英语词汇“gastrula”造句的方法、技巧、例句及翻译-英语例句辞典

As Prof. Holstein underscores, the data obtained paint a new picture of the predatory lifestyle as a primary characteristic of the cnidarian gastrula. Did animal evolution begin with a predatory lifestyle? 2023-09-29T04:00:00Z

This leads to the formation of the next developmental stage, the gastrula, in which the future digestive cavity is formed. Fundamentals of Biology 2015-01-01T00:00:00Z

Such hybrids typically die before they reach the gastrula stage, the point in embryonic development at which major cell differences first become obvious. Transplanted Nuclei and Cell Differentiation, by Sir John B. Gurdon 2012-10-09T23:45:00.177Z

It has usually been regarded as representing both endoderm and mesoderm, and the groove which usually leads to its formation has been compared to the abnormally elongated blastopore of a typical gastrula. Encyclopaedia Britannica, 11th Edition, Volume 13, Slice 4 "Hero" to "Hindu Chronology" 2012-04-04T02:00:56.447Z

Applied to a gastrula when the blastorope does not entirely up. Webster's Unabridged Dictionary 2012-03-24T02:00:23.513Z

From the occurrence of the gastrula in all the divisions of the animal kingdom, we may conclude that it is a temporary phase, inevitable in the growth of animals. The Biological Problem of To-day Preformation Or Epigenesis? The Basis of a Theory of Organic Development 2011-08-29T02:01:04.170Z

In protostomes, two circular layers of mesoderm form inside the gastrula, containing the coelom cavity. Fundamentals of Biology 2015-01-01T00:00:00Z

Toward the end of the blastula stage "transfer" RNA synthesis is first detected; this is followed a few hours later, during the formation of the gastrula, by the synthesis of ribosomal RNA. Transplanted Nuclei and Cell Differentiation, by Sir John B. Gurdon 2012-10-09T23:45:00.177Z

This cup-stage is called the gastrula stage; the outer wall of the gastrula is the ectoderm, and its inner the endoderm; while its cavity is the enteron, and the opening to the exterior the blastopore. Encyclopaedia Britannica, 11th Edition, Volume 9, Slice 3 "Electrostatics" to "Engis" 2011-02-06T03:00:53.093Z

The primitive enteron or undifferentiated digestive sac of a gastrula or other embryo. Webster's Unabridged Dictionary 2012-03-24T02:00:23.513Z

The blastosphere determines the orientation of the gastrula, and so forth. The Biological Problem of To-day Preformation Or Epigenesis? The Basis of a Theory of Organic Development 2011-08-29T02:01:04.170Z

As the protostome develops, the mesoderm grows and fuses with the gastrula cell layer. Fundamentals of Biology 2015-01-01T00:00:00Z

Slides or diagrams, showing various stages in the development of some animal through the gastrula stage. A Guide for the Study of Animals 2011-01-18T03:00:14.913Z

The segmentation is complete; one side of the hollow blastosphere invaginates and forms a gastrula. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 7 "Cerargyrite" to "Charing Cross"

This gastrula theory, now generally accepted, is one of Haeckel's two great fundamental contributions to the evolution philosophy with the history of which his life work is so intimately linked. A History of Science, Volume 5(of 5) Aspects Of Recent Science

Consider its mode of division, and the formation of the blastula, gastrula, and germinal layers. The Biological Problem of To-day Preformation Or Epigenesis? The Basis of a Theory of Organic Development 2011-08-29T02:01:04.170Z

In deuterostomes, two groups of gastrula cells in the blastopore grow inward to form the mesoderm. Fundamentals of Biology 2015-01-01T00:00:00Z

This exceedingly important larval form, the "gastrula," makes its appearance in the ontogenesis of all tribes of animals. Was Man Created?

The point to remember is, that in all cases a gastrula is an open sac composed of two layers of cells—the outer layer being called the ectoderm, and the inner the endoderm. Darwin, and After Darwin (Vol. 1 and 3, of 3) An Exposition of the Darwinian Theory and a Discussion of Post-Darwinian Questions

The gastrula in section, anterior end to the right. Text Book of Biology, Part 1: Vertebrata

Invagination, the infolding of a layer of cells, as, for instance, in the transformation of a blastosphere into a gastrula, xvii. The Biological Problem of To-day Preformation Or Epigenesis? The Basis of a Theory of Organic Development 2011-08-29T02:01:04.170Z

The archenteron develops into the alimentary canal, and a mouth opening is formed by invagination of ectoderm at the pole opposite the blastopore of the gastrula. Fundamentals of Biology 2015-01-01T00:00:00Z

The gastrula stage was the palingenetic repetition of the ancestral form of all Metazoa, the Gastræa. Form and Function A Contribution to the History of Animal Morphology

Before the egg of the frog becomes an elliptical mass of cells, it is at one time a double-walled sac enclosing a central cavity; in this stage it is called a gastrula. The Doctrine of Evolution Its Basis and Its Scope

There is no open invagination of an archenteron in the fowl, as in the frog--, the gastrula, like the blastosphere, stage is also masked. Text Book of Biology, Part 1: Vertebrata

From causes of which we are ignorant two, instead of one, gastrula stages may arise at separate regions of the germinal layer of the egg. The Biological Problem of To-day Preformation Or Epigenesis? The Basis of a Theory of Organic Development 2011-08-29T02:01:04.170Z

But how is an adult worm or vertebrate formed out of such a gastrula? The Whence and the Whither of Man A Brief History of His Origin and Development through Conformity to Environment; Being the Morse Lectures of 1895

The gastrula, finally, is the two-layered sac formed from the blastula, typically by invagination of its wall. Form and Function A Contribution to the History of Animal Morphology

In other words, the starting point in the development of the frog is a single biological unit; this divides and its products redivide to constitute the many-celled blastula and the double-walled gastrula. The Doctrine of Evolution Its Basis and Its Scope

We naturally assume, from what we have learnt, that the next stages will be the formation of a hollow blastosphere, invagination, a gastrula forming mesoblast by hollow outgrowths from the archenteron, and so on. Text Book of Biology, Part 1: Vertebrata

In the gastrula stage, the segmentation cavity in which the mesoblast is formed lies between the entoblast and ectoblast. The Gutenberg Webster's Unabridged Dictionary Section S

And our ancestor was almost certainly a free swimming gastræa, or hypothetical form corresponding in form and structure to the gastrula. The Whence and the Whither of Man A Brief History of His Origin and Development through Conformity to Environment; Being the Morse Lectures of 1895

A corresponding germinal condition, the two-layered gastrula, occurs transitorily in the embryological history of all the other Metazoa, from the lowest Cnidaria and Vermes up to man. Monism as Connecting Religion and Science A Man of Science

This cavity is the primitive alimentary cavity or archenteron; the inner or invaginated layer is the hypoblast; the outer the epiblast; and the embryo, in this stage, is termed a gastrula. Darwiniana : Essays — Volume 02

Figure 7 i. is a dorsal view of the gastrula at a somewhat later stage, and here indications of distinctly vertebrate relationships already appear. Text Book of Biology, Part 1: Vertebrata

The Gastraea bilateralis, of which we may conceive the bilateral gastrula of the amphioxus to be a palingenetic reproduction, represented the two-sided organism of the earliest Metazoa in its simplest form. The Evolution of Man — Volume 2

Between the ectoderm and entoderm of the gastrula, in the space occupied by the supporting membrane of hydra, a new layer of cells, the mesoderm, appears. The Whence and the Whither of Man A Brief History of His Origin and Development through Conformity to Environment; Being the Morse Lectures of 1895

The point of origin is always the properistoma, the border of the original primitive mouth of the gastrula, at which the two primary layers pass directly into each other. The Evolution of Man — Volume 1

From the gastrula type the higher sub- divisions of animal life probably diverged, as separate branches from a common trunk. The Elements of Geology

Such a gastrula, formed mainly by overgrowth of the epiblast, is called an epibolic gastrula, as distinguished from the invaginate gastrula of amphioxus. Text Book of Biology, Part 1: Vertebrata

The solid foundation of this important thesis is the gastrula, the most instructive embryonic form in the animal world, which we still find in the same shape in the most diverse classes of animals. The Evolution of Man — Volume 2

But our mid-intestine is still the greatly elongated archenteron of the gastrula. The Whence and the Whither of Man A Brief History of His Origin and Development through Conformity to Environment; Being the Morse Lectures of 1895

The chief of the viscera in the body-cavity is the alimentary canal, the organ that represents the whole body in the gastrula. The Evolution of Man — Volume 1

We give the name of the gastrula to the important embryonic form that has these primitive organs, and the name of gastrulation to the formation of it. The Evolution of Man — Volume 1

With what lower type has the gastrula been compared? Text Book of Biology, Part 1: Vertebrata

Probably it differed from the existing gastrula only in one essential point, though extinct millions of years ago. The Evolution of Man — Volume 2

We may therefore compare the hydra or gastrula to a little portion of the lining of the human mid-intestine covered with a little flake of epidermis. The Whence and the Whither of Man A Brief History of His Origin and Development through Conformity to Environment; Being the Morse Lectures of 1895

In fact, these variations have become so great in the course of time that the segmentation was not rightly understood in most animals, and the gastrula was unrecognised. The Evolution of Man — Volume 1

In the growth of this hooded gastrula we cannot sharply mark off the various stages which we distinguish successively in the bell-gastrula as morula and gastrula. The Evolution of Man — Volume 1

All animals that have little yolk, and start early in life for themselves, pass through a gastrula stage, substantially the same as this of amphioxus. Text Book of Biology, Part 1: Vertebrata

In accordance with the biogenetic law, we find solid proof of this in the fact that the two-layered embryos of all the Metazoa can be reduced to a primitive common type, the gastrula. The Evolution of Man — Volume 2

Take a boiled egg, make a hole in the smaller end and remove the yolk, and you have a passable model of a gastrula. The Whence and the Whither of Man A Brief History of His Origin and Development through Conformity to Environment; Being the Morse Lectures of 1895

The authors who regard this embryonic form as the primary gastrula of the placental conceive the outer layer as the ectoderm and the inner as the entoderm. The Evolution of Man — Volume 1

There are many difficulties in the way of understanding this partial segmentation and the gastrula that arises from it. The Evolution of Man — Volume 1

The young amphioxus has, at this stage, which is called the gastrula stage, a curious parallelism with such a lowly form as the Hydra of our ditches. Text Book of Biology, Part 1: Vertebrata

The actual ontogenetic development of the gastrula from the blastula furnishes sound evidence as to the phylogenetic origin of the Gastraea from the Blastaea. The Evolution of Man — Volume 2

Both the blastosphere and gastrula often swim freely by flagella. The Whence and the Whither of Man A Brief History of His Origin and Development through Conformity to Environment; Being the Morse Lectures of 1895

The uni-axial type of the mammal gastrula is accentuated in this way. The Evolution of Man — Volume 1

However, opinions still differ considerably as to the real nature of this "provisional gastrula" of the placental and its relation to the blastula into which it is converted. The Evolution of Man — Volume 1

This stage is called the gastrula stage; ar. is the cavity of the gastrula, the archenteron; b.p. is its opening or blastopore. Text Book of Biology, Part 1: Vertebrata

From the epidermis of the gastrula a medullary tube is formed on the dorsal side, and, between this and the primitive gut, a chorda; these are the organs that are otherwise only found in Vertebrates. The Evolution of Man — Volume 2

But this small white "germinal disk" is now further developed, and is really the gastrula of the chick. The Evolution of Man — Volume 1

In the bell-gastrula of the amphioxus and in the hooded gastrula of the lamprey and the frog the germinal layers are found to be closed tubes or vesicles from the first. The Evolution of Man — Volume 1

This white region at the south pole corresponds, as we shall see afterwards, to the primitive mouth of the gastrula. The Evolution of Man — Volume 1

Nevertheless, the gastrula is formed here, as in the previous cases, by the folding or invagination of the blastula. The Evolution of Man — Volume 1

In the Amphioxus the earliest and most important embryonic processes take place so rapidly that the blastula is formed in four hours, the gastrula in six, and the typical vertebrate form in twenty-four. The Evolution of Man — Volume 2

In both cases a discoid gastrula with primitive streak arises from the segmented ovum, a two-layered germinal disk with long and small hinder primitive mouth. The Evolution of Man — Volume 1

As a matter of fact, we already have the embryo in the stem-cell, the gastrula, and all the subsequent stages. The Evolution of Man — Volume 1

This is not the case in the gastrula of the amphioxus. The Evolution of Man — Volume 1

The gastrula is then formed by invagination, or a kind of turning-up of the edge of the blastoderm. The Evolution of Man — Volume 1

In reality, the whole body of the gastrula is merely a "primitive gut." The Evolution of Man — Volume 2

Thus the formation of the gastrula of our fish is complete. The Evolution of Man — Volume 1

In view of this extraordinary significance of the gastrula, we must make a very careful study of its original structure. The Evolution of Man — Volume 1

While the amphiblastic ova of the latter are small and develop like those of the amphibia, the cucumber-shaped ova of the hag are about an inch long, and form a discoid gastrula. The Evolution of Man — Volume 1

This takes no direct part in the building of the germinal layers, and completely fills the primitive gut-cavity of the gastrula, even protruding at the mouth-opening. The Evolution of Man — Volume 1

Thus the human alimentary canal is as simple as the primitive gut of the gastrula in its original structure. The Evolution of Man — Volume 2

Hence we may derive the discoid gastrula from the original bell-gastrula, through the intermediate stage of the hooded gastrula. The Evolution of Man — Volume 1

As a rule, the cells which compose the two primary germinal layers show appreciable differences even in the gastrula stage. The Evolution of Man — Volume 1

Longitudinal section of the discoid gastrula of the nightingale. The Evolution of Man — Volume 1

In all other animals, particularly the vertebrates, the gastrula is merely a brief transitional stage. The Evolution of Man — Volume 1

In all these stems the gastrula recurs in the same very simple form. The Evolution of Man — Volume 2

By repeated cleavage of it a morula is formed, and from this a blastula, which changes in a very characteristic way into the greatly modified gastrula. The Evolution of Man — Volume 1

The more or less divergent form of gastrula that is produced may be called a secondary, modified gastrula, or a metagastrula. The Evolution of Man — Volume 1

It is clear that the important features which distinguish the discoid gastrula from the other chief forms we have considered are determined by the large food-yelk. The Evolution of Man — Volume 1

We must therefore distinguish carefully between the primitive gut and mouth of the gastrula and the later alimentary canal and mouth of the fully developed vertebrate.* The Evolution of Man — Volume 1

The elaborate alimentary canal of the higher animals develops ontogenetically from the same simple primitive gut of the gastrula. The Evolution of Man — Volume 2

I have in my Natural History of Creation given the name of depula to the remarkable intermediate form which appears at the passage of the blastula into the gastrula. The Evolution of Man — Volume 1

Also, in every case, the gastrula develops from the blastula by curving or invagination. The Evolution of Man — Volume 1

I regard the gastrula as the most important and significant embryonic form in the animal world. The Evolution of Man — Volume 1

The narrow longitudinal groove in it—the so-called "primitive groove"—is, as we have seen, the primitive mouth of the gastrula. The Evolution of Man — Volume 1

If all animals pass through the curious gastrula stage, it must be because they all had a common ancestor of that nature. The Evolution of Man — Volume 1

These two coelom-pouches proceed from the rudimentary mouth of the gastrula, between the two primary layers. The Evolution of Man — Volume 1

Some said that the original embryonic form of the metazoa was not the gastrula, but the "planula"—a double-walled vesicle with closed cavity and without mouth-aperture; the latter was supposed to pierce through gradually. The Evolution of Man — Volume 1

Median longitudinal section of the gastrula of four vertebrates. The Evolution of Man — Volume 1

Either here in the oviduct or after the mammal gastrula has passed into the uterus it is converted into the globular vesicle which is shown externally in Figure 1.106, and in section in Figure 1.107. The Evolution of Man — Volume 1

I am convinced that it is nothing else than the discoid, flattened gastrula of the birds. The Evolution of Man — Volume 1

The cleavage and formation of the gastrula take place in the oviduct. The Evolution of Man — Volume 1

单词	gastrula
例句	gastrula As Prof. Holstein underscores, the data obtained paint a new picture of the predatory lifestyle as a primary characteristic of the cnidarian gastrula. Did animal evolution begin with a predatory lifestyle? 2023-09-29T04:00:00Z This leads to the formation of the next developmental stage, the gastrula, in which the future digestive cavity is formed. Fundamentals of Biology 2015-01-01T00:00:00Z Such hybrids typically die before they reach the gastrula stage, the point in embryonic development at which major cell differences first become obvious. Transplanted Nuclei and Cell Differentiation, by Sir John B. Gurdon 2012-10-09T23:45:00.177Z It has usually been regarded as representing both endoderm and mesoderm, and the groove which usually leads to its formation has been compared to the abnormally elongated blastopore of a typical gastrula. Encyclopaedia Britannica, 11th Edition, Volume 13, Slice 4 "Hero" to "Hindu Chronology" 2012-04-04T02:00:56.447Z Applied to a gastrula when the blastorope does not entirely up. Webster's Unabridged Dictionary 2012-03-24T02:00:23.513Z From the occurrence of the gastrula in all the divisions of the animal kingdom, we may conclude that it is a temporary phase, inevitable in the growth of animals. The Biological Problem of To-day Preformation Or Epigenesis? The Basis of a Theory of Organic Development 2011-08-29T02:01:04.170Z In protostomes, two circular layers of mesoderm form inside the gastrula, containing the coelom cavity. Fundamentals of Biology 2015-01-01T00:00:00Z Toward the end of the blastula stage "transfer" RNA synthesis is first detected; this is followed a few hours later, during the formation of the gastrula, by the synthesis of ribosomal RNA. Transplanted Nuclei and Cell Differentiation, by Sir John B. Gurdon 2012-10-09T23:45:00.177Z This cup-stage is called the gastrula stage; the outer wall of the gastrula is the ectoderm, and its inner the endoderm; while its cavity is the enteron, and the opening to the exterior the blastopore. Encyclopaedia Britannica, 11th Edition, Volume 9, Slice 3 "Electrostatics" to "Engis" 2011-02-06T03:00:53.093Z The primitive enteron or undifferentiated digestive sac of a gastrula or other embryo. Webster's Unabridged Dictionary 2012-03-24T02:00:23.513Z The blastosphere determines the orientation of the gastrula, and so forth. The Biological Problem of To-day Preformation Or Epigenesis? The Basis of a Theory of Organic Development 2011-08-29T02:01:04.170Z As the protostome develops, the mesoderm grows and fuses with the gastrula cell layer. Fundamentals of Biology 2015-01-01T00:00:00Z Slides or diagrams, showing various stages in the development of some animal through the gastrula stage. A Guide for the Study of Animals 2011-01-18T03:00:14.913Z The segmentation is complete; one side of the hollow blastosphere invaginates and forms a gastrula. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 7 "Cerargyrite" to "Charing Cross" This gastrula theory, now generally accepted, is one of Haeckel's two great fundamental contributions to the evolution philosophy with the history of which his life work is so intimately linked. A History of Science, Volume 5(of 5) Aspects Of Recent Science Consider its mode of division, and the formation of the blastula, gastrula, and germinal layers. The Biological Problem of To-day Preformation Or Epigenesis? The Basis of a Theory of Organic Development 2011-08-29T02:01:04.170Z In deuterostomes, two groups of gastrula cells in the blastopore grow inward to form the mesoderm. Fundamentals of Biology 2015-01-01T00:00:00Z This exceedingly important larval form, the "gastrula," makes its appearance in the ontogenesis of all tribes of animals. Was Man Created? The point to remember is, that in all cases a gastrula is an open sac composed of two layers of cells—the outer layer being called the ectoderm, and the inner the endoderm. Darwin, and After Darwin (Vol. 1 and 3, of 3) An Exposition of the Darwinian Theory and a Discussion of Post-Darwinian Questions The gastrula in section, anterior end to the right. Text Book of Biology, Part 1: Vertebrata Invagination, the infolding of a layer of cells, as, for instance, in the transformation of a blastosphere into a gastrula, xvii. The Biological Problem of To-day Preformation Or Epigenesis? The Basis of a Theory of Organic Development 2011-08-29T02:01:04.170Z The archenteron develops into the alimentary canal, and a mouth opening is formed by invagination of ectoderm at the pole opposite the blastopore of the gastrula. Fundamentals of Biology 2015-01-01T00:00:00Z The gastrula stage was the palingenetic repetition of the ancestral form of all Metazoa, the Gastræa. Form and Function A Contribution to the History of Animal Morphology Before the egg of the frog becomes an elliptical mass of cells, it is at one time a double-walled sac enclosing a central cavity; in this stage it is called a gastrula. The Doctrine of Evolution Its Basis and Its Scope There is no open invagination of an archenteron in the fowl, as in the frog--, the gastrula, like the blastosphere, stage is also masked. Text Book of Biology, Part 1: Vertebrata From causes of which we are ignorant two, instead of one, gastrula stages may arise at separate regions of the germinal layer of the egg. The Biological Problem of To-day Preformation Or Epigenesis? The Basis of a Theory of Organic Development 2011-08-29T02:01:04.170Z But how is an adult worm or vertebrate formed out of such a gastrula? The Whence and the Whither of Man A Brief History of His Origin and Development through Conformity to Environment; Being the Morse Lectures of 1895 The gastrula, finally, is the two-layered sac formed from the blastula, typically by invagination of its wall. Form and Function A Contribution to the History of Animal Morphology In other words, the starting point in the development of the frog is a single biological unit; this divides and its products redivide to constitute the many-celled blastula and the double-walled gastrula. The Doctrine of Evolution Its Basis and Its Scope We naturally assume, from what we have learnt, that the next stages will be the formation of a hollow blastosphere, invagination, a gastrula forming mesoblast by hollow outgrowths from the archenteron, and so on. Text Book of Biology, Part 1: Vertebrata In the gastrula stage, the segmentation cavity in which the mesoblast is formed lies between the entoblast and ectoblast. The Gutenberg Webster's Unabridged Dictionary Section S And our ancestor was almost certainly a free swimming gastræa, or hypothetical form corresponding in form and structure to the gastrula. The Whence and the Whither of Man A Brief History of His Origin and Development through Conformity to Environment; Being the Morse Lectures of 1895 A corresponding germinal condition, the two-layered gastrula, occurs transitorily in the embryological history of all the other Metazoa, from the lowest Cnidaria and Vermes up to man. Monism as Connecting Religion and Science A Man of Science This cavity is the primitive alimentary cavity or archenteron; the inner or invaginated layer is the hypoblast; the outer the epiblast; and the embryo, in this stage, is termed a gastrula. Darwiniana : Essays — Volume 02 Figure 7 i. is a dorsal view of the gastrula at a somewhat later stage, and here indications of distinctly vertebrate relationships already appear. Text Book of Biology, Part 1: Vertebrata The Gastraea bilateralis, of which we may conceive the bilateral gastrula of the amphioxus to be a palingenetic reproduction, represented the two-sided organism of the earliest Metazoa in its simplest form. The Evolution of Man — Volume 2 Between the ectoderm and entoderm of the gastrula, in the space occupied by the supporting membrane of hydra, a new layer of cells, the mesoderm, appears. The Whence and the Whither of Man A Brief History of His Origin and Development through Conformity to Environment; Being the Morse Lectures of 1895 The point of origin is always the properistoma, the border of the original primitive mouth of the gastrula, at which the two primary layers pass directly into each other. The Evolution of Man — Volume 1 From the gastrula type the higher sub- divisions of animal life probably diverged, as separate branches from a common trunk. The Elements of Geology Such a gastrula, formed mainly by overgrowth of the epiblast, is called an epibolic gastrula, as distinguished from the invaginate gastrula of amphioxus. Text Book of Biology, Part 1: Vertebrata The solid foundation of this important thesis is the gastrula, the most instructive embryonic form in the animal world, which we still find in the same shape in the most diverse classes of animals. The Evolution of Man — Volume 2 But our mid-intestine is still the greatly elongated archenteron of the gastrula. The Whence and the Whither of Man A Brief History of His Origin and Development through Conformity to Environment; Being the Morse Lectures of 1895 The chief of the viscera in the body-cavity is the alimentary canal, the organ that represents the whole body in the gastrula. The Evolution of Man — Volume 1 We give the name of the gastrula to the important embryonic form that has these primitive organs, and the name of gastrulation to the formation of it. The Evolution of Man — Volume 1 With what lower type has the gastrula been compared? Text Book of Biology, Part 1: Vertebrata Probably it differed from the existing gastrula only in one essential point, though extinct millions of years ago. The Evolution of Man — Volume 2 We may therefore compare the hydra or gastrula to a little portion of the lining of the human mid-intestine covered with a little flake of epidermis. The Whence and the Whither of Man A Brief History of His Origin and Development through Conformity to Environment; Being the Morse Lectures of 1895 In fact, these variations have become so great in the course of time that the segmentation was not rightly understood in most animals, and the gastrula was unrecognised. The Evolution of Man — Volume 1 In the growth of this hooded gastrula we cannot sharply mark off the various stages which we distinguish successively in the bell-gastrula as morula and gastrula. The Evolution of Man — Volume 1 All animals that have little yolk, and start early in life for themselves, pass through a gastrula stage, substantially the same as this of amphioxus. Text Book of Biology, Part 1: Vertebrata In accordance with the biogenetic law, we find solid proof of this in the fact that the two-layered embryos of all the Metazoa can be reduced to a primitive common type, the gastrula. The Evolution of Man — Volume 2 Take a boiled egg, make a hole in the smaller end and remove the yolk, and you have a passable model of a gastrula. The Whence and the Whither of Man A Brief History of His Origin and Development through Conformity to Environment; Being the Morse Lectures of 1895 The authors who regard this embryonic form as the primary gastrula of the placental conceive the outer layer as the ectoderm and the inner as the entoderm. The Evolution of Man — Volume 1 There are many difficulties in the way of understanding this partial segmentation and the gastrula that arises from it. The Evolution of Man — Volume 1 The young amphioxus has, at this stage, which is called the gastrula stage, a curious parallelism with such a lowly form as the Hydra of our ditches. Text Book of Biology, Part 1: Vertebrata The actual ontogenetic development of the gastrula from the blastula furnishes sound evidence as to the phylogenetic origin of the Gastraea from the Blastaea. The Evolution of Man — Volume 2 Both the blastosphere and gastrula often swim freely by flagella. The Whence and the Whither of Man A Brief History of His Origin and Development through Conformity to Environment; Being the Morse Lectures of 1895 The uni-axial type of the mammal gastrula is accentuated in this way. The Evolution of Man — Volume 1 However, opinions still differ considerably as to the real nature of this "provisional gastrula" of the placental and its relation to the blastula into which it is converted. The Evolution of Man — Volume 1 This stage is called the gastrula stage; ar. is the cavity of the gastrula, the archenteron; b.p. is its opening or blastopore. Text Book of Biology, Part 1: Vertebrata From the epidermis of the gastrula a medullary tube is formed on the dorsal side, and, between this and the primitive gut, a chorda; these are the organs that are otherwise only found in Vertebrates. The Evolution of Man — Volume 2 But this small white "germinal disk" is now further developed, and is really the gastrula of the chick. The Evolution of Man — Volume 1 In the bell-gastrula of the amphioxus and in the hooded gastrula of the lamprey and the frog the germinal layers are found to be closed tubes or vesicles from the first. The Evolution of Man — Volume 1 This white region at the south pole corresponds, as we shall see afterwards, to the primitive mouth of the gastrula. The Evolution of Man — Volume 1 Nevertheless, the gastrula is formed here, as in the previous cases, by the folding or invagination of the blastula. The Evolution of Man — Volume 1 In the Amphioxus the earliest and most important embryonic processes take place so rapidly that the blastula is formed in four hours, the gastrula in six, and the typical vertebrate form in twenty-four. The Evolution of Man — Volume 2 In both cases a discoid gastrula with primitive streak arises from the segmented ovum, a two-layered germinal disk with long and small hinder primitive mouth. The Evolution of Man — Volume 1 As a matter of fact, we already have the embryo in the stem-cell, the gastrula, and all the subsequent stages. The Evolution of Man — Volume 1 This is not the case in the gastrula of the amphioxus. The Evolution of Man — Volume 1 The gastrula is then formed by invagination, or a kind of turning-up of the edge of the blastoderm. The Evolution of Man — Volume 1 In reality, the whole body of the gastrula is merely a "primitive gut." The Evolution of Man — Volume 2 Thus the formation of the gastrula of our fish is complete. The Evolution of Man — Volume 1 In view of this extraordinary significance of the gastrula, we must make a very careful study of its original structure. The Evolution of Man — Volume 1 While the amphiblastic ova of the latter are small and develop like those of the amphibia, the cucumber-shaped ova of the hag are about an inch long, and form a discoid gastrula. The Evolution of Man — Volume 1 This takes no direct part in the building of the germinal layers, and completely fills the primitive gut-cavity of the gastrula, even protruding at the mouth-opening. The Evolution of Man — Volume 1 Thus the human alimentary canal is as simple as the primitive gut of the gastrula in its original structure. The Evolution of Man — Volume 2 Hence we may derive the discoid gastrula from the original bell-gastrula, through the intermediate stage of the hooded gastrula. The Evolution of Man — Volume 1 As a rule, the cells which compose the two primary germinal layers show appreciable differences even in the gastrula stage. The Evolution of Man — Volume 1 Longitudinal section of the discoid gastrula of the nightingale. The Evolution of Man — Volume 1 In all other animals, particularly the vertebrates, the gastrula is merely a brief transitional stage. The Evolution of Man — Volume 1 In all these stems the gastrula recurs in the same very simple form. The Evolution of Man — Volume 2 By repeated cleavage of it a morula is formed, and from this a blastula, which changes in a very characteristic way into the greatly modified gastrula. The Evolution of Man — Volume 1 The more or less divergent form of gastrula that is produced may be called a secondary, modified gastrula, or a metagastrula. The Evolution of Man — Volume 1 It is clear that the important features which distinguish the discoid gastrula from the other chief forms we have considered are determined by the large food-yelk. The Evolution of Man — Volume 1 We must therefore distinguish carefully between the primitive gut and mouth of the gastrula and the later alimentary canal and mouth of the fully developed vertebrate.* The Evolution of Man — Volume 1 The elaborate alimentary canal of the higher animals develops ontogenetically from the same simple primitive gut of the gastrula. The Evolution of Man — Volume 2 I have in my Natural History of Creation given the name of depula to the remarkable intermediate form which appears at the passage of the blastula into the gastrula. The Evolution of Man — Volume 1 Also, in every case, the gastrula develops from the blastula by curving or invagination. The Evolution of Man — Volume 1 I regard the gastrula as the most important and significant embryonic form in the animal world. The Evolution of Man — Volume 1 The narrow longitudinal groove in it—the so-called "primitive groove"—is, as we have seen, the primitive mouth of the gastrula. The Evolution of Man — Volume 1 If all animals pass through the curious gastrula stage, it must be because they all had a common ancestor of that nature. The Evolution of Man — Volume 1 These two coelom-pouches proceed from the rudimentary mouth of the gastrula, between the two primary layers. The Evolution of Man — Volume 1 Some said that the original embryonic form of the metazoa was not the gastrula, but the "planula"—a double-walled vesicle with closed cavity and without mouth-aperture; the latter was supposed to pierce through gradually. The Evolution of Man — Volume 1 Median longitudinal section of the gastrula of four vertebrates. The Evolution of Man — Volume 1 Either here in the oviduct or after the mammal gastrula has passed into the uterus it is converted into the globular vesicle which is shown externally in Figure 1.106, and in section in Figure 1.107. The Evolution of Man — Volume 1 I am convinced that it is nothing else than the discoid, flattened gastrula of the birds. The Evolution of Man — Volume 1 The cleavage and formation of the gastrula take place in the oviduct. The Evolution of Man — Volume 1
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