It is difficult to demonstrate ontogenetic variation because specimens of corresponding size from the same general area may have ocelli of different sizes.
From what has been said, it follows that the past history of the skeletal covering of the whole head-region of Ammocoetes, both frontal and occipital, can be conjectured by means of the ontogenetic history of the foremost myomeres.
The appearance, which Descartes turned into the premise of the rational discourse adopted by Western civilization, makes us fall captive to representational explanations rather than to ontogenetic descriptions.
The ontogenetic history of the eye-lines of trilobites with compound eyes is instructive, and has already been discussed by Lindstroem (1901, pp.
Moreover, as we have already seen, at whatever ontogenetic grade of differentiation it may be present in a given somatic-tissue, it must there be capable of indefinite self-multiplication.
On the other hand, I do not see why Weismann should object to supposing that similar determinants compete among themselves for ontogenetic development.
B belonging to the first ontogenetic stage), and one half of this is next got rid of by the second segmentation in the form of the second polar body.
But even three hundred generations of the former can scarcely be regarded as equal to all the “ontogenetic stages” of the latter.
This phylogenetic principle is as firmly established as the ontogenetic fact that every articulated animal-form develops from an unarticulated embryo.
These ontogenetic facts are of the greatest importance for the purpose of learning those ancestral forms of the vertebrates which we have to seek in the group of the unarticulated vermalia.
The most important feature in this sense, and the best starting-point for ontogenetic study, is the fact that man is developed from an ovum, and that this ovum is a simple cell.
This progressive divergence of the human from the animal form, which is based on the law of the ontogeneticconnection between related forms, is found in the structure of the internal organs as well as in external form.
This is the law of the ontogenetic connection of related animal forms.
And if we seek to understand this ontogenetic agreement in the light of the biogenetic law, we find that it proves clearly and necessarily the descent of man from a series of other mammals, and proximately from the primates.
It is precisely in the study of these difficult features that we see the incalculable value of phylogenetic considerations in explaining complex ontogenetic facts, and the need of separating cenogenetic phenomena from palingenetic.
This ontogeneticprocess has a very great significance, and is the real starting-point of the construction of the multicellular animal body.
This is an ontogeneticfact of the utmost significance.
The five-lined pattern is characteristic of the hatchling, but gradual ontogeneticchange results in its dulling, suppression, and eventual loss.
Whereas males and females are strikingly different in appearance in the breeding season, visual sex recognition is complicated by ontogenetic changes.
Ontogenetic change in the color pattern is of significance in connection with the secretive habits.
It is by far less probable that the persistence or rather the intercalation of the ancestral form would occur in an ontogenetic cycle, consisting of a series of stages, and not of two only, as in our example.
If at each ontogenetic stage, the quantity of nucleoplasm is just sufficient to produce the following stage, we might well imagine that the whole ontogeny would necessarily be completed.
And these combinations will not only take place at fertilization, but also at every stage of the whole ontogenetic history, for each stage is represented by its idioplasm, which is itself composed of ancestral idioplasms.
It may be argued that von Baer’s well-known and fundamental law of development is opposed to the hypothesis that the idioplasm of successive ontogenetic stages must gradually assume a simpler molecular structure.
The ontogenetic facts which are systematically represented on Plate XII.
The second ontogenetic process consists in a new kernel being formed in the Monerula, or egg-cytod, which thus returns again to the value of a true egg-cell.
This ontogeneticstage of development which we called Morula (p.
This name we give to those extinct Protozoa which correspond to the two ontogenetic embryonic forms of the six higher animal tribes, namely, the Planula and the Gastrula.
If new characters have a general tendency to become transferred to the younger ontogenetic stages, why are not new imaginal characters first transferred to the pupa, and finally to the larva?
It is, of course, not hereby implied, that throughout the whole animal kingdom new characters can only appear in the last ontogenetic stage.
Staudinger’s collection, three of which are certainly in the last ontogenetic stage.
This species exactly corresponds therefore with the second ontogenetic stage of C.
In the latter, however, is comprised the question--is not the cycle of generations produced by cyclical heredity ultimately equivalent to Darwin and Haeckel’s homochronic heredity which forms the ontogenetic stages into a cycle?
The latter indicate the gradual backward transference of a new character from the latest to the earlier ontogenetic stages.
It would then be no longer possible, from the ontogenetic course of development of an organ or of a character, to draw a conclusion as to its phylogeny.
Gilia, in another and more advanced stage, which is also passed through by Lophura Hyas in the course of its ontogenetic development.
Our opponents either cannot boast of such harmony in their conception of nature, or else they must, together with the phyletic vital force, re-admit into their theory the old ontogenetic vital force.
The manner of union between the cells in the most primitive living colonies, whether vegetable or animal, is analogous to that followed in the segmentation of the ovum in its ontogenetic (i.
We hide the mechanism of growth under very vague expressions: biological final causes, ontogenetic evolution, heredity.
The ontogenetic development of this organ probably indicates that it arose as a differentiation of the dorsal wall of the archenteron; at the same time it is not perhaps safe to lay too much stress upon its mode of development.
In all the higher types the nasal pits have originally only a single opening, and the ontogenetic process by which the posterior nasal opening is formed has been studied in the Amniota and Amphibia.
In this case also the new characters predominate in the later periods of life, and are then transferred back to the younger ontogenetic stages in the course of phyletic development.
As this subsequent development advanced, the older phyletic stages would always be relegated to younger ontogenetic stages, until finally they would be but feebly represented even in the youngest stage (D.
Parallelism between the ontogenetic and the phyletic vital force, 687.
Nicæa, and is distinguished from the seventh chiefly by the ontogeny, in the third stage of which the seventh phyletic stage is reached, whilst in Euphorbiæ and Dahlii this stage is reached in the fourth ontogenetic stage.
It must be expected that any ontogenetic stage would most readily revert to the preceding phyletic stage, so that characters present in the preceding stage are consequently those which would most commonly arise by reversion.
Illustration: PLATE 24] Ontogenetic change in color and markings of plastron.
Illustration: PLATE 25] Ontogenetic change and sexual dimorphism in shape, color, and markings of head and neck.
Illustration: PLATE 23] Ontogenetic change in color and markings of carapace.
By the aid of the correlated ontogenetic stages and the succession of the adult forms in the rocks, many phylogenetic series have been established and a basis for the natural arrangement of the whole class has been laid.
Be it remembered that all the recent Amphibia still undergo the same metamorphosis during their ontogenetic development.
But in a phylogenetic as well as in an ontogenetic sense the former are the ancestral stock of the latter.
The three genera named represent a phylogenetic series, which is repeated in the ontogenetic development of Cyphocolpus.
May be regarded in a phylogenetic as well as an ontogenetic sense, as the further developmental form of Desmocampe catenula and Ommatocampe polyarthra.
Cyclodiscaria#, but also the common ontogenetic original form of all Porodiscida, or at least of the greater part of them.
It is therefore extremely probably that Actissa not only forms the common stem-form of the whole class in a phylogenetic sense, but is also its common ontogenetic or germinal form.
This species exhibits the progressive (ontogenetic as well as phylogenetic) development of Panartus amphiconus.
May be considered in a phylogenetic and ontogenetic sense as a further developmental stage of Desmocampe aphrodite and Ommatocampe nereis, Pl.
The genus Triolena is the most simple form of all Pylodiscida, and must be regarded as their common ancestral form, from an ontogenetic as well as a phylogenetic point of view.
It may be the ancestral form of it (both in an ontogenetic and phylogenetic sense).
Ontogenetic change in coloration consists of the splitting of the second and third pairs of dark stripes in the juvenile.
There is no ontogenetic change in color pattern; juveniles have the same coloration as adults from the same geographic area.
In some species there is considerable ontogenetic change in color pattern, although the juveniles bear the basic color characteristics of the adults.
Ontogenetic change in coloration consists of the splitting of the second pair of dark stripes in the juvenile.
The first is the true ontogenetic epitome or short recapitulation of past evolutionary history; the second is the exact contrary, a new foreign ingredient, a falsifying or concealing of the epitome of phylogeny.
The trend of opinion was to reject theontogenetic criterion of homology, and to refuse any morphological or phylogenetic value to the germ-layers.
The ovum after the nucleus had been re-formed became the cytula, which was the ontogenetic counterpart of the amoeba.
There are also striking ontogenetic changes in the proportions of the head, body and tail.
Since ontogenetic processes are so often cut short by external conditions, we can understand the variability in the degree of development of positive characters.
But, on the well-known principle of imperfection of dominance in F1, the median comb is usually incomplete and, probably for some ontogenetic reason, incomplete only behind.
Only the ontogenetic fluctuations of other real characters may influence the defect.
Apparently, within limits, these quantitative variations have so exclusively an ontogenetic signification that they are not reproduced so long, at least, as environmental conditions are not allowed to vary widely.
It is clear that the ontogenetic failure of an inhibitor is easier to understand than the development of a character that is not represented at all in the germ-plasm.
A-D represent, in ontogenetic sequence from left to right, upper tooth-rows of the tribe Geomyini.
This is perceived from the succession of the visible ontogenetic characteristics which in general run parallel with it.
In the lowest forms of cell differentiation the cells of successive generations are all independent; the ontogenetic period consists of a cycle of generations of unicellular plants.
Among these periods the ontogenetic period or ontogeny embraces all generations from one cell to the return of the exactly similar kind of cell.
If all the cell generations of an ontogenetic period have been united into a single individual, the successive plant generations are alike and alternation of generations has ceased.
Their ontogenetic history does not explain their true significance; this can be known only in a phylogenetic way by comparison of one phenomenon with those phenomena from which it has arisen in the course of evolution.
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.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "ontogenetic" in a variety of sentences. We hope that you will now be able to make sentences using this word. Other words: evolutionary; evolving; genetic; phylogenetic; progressing; unfolding
