Here the first place belongs to the invaluable results which modern comparative ontogeny has gained by the aid of the biogenetic law or the theory of recapitulation.
The intimate causal connection between ontogeny and phylogeny, between the development of the individual and the history of its ancestors, enables us to gain a safe and certain knowledge of our ancestral series.
Moult in the shag Phalacrocorax aristotelis, and the ontogeny of the "Staffelmauser.
Body temperature and the ontogeny of thermoregulation in the slender-billed shearwater.
Nägeli does not produce such reasons, but considers the metamorphosis of the idioplasm in ontogeny as mere differences in the ‘conditions of tension and movement.
The essential point is that the differentiation was originally due to some change in the reproductive cells, just as this change itself produces all the differentiations which appear in the ontogeny of all species at the present day.
The development of the nucleoplasm during ontogeny may be to some extent compared to an army composed of corps, which are made up of divisions, and these of brigades, and so on.
The gradual decrease in complexity of the structure of 190 the nucleus during ontogeny 8.
The phyletic displacements of the localized areas are brought about during ontogeny by an actual migration of primitive germ-cells from the place where they arose to the position at which they undergo differentiation into germ-cells.
This removal takes place in the same manner as that in which differing nuclear substances are separated during the ontogeny of the embryo: viz.
I imagine that I have now sufficiently explained the above proposition, that the repetition of the phylogeny in the ontogeny does not and cannot occur among unicellular organisms.
In the first place he declares definitely that ontogeny alone, i.
We must, however, not forget that we possess the wonderful analogy of ontogeny (individual development) and above all, the fact of mutation and of metagenesis.
The ontogeny of this species is obviously but a very incomplete representation of its phyletic development.
Of the four phyletic stages indicated by the ontogeny of Elpenor and Porcellus, three still form the terminus of the development of existing species.
The phyletic stages indicated by queries are extinct, and only known through the ontogeny of existing species.
This would be raised into a certainty if we could demonstrate the phyletic development of the maggot-formed out of the caterpillar-formed Hymenopterous larvæ by means of the ontogeny of the former.
If we were able to ascertain the ontogeny of these species, we should find that the oblique stripes appeared late in life, as has already been shown in the case of Pterogon Œnotheræ.
Much light would be thrown upon this by studying the ontogeny of the species.
This species may possibly retain in its ontogeny a stage in which the oblique stripes are also absent, whilst the subdorsal line is present.
Here again we have a clashing of the results arrived at by a study of the ontogeny of the larvæ, on the one hand, and the founding of genera on the characters of the imagines only, on the other.
In the second volume I dealt broadly with the principle of evolution, distinguishing ontogeny and phylogeny as its two coordinate main branches, and associating the two in the Biogenetic Law.
I endeavoured to employ all the known facts of comparative ontogeny (embryology) for the purpose of completing my scheme of human phylogeny (evolution).
The ontogeny of speech showed that its gradual development in the child is (in accordance with the biogenetic law) a recapitulation of its phylogenetic process.
There was then no such thing as the cell-theory or as physiological chemistry; ontogeny and paleontology were still in their cradles.
However, comparative ontogeny teaches us that all these various structures have been developed from one simple fundamental form, as I have shown in my theory of the gastraea (1872).
Either there is or is not a direct and causal connection between ontogeny and phylogeny.
I have, from the first, insisted on the close causal connection between ontogeny and phylogeny, ever since I distinguished these two parts of biogeny in the fifth book of the General Morphology.
Ontogeny teaches unmistakably that its elementary organs, the epidermic cells, develop entirely from the ectoderm.
The ontogeny of the mind--or the embryology of the human soul--brings before us in direct observation the various stages of development through which the mind of every man passes from the beginning to the close of life.
Further study of the records, however, soon convinces one familiar with the ontogeny of the case that we are here face to face with the species, described by Alb.
Ontogeny repeats phylogeny," and phylogeny, or line of descent of organisms and structures, is what we are seeking.
This hypothesis is most strongly supported by the comparative anatomy, and by the ontogeny of some Star-fishes (Colastra), and of segmented worms.
It is just here that ontogeny guides us with the greatest certainty on to the track of phylogeny.
Thus ontogenyhelps us over many and large gaps in palaeontology.
The pedigree of the Arthropoda can on the whole be clearly made out from the palaeontology, comparative anatomy, and ontogeny of its four classes, although here, as everywhere else, many details remain very obscure.
Even at the beginning of our century Cuvier's comparative anatomy and palaeontology, and Baer's ontogeny of the Vertebrate animals, had brought us to a high level of accurate knowledge on this matter.
Of this the ontogeny of skulled animals leaves no doubt.
The ontogeny of these animals is extremely interesting and, like that of Vertebrate animals, distinctly reveals the essential outlines of the history of their tribe, that is, their phylogeny.
The proof that even the direct ancestors of man belonged to these Scolecida, is furnished by the comparative anatomy and the ontogeny of Worms and of the Amphioxus.
No petrifactions could inform us of the fundamental and important fact which ontogeny reveals to us, that the most ancient common ancestors of all the different animal and vegetable species were quite simple cells like the egg-cell.
Probably the number of these Protista will be considerably increased in future days by the progressive investigations of the ontogeny of the simplest forms of life, which have only lately been carried on with any great zeal.
The certain proof that Genuine Apes, and hence also our own race, are the direct descendants of Semi-apes, is to be found in the comparative anatomy and the ontogeny of Placental animals.
We have just traced the change in the ontogeny of the frog, but the steps of the same change are traceable in passing from the typical fish (teleosts), through dipnoi and amphibians to reptiles.
In ontogenywe have still the same order, because ancestral characteristics are inherited, and family history recapitulated in the individual history.
The ontogeny still passes through the stages of the phylogeny.
Lastly, the law of cyclical movement is also a law of ontogeny and therefore of evolution.
How far some special embryonic larval form is constantly reproduced in the ontogeny of the members of one or more groups of the animal kingdom; and how far such larval forms may be interpreted as the ancestral type for those groups.
Each organism reproduces the variations inherited from all its ancestors at successive stages in its individual ontogeny which correspond with those at which the variations appeared in its ancestors.
Although there is perhaps no group in the animal kingdom the ontogeny of which would better repay a thorough investigation than the Turbellarians, yet the difficulties to be overcome have hitherto proved too great.
Amongst the Acraspeda it is also present, but has an exceptional mode of ontogeny which is discussed in connection with the germinal layers.
Ontogeny nevertheless brings clearly to light the existence of a larval form--the planula--which recurs with fair constancy amongst all the groups except the Ctenophora.
This law, interpreted in accordance with the theory of descent, asserts that each organism in the course of its individual ontogeny repeats the history of its ancestral development.
The considerations which were used to shew that the ancestral history is reproduced in the ontogeny of the individual apply with equal force to the evolution of organs.
It makes its appearance in an altered garb in the ontogenyof some of the other groups.
Probably in all Pylonida the ontogenyof the shell begins with the formation of a Monozonium.
The causal connection between ontogeny and phylogeny, which finds its most precise statement in the fundamental biogenetic law, holds in general for the Radiolaria as for all other organisms.
Differentiation is repeated in the course of the phylogeny, since at first all parts of an ontogeny diverge into two or more parts, then the parts of these parts divide again, etc.
The parts of an ontogeny become dissimilar, since the functions which were previously united become differentiated and since new dissimilar functions are produced in the various parts.
Each ontogeny (individual) begins in a minute germ cell, in which a small quantity of idioplasm is contained.
Among these periods the ontogenetic period or ontogeny embraces all generations from one cell to the return of the exactly similar kind of cell.
Later the cell generations of an ontogeny are united by parts into plant individuals; the ontogenetic period consists of a cycle of multicellular and unicellular, or only of multicellular plant generations.
Since the stimulus is discontinued with each change of the ontogeny and only the idioplasm persists, permanent variations are produced only in the idioplasm by those conditions that produce visible transformations in the mature organism.
Both causes acting together--the phylogenetic configuration of the idioplasm and the successive morphological stages of development of the individual conditioned on it--necessarily result in the ontogeny being the repetition of the phylogeny.
This differentiation is either one of space between the parts of the ontogeny that appear near each other, or one of time between those that are derived from each other.
Since the capability of the primordial plasma to grow is the original and only vital quality (Anlage), the whole ontogeny in this first stage consists in the growth of the detached parts to the adult size.
The fact that two organisms belong to the same line of descent is recognized from the ontogeny of the higher including the ontogeny of the lower.
A definite and previously limited growth continues, or a definite formation of parts of an ontogeny which has previously been present but once, is repeated.
On page 88 I tried to show how common in ontogenysuch restraining and inhibiting factors are.
As we have seen, ontogeny is not completed at hatching or birth.
Thus in the ontogeny that is proceeding under the control of heredity all is motion and change.
From the comparative anatomy and ontogeny of the existing Marsupials we may draw very interesting conclusions as to their intermediate position between the earlier Monotremes and the later Placentals.
It can only be said positively that the peculiar ontogeny of the complicated optic apparatus in man follows just the same laws as in all the other Vertebrates.
Comparative anatomy and ontogenyshow clearly that the Ganoids descended from the Selachii, and the Teleostei from the Ganoids.
The ontogenyof the organs can only be understood in the light of their phylogeny, just as we found of the embryology of the whole body.
Man has faithfully preserved the main features of his stem-history in the ontogeny of his urinary and sexual organs.
The first thought that occurs to one in this connection is the vast difference between the duration of man's ontogeny and phylogeny.
The origin of the Mullerian duct is still obscure; comparative anatomy and ontogeny seem to indicate that it originates by differentiation from the Wolffian duct.
But the comparative anatomy and ontogeny of the muscular system are much more difficult and inaccessible, and consequently have hitherto been less studied.
Here again, therefore, on the ground of the pithecometra-principle, comparative anatomy and ontogeny teach with full confidence the descent of man from the ape.
But we have also many important grounds in comparative anatomy and ontogeny for assuming a common origin for all the Vertebrates.
The recapitulation of phylogeny by ontogeny is only fairly complete in a few cases, and is never wholly complete.
In tracing the evolution of the various organs we shall follow the method that has hitherto guided us, except that we shall now have to consider the ontogeny and phylogeny of the organs together.
Even if we entirely ignore it, all that we have learned from the zoological facts of comparative anatomy and ontogeny as to the placental character of man remains untouched.
The association of ontogeny and phylogeny and the proof of the intimate causal connection between these two sections of the science of evolution, which I expounded in my work, met with the most spirited opposition on nearly all sides.
Thus it is clear that the ontogeny of the heart can only be understood in the light of its phylogeny (or development in the past), both as regards function and structure.
Our chief support in this comes from the embryological study of it, or the ontogeny of the soul.
More recent investigations have shown that it is of the greatest importance in connection with the comparative anatomy and ontogeny of the vertebrates, and therefore with human phylogeny.
It was thus Darwinism that first opened our eyes to a true comprehension of the supremely important relations between the two parts of the science of organic evolution--Ontogeny and Phylogeny.
Unfortunately, the distinguished Wurtzburg anatomist, to whom comparative anatomy, histology, and ontogenyowe so much, is opposed to the theory of descent generally and to Darwinism in particular.
Roughly, ontogeny may be taken to mean embryology, and phylogeny what we generally call evolution.
This is very clearly shown by the comparativeontogeny of the fishes and amphibia.
As in the lower teeth, the bicolumnar crowns of early ontogeny in both Pliosaccomys and the Geomyini become eventually united, with wear, into a single column.
Even though the intermediate stages of ontogeny in m1 and m2 of Pliosaccomys and the Geomyini are entirely different, the bicolumnar crowns of both eventually unite, upon wear, into a single column.
That a certain temperature is necessary for ontogenyhas long been known; this was carefully studied by O.
Of the inner factors of ontogeny there is another category that may be called physical, that already spoken of being physiological.
For an excellent discussion on the ontogeny of the child in this connexion, see Some Laws of Heredity, by Mr. S.
For my own part, I cannot perceive any difficulty about this: in fact, there is an admirable repetition of the process in the ontogeny of our own children[15].
Ontogeny is the short and rapid recapitulation of phylogeny, conditioned by the physiological functions of heredity (reproduction) and adaptation (nutrition).
Even in the General Morphology Haeckel had recognised that ontogeny is neither a complete nor an entirely accurate recapitulation of phylogeny; he had admitted, following F.
The Gastræa theory gave point and substance to the biogenetic law, and enabled Haeckel to state much more concretely the parallelism existing between ontogeny and phylogeny.
The stages which are passed through by higher organisms in their ontogeny correspond to stages which are maintained in others as the definitive organisation.
But he accepted the main tenet of it when he asserted that each stage of ontogeny had its counterpart in an adult ancestral form.
He tried also to explain the recapitulation of phylogeny by ontogeny as due to habit.
There must be a threefold parallelism between the natural system, ontogeny and phylogeny (ii.
In this way it comes about naturally that organs which become differentiated rapidly, as, for example, the medullary tube, as a rule dominate earlier periods of ontogeny than do the organs of locomotion.
The facts of development, Gegenbaur goes on to say, help us out greatly in our search for ancestral forms, for the early stages in the ontogeny of a highly organised animal give us some idea of the organisation of its original ancestor.
The Meckel-Serres law, it will be remembered, expressed the idea that the higher animals repeat in their ontogeny the adult organisation of animals lower in the scale.
Characters common to the early ontogenyof all the members of a large group are particularly important in this respect (cf.
In ontogeny the notochord is a derivative of the dorsal wall of the archenteron.
In the other two surviving Dipnoans, similar large teeth exist, though here there is no longer trace in ontogeny of their formation by the basal fusion of originally separate denticles.
The genital ducts of Ganoids and Teleostei have for some time been a source of great difficulty to morphologists; and any contributions with reference to the ontogeny of these structures are of interest.
The observations just recorded practically deal with two much disputed points in the ontogeny of birds, viz.
Their ontogeny would be conclusive on this matter, and we trust that some of the anatomists who have the opportunity of studying the development of the Sturgeon will soon let us know the facts of the case.
It is true that there are nonconformities to the general law that individual development tends to recapitulate racial history, or that ontogeny tends to recapitulate phylogeny.
The phenomena of the hereditary mneme show clearly how ontogeny is the result of engraphia combined with selection, in the series of ancestors.
In its chief outlines ontogeny is determined by phylogeny by means of the laws of heredity, even when it is only an abridged recapitulation.
In woman, sexual ontogeny is not the same as in man.
At least this is what it should be, and then the fundamental biogenetic law of Haeckel (ontogeny is an abridged repetition of phylogeny) will receive an ultimate confirmation.
In the laws of ontogeny and heredity alternating ecphoria plays an important part.
In the sexual ontogeny of normal woman, pregnancies, childbirth, the nursing and education of children play an infinitely greater role than the sexual appetite.
This denture is nothing else than a phylogenetic incident in the ontogeny of the whale.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "ontogeny" in a variety of sentences. We hope that you will now be able to make sentences using this word.
