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Gastrulation

Gastrulation, Biology Lecture | Sabaq

The term gastrulation means the formation of gut (Greek, gastrula = belly), but has now a more broad sense to to describe the formation of the trilaminar embryo. The epiblast layer, consisting of totipotential cells, derives all 3 embryo layers: ectoderm , mesoderm and endoderm Gastrulation. Gastrulation is a central process in mammalian development in which a spatiotemporally coordinated series of events driven by cross-talk between adjacent embryonic and extra-embryonic tissues results in stereotypical morphogenetic cell behaviors, massive cell proliferation and the acquisition of distinct cell identities Gastrulation is the process that takes place after blastulation. Gastrulation is the process by which the germ layers of the cells are formed by the arrangement of cells in the blastula. When cleavage or division takes place in the blastula, then due to this process the gastrula is formed Gastrulation Definition. Gastrulation is the process during embryonic development that changes the embryo from a blastula with a single layer of cells to a gastrula containing multiple layers of cells. Gastrulation typically involves the blastula folding in upon itself or dividing, which creates two layers of cells Gastrulation is a formative process by which the three germ layers, which are precursors of all embryonic tissues, and the axial orientation are established in embryos. During gastrulation, the bilaminar embryonic disc is converted into a trilaminar embryonic disc

Gastrulation means gut forming and converts the inner cell mass which then formed the bilaminar embryo (epiblast, hypoblast) into the trilaminar embryo (ectoderm, mesoderm, endoderm). The process involves the migration of cells from the epiblast layer through the primitive streak to form first the endoderm layer and then a second intermediate layer the mesoderm layer Gastrulation involves changes in cell motility, cell shape, and cell adhesion. Below are schematic diagrams of the major types of cell movements that occur during gastrulation. Invagination: a sheet of cells (called an epithelial sheet) bends inward تكوُّن المُعَيدَة أو تكوُّن الجسْترولَة (بالإنجليزية: Gastrulation)‏ هي مرحلةٌ أولية في التطور الجنيني لمعظم الحيوانات، حيثُ يحدث فيها إعادة ترتيبٍ للأريمة وحيدة الطبقة لتصبح هيكلًا مُتعدد الطبقات يُعرف باسم المُعيْدة.

Gastrulation - Embryolog

  1. Early embryogenesis - Cleavage, blastulation, gastrulation, and neurulation Our mission is to provide a free, world-class education to anyone, anywhere. Khan Academy is a 501(c)(3) nonprofit organization
  2. Gastrulation is a fundamental phase of animal embryogenesis during which germ layers are specified, rearranged, and shaped into a body plan with organ rudiments. The term gastrulation, derived from the Greek word gaster, denoting stomach or gut, is a fundamental process of anima
  3. Gastrulation is a process of cellular rearrangement which involves migration, invagination and differentiation of the epiblast. It is largely controlled and orchestrated by the primitive streak. The primitive streak is a groove in the midline of the epiblast which appears during the third week
  4. The germ disc is composed of epiblast and hypoblast. In the embryo of pig, the gastrulation activities are observed at two centres—the posterior end forms the primitive streak while the anterior end forms the Hensen's node. The behaviour of these portions is almost similar to that observed in the gastrulation of chick
  5. ar embryonic disc undergoes reorganization to form three primary germ layers. This is just.

Gastrulatie is een fase aan het begin van de embryonale ontwikkeling van de meeste dieren.In deze fase wordt de enkellaagse blastocyste gereorganiseerd in een meerlagige structuur die de gastrula heet. Vóór de gastrulatie is het embryo een kiemblad (een epitheelblad van cellen); tegen het einde van de gastrulatie is het embryo begonnen met differentiatie om verschillende cellijnen te bepalen. Gastrulation is a developmental phenomenon by which a relatively limited number of blastodermal cells undergoes a stereotypical set of cellular movements tha.. Gastrulation is a morphogenetic process that results in the formation of mesoderm and the generation of a three germlayered embryo composed of ectoderm. mesoderm. and endoderm. In the mouse. gastrulation also leads to the formation of a transient specialized structure called the node that generates new tissues with axis patterning activities (see below )

Gastrulation - an overview ScienceDirect Topic

Gastrulation is a necessary process that occurs in all multicellular organisms except for sponges. Sponges are unique among multicellular animals in that they do not contain multiple tissue types. La gastrulation correspond à la seconde phase de développement embryonnaire lors de laquelle la mitose est en continuel ralentissement. C'est la période durant laquelle les mouvements morphogéniques permettent le remaniement des blastomères qui se répartissent en 2 ou 3 feuillets: un feuillet externe, un feuillet moyen présent seulement chez les triploblastiques et un feuillet interne. La gastrulation, comme stade du développement embryonnaire de tous les animaux, a été découverte. La gastrulation est une étape précoce du développement embryonnaire d'un animal. À ce stade, l'embryon est appelé une gastrula. D'importants mouvements cellulaires mettent en place les. Gastrulation. Late in the second week after fertilization, gastrulation occurs when a blastula, made up of one layer, folds inward and enlarges to create a gastrula. A gastrula has 3 germ layers--the ectoderm, the mesoderm, and the endoderm.Some of the ectoderm cells from the blastula collapse inward and form the endoderm 原腸胚形成 (Gastrulation)是大部分動物胚胎發育中都會經歷的一個階段。. 在本階段中,只有一層細胞的囊胚會發生重組,形成一個含有三個胚層(即 外胚層 (ectoderm)、 中胚層 (mesoderm)、 內胚層 (endoderm))細胞的 原腸胚 (gastrula) 。. 原腸胚形成發生於 卵裂 之後,原腸胚形成完成後,胚胎進入原腸胚時期,開始 器官發生 (英語:organgenesis) 過程。. 新形成的三.

Gastrulation occurs according to a conserved series of movements defined by their morphogenetic outcome; emboly (internalization), epiboly, and convergence and extension 1 - blastula, 2 - gastrula; orange - ektoderm, röd - endoderm. Gastrulan är en fas i den embryotiska utvecklingen som ses hos alla djur förutom svampdjuren. Den följer blastula -fasen. Gastrulan uppkommer genom att den blåsformiga blastulans cellmaterial på något ställe förs in i embryots inre, vanligen genom inbuktning och bildar en.

Medical Definition of gastrulation. : the process of becoming or of forming a gastrula The process of gastrulation allows for the formation of the germ layers in metazoan embryos, and is generally achieved through a series of complex and coordinated cellular movements. The process of gastrulation can be either diploblastic or triploblastic. In diploblastic organisms like cnidaria or ctenophora, only the endoderm and the ectoderm.

Gastrulation - Explanation, Stage, Formation and Gastrulatio

Gastrulation is a phase in embryonic development during which the single layered blastula develops into a three layered gastrula. Gastrulation takes place after cleavage. The cells in the blastula rearrange themselves spatially to form three layers of cells in a process known as gastrulation. During gastrulation the blastula folds in on itself to form three germ layers :-- the ectoderm, the. Gastrulation. The typical blastula is a ball of cells. The next stage in embryonic development is the formation of the body plan. The cells in the blastula rearrange themselves spatially to form three layers of cells in a process known as gastrulation. During gastrulation, the blastula folds upon itself to form the three layers of cells

Gastrulation - Definition and Types Biology Dictionar

Gastrulation: it's Definition, Mechanisms and Significance! Definition: It is a process by which blastocyst is changed into a gastrula larva with three primary germ layers. It starts immediately after implantation. In this, cells of blastodermic vesicle visibly move in small masses to their final and pre-determined positions Gastrulation involves the drastic reshuffling of the blastula's cells into these three germinal layers, which in turn become the various organ systems of the animal's body. Gastrulation consists of the inward movement, or invagination, of the cells of one side of the blastula until they are juxtaposed to the opposite side; thus the. Transformation of the blastula or blastocyst into the gastrula; the development and invagination of the embryonic germ layers. In human embryos, gastrulation is the process by which the bilaminar embryonic disk is converted into a trilaminar embryonic disk Gastrulation is a phase early in the embryonic development of most animals during which the single-layered blastula is reorganized into a trilaminar (three-layered) structure known as the gastrula. These three germ layers are known as the ectoderm, mesoderm, and endoderm. Gastrulation: Formation of the three primary germ layers occurs during.

Gastrulation, die erste Phase der Bildung der Keimblätter in der frühen Embryonalentwicklung, die durch das Einwandern von Entoderm und Mesoderm, die später die inneren Organe ausbilden, in das Innere des Keims gekennzeichnet ist. Dabei bildet sich durch Zellbewegungen und -verlagerungen aus der. Gastrulation is arguably the most important evolutionary innovation in the animal kingdom. This process provides the basic embryonic architecture, an inner layer separated from an outer layer, from which all animal forms arise. An extraordinarily simple and elegant process of gastrulation is. Gastrulation. At the time of midblastula transition, gastrulation begins. The first movements of Drosophila gastrulation segregate the presumptive mesoderm, endoderm, and ectoderm. The prospective mesoderm—about 1000 cells constituting the ventral midline of the embryo—folds inward to produce the ventral furrow . This furrow eventually. Gastrulation (von griech.gaster Magen) bezeichnet eine Phase der Embryogenese der vielzelligen Tiere, zu denen auch der Mensch gehört.Dabei stülpt sich die Blastula ein und es kommt zur Ausbildung der Keimblätter.Vorausgegangen ist die Ausbildung des Blasenkeimes, die sogenannte Blastulation.Dem britischen Entwicklungsbiologen Lewis Wolpert wird folgendes Zitat über die Gastrulation.

Epiboly describes one of the five major types of cell movements that occur in the Gastrulation stage of embryonic development of some organisms. Epibolic movement is the way in which a layer epithelial cells spreads. This can be achieved in multiple ways. When undergoing epiboly, a monolayer of cells must undergo a physical change in shape in order to spread. Alternatively, multiple layers of. Accordingly, all cells moving through the PS during the first day of gastrulation express Eomes AM and DE specification occurs before cells leave the PS from Eomes-positive progenitors in a distinct spatiotemporal pattern

Dai, H. Q. et al. TET-mediated DNA demethylation controls gastrulation by regulating Lefty-Nodal signalling. Nature 538 , 528-532 (2016). Google Schola GASTRULATION By:R.E.MALEKSHAH SHAHID BEHESHTI MEDICAL UNIVERSITY 3. TWO-GERM-LAYER STAGE Epiblast and Hypoblast Formation Just before the embryo implants early in the second week, cells of the inner cell mass become rearranged into an epithelial configuration. (embryonic shield). The main upper layer (epiblast), and the lower layer (hypoblast. La gastrulación es el proceso mediante el cual se forma, a partir de la migración de poblaciones celulares ubicadas en el epiblasto, un embrión trilaminar. [1] Forma parte del desarrollo embrionario y ocurre después de la formación de la blástula, esto es, que sigue a la de segmentación o clivaje, y tiene como consecuencia la formación de las capas fundamentales del embrión (capas. Gastrulation is a phase early in the development of most animal embryos.In it the embryo is dramatically restructured by cell migration.. Gastrulation varies in different phyla.It is followed by organogenesis, when individual organs develop within the newly formed germ layers.. The gastrula is the double-walled stage of the embryo. During gastrulation, some of the cells of the blastula migrate. GASTRULATION. gastrula, from the Greek word gaster,.meaning stomach The 2nd major phase of embryonic dvtThe embryo is transformed from hollow ball of cells (the blastula) into a 3-layered stage Gastrula A dramatic re-arrangement of the cells of the blastula Cells are given new positions and new neighbours, and the multilayered body plan of

Gastrulation is the process of germ layer formation. Three germ layers (ectoderm, mesoderm and endoderm) are formed during gastrulation. The pattern of gastrulation is similar in mammals and avian species. In mammals, the hypoblast and epiblast are derived from the inner cell mass. The primitive streak acts as the initiation site for gastrulation Gastrulation is a fundamental phase of animal embryogenesis during which germ layers are specified, rearranged, and shaped into a body plan with organ rudiments. Gastrulation involves four evolutionarily conserved morphogenetic movements, each of which results in a specific morphologic transformation. During emboly, mesodermal and endodermal cells become internalized beneath the ectoderm. In mice, ActRIA is expressed primarily in the extraembryonic visceral endoderm before gastrulation and later in both embryonic and extraembryonic cells during gastrulation. To elucidate its function in mouse development, we disrupted the transmembrane domain of ActRIA by gene targeting Gastrulation and neurulation. ibrahim shdeifat يونيو 21, 2021. YouTube. Medical Sciences Animations. 7.39K subscribers. Subscribe. Gastrulation and Neurulation Animated I Embryology I Early Embryogenesis. Watch later. Copy link Setting up for gastrulation in zebrafish Curr Top Dev Biol. 2020;136:33-83. doi: 10.1016/bs.ctdb.2019.08.002. Epub 2019 Sep 3. Author Florence L Marlow 1 Affiliation 1 Icahn School of Medicine Mount Sinai Department of Cell, Developmental and Regenerative Biology, New York, NY, United States. Electronic address: florence.marlow@mssm.edu..

Gastrulation is the process by which the germ layers become positioned in an embryo. C. elegans gastrulation serves as a model for studying the molecular mechanisms of diverse cellular and developmental phenomena, including morphogenesis, cell polarization, cell-cell signaling, actomyosin contraction and cell-cell adhesion Media in category Gastrulation. The following 63 files are in this category, out of 63 total. Arquénteron.jpg 1,066 × 1,061; 73 KB. CENTROLECITHES.png 351 × 540; 12 KB. Play media. Control-of-Directed-Cell-Migration-In-Vivo-by-Membrane-to-Cortex-Attachment-pbio.1000544.s009.ogv 6.2 s, 264 × 264; 701 KB. Play media gastrulation. 名詞. 1. 原腸胚 が 細胞の 内部移動 によって 胞胚 から 発達する 過程. (the process in which a gastrula develops from a blastula by the inward migration of cells) 「gastrulation」に関する類語一覧. 索引 用語索引 ランキング We hypothesized that small chemicals that interrupt zebrafish gastrulation might also suppress metastatic progression of cancer cells and developed a phenotype-based chemical screen to test the hypothesis. The screen used epiboly, the first morphogenetic movement in gastrulation, as a marker and enabled 100 chemicals to be tested in five hours

gastrulation: Search Ontology: Synonyms: Definition: A complex and coordinated series of cellular movements that occurs at the end of cleavage during embryonic development of most animals. The details of gastrulation vary from species to species, but usually result in the formation of the three primary germ layers, ectoderm, mesoderm and endoderm As gastrulation continues, the cells that got pulled into the frog blastula will arrange themselves so the innermost layer is the endoderm. On top of this is the mesoderm, which will exist in. The embryo in the stage of development following the blastula or blastocyst; in lower forms with minimal yolk, it is a simple double-layered structure consisting of ectoderm and endoderm enclosing the archenteron, which opens to the outside by way of the blastopore; in forms with considerable yolk, the configuration of the gastrula is greatly modified owing to the persistence of the yolk. Gastrulation. Gastrulation was initiated at the 32-cell stage, 1 h 50 min after fertilization at 13°C. This is rather earlier than in ascidians (at the 110-cell stage, for example, 9 h after fertilization at 13°C in Halocynthia) and other vertebrates. Internalization of the vegetal cells proceeded by ingression, keeping the embryonic outline. Gastrulation. The formation of the primordial gut, the archenteron, or digestive cavity of an early animal embryo. More generally, and originally, the term gastrulation referred to the process by which the gastrula stage of the embryo is formed. Thus to nineteenth-century embryologists, gastrulation was the process by which the single-layered.

Gastrulation is the formation of the three principal germ layers—endoderm, mesoderm and ectoderm. Understanding the formation of the basic body plan is not only important to reveal how the. Define gastrulation. gastrulation synonyms, gastrulation pronunciation, gastrulation translation, English dictionary definition of gastrulation. intr.v. gas·tru·lat·ed , gas·tru·lat·ing , gas·tru·lates To form or become a gastrula. gas′tru·la′tion n. American Heritage® Dictionary of the English.. Examples of how to use gastrulation in a sentence from the Cambridge Dictionary Lab A time-resolved, high-resolution model charts differentiation dynamics during mouse gastrulation and reveals that for most lineages, cell fates arise from multi-furcation events rather than classical tree-like bifurcation

Gastrulation in frog embryo. The process of gastrulation is a continuous activity succeeding, cleav-age. During this process the blastodermal cells begin to move. They wander and occupy their prospective organ forming zones. During this movement at one region on the blastula, the cells wander inside and occupy the blastocoelic cavity Synonyms for gastrulation in Free Thesaurus. Antonyms for gastrulation. 8 words related to gastrulation: growing, growth, ontogenesis, ontogeny, maturation, development, biological process, organic process. What are synonyms for gastrulation Gastrulation is a phase early in the development of animal embryos, during which the morphology of the embryo is dramatically restructured by cell migration.Gastrulation varies in different phyla. Gastrulation is followed by organogenesis, when individual organs develop within the newly formed germ layers Gastrulation is the formation of the three principal germ layers—endoderm, mesoderm and ectoderm. Understanding the formation of the basic body plan is not only important to reveal how the fertilized egg gives rise to an adult organism, but also how congenital diseases arise

Gastrulation in the sea urchin embryo involves two separable morphogenetic processes: ingression of primary mesenchyme cells and invagination of the archenteron, or the primitive gut. As a consequence of gastrulation, cells of the embryo are rearranged to establish the early body plan of the larval stage. Most sea urchin embryos develop indirectly Gastrulation—wherein cells of the embryonic epiblast simultaneously segregate and differentiate into the three primary germ layers: ectoderm, mesoderm, and endoderm—requires precise coordination of morphogenesis and cell fate specification. The morphogenesis that occurs during gastrulation relies on cell tension and tissue-level forces to.

Gastrulation is the formation of the three principal germ layers - endoderm, mesoderm and ectoderm. Understanding the formation of the basic body plan is not only important to reveal how the. Gastrulation is a key event in embryonic development when the germ layers are specified and the basic animal body plan is established. The complexities of primate gastrulation remain a mystery because of the difficulties in accessing primate embryos at this stage During gastrulation, ventrolateral cells of has2 morphant embryos fail to develop lamellipodia and to migrate dorsally, resulting in a blockage of dorsal convergence, whereas extension of the dorsal axis is normal. The effect is cell autonomous, suggesting that HA acts as an autocrine signal to stimulate the migration of HA-generating cells The term gastrulation is applied to the process which produces the gastrula (Greek: gaster, stomach). It is a process of highly coordinated cell and tissue movement whereby the cells of the blastula are rear­ranged to form the-three germ layers ecto­derm, mesoderm and endoderm

Gastrulation- Process, Consequences Developmental

Gastrulation is the process of cell movements that give rise to the primary germ layers of the embryo. The initial positions and neighbors of the blastomeres is determined by the pattern of cleavages. New positions and neighbor relationships are determined by the pattern of cell movements at gastrulation Gastrulation is a key embryonic event during which the three-dimensional framework of an animal is established. Indeed, it has been said that 'it is not birth, marriage or death, but gastrulation which is truly the most important time in your life' (Slack, 1991).Generally speaking, the process of gastrulation accomplishes two goals 3. Gastrulation, Cellular Movements and Formation of Three Germ Layers Gastrulation follows cleavage. During gastrulation, extensive cellular movements and rearrangements lead to formation of the three germ layers. The cells fated to become the endoderm and the mesoderm enter the inside of the embryo, whereas the ectoderma Morten Vejlsted, Hanne Offenberg, Flemming Thorup, Poul Maddox‐Hyttel, Confinement and clearance of OCT4 in the porcine embryo at stereomicroscopically defined stages around gastrulation, Molecular Reproduction and Development, 10.1002/mrd.20461, 73, 6, (709-718), (2006)

BGDA Practical 3 - Gastrulation - Embryolog

Dès le début de la gastrulation les cellules épiblastiques produisent de l'acide hyaluronique, qui s'accumule dans l'espace intercellulaire entre l'épiblaste et l'hypoblaste. L'acide hyaluronique est fréquemment associé à la migration cellulaire. Cette molécule peut lier massivement l'eau (jusqu'à 1000 fois son propre poids !) et. Gastrulation is fundamental to the development of multicellular animals. Along with neurulation, gastrulation is one of the major processes of morphogenesis in which cells or whole tissues move from the surface of an embryo to its interior. Cell internalization mechanisms that have been discovered to date in Caenorhabditis elegans gastrulation bear some similarity to internalization mechanisms. Gastrulation in Chick: Its Significance and Mechanism! In the chick, the process of gastrulation is prolonged and highly modified than that of frog and Amphioxus. It is already started when the egg of chick is laid and completes well into the second day of in cubation. The main characteristic of avian gastrulation is primitive streak Start studying Biology 205 - Gastrulation (3.1). Learn vocabulary, terms, and more with flashcards, games, and other study tools Description During gastrulation, tissue layers are formed and the overall body plan is established. This book is the definitive guide to this vitally important period in embryonic development, providing authoritative and up to date information that includes the first comprehensive interspecies comparison, cell movements and patterning events, the roles of individual genes and gene families.

Video: Chapter 14. Gastrulation and Neurulatio

تكون المعيدة - ويكيبيدي

Gastrulation is the fundamental process during the embryogenesis of all multicellular animals through which the basic body plan is first laid down. It is pivotal in generating cellular diversity coordinated with spatial patterning. Gastrulation in humans occurs in the third week following fertilization. Our understanding of this process in humans is extremely limited, and based almost entirely. Gastrulation and the Formation of Germ Layers Gastrulation involves extensive and highly integrated cell and tissue movements, resulting in dramatic rearrangement of cells of the blastula. Gastrulation converts the spherical blastula into a more complex configuration of three germ layers. At the end of gastrulation, the ectoderm covers the. Protein involved in gastrulation, a stage in early embryogenesis in which cell movements result in a massive reorganization of the embryo from an initially unstructured group of cells, the blastula, into a multi-layered organism. During gastrulation, the primary germ layers (endoderm, mesoderm, and ectoderm) are formed and organized in their. Fr om Cleavage T o Gastrulation Dr . Ann-Judith Silverman Department of Anatomy & Cell Biology T elephone: 5-3450 Email: as36@columbia.edu. 2 Hypoblast: Bottom layer (facing the blastocoel) of the 2-layered embryo. Plays a role in establishing polarity but does not contribute cells to the embryo

La gastrulation: Après environ 4 heures d'incubation, les cellules du blastoderme subissent des mouvements coordonnés qui marquent le début de la gastrulation. Deux zones se distinguent par leur texture ; l'aire opaque, périphérique qui entoure l'aire pellucide, centrale (Fig.3) gastrulation ( plural gastrulations ) ( embryology, biology) The stage of embryo development at which a gastrula is formed from the blastula by the inward migration of cells Gastrulation involves a series of cell migrations to positions where they will form the three primary cell layers. Ectoderm forms the outer layer. Endoderm forms the inner layer. Mesoderm forms the middle layer. Ectoderm. Ectoderm forms tissues associated with outer layers: skin, hair, sweat glands, epithelium. The brain and nervous system also.

We would like to show you a description here but the site won't allow us Development of a chick was the difficult most thing in my study of Biology. In the whole chapter of Growth and Development, I paid a lot of time in understanding this topic. The most difficult part is the Gastrulation and, in it, the Notochord formation and Neurulation. Unfortunately, in the book of FSc II, ther

Human embryogenesis (article) Embryology Khan Academ

A single-cell molecular map of mouse gastrulation and early organogenesis. This is the accompanying interactive server for the paper A single-cell molecular map of mouse gastrulation and early organogenesis. Please note: when you reach this page, the server needs to load some data for your session Gastrulation results in the production of the three germ layers and sets the stage for the formation of the coelom, a space completely enclosed in mesoderm.Your body cavity— the space between the gut and body wall— is a coelom (see Concept 23.1).Because of the coelom, gut contractions and heartbeats are independent of an animal's outer body wall Gastrulation (Deutsch): ·↑ Evolutionsbiologie: Forscher knacken Evolutionscode - FOCUS Online. In: FOCUS Online. 11. Oktober 2007, ISSN 0943-7576 (URL, abgerufen am 3. Juli 2020) .· ↑ Claus Thomsen: Der Mensch ist doch kein Auto - WELT. In: Welt Online. 13. August 2004, ISSN 0173-8437 (URL, abgerufen am 3. Juli 2020) .· ↑ Berthold Hatschek. Gastrulation is a super-process, if you will, that involves a number of processes taking place simultaneously and co-ordinately, to achieve the formation of the three germ layers and the extraembryonic mesoderm for the extraembryonic membranes. While most of us would recognise the onset of gastrulation at the time when we observe the first.

The evolutionary origin of gastrulation—defined as a morphogenetic event that leads to the establishment of germ layers—remains a vexing question. Central to this debate is the evolutionary relationship between the cell layers of sponges (poriferans) and eumetazoan germ layers. Despite considerable attention, it remains unclear whether sponge cell layers undergo progressive fate. Gastrulation = formation of germinative layers − epiblast of the primitive streak o contributes to the ectoderm o migrates to the hypoblast and replaces it by forming the embryonic entoderm o migrates between the ecto- a entoderm = embryonic (secondary) mesoderm − trilaminar gastrula with ecto-, meso- and entoder gastrulation [6] varies across species, studies in Xenopus have shed considerable light on the process in general. The raw material for gastrulation [6] is the blastula [16], a hollow sphere of cells; the space inside of theb lastula [16] is called the blastocoel [17]

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