undergone—in a word, by the power which new situations and new habits have of modifying the organs of living beings, all those which now exist have been gradually formed such as we now see them;

"6. Finally, that, according to a similar order of things, living beings having undergone each of the more or less great changes in the condition of their structure and parts, that which we call a species among them has been gradually and successively so formed, having only a relative constancy in its condition, and not being as old as Nature herself.

"But, it will be said, when it is supposed that by the aid of much time and of an infinite variation in circumstances, Nature has gradually formed the different animals known to us, shall we not be stopped in this supposition by the simple consideration of the admirable diversity which we observe in the instincts of different animals, and by that of the marvels of every kind presented by their different kinds of industry?

"Shall we dare to extend the spirit of system so far as to say that it is Nature who has herself alone created this astonishing diversity of means, of contrivances, of skill, of precautions, of patience, of which the industry of animals offers us so many examples? What we observe in this respect in the simple class of insects, is it not a thousand times more than sufficient to make us realize that the limit to the power of Nature in nowise permits her to herself produce so many marvels, but to force the most obstinate philosopher to recognize that here the will of the Supreme Author of all things has been necessary, and has alone sufficed to create so many admirable things?

"Without doubt, one would be rash or, rather, wholly insensate, to pretend to assign limits to the power of the first Author of all things; but, aside from that, no one could dare to say that this infinite power could not will that which Nature even shows us it has willed"[181] (p. 67).

Referring to the alleged proof of the fixity of species brought forward by Cuvier in the Annales du Museum d'Histoire naturelle (i., pp. 235 and 236) that the mummied birds, crocodiles, and other animals of Egypt present no differences from those now living, Lamarck says:

"It would assuredly be very singular if it were otherwise, because the position of Egypt and its climate are still almost exactly what they were at that epoch. Moreover, the birds which live there still exist under the same circumstances as they were then, not having been obliged to change their habits.

"Moreover, who does not perceive that birds, which can so easily change their situation and seek places which suit them are less subject than many other animals to the variations of local circumstances, and hence less restricted in their habits."

He adds the fact that the animals in question have inhabited Egypt for two or three thousand years, and not necessarily from all time, and that this is not time enough for marked changes. He then gives the following definition of species, which is the best ever offered: "Species, then, have only a relative stability, and are invariable only temporarily."

"Yet, to facilitate the study and knowledge of so many different organisms it is useful to give the name of species to every similar collection of similar individuals which are perpetuated by heredity (generation) in the same condition, so long as the circumstances of their situation do not change enough to render variable their habits, character, and form."

He then discusses fossil species in the way already described in Chapter III. (p. 75).

The subject of the checks upon over-population by the smaller and weaker animals, or the struggle for existence, is thus discussed in Chapter IV.:

"Owing to the extreme multiplication of the small species, and especially of the most imperfect animals, the multiplicity of individuals might be prejudicial to the preservation of the species, to that of the progress acquired in the improvement of the organization—in a word, to the general order, if nature had not taken precautions to keep this multiplication within due limits over which she would never pass.

"Animals devour one another, except those which live only on plants; but the latter are exposed to being devoured by the carnivorous animals.

"We know that it is the strongest and the best armed which devour the weaker, and that the larger kinds devour the smaller. Nevertheless, the individuals of a single species rarely devour each other: they war upon other races.[182]

"The multiplication of the small species of animals is so considerable, and the renewals of their generations are so prompt, that these small species would render the earth uninhabitable to the others if nature had not set a limit to their prodigious multiplication. But since they serve as prey for a multitude of other animals, as the length of their life is very limited, and as the lowering of the temperature kills them, their numbers are always maintained in proper proportions for the preservation of their races and that of others.

"As to the larger and stronger animals, they would be too dominant and injure the preservation of other races if they should multiply in too great proportions. But their races devouring each other, they would only multiply slowly and in a small number at a time; this would maintain in this respect the kind of equilibrium which should exist.

"Finally, only man, considered separately from all which is characteristic of him, seems capable of multiplying indefinitely, because his intelligence and his resources secure him from seeing his increase arrested by the voracity of any animals. He exercises over them such a supremacy that, instead of fearing the larger and stronger races of animals, he is thus rather capable of destroying them, and he continually checks their increase.

"But nature has given him numerous passions, which, unfortunately, developing with his intelligence, thus place a great obstacle to the extreme multiplication of the individuals of his species.

"Indeed, it seems as if man had taken it upon himself unceasingly to reduce the number of his fellow-creatures; for never, I do not hesitate to say, will the earth be covered with the population that it could maintain. Several of its habitable parts would always be alternately very sparsely populated, although the time for these alternate changes would be to us measureless.

"Thus by these wise precautions everything is preserved in the established order; the changes and perpetual renewals which are observable in this order are maintained within limits over which they cannot pass; the races of living beings all subsist in spite of their variations; the progress acquired in the improvement of the organization is not lost; everything which appears to be disordered, overturned, anomalous, reenters unceasingly into the general order, and even cooeperates with it; and especially and always the will of the sublime Author of nature and of all existing things is invariably executed" (pp. 98-101).

In the sixth chapter the author treats of the degradation and simplification of the structure from one end to the other of the animal series, proceeding, as he says, inversely to the general order of nature, from the compound to the more simple. Why he thus works out this idea of a general degradation is not very apparent, since it is out of tune with his views, so often elsewhere expressed, of a progressive evolution from the simple to the complex, and to his own classification of the animal kingdom, beginning as it does with the simplest forms and ending with man. Perhaps, however, he temporarily adopts the prevailing method of beginning with the highest forms in order to bring out clearly the successive steps in inferiority or degradation presented in descending the animal scale.

We will glean some passages of this chapter which bear on his theory of descent. Speaking of the different kinds of aquatic surroundings he remarks:

"In the first place it should be observed that in the waters themselves she [Nature] presents considerably diversified circumstances; the fresh waters, marine waters, calm or stagnant waters, running waters or streams, the waters of warm climates, those of cold regions, finally those which are shallow and those which are very deep, offer many special circumstances, each of which acts differently on the animals living in them. Now, in a degree equal to the make-up of the organization, the races of animals which are exposed to either of these circumstances have been submitted to special influences and have been diversified by them."

He then, after referring to the general degradation of the Batrachians, touches upon the atrophy of legs which has taken place in the snakes:

"If we should consider as a result of degradation the loss of legs seen in the snakes, the Ophidia should be regarded as constituting the lowest order of reptiles; but it would be an error to admit this consideration. Indeed, the serpents being animals which, in order to hide themselves, have adopted the habit of gliding directly along the ground, their body has lengthened very considerably and disproportionately to its thickness. Now, elongated legs proving disadvantageous to their necessity of gliding and hiding, very short legs, being only four in number, since they are vertebrate animals, would be incapable of moving their bodies. Thus the habits of these animals have been the cause of the disappearance of their legs, and yet the batrachians, which have them, offer a more degraded organization, and are nearer the fishes" (p. 155).

Referring on the next page to the fishes, he remarks:—

"Without doubt their general form, their lack of a constriction between the head and the body to form a neck, and the different fins which support them in place of legs, are the results of the influence of the dense medium which they inhabit, and not that of the degradation of their organization. But this modification (degradation) is not less real and very great, as we can convince ourselves by examining their internal organs; it is such as to compel us to assign to the fishes a rank lower than that of the reptiles."

He then states that the series from the lamprey and fishes to the mammals is not a regularly gradated one, and accounts for this "because the work of nature has been often changed, hindered, and diverted in direction by the influences which singularly different, even contrasted, circumstances have exercised on the animals which are there found exposed in the course of a long series of their renewed generations."

Lamarck thus accounts for the production of the radial symmetry of the medusae and echinoderms, his Radiaires. At the present day this symmetry is attributed perhaps more correctly to their more or less fixed mode of life.

"It is without doubt by the result of this means which nature employs, at first with a feeble energy with polyps, and then with greater developments in the Radiata, that the radial form has been acquired; because the subtile ambient fluids, penetrating by the alimentary canal, and being expansive, have been able, by an incessantly renewed repulsion from the centre towards every point of the circumference, to give rise to this radiated arrangement of parts.

"It is by this cause that, in the Radiata, the intestinal canal, although still very imperfect, since more often it has only a single opening, is yet complicated with numerous radiating vasculiform, often ramified, appendages.

"It is, doubtless, also by this cause that in the soft Radiates, as the medusae, etc., we observe a constant isochronic movement, movement very probably resulting from the successive intermissions between the masses of subtile fluids which penetrate into the interior of these animals and those of the same fluids which escape from it, often being spread throughout all their parts.

"We cannot say that the isochronic movements of the soft Radiates are the result of their respiration; for below the vertebrate animals nature does not offer, in that of any animal, these alternate and measured movements of inspiration and expiration. Whatever may be the respiration of Radiates, it is extremely slow, and is executed without perceptible movements" (p. 200).

The Influence of Circumstances on the Actions and Habits of Animals.

It is in Chapter VII. that the views of Lamarck are more fully presented than elsewhere, and we therefore translate all of it as literally as possible, so as to preserve the exact sense of the author.

"We do not here have to do with a line of argument, but with the examination of a positive fact, which is more general than is supposed, and which has not received the attention it deserves, doubtless because, very often, it is quite difficult to discover. This fact consists in the influence which circumstances exert on the different organisms subjected to them.

"In truth, for a long time there has been noticed the influence of different states of our organization on our character, our propensities (penchants), our actions, and even our ideas; but it seems to me that no one has yet recognized that of our actions and of our habits on our organization itself. Now, as these actions and these habits entirely depend on the circumstances in which we habitually find ourselves, I shall try to show how great is the influence which these circumstances exercise on the general form, on the condition of the parts, and even on the organization of living bodies. It is therefore this very positive fact which is to be the subject of this chapter.

"If we have not had numerous occasions to plainly recognize the effects of this influence on certain organisms which we have transported under entirely new and different circumstances, and if we had not seen these effects and the changes resulting from them produced, in a way, under our very eyes, the important fact in question would have always remained unknown.

"The influence of circumstances is really continuously and everywhere active on living beings, but what renders it difficult for us to appreciate this influence is that its effects only become sensible or recognizable (especially in the animals) at the end of a long period.

"Before stating and examining the proofs of this fact, which deserves our attention, and which is very important for a zooelogical philosophy, let us resume the thread of the considerations we had begun to discuss.

"In the preceding paragraph we have seen that it is now an incontrovertible fact that, in considering the animal scale in a sense the inverse of that of nature, we find that there exists in the groups composing this scale a continuous but irregular modification (degradation) in the organization of animals which they comprise, an increasing simplification in the organization of these organisms; finally, a proportionate diminution in the number of faculties of these beings.

"This fact once recognized may throw the greatest light on the very order which nature has followed in the production of all the existing animals; but it does not show why the structure of animals in its increasing complexity from the more imperfect up to the most perfect offers only an irregular gradation, whose extent presents a number of anomalies or digressions which have no appearance of order in their diversity.

"Now, in seeking for the reason of this singular irregularity in the increasing complexity of organization of animals, if we should consider the outcome of the influences that the infinitely diversified circumstances in all parts of the globe exercise on the general form, the parts, and the very organization of these animals, everything will be clearly explained.

"It will, indeed, be evident that the condition in which we find all animals is, on one side, the result of the increasing complexity of the organization which tends to form a regular gradation, and, on the other, that it is that of the influences of a multitude of very different circumstances which continually tend to destroy the regularity in the gradations of the increasing complexity of the organization.

"Here it becomes necessary for me to explain the meaning I attach to the expression circumstances influencing the form and structure of animals—namely, that in becoming very different they change, with time, both their form and organization by proportionate modifications.

"Assuredly, if these expressions should be taken literally, I should be accused of an error; for whatever may be the circumstances, they do not directly cause any modification in the form and structure of animals.

"But the great changes in the circumstances bring about in animals great changes in their needs, and such changes in their needs necessarily cause changes in their actions. Now, if the new needs become constant or very permanent, the animals then assume new habits, which are as durable as the needs which gave origin to them. We see that this is easily demonstrated and even does not need any explanation to make it clearer.

"It is then evident that a great change in circumstances having become constant in a race of animals leads these animals into new habits.

"Now, if new circumstances, having become permanent in a race of animals, have given to these animals new habits—that is to say, have led them to perform new actions which have become habitual—there will from this result the use of such a part by preference to that of another, and in certain cases the total lack of use of any part which has become useless.

"Nothing of all this should be considered as a hypothesis or as a mere peculiar opinion; they are, on the contrary, truths which require, in order to be made evident, only attention to and the observation of facts.

"We shall see presently by the citation of known facts which prove it, on one side that the new wants, having rendered such a part necessary, have really by the result of efforts given origin to this part, and that as the result of its sustained use it has gradually strengthened it, developed, and has ended in considerably increasing its size; on the other side we shall see that, in certain cases, the new circumstances and new wants having rendered such a part wholly useless, the total lack of use of this part has led to the result that it has gradually ceased to receive the development which the other parts of the animal obtain; that it gradually becomes emaciated and thin; and that finally, when this lack of use has been total during a long time, the part in question ends in disappearing. All this is a positive fact; I propose to give the most convincing proofs.

"In the plants, where there are no movements, and, consequently, no habits properly so called, great changes in circumstances do not bring about less great differences in the development of their parts; so that these differences originate and develop certain of them, while they reduce and cause several others to disappear. But here everything operates by the changes occurring in the nutrition of the plant, in its absorptions and transpirations, in the amount of heat, light, air, and humidity which it habitually receives; finally, in the superiority that certain of the different vital movements may assume over others.

"Between individuals of the same species, some of which are constantly well nourished, and in circumstances favorable to their entire development, while the others live under reversed circumstances, there is brought about a difference in the condition of these individuals which gradually becomes very remarkable. How many examples could I not cite regarding animals and plants, which would confirm the grounds for this view! Now, if the circumstances remain the same, rendering habitual and constant the condition of individuals badly fed, diseased, or languishing, their internal organization becomes finally modified, and reproduction between the individuals in question preserves the acquired modifications, and ends in giving rise to a race very distinct from that of the individuals which unceasingly meet with circumstances favorable to their development.

"A very dry spring-time is the cause of the grass of a field growing very slowly, remaining scraggy and puny, flowering and fruiting without growing much.

"A spring interspersed with warm days and rainy days makes the same grass grow rapidly, and the harvest of hay is then excellent.

"But if any cause perpetuates the unfavorable circumstances surrounding these plants, they vary proportionally, at first in their appearance and general condition, and finally in several particulars of their characters.

"For example, if some seed of any of the grasses referred to should be carried into an elevated place, on a dry and stony greensward much exposed to the winds, and should germinate there, the plant which should be able to live in this place would always be badly nourished, and the individuals reproduced there continuing to exist under these depressing circumstances, there would result a race truly different from that living in the field, though originating from it. The individuals of this new race would be small, scraggy, and some of their organs, having developed more than others, would then offer special proportions.

"Those who have observed much, and who have consulted the great collections, have become convinced that in proportion as the circumstances of habitat, exposure, climate, food, mode of life, etc., come to change, the characters of size, form, proportion between the parts, color, consistence, agility, and industry in the animals change proportionally.

"What nature accomplishes after a long time, we bring about every day by suddenly changing, in the case of a living plant, the circumstances under which it and all the individuals of its species exist.

"All botanists know that the plants which they transplant from their birthplace into gardens for cultivation gradually undergo changes which at last render them unrecognizable. Many plants naturally very hairy then become glabrous, or almost so; many of those which were creeping and trailing, then become erect; others lose their spines or their prickles; others still, from the woody and perennial condition which their stem possesses in a warm climate, pass, in our climate, into an herbaceous condition, and among these several are nothing more than annual plants; finally, the dimensions of their parts themselves undergo very considerable changes. These effects of changes of circumstances are so well known that botanists prefer not to describe garden plants, at least only those which have been newly cultivated.

"Is not cultivated wheat (Triticum sativum) only a plant brought by man into the condition in which we actually see it? Who can tell me in what country such a plant lives in a state of nature—that is to say, without being there the result of its culture in some neighboring region?

"Where occur in nature our cabbage, lettuce, etc., in the condition in which we see them in our kitchen-gardens? Is it not the same as regards a number of animals which domestication has changed or considerably modified?

"What very different races among our fowls and domestic pigeons, which we have obtained by raising them in different circumstances and in different countries, and how vainly do we now endeavor to rediscover them in nature!

"Those which are the least changed, without doubt by a more recent process of domestication, and because they do not live in a climate which is foreign to them, do not the less possess, in the condition of some of their parts, great differences produced by the habits which we have made them contract. Thus our ducks and our domestic geese trace back their type to the wild ducks and geese; but ours have lost the power of rising into the high regions of the air, and of flying over extensive regions; finally, a decided change has been wrought in the state of their parts compared with that of animals of the race from which they have descended.

"Who does not know that such a native bird, which we raise in a cage and which lives there five or six years in succession, and after that replaced in nature—namely, set free—is then unable to fly like its fellows which have always been free? The slight change of circumstance operating on this individual has only diminished its power of flight, and doubtless has not produced any change in the shape of its parts. But if a numerous series of generations of individuals of the same race should have been kept in captivity for a considerable time, there is no doubt but that even the form of the parts of these individuals would gradually undergo notable changes. For a much stronger reason, if, instead of a simple captivity constantly maintained over them, this circumstance had been at the same time accompanied by a change to a very different climate, and if these individuals by degrees had been habituated to other kinds of food, and to other kinds of movements to obtain it; certainly these circumstances, united and becoming constant, would insensibly form a new and special race.

"Where do we find, in nature, this multitude of races of dogs, which, as the result of domesticity to which we have reduced these animals, have been brought into their present condition? Where do we find these bull-dogs, greyhounds, water spaniels, spaniels, pug-dogs, etc., etc., races which present among themselves much greater differences than those which we admit to be specific in wild animals of the same genus?

"Without doubt, a primitive single race, very near the wolf, if it is not itself the true type, has been submitted by man, at some period, to the process of domestication. This race, which then offered no difference between its individuals, has been gradually dispersed by man into different countries, with different climates; and after a time these same individuals, having undergone the influences of their habitats, and of the different habits they were obliged to contract in each country, have undergone remarkable changes, and have formed different special races. Now, the man who, for commercial reasons or from interests of any other kind, travels a very great distance, having carried into a densely populated place, as for example a great capital, different races of dogs originated in some very distant country, then the increase of these races by heredity (generation) has given rise successively to all those we now know.

"The following fact proves, as regards plants, how a change in any important circumstance leads to a change in the parts of their organisms.

"So long as Ranunculus aquatilis is submerged in the water, its leaves are all finely incised and the divisions hair-like; but when the stalks of this plant reach the surface of the water, the leaves which grow out in the air are wider, rounded, and simply lobed. If some feet from the same plant the roots succeed in pushing into a soil only damp, without being submerged, their stalks then are short, none of their leaves are divided into capillary divisions, which gives rise to Ranunculus hederaceus, which the botanists regard as a species whenever they meet with it.

"There is no doubt that as regards animals important changes in the circumstances under which they are accustomed to live do not produce alteration in their organs; for here the changes are much slower in operating than in plants, and, consequently, are to us less marked, and their cause less recognizable.

"As to the circumstances which have so much power in modifying the organs of living beings, the most influential are, doubtless, the diversity of the surroundings in which they live; but besides this there are many others which, in addition, have a considerable influence in the production of the effects in question.

"It is known that different localities change in nature and quality owing to their position, their nature, and their climate, as is easily seen in passing over different places distinguished by special features; hence we see a cause of variation for the animals and plants which live in these different places. But what we do not sufficiently know, and even what we generally refuse to believe, is that each place itself changes with time in exposure, in climate, in nature, and quality, although with a slowness so great in relation to our own continuance that we attribute to it a perfect stability.

"Now, in either case, these changed localities proportionally change the circumstances relative to the organisms which inhabit them, and the latter then give rise to other influences bearing on these same beings.

"We perceive from this that, if there are extremes in these changes, there are also gradations—namely, degrees which are intermediate and which fill the interval. Consequently there are also gradations in the differences which distinguish what we call species.

"It is then evident that the whole surface of the earth offers, in the nature and situation of the matters which occupy its different points, a diversity of circumstances which is throughout in relation with that of the forms and parts of animals, independent of the special diversity which necessarily results from the progress of the composition of organization in each animal.

"In each locality where animals can live, the circumstances which establish there an order of things remain for a long time the same, and really change there only with a slowness so great that man cannot directly notice them. He is obliged to consult monuments to recognize that in each one of these places the order of things that he discovers there has not always been the same, and to perceive that it will change more.

"The races of animals which live in each of these places should, then, retain their customary habits there also for a long time; hence to us seems an apparent constancy of races which we call species—constancy which has originated among us the idea that these races are as ancient as nature.

"But in the different points of the earth's surface which can be inhabited, nature and the situation of the places and climates constitute there, for the animals as for the plants, different circumstances of all sorts of degrees. The animals which inhabit these different places should then differ from each other, not only on account of the state of nature of the organization in each race, but, besides, by reason of the habits that the individuals of each race there are forced to have; so, in proportion as he traverses the larger parts of the earth's surface the observing naturalist sees circumstances changing in a manner somewhat noticeable; he constantly sees that the species change proportionately in their characters.

"Now, the true order of things necessary to consider in all this consists in recognizing:

"1. That every slight change maintained under the circumstances where occur each race of animals, brings about in them a real change in their wants.

"2. That every change in the wants of animals necessitates in them other movements (actions) to satisfy the new needs, and consequently other habits.

"3. That every new want necessitating new actions to satisfy it, demands of the animal which feels it both the more frequent use of such of its parts of which before it made less use, which develops and considerably enlarges them, and the use of new parts which necessity has caused to insensibly develop in it by the effects of its inner feelings; which I shall constantly prove by known facts.

"Thus, to arrive at a knowledge of the true causes of so many different forms and so many different habits of which the known animals offer us examples, it is necessary to consider that circumstances infinitely diversified, but all slowly changing, into which the animals of each race are successively thrown, have caused, for each of them, new wants and necessarily changes in their habits. Moreover, this truth, which cannot be denied, being once recognized, it will be easy to see how the new needs have been able to be satisfied, and the new habits formed, if any attention be given to the two following laws of nature, which observation always confirms:

"First Law.

"In every animal which has not exceeded the term of its development, the more frequent and sustained use of any organ gradually strengthens this organ, develops and enlarges it, and gives it a strength proportioned to the length of time of such use; while the constant lack of use of such an organ imperceptibly weakens it, causes it to become reduced, progressively diminishes its faculties, and ends in its disappearance.

"Second Law.

"Everything which nature has caused individuals to acquire or lose by the influence of the circumstances to which their race may be for a long time exposed, and consequently by the influence of the predominant use of such an organ, or by that of the constant lack of use of such part, it preserves by heredity (generation) and passes on to the new individuals which descend from it, provided that the changes thus acquired are common to both sexes, or to those which have given origin to these new individuals.

"These are the two fundamental truths which can be misunderstood only by those who have never observed or followed nature in its operations, or only by those who allow themselves to fall into the error which I have combated.

"Naturalists having observed that the forms of the parts of animals compared with the uses of these parts are always in perfect accord, have thought that the forms and conditions of parts have caused the function; but this is a mistake, for it is easy to demonstrate by observation that it is, on the contrary, the needs and uses of organs which have developed these same parts, which have even given origin to them where they did not exist, and which consequently have given rise to the condition in which we observe them in each animal.

"If this were not so, it would have been necessary for nature to have created for the parts of animals as many forms as the diversity of circumstances in which they have to live had required, and that these forms and also the circumstances had never varied.

"This is certainly not the existing order of things, and if it were really such, we should not have the race-horses of England; we should not have our great draft horses, so clumsy and so different from the first named, for nature herself has not produced their like; we should not, for the same reason, have terrier dogs with bow legs, greyhounds so swift in running, water-spaniels, etc.; we should not have tailless fowls, fantail pigeons, etc.; finally, we could cultivate the wild plants as much as we pleased in the rich and fertile soil of our gardens without fearing to see them change by long culture.

"For a long time we have felt the force of the saying which has passed into the well-known proverb—habits form a second nature.

"Assuredly, if the habits and nature of each animal can never vary, the proverb is false, has no foundation, and does not apply to the instances which led to its being spoken.

"If we should seriously consider all that I have just stated, it might be thought that I had good reason when in my work entitled Recherches sur les Corps vivans (p. 50) I established the following proposition:

"'It is not the organs—that is to say, the nature and form of the parts of the body of an animal—which have given rise to its habits and its special faculties; but it is, on the contrary, its habits, its manner of life, and the circumstances in which are placed the individuals from which it originates, which have, with time, brought about the form of its body, the number and condition of its organs, finally, the faculties which it enjoys.'

"If we weigh this proposition, and if we recall all the observations which nature and the state of things continually lead us to do, then its importance and its solidity will become more evident.

"Time and favorable circumstances are, as I have already said, the two principal means which nature employs to give existence to all her productions: we know that time for her has no limits, and that consequently it is ever at her disposal.

"As to the circumstances of which she has need, and which she uses still daily to cause variations in all that she continues to produce, we can say that they are, in some degree, for her inexhaustible.

"The principal circumstances arise from the influence of climate; from those of different temperatures of the atmosphere, and from all the environing media; from that of the diversity of different localities and their situation; from that of habits, the ordinary movements, the most frequent actions; finally, from that of means of preservation, of mode of living, of defence, of reproduction, etc.

"Moreover, owing to these diverse influences, the faculties increase and become stronger by use, become differentiated by the new habits preserved for long ages, and insensibly the organization, the consistence—in a word, the nature and condition of parts, as also of the organs—participate in the results of all these influences, become preserved, and are propagated by generation.

"These truths, which are only the results of the two natural laws above stated, are in every case completely confirmed by facts; they clearly indicate the course of nature in all the diversity of its products.

"But instead of contenting ourselves with generalities which might be considered as hypothetical, let us directly examine the facts, and consider, in the animals, the result of the use or disuse of their organs on the organs themselves, according to the habits that each race has been compelled to contract.

"I shall now attempt to prove that the constant lack of exercise of organs at first diminishes their faculties, gradually impoverishes them, and ends by making them disappear, or even causing them to be atrophied, if this lack of use is perpetuated for a very long time through successive generations of animals of the same race.

"I shall next prove that, on the contrary, the habit of exercising an organ, in every animal which has not attained the limit of the diminution of its faculties, not only perfects and increases the faculties of this organ, but, besides, enables it to acquire developments and dimensions which insensibly change it; so that with time it renders it very different from the same organ in another animal which exercises it much less.

"The lack of use of an organ, become constant by the habits formed, gradually impoverishes this organ, and ends by causing it to disappear and even to destroy it.

"As such a proposition can only be admitted on proof, and not by its simple announcement, let us prove it by the citation of the leading known facts on which it is based.

"The vertebrate animals, whose plan of organization is in all nearly the same, although they offer much diversity in their parts, have jaws armed with teeth; moreover, those among them which circumstances have placed in the habit of swallowing their food without previous mastication are exposed to the result that their teeth become undeveloped. These teeth, then, either remain concealed between the bony edges of the jaws, without appearing above, or even their gums are found to have been atrophied.

"In the baleen whales, which have been supposed to be completely deprived of teeth, M. Geoffroy has found them concealed in the jaws of the foetus of this animal. This professor has also found in the birds the groove where the teeth should be situated; but they are no longer to be seen there.

"In the class even of mammals, which comprises the most perfect animals, and chiefly those in which the vertebrate plan of organization is most perfectly carried out, not only the baleen has no usable teeth, but the ant-eater (Myrmecophaga) is also in the same condition, whose habit of not masticating its food has been for a long time established and preserved in its race.

"The presence of eyes in the head is a characteristic of a great number of different animals, and becomes an essential part of the plan of organization of vertebrates.

"Nevertheless the mole, which owing to its habits makes very little use of vision, has only very small eyes, which are scarcely visible, since they exercise these organs to a very slight extent.

"The Aspalax of Olivier (Voyage en Egypte et en Perse, ii. pl. 28 f. 2), which lives under ground like the mole, and which probably exposes itself still less than that animal to the light of day, has totally lost the power of sight; also it possesses only vestiges of the organ of which it is the seat; and yet these vestiges are wholly concealed under the skin and other parts which cover them, and do not permit the least access to the light.

"The Proteus, an aquatic reptile allied to the salamander in its structure, and which lives in the dark subterranean waters of deep caves, has, like the Aspalax, only vestiges of the organs of sight—vestiges which are covered and concealed in the same manner.

"We turn to a decisive consideration relative to this question.

"Light does not penetrate everywhere; consequently animals which habitually live in situations where it does not penetrate lack the occasion of exercising the organs of sight, if nature has provided them with them. Moreover, the animals which make part of the plan of organization in which eyes are necessarily present, have originally had them. However, since we find them among those which are deprived of the use of this organ, and which have only vestiges concealed and covered over, it should be evident that the impoverishment and even the disappearance of these organs are the result of a constant lack of exercise.

"What proves it is that the organ of hearing is never in this condition, and that we always find it in the animals when the nature of their organization should require its existence; the reason is as follows.

"The cause of sound, that which, moved by the shock or the vibrations of bodies, transmits to the organ of hearing the impression which it receives, penetrates everywhere, traverses all the media, and even the mass of the densest bodies: from this it results that every animal which makes a part of a plan of organization to which hearing is essential, has always occasion to exercise this organ in whatever situation it lives. So, among the vertebrate animals we see none deprived of their organs of hearing; but in the groups below them, when the same organs are once wanting, we do not again find them.

"It is not so with the organ of sight, for we see this organ disappear, reappear, and again disappear, in proportion to the possibility or impossibility of the animal's exercising it.

"In the acephalous molluscs, the great development of the mantle of these molluscs has rendered their eyes and even their head entirely useless. These organs, also forming a part of a plan of organization which should comprise them, have disappeared and atrophied from constant lack of use.

"Finally, it is a part of the plan of organization of reptiles, as in other vertebrate animals, to have four legs appended to their skeleton. The serpents should consequently have four, though they do not form the lowest order of reptiles, and are not so near the fishes as the batrachians (the frogs, the salamanders, etc.).

"However, the serpents having taken up the habit of gliding along the ground, and of concealing themselves in the grass, their body, owing to continually repeated efforts to elongate itself so as to pass through narrow spaces, has acquired a considerable length disproportionate to its size. Moreover, limbs would have been very useless to these animals, and consequently would not have been employed: because long legs would have interfered with their need of gliding, and very short legs, not being more than four in number, would have been incapable of moving their body. Hence the lack of use of these parts having been constant in the races of these animals, has caused the total disappearance of these same parts, although really included in the plan of organization of the animals of their class.

"Many insects which by the natural character of their order, and even of their genus, should have wings, lack them more or less completely from disuse. A quantity of Coleoptera, Orthoptera, Hymenoptera, and of Hemiptera, etc., afford examples; the habits of these animals do not require them to make use of their wings.

"But it is not sufficient to give the explanation of the cause which has brought about the condition of the organs of different animals—a condition which we see to be always the same in those of the same species; we must besides observe the changes of condition produced in the organs of one and the same individual during its life, by the single result of a great change in the special habits in the individuals of its species. The following fact, which is one of the most remarkable, will serve to prove the influence of habits on the condition of organs, and show how changes wrought in the habits of an individual, produce the condition of the organs which are brought into action during the exercise of these habits.

"M. Tenon, member of the Institute, has given an account to the Class of Sciences, that having examined the intestinal canal of several men who had been hard drinkers all their lives, he had constantly found it to be shortened to an extraordinary extent, compared with the same organ in those not given to such a habit.

"We know that hard drinkers, or those who are addicted to drunkenness, take very little solid food, that they eat very lightly, and that the beverage which they take in excess frequently suffices to nourish them.

"Moreover, as fluid aliments, especially spirituous liquors, do not remain a long time either in the stomach or in the intestines, the stomach and the remainder of the intestinal canal lose the habit of being distended in intemperate persons, so also in sedentary persons and those engaged in mental labor, who are habituated to take but little food. Gradually and at length their stomach becomes contracted, and their intestines shortened.

"We are not concerned here with the shrinkage and shortening produced by a puckering of the parts, which permit ordinary extension, if instead of a continued emptiness these viscera should be filled; the shrinkage and shortening in question are real, considerable, and such that these organs would burst open rather than yield suddenly to the causes which would require ordinary extension.

"In circumstances of persons of the same age, compare a man who, in order to devote himself to habitual study and mental work, which have rendered his digestion more difficult, has contracted the habit of eating lightly, with another who habitually takes a good deal of exercise, walks out often, and eats heartily; the stomach of the first will be weakened, and a small quantity of food will fill it, while that of the second will be not only maintained in its ordinary health but even strengthened.

"We have here the case of an organ much modified in its dimensions and in its faculties by the single cause of a change in habits during the life of the individual.

"The frequent use of an organ become constant by habit increases the faculties of this organ, even develops it, and enables it to acquire dimensions and a power of action which it does not possess in animals which exercise less.

"We have just said that the lack of employment of an organ which necessarily exists modifies it, impoverishes it, and ends by its disappearing entirely.

"I shall now demonstrate that the continued employment of an organ, with the efforts made to draw out its powers under circumstances where it would be of service, strengthens, extends, and enlarges this organ, or creates a new one which can exercise the necessary functions.

"The bird which necessity drives to the water to find there prey fitted for its sustenance, opens the digits of its feet when it wishes to strike the water and propel itself along its surface. The skin which unites these digits at their base, by these acts of spreading apart being unceasingly repeated contracts the habit of extending; so that after a while the broad membranes which connect the digits of ducks, geese, etc., are formed as we see them. The same efforts made in swimming—i.e., in pushing back the water, in order to advance and to move in this liquid—have likewise extended the membrane situated between the digits of the frogs, the sea-turtles, the otter, beaver, etc.

"On the contrary, the bird whose mode of life habituates it to perch on trees, and which is born of individuals who have all contracted this habit, has necessarily the digits of the feet longer and shaped in another way than those of the aquatic animals which I have just mentioned. Its claws, after a while, became elongated, pointed, and curved or hook-like in order to grasp the branches on which the animal often rests.

"Likewise we see that the shore bird, which is not inclined to swim, and which moreover has need of approaching the edge of the water to find there its prey, is in continual danger of sinking in the mud. Now, this bird, wishing to act so that its body shall not fall into the water, makes every effort to extend and elongate its legs. It results from this that the long-continued habit that this bird and the others of its race contract, of extending and continually elongating their legs, is the cause of the individuals of this race being raised as if on stilts, having gradually acquired long, naked legs, which are denuded of feathers up to the thighs and often above them (Systeme des Animaux sans Vertebres, p. 16).

"We also perceive that the same bird, wishing to catch fish without wetting its body, is obliged to make continual efforts to lengthen its neck. Now, the results of these habitual efforts in this individual and in those of its race have enabled them, after a time, to singularly elongate them—as, indeed, is proved by the long neck of all shore birds.

"If any swimming birds, such as the swan and the goose, whose legs are short, nevertheless have a very long neck, it is because these birds in swimming on the surface of the water have the habit of plunging their head down as far as they can, to catch aquatic larvae and different animalcules for food, and because they make no effort to lengthen their legs.

"When an animal to satisfy its wants makes repeated efforts to elongate its tongue, it will acquire a considerable length (the ant-eater, green wood-pecker); when it is obliged to seize anything with this same organ, then its tongue will divide and become forked. That of the humming-birds, which seize with their tongue, and that of the lizard and serpents, which use it to feel and examine objects in front of them, are proofs of what I advocate.

"Wants, always occasioned by circumstances, and followed by sustained efforts to satisfy them, are not limited in results, in modifying—that is to say, in increasing or diminishing—the extent and the faculties of organs; but they also come to displace these same organs when certain of these wants become a necessity.

"The fishes which habitually swim in large bodies of water, having need of seeing laterally, have, in fact, their eyes placed on the sides of the head. Their bodies, more or less flattened according to the species, have their sides perpendicular to the plane of the water, and their eyes are placed in such a way that there is an eye on each flattened side. But those fishes whose habits place them under the necessity of constantly approaching the shores, and especially the shelving banks or where the slope is slight, have been forced to swim on their flattened faces, so as to be able to approach nearer the edge of the water. In this situation, receiving more light from above than from beneath, and having a special need of being always attentive to what is going on above them, this need has forced one of their eyes to undergo a kind of displacement, and to assume the very singular situation which is familiar to us in the soles, turbots, dabs, etc. (Pleuronectes and Achirus). The situation of these eyes is asymmetrical, because this results from an incomplete change. Now, this change is entirely completed in the rays, where the transverse flattening of the body is entirely horizontal, as also the head. Also the eyes of the rays, both situated on the upper side, have become symmetrical.

"The serpents which glide along the surface of the ground are obliged chiefly to see elevated objects, or what are above their eyes. This necessity has brought an influence to bear on the situation of the organs of vision in these animals; and, in fact, they have the eyes placed in the lateral and upper parts of the head, so as to easily perceive what is above or at their sides; but they only see for a short distance what is in front of them. Moreover, forced to supply the lack of ability to see and recognize what is in front of their head, and which might injure them, they need only to feel such objects with the aid of their tongue, which they are obliged to dart out with all their power. This habit has not only contributed to render the tongue slender, very long and retractile, but has also led in a great number of species to its division, so as to enable them to feel several objects at once; it has likewise allowed them to form an opening at the end of their head, to enable the tongue to dart out without their being obliged to open their jaws.

"Nothing is more remarkable than the result of habits in the herbivorous mammals.

"The quadruped to whom circumstances and the wants which they have created have given for a long period, as also to others of its race, the habit of browsing on grass, only walks on the ground, and is obliged to rest there on its four feet the greater part of its life, moving about very little, or only to a moderate extent. The considerable time which this sort of creature is obliged to spend each day to fill itself with the only kind of food which it requires, leads it to move about very little, so that it uses its legs only to stand on the ground, to walk, or run, and they never serve to seize hold of or to climb trees.

"From this habit of daily consuming great amounts of food which distend the organs which receive it, and of only moving about to a limited extent, it has resulted that the bodies of these animals are thick, clumsy, and massive, and have acquired a very great volume, as we see in elephants, rhinoceroses, oxen, buffaloes, horses, etc.

"The habit of standing upright on their four feet during the greater part of the day to browse has given origin to a thick hoof which envelops the extremity of the digits of their feet; and as their toes are not trained to make any movement, and because they have served no other use than as supports, as also the rest of the leg, the most of them are short, are reduced in size, and even have ended by totally disappearing. Thus in the pachyderms, some have five toes enveloped in horn, and consequently their foot is divided into five parts; others have only four, and still others only three. But in the ruminants, which seem to be the most ancient of mammals, which are limited only to standing on the ground, there are only two digits on each foot, and only a single one is to be found in the solipedes (the horse, the ass).

"Moreover, among these herbivorous animals, and especially among the ruminants, it has been found that from the circumstances of the desert countries they inhabit they are incessantly exposed to be the prey of carnivorous animals, and find safety only in precipitous flight. Necessity has forced them to run swiftly; and from the habit they have thus acquired their body has become slenderer and their limbs much more delicate: we see examples in the antelopes, the gazelles, etc.

"Other dangers in our climate to which are continually exposed the deer, the roebuck, the fallow-deer, of perishing from the chase made by man, have reduced them to the same necessity, restrained them to similar habits, and have given rise to the same results.

"The ruminating animals only using their legs as supports, and not having strong jaws, which are only exercised in cutting and browsing on grass, can only fight by striking with the head, by directing against each other the vertex of this part.

"In their moments of anger, which are frequent, especially among the males, their internal feelings, by their efforts, more strongly urge the fluids toward this part of their head, and it there secretes the corneous matter in some, and osseous matter mixed with corneous matter in others, which gives origin to solid protuberances; hence the origin of horns and antlers, with which most of these animals have the head armed.

"As regards habits, it is curious to observe the results in the special form and height of the giraffe (camelopardalis); we know that this animal, the tallest of mammals, inhabits the interior of Africa, and that it lives in localities where the earth, almost always arid and destitute of herbage, obliges it to browse on the foliage of trees, and to make continual efforts to reach it. It has resulted from this habit, maintained for a long period in all the individuals of its race, that its forelegs have become longer than the hinder ones, and that its neck is so elongated that the giraffe, without standing on its hind legs, raises its head and reaches six meters in height (almost twenty feet).

"Among the birds, the ostriches, deprived of the power of flight, and raised on very long legs, probably owe their singular conformation to analogous circumstances.

"The result of habits is as remarkable in the carnivorous mammals as it is in the herbivorous, but it presents effects of another kind.

"Indeed, those of these mammals which are habituated, as their race, both to climb as well as to scratch or dig in the ground, or to tear open and kill other animals for food, have been obliged to use the digits of their feet; moreover, this habit has favored the separation of their digits, and has formed the claws with which they are armed.

"But among the carnivores there are some which are obliged to run in order to overtake their prey; moreover, since these need and consequently have the habit of daily tearing with their claws and burying them deeply in the body of another animal, to seize and then to tear the flesh, and have been enabled by their repeated efforts to procure for these claws a size and curvature which would greatly interfere in walking or running on stony soil, it has resulted in this case that the animal has been obliged to make other efforts to draw back these too salient and curved claws which would impede it, and hence there has resulted the gradual formation of those special sheaths in which the cats, tigers, lions, etc., withdraw their claws when not in action.

"Thus the efforts in any direction whatever, maintained for a long time or made habitually by certain parts of a living body to satisfy necessities called out by nature or by circumstances, develop these parts and make them acquire dimensions and a shape which they never would have attained if these efforts had not become the habitual action of the animals which have exercised them. The observations made on all the animals known will everywhere furnish examples.

"Can any of them be more striking than that which the kangaroo offers us? This animal, which carries its young in its abdominal pouch, has adopted the habit of holding itself erect, standing only on its hind feet and tail, and only changing its position by a series of leaps, in which it preserves its erect attitude so as not to injure its young.

"Let us see the result:

"1. Its fore legs, of which it makes little use, and on which it rests only during the instant when it leaves its erect attitude, have never reached a development proportionate to that of the other parts, and have remained thin, very small, and weak;

"2. The hind legs, almost continually in action, both for supporting the body and for leaping, have, on the contrary, obtained a considerable development, and have become very large and strong;

"3. Finally, the tail, which we see is of much use in supporting the animal and in the performance of its principal movements, has acquired at its base a thickness and a strength extremely remarkable.

"These well-known facts are assuredly well calculated to prove what results from the habitual use in the animals of any organ or part; and if, when there is observed in an animal an organ especially well developed, strong, and powerful, it is supposed that its habitual use has not produced it, that its continual disuse will make it lose nothing, and, finally, that this organ has always been such since the creation of the species to which this animal belongs, I will ask why our domestic ducks cannot fly like wild ducks—in a word, I might cite a multitude of examples which prove the differences in us resulting from the exercise or lack of use of such of our organs, although these differences might not be maintained in the individuals which follow them genetically, for then their products would be still more considerable.

"I shall prove, in the second part, that when the will urges an animal to any action, the organs which should execute this action are immediately provoked by the affluence of subtile fluids (the nervous fluid), which then become the determining cause which calls for the action in question. A multitude of observations prove this fact, which is now indisputable.

"It results that the multiplied repetitions of these acts of organization strengthen, extend, develop, and even create the organs which are necessary. It is only necessary attentively to observe that which is everywhere occurring to convince ourselves of the well-grounded basis of this cause of organic developments and changes.

"Moreover, every change acquired in an organ by a habit of use sufficient to have produced it is then preserved by heredity (generation) if it is common to the individuals which, in fecundation, unite in the reproduction of their species. Finally, this change is propagated, and thus is transmitted to all the individuals which succeed and which are submitted to the same circumstances, unless they have been obliged to acquire it by the means which have in reality created it.

"Besides, in reproductive unions the crossings between the individuals which have different qualities or forms are necessarily opposed to the continuous propagation of these qualities and these forms. We see that in man, who is exposed to so many diverse circumstances which exert an influence on him, the qualities or the accidental defects which he has been in the way of acquiring, are thus prevented from being preserved and propagated by generation. If, when some particular features of form or any defects are acquired, two individuals under this condition should always pair, they would reproduce the same features, and the successive generations being confined to such unions, a special and distinct race would then be formed. But perpetual unions between individuals which do not have the same peculiarities of form would cause all the characteristics acquired by special circumstances to disappear.

"From this we can feel sure that if distances of habitation did not separate men the intermixture by generation would cause the general characteristics which distinguish the different nations to disappear.

"If I should choose to pass in review all the classes, all the orders, all the genera, and all the species of animals which exist, I should show that the structure of individuals and their parts, their organs, their faculties, etc., etc., are in all cases the sole result of the circumstances in which each species is found to be subjected by nature and by the habits which the individuals which compose it have been obliged to contract, and which are only the product of a power primitively existing, which has forced the animals into their well-known habits.

"We know that the animal called the ai, or the sloth (Bradypus tridactylus), is throughout life in a condition so very feeble that it is very slow and limited in its movements, and that it walks on the ground with much difficulty. Its movements are so slow that it is thought that it cannot walk more than fifty steps in a day. It is also known that the structure of this animal is in direct relation with its feeble state or its inaptitude for walking; and that should it desire to make any other movements than those which it is seen to make, it could not do it.

"Therefore, supposing that this animal had received from nature its well-known organization, it is said that this organization has forced it to adopt the habits and the miserable condition it is in.

"I am far from thinking so; because I am convinced that the habits which the individuals of the race of the ai were originally compelled to contract have necessarily brought their organization into its actual state.

"Since continual exposure to dangers has at some time compelled the individuals of this species to take refuge in trees and to live in them permanently, and then feed on their leaves, it is evident that then they would give up making a multitude of movements that animals which live on the ground perform.

"All the needs of the ai would then be reduced to seizing hold of the branches, to creeping along them or to drawing them in so as to reach the leaves, and then to remain on the tree in a kind of inaction, so as to prevent falling. Besides, this kind of sluggishness would be steadily provoked by the heat of the climate; for in warm-blooded animals the heat urges them rather to repose than to activity.

"Moreover, during a long period of time the individuals of the race of the ai having preserved the habit of clinging to trees and of making only slow and slightly varied movements, just sufficient for their needs, their organization has gradually become adapted to their new habits, and from this it will result:

"1. That the arms of these animals making continual efforts readily to embrace the branches of trees, would become elongated;

"2. That the nails of their digits would acquire much length and a hooked shape, by the continued efforts of the animal to retain its hold;

"3. That their digits never having been trained to make special movements, would lose all mobility among themselves, would become united, and would only preserve the power of bending or of straightening out all together;

"4. That their thighs, continually embracing both the trunks and the larger branches of trees, would contract a condition of habitual separation which would tend to widen the pelvis and to cause the cotyloid cavities to be directed backward;

"5. Finally, that a great number of their bones would become fused, and hence several parts of their skeleton would assume an arrangement and a figure conformed to the habits of these animals, and contrary to what would be necessary for them to have for other habits.

"Indeed, this can never be denied, because, in fact, nature on a thousand other occasions shows us, in the power exercised by circumstances on habits, and in that of the influence of habits on forms, dispositions, and the proportion of the parts of animals, truly analogous facts.