No sensible person supposes that carefully devised inst.i.tutions, which have been established for the good of the whole, as well as for the individual, in every human state, are the results of the action of a personal and supernatural Creator, acting for a definite purpose. On the contrary, every one knows that these useful inst.i.tutions of organization in the state are the consequences of the co-operation of the individual citizens and their common government, as well as of adaptation to the conditions of existence of the outer world. Just in the same way we must judge of the many-celled organism. In it also all the useful arrangements are solely the natural and necessary result of the co-operation, differentiation, and perfecting of the individual citizens-the cells-and by no means the artificial arrangements of a Creator acting for a definite purpose. If we rightly consider this comparison, and pursue it further, we can distinctly see the perversity of that dualistic conception of nature which discovers the action of a creative plan of construction in the various adaptations of the organization of living things.

Let us pursue the individual development of the vertebrate animal body a few stages further, and see what is next done by the citizens of this embryonic organism. In the central line of the violin-shaped disc, which is composed of the three cellular germ-layers, there arises a straight delicate furrow, the so-called "primitive streak," by which the violin-shaped body is divided into two equal lateral halves-a right and a left part or "antimer." On both sides of that streak or furrow, the upper or external germ-layer rises in the form of a longitudinal fold, and both folds then grow together over the furrow in the central line, and thus form a cylindrical tube. This tube is called the marrow-tube, or medullary ca.n.a.l, because it is the foundation of the central nervous system, the _spinal marrow_ (medulla spinalis). At first it is pointed both in front and behind, and it remains so for life in the lowest vertebrate animal, the brainless, skull-less Lancelet (Amphioxus). But in all other vertebrate animals, which we distinguish from the latter as skulled animals, or Craniota, a difference between the fore and hinder end of the marrow tube soon becomes visible, the fore end becoming dilated, and changing into a roundish bladder, the foundation of the _brain_.

In all Craniota, that is, in all vertebrate animals possessing skull and brain, the brain, which is at first only the bladder-shaped dilatation of the anterior end of the spinal marrow, divides into five bladders lying one behind the other, four superficial, transverse in-nippings being formed. These _five brain-bladders_, out of which afterwards arise all the different parts of the intricately constructed brain, can be seen in their original condition in the embryo represented in Fig. 7. It is just the same whether we examine the embryo of a dog, a fowl, a lizard, or any other higher vertebrate animal. For the embryos of the different skulled animals (at least the three higher cla.s.ses of them, the reptiles, birds and mammals) cannot be in any way distinguished at the stage represented in Fig. 7. The whole form of the body is as yet exceedingly simple, being merely a thin, leaf-like disc. Face, legs, intestines, etc., are as yet completely wanting. But the five bladders are already quite distinct from one another.

[Ill.u.s.tration: FIG. 7.-Embryo of a mammal or bird, in which the five brain-bladders have just commenced to develop. _v._ Fore brain. _z._ Twixt brain. _m._ Mid brain. _h._ Hind brain. _n._ After brain. _p._ Spinal-marrow. _a._ Eye-bladders. _w._ Primitive vertebrae. _d._ Spinal-axis or notochord.]

The _first_ bladder, the _fore brain_ (_a_), is in so far the most important that it princ.i.p.ally forms the hemispheres of the so-called larger brain (cerebrum), that part which is the seat of the higher mental activities. The more these activities are developed in the series of vertebrate animals, the more do the two lateral halves of the fore brain, or the hemispheres, grow at the expense of the other bladders, and overlap them in front and from above. In man, where they are most strongly developed, agreeing with his higher mental activity, they eventually almost entirely cover the other parts from above (compare Plates II. and III.) The _second_ bladder, the _twixt brain_ (_z_), forms that portion of the brain which is called the _centre of sight_, and stands in the closest relation to the eyes (_a_), which grow right and left out of the fore brain in the shape of two bladders, and later lie at the bottom of the twixt brain. The _third_ bladder, the _mid brain_ (_m_), for the most part vanishes in the formation of the so-called _four bulbs_, a bossy portion of the brain, which is strongly developed in reptiles and birds (Fig. _E_, _F_, Plate II.), whereas in mammals it recedes much more (Fig. _G_, _H_, Plate III.). The _fourth_ bladder, the _hind brain_ (_h_), forms the so-called _little hemispheres_, together with the middle part of the _small brain_ (cerebellum), a part of the brain as to the function of which the most contradictory conjectures are entertained, but which seems princ.i.p.ally to regulate the co-ordination of movements. Lastly, the _fifth_ bladder, the _after brain_ (_n_), develops into that very important part of the central nervous system which is called the _prolonged marrow_ (medulla oblongata). It is the central organ of the respiratory movements, and of other important functions, and an injury to it immediately causes death, whereas the large hemispheres of the fore brain (or the organ of the "soul," in a restricted sense) can be removed bit by bit, and even completely destroyed, without causing the death of the vertebrate animal-only its higher mental activities disappearing in consequence.

These five brain bladders, in all vertebrate animals which possess a brain at all, are originally arranged in the same manner and develop gradually in the different groups so differently, that it is afterwards very difficult to recognize the corresponding parts in the fully-developed brains. In the early stage of development which is represented in Fig. 7, it seems as yet quite impossible to distinguish the embryos of the different mammals, birds, and reptiles, from one another. But if we compare the much more developed embryos on Plates II.

and III. with one another, we can clearly see an inequality in their development, and especially it will be perceived that the brain of the two mammals (_G_ and _H_) already strongly differ from that of birds (_F_) and of reptiles (_E_). In the two latter the mid brain predominates, but in the former the fore brain. Even at this stage the brain of the bird (_F_) is scarcely distinguishable from that of the tortoise (_E_), and in like manner the brain of the dog (_G_) is as yet almost the same as that of man (_H_). If, on the other hand, we compare the brains of these four vertebrate animals in a fully developed condition, we find them so very different in all anatomical particulars, that we cannot doubt for a moment as to which animal each brain belongs.

I have here explained the original equality, the gradual commencement, and the ever increasing separation or differentiation of the embryos in the different vertebrate animals, taking the brain as a special example, just because this organ of the soul's activity is of special interest.

But I might as well have discussed in its stead the heart, or the liver, or the limbs, in short, any other part of the body, since the same wonder of creation is here ever repeated, namely, this, that all parts are originally the same in the different vertebrate animals, and that the variations by which the different cla.s.ses, orders, families, genera, etc., differ and deviate from one another, are only gradually developed.

There are certainly few parts of the body which are so differently constructed as the _limbs or extremities_ of the vertebrate animals.

Now, I wish the reader to compare in Fig. _A-H_ on Plates II. and III., the four extremities (_bv_) of the embryos with one another, and he will scarcely be able to perceive any important differences between the human arm (_H bv_), the wing of a bird (_F bv_), the slim foreleg of a dog (_G bv_), and the plump foreleg of the tortoise (_E bv_). In comparing the hinder extremities (_bh_) in these figures he will find it equally difficult to distinguish the leg of a man (_H bh_), of a bird (_F bh_), the hind-leg of a dog (_G bh_), and that of a tortoise (_E bh_). The fore as well as the hinder extremities are as yet short, broad lumps, at the ends of which the foundations of the five toes are placed, connected as yet by a membrane. At a still earlier stage (Fig. _A-D_) the five toes are not marked out at all, and it is quite impossible to distinguish even the fore and hinder extremities from one another. The latter, as well as the former, are nothing but simple roundish processes, which have grown out of the side of the trunk. At the very early stage represented in Fig. 7 they are completely wanting, and the whole embryo is a simple trunk without a trace of limbs.

[Ill.u.s.tration: Pl. II. Germs or Embryos of four Vertebrates.

_v._ Fore-brain. _z._ Twixt-brain. _m._ Mid-brain. _h._ Hind-brain. _n._ After-brain. _w._ Spine. _r._ Spinal-cord.]

[Ill.u.s.tration: Pl. III. Germs or Embryos of four Vertebrates.

_na._ Nose. _a._ Eyes. _o._ Ear. _k{1} k{2} k{3}._ Gill-arches.

_s._ Tail. _bv._ Fore-leg. _bh._ Hind-leg.]

I wish especially to draw attention in Plates II. and III., which represents embryos in early stages of development (Fig. _A-D_)-and in which we are not able to recognize a trace of the full-grown animal-to an exceedingly important formation, which originally is common to all vertebrate animals, but which at a later period is transformed into the most different organs. Every one surely knows the _gill-arches_ of fish, those arched bones which lie behind one another, to the number of three or four, on each side of the neck, and which support the gills, the respiratory organs of the fish (double rows of red leaves, which are popularly called "fishes' ears.") Now, these gill-arches originally exist exactly the same in man (_D_), in dogs (_C_), in fowls (_B_), and in tortoises (_A_), as well as in all other vertebrate animals. (In Fig.

_A-D_ the three gill-arches of the right side of the neck are marked _k{1} k{2} k{3}_). Now, it is only in fishes that these remain in their original form, and develop into respiratory organs. In the other vertebrate animals they are partly employed in the formation of the face (especially the jaw apparatus), and partly in the formation of the organ of hearing.

Finally, when comparing the embryos on Plates II. and III., we must not fail to give attention again to the _human tail_ (_s_), an organ which, in the original condition, man shares with all other vertebrate animals.

The discovery of tailed men was long anxiously expected by many monistic philosophers, in order to establish a closer relationship between man and the other mammals. And in like manner their dualistic opponents often maintained with pride that the complete want of a tail formed one of the most important bodily distinctions between men and animals, though they did not bear in mind the many tailless animals which really exist. Now, man in the first months of development possesses a real tail as well as his nearest kindred, the tailless apes (orang-outang, chimpanzee, gorilla), and vertebrate animals in general. But whereas, in most of them-for example, the dog (_C_, _G_)-in the course of development it always grows longer, in man (Fig. _D_, _H_) and in tailless mammals, at a certain period of development, it degenerates and finally completely disappears. However, even in fully developed men, the remnant of the tail is seen in the three, four, or five tail vertebrae (vertebrae coccygeae) as an aborted or rudimentary organ, which forms the hinder or lower end of the vertebral column (p. 289).

Most persons even now refuse to acknowledge the most important deduction of the Theory of Descent, that is, the palaeontological development of man from ape-like, and through them from still lower, mammals, and consider such a transformation of organic form as impossible. But, I ask, are the phenomena of the individual development of man, the fundamental features of which I have here given, in any way less wonderful? Is it not in the highest degree remarkable that all vertebrate animals of the most different cla.s.ses-fishes, amphibious animals, reptiles, birds, and mammals-in the first periods of their embryonic development cannot be distinguished at all, and even much later, at a time when reptiles and birds are already distinctly different from mammals, that the dog and the man are almost identical?

Verily, if we compare those two series of development with one another, and ask ourselves which of the two is the more wonderful, it must be confessed that _ontogeny_, or the short and quick history of development of the _individual_, is much more mysterious than _phylogeny_, or the long and slow history of development of the _tribe_. For one and the same grand change of form is accomplished by the latter in the course of many thousands of years, and by the former in the course of a few months. Evidently this most rapid and astonishing transformation of the individual in ontogenesis, which we can actually point out at any moment by direct observation, is in itself much more wonderful and astonishing than the corresponding, but much slower and gradual transformation which the long chain of ancestors of the same individual has gone through in phylogenesis.

The two series of organic development, the ontogenesis of the individual and the phylogenesis of the tribe to which it belongs, stand in the closest causal connection with each other. I have endeavoured, in the second volume of the "General Morphology,"(4) to establish this theory in detail, as I consider it exceedingly important. As I have there shown, _ontogenesis, or the development of the individual, is a short and quick repet.i.tion_ (recapitulation) _of phylogenesis, or the development of the tribe to which it belongs, determined by the laws of inheritance and adaptation_; by tribe I mean the ancestors which form the chain of progenitors of the individual concerned. (Gen. Morph. ii.

110-147, 371.)

In this intimate connection of ontogeny and phylogeny, I see one of the most important and irrefutable proofs of the Theory of Descent. No one can explain these phenomena unless he has recourse to the laws of Inheritance and Adaptation; by these alone are they explicable. These laws, which we have previously explained, are _the laws of abbreviated, of h.o.m.ochronic, and of h.o.m.otopic inheritance_, and here deserve renewed consideration. As so high and complicated an organism as that of man, or the organism of every other mammal, rises upwards from a simple cellular state, and as it progresses in its differentiation and perfecting it pa.s.ses through the same series of transformations which its animal progenitors have pa.s.sed through, during immense s.p.a.ces of time, inconceivable ages ago. I have already pointed out this extremely important parallelism of the development of individuals and tribes (p.

10). Certain very early and low stages in the development of man, and the other vertebrate animals in general, correspond completely in many points of structure with conditions which last for life in the lower fishes. The next phase which follows upon this presents us with a change of the fish-like being into a kind of amphibious animal. At a later period the mammal, with its special characteristics, develops out of the amphibian, and we can clearly see, in the successive stages of its later development, a series of steps of progressive transformation which evidently correspond with the differences of different mammalian orders and families. Now, it is precisely in the same succession that we also see the ancestors of man, and of the higher mammals, appear one after the other in the earth's history; first fishes, then amphibians, later the lower, and at last the higher mammals. Here, therefore, the embryonic development of the individual is completely parallel to the palaeontological development of the whole tribe to which it belongs, and this exceedingly interesting and important phenomenon can be explained only by the interaction of the laws of Inheritance and Adaptation.

The example last mentioned, of the parallelism of the palaeontological and of the individual developmental series, now directs our attention to a third developmental series, which stands in the closest relations to these two, and which likewise runs, on the whole, parallel to them. I mean that series of development of forms which const.i.tutes the object of investigation in _comparative anatomy_, and which I will briefly call the _systematic developmental series of species_. By this we understand the chain of the different, but related and connected forms, which exist _side by side_ at any one period of the earth's history; as for example, at the present moment. While comparative anatomy compares the different forms of fully-developed organisms with one another, it endeavours to discover the common prototypes which underlie, as it were, the manifold forms of kindred genera, cla.s.ses, etc., and which are more or less concealed by their particular differentiation. It endeavours to make out the series of progressive steps which are indicated in the different degrees of perfection of the divergent branches of the tribe. To make use again of the same particular instance, comparative anatomy shows us how the individual organs and systems of organs in the tribe of vertebrate animals-in the different cla.s.ses, families, and species of it-have unequally developed, differentiated, and perfected themselves.

It shows us how far the succession of cla.s.ses of vertebrate animals, from the Fishes upwards, through the Amphibia to the Mammals, and here again, from the lower to the higher orders of Mammals, forms a progressive series or ladder. This attempt to establish a connected anatomical developmental series we may discover in the works of the great comparative anatomists of all ages-in the works of Goethe, Meckel, Cuvier, Johannes Muller, Gegenbaur, and Huxley.

The developmental series of mature forms, which comparative anatomy points out in the different diverging and ascending steps of the organic system, and which we call the systematic developmental series, is parallel to the palaeontological developmental series, because it deals with the _result_ of palaeontological development, and it is parallel to the individual developmental series, because this is parallel to the palaeontological series. If two parallels are parallel to a third, they must be parallel to one another.

The varied differentiation, and the unequal degree of perfecting which comparative anatomy points out in the developmental series of the System, is chiefly determined by the ever increasing variety of conditions of existence to which the different groups adapt themselves in the struggle for life, and by the different degrees of rapidity and completeness with which this adaptation has been effected. Conservative groups which have retained their inherited peculiarities most tenaciously remain, in consequence, at the lowest and rudest stage of development. Those groups progressing most rapidly and variously, and which have adapted themselves to changed conditions of existence most readily have attained the highest degree of perfection. The further the organic world developed in the course of the earth's history, the greater must the gap between the lower conservative and the higher progressive groups have become, as in fact may be seen too in the history of nations. In this way also is explained the historical fact, that the most perfect animal and vegetable groups have developed themselves in a comparatively short time to a considerable height, while the lowest or most conservative groups have remained stationary throughout all ages in their original simple stage, or have progressed, but very slowly and gradually. The series of man's progenitors clearly shows this state of things. The sharks of the present day are still very like the primary fish, which are among the most ancient vertebrate progenitors of man, and the lowest amphibians of the present day (the gilled salamanders and salamanders) are very like the amphibians which first developed themselves out of fishes. So, too, the later ancestors of man, the Monotremata and Marsupials, the most ancient mammals, are at the same time the most imperfect animals of the cla.s.s which still exist.

The laws of inheritance and adaptation known to us are completely sufficient to explain this exceedingly important and interesting phenomenon, which may be briefly designated as the _parallelism of individual, of palaeontological, and of systematic development_. No opponent of the Theory of Descent has been able to give an explanation of this extremely wonderful fact, whereas it is perfectly explained, according to the Theory of Descent, by the laws of Inheritance and Adaptation.

If we examine this parallelism of the three organic series of development more accurately, we have to add the following special qualifications. _Ontogeny_, or the history of the individual development of every organism (embryology and metamorphology), presents us with a simple _unbranching_ or graduated chain of forms; and so it is with that _portion of phylogeny_ which comprises the palaeontological history of development of the _direct ancestors only_ of an individual organism.

But _the whole of phylogeny_-which meets us in the _natural system_ of every organic tribe or phylum, and which is concerned with the investigation of the palaeontological development _of all_ the branches of this tribe-forms a _branching_ or tree-shaped developmental series, a veritable pedigree. If we examine and compare the branches of this pedigree, and place them together according to the degree of their differentiation and perfection, we obtain the tree-shaped, branching, _systematic developmental series of comparative anatomy_. Strictly speaking, therefore, the latter is parallel to _the whole of phylogeny_, and consequently is only partially parallel to ontogeny; for ontogeny itself is parallel only to _a portion_ of phylogeny.

All the phenomena of organic development above discussed, especially the threefold genealogical parallelism, and the laws of differentiation and progress, which are evident in each of these three series of organic development, and, further, the whole history of rudimentary organs, are exceedingly important proofs of the truth of the Theory of Descent. For by it alone can they be explained, whereas its opponents cannot even offer a shadow of an explanation of them. Without the Doctrine of Filiation, the fact of organic development in general cannot be understood. We should therefore, for this reason alone, be forced to accept Lamarck's Theory of Descent, even if we did not possess Darwin's Theory of Selection.

CHAPTER XIII.

THEORY OF THE DEVELOPMENT OF THE UNIVERSE AND OF THE EARTH. SPONTANEOUS GENERATION. THE CARBON THEORY. THE PLASTID THEORY.

History of the Development of the Earth.-Kant's Theory of the Development of the Universe, or the Cosmological Gas Theory.-Development of Suns, Planets, and Moons.-First Origin of Water.-Comparison of Organisms and Anorgana.-Organic and Inorganic Substances.-Degrees of Density, or Conditions of Aggregation.-Alb.u.minous Combinations of Carbon.-Organic and Inorganic Forms.-Crystals and Formless Organisms without Organs.-Stereometrical Fundamental Forms of Crystals and of Organisms.-Organic and Inorganic Forces.-Vital Force.-Growth and Adaptation in Crystals and in Organisms.-Formative Tendencies of Crystals.-Unity of Organic and Inorganic Nature.-Spontaneous Generation, or Archigony.-Autogony and Plasmogony.-Origin of Monera by Spontaneous Generation.-Origin of Cells from Monera.-The Cell Theory.-The Plastid Theory.-Plastids, or Structural Units.-Cytods and Cells.-Four Different Kinds of Plastids.

In our considerations. .h.i.therto we have endeavoured to answer the question, "By what causes have new species of animals and plants arisen out of existing species?" We have answered this question according to Darwin's theory, that natural selection in the struggle for existence-that is, the interaction of the laws of Inheritance and Adaptation-is completely sufficient for producing mechanically the endless variety of the different animals and plants, which have the appearance of being organized according to a plan for a definite purpose. Meanwhile the question must have already repeatedly presented itself to the reader, how did the first organisms, or that one original and primaeval organism arise, from which we derive all the others?

This question Lamarck(2) answered by the hypothesis of _spontaneous generation_, or _archigony_. But Darwin pa.s.ses over and avoids this subject, as he expressly remarks that he has "nothing to do with the origin of the soul, nor with that of life itself." At the conclusion of his work he expresses himself more distinctly in the following words:-"I imagine that probably all organic beings which ever lived on this earth descended from some primitive form, which was first called into life by the Creator." Moreover, Darwin, for the consolation of those who see in the Theory of Descent the destruction of the whole "moral order of the universe," appeals to the celebrated author and divine who wrote to him, that "he has gradually learnt to see that it is just as n.o.ble a conception of the Deity to believe that he created a few original forms capable of self-development into other and needful forms, as to believe that he required a fresh act of creation to supply the voids caused by the action of his laws."

Those to whom the belief in a supernatural creation is an emotional necessity may rest satisfied with this conception. They may reconcile that belief with the Theory of Descent; for in the creation of a single original organism possessing the capability to develop all others out of itself by inheritance and adaptation, they can really find much more cause for admiring the power and wisdom of the Creator than in the independent creation of different species.

If, taking this point of view, we were to explain the origin of the first terrestrial organisms, from which all the others are descended, as due to the action of a personal Creator acting according to a definite plan, we should of course have to renounce all scientific knowledge of the process, and pa.s.s from the domain of true science to the completely distinct domain of poetical faith. By a.s.suming a supernatural act of creation we should be taking a leap into the inconceivable. Before we decide upon this latter step, and thereby renounce all pretension to a scientific knowledge of the process, we are at all events in duty bound to endeavour to examine it in the light of a mechanical hypothesis. We must at least examine whether this process is really so wonderful, and whether we cannot form a tenable conception of a completely non-miraculous origin of the first primary organism. We might then be able entirely to reject miracle in creation.

It will be necessary for this purpose, first of all, to go back further into the past, and to examine the history of the creation of the earth.

Going back still further, we shall find it necessary to consider the history of the creation of the whole universe in its most general outlines. All my readers undoubtedly know that from the structure of the earth, as it is at present known to us, the notion has been derived, and as yet has not been refuted, that its interior is in a fiery fluid condition, and that the firm crust, composed of different strata, on the surface of which organisms are living, forms only a very thin pellicle or sh.e.l.l round the fiery fluid centre. We have arrived at this idea by different confirmatory experiments and reasonings. In the first place, the observation that the temperature of the earth's crust continually increases towards the centre is in favour of this supposition. The deeper we descend, the greater the warmth of the ground, and in such proportion, that with every 100 feet the temperature increases about one degree. At a depth of six miles, therefore, a heat of 1500 would be attained, sufficient to keep most of the firm substances of our earth's crust in a molten, fiery, fluid state. This depth, however, is only the 286th part of the whole diameter of the earth (1717 miles). We further know that springs which rise out of a considerable depth possess a very high temperature, and sometimes even throw water up to the surface in a boiling state. Lastly, very important proofs are furnished by volcanic phenomena, the eruption of fiery fluid ma.s.ses of stone bursting through certain parts of the earth's crust. All these phenomena lead us with great certainty to the important a.s.sumption that the firm crust of the earth forms only quite a small fraction, not nearly the one-thousandth part of the whole diameter of the terrestrial globe, and that the rest is still for the most part in a molten or fiery fluid state.

Now if, starting with this a.s.sumption, we reflect on the ancient history of the development of the globe, we are logically carried back a step further, namely, to the a.s.sumption that at an earlier date the whole earth was a fiery fluid body, and that the formation of a thin, stiffened crust on the surface was only a later process. Only gradually, by radiating its intrinsic heat into the cold s.p.a.ce of the universe, has the surface of the glowing ball become condensed into a thin crust.

That the temperature of the earth in remote times was much higher than it is now, is proved by many phenomena. Among other things, this is rendered probable by the equal distribution of organisms in remote times of the earth's history. While at present, as is well known, the different populations of animals and plants correspond to the different zones of the earth and their appropriate temperature, in earlier times this was distinctly not the case.

We see from the distribution of fossils in the remoter ages, that it was only at a very late date, in fact, at a comparatively recent period of the organic history of the earth (at the beginning of the so-called caenolithic or tertiary period), that a separation of zones and of the corresponding organic populations occurred. During the immensely long primary and secondary periods, tropical plants, which require a very high degree of temperature, lived not only in the present torrid zone, under the equator, but also in the present temperate and frigid zones.

Many other phenomena also demonstrate a gradual decrease of the temperature of the globe as a whole, and especially a late and gradual cooling of the earth's crust about the poles. Bronn, in his excellent "Investigations of the Laws of Development of the Organic World," has collected numerous geological and palaeontological proofs of this fact.

These phenomena and the mathematico-astronomical knowledge of the structure of the universe justify the theory that, inconceivable ages ago, long before the first existence of organisms, the whole earth was a fiery fluid globe. Now, this theory corresponds with the grand theory of the origin of the universe, and especially of our planetary system, which, on the ground of mathematical and astronomical facts, was put forward in 1755 by our critical philosopher Kant,(22) and was later more thoroughly established by the celebrated mathematicians, Laplace and Herschel. This cosmogeny, or theory of the development of the universe, is now almost universally acknowledged; it has not been replaced by a better one, and mathematicians, astronomers, and geologists have continually, by various arguments, strengthened its position.

Kant's cosmogeny maintains that _the whole universe, inconceivable ages ago, consisted of a gaseous chaos_. All the substances which are found at present separated on the earth, and other bodies of the universe, in different conditions of density-in the solid, semi-fluid, liquid, and elastic fluid or gaseous states of aggregation-originally const.i.tuted together one single h.o.m.ogeneous ma.s.s, equally filling up the s.p.a.ce of the universe, which, in consequence of an extremely high degree of temperature, was in an exceedingly thin gaseous or nebulous state. The millions of bodies in the universe which at present form the different solar systems did not then exist. They originated only in consequence of a universal rotatory movement, or rotation, during which a number of ma.s.ses acquired greater density than the remaining gaseous ma.s.s, and then acted upon the latter as central points of attraction. Thus arose a separation of the chaotic primary nebula, or gaseous universe, into a number of rotating nebulous spheres, which became more and more condensed. Our solar system was such a gigantic gaseous or nebulous ball, all the particles of which revolved round a common central point, the solar nucleus. The nebulous ball itself, like all the rest, in consequence of its rotatory movement, a.s.sumed a spheroidal or a flattened globular form.

While the centripetal force attracted the rotating particles nearer and nearer to the firm central point of the nebulous ball, and thus condensed the latter more and more, the centrifugal force, on the other hand, always tended to separate the peripheral particles further and further from it, and to hurl them off. On the equatorial sides of the ball, which was flattened at both poles, this centrifugal force was strongest, and as soon as, by increase of density, it attained predominance over the centripetal force, a circular nebulous ring separated itself from the rotating ball. This nebulous ring marked the course of future planets. The nebulous ma.s.s of the ring gradually condensed, and became a planet, which revolved round its own axis, and at the same time rotated round the central body. In precisely the same manner, from the equator of the planetary ma.s.s, as soon as the centrifugal force gained predominance over the centripetal force, new nebulous rings were ejected, which moved round the planets as the latter moved round the sun. These nebulous rings, too, became condensed into rotating b.a.l.l.s. Thus arose the moons, only one of which moves round our earth, whilst four move round Jupiter, and six round Ura.n.u.s. The ring of Saturn still shows us a moon in its early stage of development. As by increasing refrigeration these simple processes of condensation and expulsion repeated themselves over and over again, there arose the different solar systems, the planets rotating round their central suns, and the satellites or moons moving round their planets.

The original gaseous condition of the rotating bodies of the universe gradually changed, by increasing refrigeration and condensation, into the fiery fluid or molten state of aggregation. By the process of condensation, a great quant.i.ty of heat was emitted, and the rotating suns, planets, and moons, soon changed into glowing b.a.l.l.s of fire, like gigantic drops of melted metal, which emitted light and heat. By loss of heat, the melted ma.s.s on the surface of the fiery fluid ball became further condensed, and thus arose a thin, firm crust, which enclosed a fiery fluid nucleus. In all essential respects our mother earth probably did not differ from the other bodies of the universe.

In view of the object of these pages, it will not be of especial interest to follow in detail the _history of the natural creation of the universe_, with its different solar and planetary systems, and to establish it mathematically by the different astronomical and geological proofs. The outlines of it, which I have just mentioned, must be sufficient here, and for further details I refer to Kant's[5] "General History of Nature and Theory of the Heavens."(22) I will only add that this wonderful theory, which might be called _the cosmological gas theory_, harmonizes with all the general series of phenomena at present known to us, and stands in no irreconcilable contradiction to any one of them. Moreover, it is purely mechanical or monistic, makes use exclusively of the inherent forces of eternal matter, and entirely excludes every supernatural process, every prearranged and conscious action of a personal Creator. Kant's Cosmological Gas Theory consequently occupies a similar supreme position in _Anorganology_, especially in _Geology_, and forms the crown of our knowledge in that department, in the same way as Lamarck's Theory of Descent does in _Biology_, and especially in _Anthropology_. Both rest exclusively upon mechanical or unconscious causes (causae efficientes), in no case upon prearranged or conscious causes (causae finales). (Compare above, p.

100-106.) Both therefore fulfil all the demands of a scientific theory, and consequently will remain generally acknowledged until they are replaced by better ones.

I will, however, not deny that Kant's grand cosmogeny has some weak points, which prevent our placing the same unconditional confidence in it as in Lamarck's Theory of Descent. The notion of an original gaseous chaos filling the whole universe presents great difficulties of various kinds. A great and unsolved difficulty lies in the fact that the Cosmological Gas Theory furnishes no starting-point at all in explanation of the first impulse which caused the rotary motion in the gas-filled universe. In seeking for such an impulse, we are involuntarily led to the mistaken questioning about a "first beginning."

We can as little imagine a _first beginning_ of the eternal phenomena of the motion of the universe as of its final end.

The universe is unlimited and immeasurable in both s.p.a.ce and time. It is eternal, and it is infinite. Nor can we imagine a beginning or end to the uninterrupted and eternal motion in which all particles of the universe are always engaged. The great laws of the _conservation of force_(38) and the _conservation of matter_, the foundations of our whole conception of nature, admit of no other supposition. The universe, as far as it is cognisable to human capability, appears as a connected chain of material phenomena of motion, necessitating a continual change of forms. Every form, as the temporary result of a multiplicity of phenomena of motion, is as such perishable, and of limited duration.