We will take up these and explain them successively, and then, afterward, show that they are also the laws of embryonic development, and therefore the laws of evolution.
That the embryonic development of one of the higher representatives of any group repeated in a general way the terms of the Taxonomic series in the same group, and therefore that embryology furnished the key to a true classification; and, 2.
This order of change is still retained in the embryonic development of the last introduced and most specialized order of existing fishes.
This ascending series of genetically connected stages is called the embryonic or Ontogenic series.
If there be any evolution, par excellence, it is evolution of the individual or embryonic development.
We will use this figure, therefore, to represent both the embryonic condition of air-breathing vertebrates and the mature condition of some fishes.
Not only are many steps of phylogeny, especially in its early stages, dropped out in the ontogeny, but, of course, many adaptive modifications for the peculiar conditions of embryonic life are added.
As already stated, all will admit a grand resemblance between the stages of embryonic development and those of the development of the organic kingdom.
Again, in theembryonic history of every animal we see the next change take place--i.
But does it therefore follow that the quantity of germ-plasm in the segmentation nucleus is not the factor which determines the beginning of embryonic development?
But if the first segmentation spheres are not able to develope into a complete organism, how can this be the case with one of the later embryonic cells, or one of the cells of the fully developed animal body?
The quantity of nuclear substance decides whether the egg is capable of undergoing embryonic development.
All writers agree in supposing that something which would be an obstacle to embryonic development is removed from the egg; but opinions differ as to the nature of this substance and the precise reasons for its removal[142].
Again Galton states—‘Out of the structureless ovum the embryonic elements are taken .
I believe however that they can be referred to the various external influences to which the germ is exposed before the commencement of embryonic development.
He assumed that the formation of germ-cells takes place at the earliest stage of embryonic life, and he thus believed the connexion between the germ-plasm of the parent and of the offspring had received a satisfactory explanation.
For instance, the eggs are not extruded at all, but embryonic development takes place within the body of the mother, which has previously undergone spontaneous division into several pieces.
The city, too, was coming to be recognized as an embryonic cosmopolis.
Whether at the beginning of embryonic life within the egg, however, oxygen was necessary, remained somewhat in doubt.
Mueller first demonstrated the harmony which existed between the pathological and the embryonic development of tumors.
It was well known that an air-chamber existed in the egg even at the earliest stages ofembryonic life.
Mueller's observation of the identity of the pathological and the embryonic development of tumors is really the key to the whole doctrine of morbid formations.
At the crest of the hill travellers with even the merest embryonic aesthetic taste were forced to pause.
As an independent institution the Inquisition of Navarre seems never to have advanced beyond an embryonic condition.
In spite of the efforts of the embryonic Inquisition there, heresy was undisguised, and the ministers of Christ were openly opposed and ridiculed.
This last work contains an admirable résumé of our knowledge of theembryonic development of insects up to the date of publication.
A valuable paper, “On the Embryonic Larvæ of Butterflies,” was published in 1871 by S.
From the beautiful investigations of Bütschli on the embryonic development of bees[197] we know that the embryo of the grub possesses a complete head, consisting of four segments and provided with the three typical pairs of jaws.
A memoir by Samuel Clarke has since been published upon the embryonic development of Amblystoma punctatum, Baird.
The embryonic convolutions again are smooth, and the author believes (on other grounds) that the more remote progenitor possessed a smooth shell.
In this country Sir John Lubbock, in 1874, appealed to the embryonic characters of larvæ in support of his views on the origin of insects.
Hymenoptera, by the embryonicdevelopment of the maggot-like larvæ.
During the embryonic development the eggs become coloured, first yellow and partly blackish, and finally completely black.
But in religious matters this fear has clung to man tenaciously; and while at first serving a protective function, at the present stage of civilization constitutes an embryonic impediment.
And the necessity exists even at this age for darkness during the formative processes ofembryonic life.
In the highest animals this symmetry is laid down at the very dawn of life, the first trace of the future creature being a longitudinal streak--the embryonic "primitive groove.
Examples of strange births are sufficiently common, and they may arise either from directembryonic modifications or apparently from some obscure change in the parental action.
Some knowledge of this embryonic growth is necessary to a correct understanding of the adult brain, its essential plan, its growth, and the correct estimate of its development.
In particular, it was established by these investigations that the human foetus, about the middle of its embryonic life, possesses a pointed ear somewhat similar to that of the monkey genus Macacus.
He had a glimpse of the selection idea, and believed in mutations or sudden leaps--induced in the embryonic condition by external influences.
He further dwells on the general agreement exhibited by young embryonic forms, and he illustrates this by two figures placed one above the other, one representing a human embryo, after Ecker, the other a dog embryo, after Bischoff.
The palingenetic phenomena, or embryonic recapitulations, are due to heredity, to the transmission of characters from one generation to another.
Finally, enamel itself and dentine are developed, and the embryonic tooth remains covered under the gums until it cuts them.
At the end of this time most of the villi disappear, and the few that remain take part in forming the f[oe]tal orembryonic portion of the placenta.
After the period of embryonic life is over, the stimulus of nutrition is still sufficient for some of these body-cells.
As we have already seen, at a very early stage in the development of the embryo, a folding of its cells takes place, so that the upper embryonic area assumes the character of a groove.
We have referred in the preceding description to the origin of some embryonic structures from a cleft in the early embryo itself.
Its respiratory function consists in allowing oxygen and carbonic acid gas to pass by osmosis between the embryonic and the maternal blood.
Around the whole, the embryonic tissue has been forming into a strong protective covering, some of which finally becomes cartilage, and some bone.
For the first part of embryonic life the developing spinal cord is of the same length as the canal, but as time goes on the canal grows longer than the cord.
He invented the term "radicle" for the embryonic root, and used the word "plume" for the organ which we now speak of in the diminutive as the plumule.
Man, who in the adult state possesses twelve pairs of ribs, is found in the embryonic state to have thirteen or fourteen.
But they will still begin as specks of protoplasm, and acquire the faculty of painting in their mother's womb at quite a late stage of their embryonic life.
It is claimed that the whole history of evolution is briefly repeated in the early stages of embryonic life.
The diarthroses represent an arrest of development at an earlier stage, for a part of the original embryonic tissue remains as a plate of round cells, while the neighbouring two rods chondrify and ossify.
Since the time of conception determines the beginning of embryonic development, to prove that the act was committed before fetal movements were perceived is no longer a valid defense.
In a broad sense, the period of gestation for each variety of mammal is determined by the time required for embryonic development to reach the point where the young may live independently of the mother.
Partly on account of this congestion and partly on account of embryonic development, the uterus becomes altered in a number of ways.
The moment the womb is instinct with embryonic life and gestation has begun, the crime may be perpetrated.
Embryonic development, therefore, in the strictest sense of the term, chiefly involves the shifting of various groups of cells and the bestowal upon them of different kinds of activity.
A very old explanation of embryonic development was that the process consisted altogether in growth.
Now that we have become familiar with the arrangements for the protection of the embryo, we are prepared to learn how it develops, and may accept the phrase, embryonic development, to cover the whole period of existence within the womb.
Professor Owen therefore considers the tail of the Archaeopteryx as exemplifying the persistency of what is now an embryonic character.
Thus community in embryonic structure reveals community of descent, however much the structure of the adult may have been modified.
Hence the embryonic states exhibited one after the other by the human individual bear a certain amount of resemblance to those of the fish, reptile, and bird before assuming those of the highest division of the vertebrata.
That is clearly seen in the embryonic evolution of the psychic organs, the nervous system, the muscles, and the sense-organs.
It was supposed that the rest of the placentals, including the apes, were without these special embryonic structures.
The ontogeny, orembryonic development, of the soul, individual or biontic psychogeny, investigates the gradual and hierarchic development of the soul in the individual, and seeks to learn the laws by which it is controlled.
In man, as in all other organisms, "the embryonic development is an epitome of the historical development of the species.
And such arrest must inevitably entail some warp or bias of a lower animal phase; which may so impress itself permanently on embryonic development as to detract more or less gravely from the final transition.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "embryonic" in a variety of sentences. We hope that you will now be able to make sentences using this word.
