"3. That the property of the movement of the fluids in the parts which contain them is to break out pa.s.sages, places of deposit, and outlets; to there create ca.n.a.ls and consequently different organs; to cause these ca.n.a.ls, as well as the organs, to vary on account of the diversity both of the movements and of the nature of the fluids which give rise to them; finally to enlarge, elongate, to gradually divide and solidify [the walls of] these ca.n.a.ls and these organs by the matters which form and incessantly separate the fluids which are there in movement, and one part of which is a.s.similated and added to the organs, while the other is rejected and cast out;
"4. That the state of organization in each organism has been gradually acquired by the progress of the influences of the movement of fluids, and by those changes that these fluids have there continually undergone in their nature and their condition through the habitual succession of their losses and of their renewals;
"5. That each organization and each form acquired by this course of things and by the circ.u.mstances which there have concurred, were preserved and transmitted successively by generation [heredity]
until new modifications of these organizations and of these forms have been acquired by the same means and by new circ.u.mstances;
"6. Finally, that from the uninterrupted concurrence of these causes or from these laws of nature, together with much time and with an almost inconceivable diversity of influential circ.u.mstances, organic beings of all the orders have been successively formed.
"Considerations so extraordinary, relatively to the ideas that the vulgar have generally formed on the nature and origin of living bodies, will be naturally regarded by you as stretches of the imagination unless I hasten to lay before you some observations and facts which supply the most complete evidence.
"From the point of view of knowledge based on observation the philosophic naturalist feels convinced that it is in that which is called the lowest cla.s.ses of the two organic kingdoms--_i.e._, in those which comprise the most simply organized beings--that we can collect facts the most luminous and observations the most decisive on the _production_ and the reproduction of the living beings in question; on the causes of the formation of the organs of these wonderful beings; and on those of their developments, of their diversity and their multiplicity, which increase with the concourse of generations, of times, and of influential circ.u.mstances.
"Hence we may be a.s.sured that it is only among the singular beings of these lowest cla.s.ses, and especially in the lowest orders of these cla.s.ses, that it is possible to find on both sides the primitive germs of life, and consequently the germs of the most important faculties of animality and vegetality."
_Modification of the organization from one end to the other of the animal chain._
"One is forced," he says, "to recognize that the totality of existing animals const.i.tute _a series of groups_ forming a true chain, and that there exists from one end to the other of this chain a gradual modification in the structure of the animals composing it, as also a proportionate diminution in the number of faculties of these animals from the highest to the lowest (the first germs), these being without doubt the form with which nature began, with the aid of much time and favorable circ.u.mstances, to form all the others."
He then begins with the mammals and descends to molluscs, annelids, and insects, down to the polyps, "as it is better to proceed from the known to the unknown;" but farther on (p. 38) he finally remarks:
"Ascend from the most simple to the most compound, depart from the most imperfect animalcule and ascend along the scale up to the animal richest in structure and faculties; constantly preserve the order of relation in the group, then you will hold the true thread which connects all the productions of nature; you will have a just idea of its progress, and you will be convinced that the most simple of its living productions have successively given existence to all the others.
"_The series which const.i.tutes the animal scale resides in the distribution of the groups, and not in that of the individuals and species._
"I have already said[166] that by this shaded graduation in the complication of structure I do not mean to speak of the existence of a linear and regular series of species or even genera: such a series does not exist. But I speak of a quite regularly graduated series in the princ.i.p.al groups, _i.e._, in the princ.i.p.al system of organizations known, which give rise to cla.s.ses and to great families, series most a.s.suredly existing both among animals and plants, although in the consideration of genera, and especially in that of species, it offers many lateral ramifications whose extremities are truly isolated points.
"However, although there has been denied, in a very modern work, the existence in the animal kingdom of a single series, natural and at the same time graduated, in the composition of the organization of beings which it comprehends, series in truth necessarily formed of groups subordinated to each other as regards structure and not of isolated species or genera, I ask where is the well-informed naturalist who would now present a different order in the arrangement of the twelve cla.s.ses of the animal kingdom of which I have just given an account?
"I have already stated what I think of this view, which has seemed sublime to some moderns, and indorsed by _Professor Hermann_."
Each distinct group or ma.s.s of forms has, he says, its peculiar system of essential organs, but each organ considered by itself does not follow as regular a course in its degradations (modifications).
"Indeed, the least important organs, or those least essential to life, are not always in relation to each other in their improvement or their degradation; and an organ which in one species is atrophied may be very perfect in another. These irregular variations in the perfecting and in the degradation of non-essential organs are due to the fact that these organs are oftener than the others submitted to the influences of external circ.u.mstances, and give rise to a diversity of species so considerable and so singularly ordered that instead of being able to arrange them, like the groups, in a single simple linear series under the form of a regular graduated scale, these very species often form around the groups of which they are part lateral ramifications, the extremities of which offer points truly isolated.
"There is needed, in order to change each internal system of organization, a combination of more influential circ.u.mstances, and of more prolonged duration than to alter and modify the external organs.
"I have observed, however, that, when circ.u.mstances demand, nature pa.s.ses from one system to another without making a leap, provided they are allies. It is, indeed, by this faculty that she has come to form them all in succession, in proceeding from the simple to the more complex.
"It is so true that she has the power, that she pa.s.ses from one system to the other, not only in two different families which are allied, but she also pa.s.ses from one system to the other in the same individual.
"The systems of organization which admit as organs of respiration true lungs are nearer to systems which admit gills than those which require tracheae. Thus not only does nature pa.s.s from gills to lungs in allied cla.s.ses and families, as seen in fishes and reptiles, but in the latter she pa.s.ses even during the life of the same individual, which successively possesses each system. We know that the frog in the tadpole state respires by gills, while in the more perfect state of frog it respires by lungs. We never see that nature pa.s.ses from a system with tracheae to a system with lungs.
"_It is not the organs, i.e., the nature and form of the parts of the body of an animal, which give rise to the special habits and faculties, but, on the contrary, its habits, its mode of life, and the circ.u.mstances in which individuals are placed, which have, with time, brought about the form of its body, the number and condition of its organs, finally the faculties which it possesses._
"Time and favorable circ.u.mstances are the two princ.i.p.al means which nature employs to give existence to all her productions. We know that time has for her no limit, and that consequently she has it always at her disposition.
"As to the circ.u.mstances of which she has need (_besoin_) and which she employs every day to bring about variations in all that she continues to produce, we can say that they are in her in some degree inexhaustible.
"The princ.i.p.al ones arise from the influence of climate, from that of different temperatures, of the atmosphere, and from all environing surroundings (_milieux_); from that of the diversity of places and their situations; from that of the most ordinary habitual movements, of actions the most frequent; finally from that of the means of preservation, of the mode of life, of defence, of reproduction, etc.
"Moreover, as the result of these different influences the faculties increase and strengthen themselves by use, diversify themselves by the new habits preserved through long periods, and insensibly the conformation, the consistence--in a word, the nature and state of the parts and also of the organs--consequently partic.i.p.ate in all these influences, are preserved and propagate themselves by generation" (_Systeme des Animaux sans Vertebres_, p. 12).
"It is easy for any one to see that the habit of exercising an organ in every living being which has not reached the term of diminution of its faculties not only makes this organ more perfect, but even makes it acquire developments and dimensions which insensibly change it, with the result that with time it renders it very different from the same organ considered in another organism which has not, or has but slightly, exercised it. It is also very easy to prove that the constant lack of exercise of an organ gradually reduces it and ends by atrophying it."
Then follow the facts regarding the mole, spalax, ant-eater, and the lack of teeth in birds, the origin of sh.o.r.e birds, swimming birds and perching birds, which are stated farther on.
"Thus the efforts in any direction, maintained for a long time or made habitually by certain parts of a living body, to satisfy the needs called out (_exiges_) by nature or by circ.u.mstances, develop these parts and cause them to acquire dimensions and a form which they never would have obtained if these efforts had not become an habitual action of the animals which have exercised them.
Observations made on all the animals known would furnish examples of this.
"When the will determines an animal to any kind of action, the organs whose function it is to execute this action are then immediately provoked by the flowing there of subtile fluids, which become the determining cause of movements which perform the action in question. A mult.i.tude of observations support this fact, which now no one would doubt.
"It results from this that multiplied repet.i.tions of these acts of organization strengthen, extend, develop, and even create the organs which are there needed. It is only necessary to closely observe that which is everywhere happening in this respect to firmly convince ourselves of this cause of developments and organic changes.
"However, each change acquired in an organ by habitual use sufficient to have formed (_opere_) it is preserved by generation, if it is common to the individuals which unite in the reproduction of their kind. Finally, this change propagates itself and is then handed down (_se pa.s.se_) to all the individuals which succeed and which are submitted to the same circ.u.mstances, without their having been obliged to acquire it by the means which have really created it.
"Besides, in the unions between the s.e.xes the intermixtures between individuals which have different qualities or forms are necessarily opposed to the constant propagation of these qualities and forms. We see that which in man, who is exposed to such different circ.u.mstances which influence individuals, prevents the qualities of accidental defects which they have happened to acquire from being preserved and propagated by heredity (_generation_).
"You can now understand how, by such means and an inexhaustible diversity of circ.u.mstances, nature, with sufficient length of time, has been able to and should produce all these results.
"If I should choose here to pa.s.s in review all the cla.s.ses, orders, genera, and species of animals in existence I could make you see that the structure of individuals and their organs, faculties, etc., is solely the result of circ.u.mstances to which each species and all its races have been subjected by nature, and of habits that the individuals of this species have been obliged to contract.
"The influences of localities and of temperatures are so striking that naturalists have not hesitated to recognize the effects on the structure, the developments, and the faculties of the living bodies subject to them.
"We have long known that the animals inhabiting the torrid zone are very different from those which live in the other zones. Buffon has remarked that even in lat.i.tudes almost the same the animals of the new continent are not the same as those of the old.
"Finally the Count Lacepede, wishing to give to this well-founded fact the precision which he believed it susceptible, has traced twenty-six zoological divisions on the dry parts of the globe, and eighteen over the ocean; but there are many other influences than those which depend on localities and temperatures.
"Everything tends, then, to prove my a.s.sertion--namely, that it is not the form either of the body or of its parts which has given rise to habits and to the mode of life of animals, but, on the contrary, it is the habits, the mode of life, and all the other influential circ.u.mstances which have with time produced the form of the bodies and organs of animals. With new forms new faculties have been acquired, and gradually nature has arrived at the state where we actually see it.
"Finally as it is only at that extremity of the animal kingdom where occur the most simply organized animals that we meet those which may be regarded as the true germs of animality, and it is the same at the same end of the vegetable series; is it not at this end of the scale, both animal and vegetable, that nature has commenced and recommenced without ceasing the first germ of her living production?
Who is there, in a word, who does not see that the process of perfection of those of these first germs which circ.u.mstances have favored will gradually and after the lapse of time give rise to all the degrees of perfection and of the composition of the organization, from which will result this multiplicity and this diversity of living beings of all orders with which the exterior surface of our globe is almost everywhere filled or covered?
"Indeed, if the manner (_usage_) of life tends to develop the organization, and even to form and multiply the organs, as the state of an animal which has just been born proves it, compared to that where it finds itself when it has reached the term where its organs (beginning to deteriorate) cease to make new developments; if, then, each particular organ undergoes remarkable changes, according as it is exercised and according to the manner of which I have shown you some examples, you will understand that in carrying you to the end of the animal chain where are found the most simple organizations, and that in considering among these organizations those whose simplicity is so great that they lie at the very door of the creative power of nature, then this same nature--that is to say, the state of things which exist--has been to form directly the first beginnings of organization; she has been able, consequently, by the manner of life and the aid of circ.u.mstances which favor its duration, to progressively render perfect its work, and to carry it to the point where we now see it.
"Time is wanting to present to you the series of results of my researches on this interesting subject, and to develop--
"1. What really is life.
"2. How nature herself creates the first traces of organization in appropriate groups where it had not existed.
"3. How the organic or vital movement is excited by it and held together with the aid of a stimulating and active cause which she has at her disposal in abundance in certain climates and in certain seasons of the year.