Carnegie stages
In embryology
Embryology is a science which is about the development of an embryo from the fertilization of the ovum to the fetus stage...

, Carnegie stages are a standardized system of 23 stages used to provide a unified developmental chronology of the vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...

An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...


The stages are delineated through the development of structures, not by size or the number of days of development, and so the chronology can vary between species, and to a certain extent between embryos. It only covers the first 60 days of development; at that point the term embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

 is usually replaced with the term fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...


It was based on work by Streeter (1942) and O'Rahilly and Müller (1987). The name "Carnegie stages" comes from the Carnegie Institution of Washington
Carnegie Institution for Science
The Carnegie Institution for Science is an organization in the United States established to support scientific research....


While the Carnegie stages provide a universal system for staging and comparing the embryonic development of most vertebrates, other systems are occasionally used for the common model organism
Model organism
A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms. Model organisms are in vivo models and are widely used to...

s in developmental biology
Developmental biology
Developmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis", which is the process that gives rise to tissues, organs and anatomy.- Related fields of study...

, such as the Hamburger-Hamilton stages
Hamburger-Hamilton stages
In developmental biology, the Hamburger-Hamilton stages are a series of 46 chronological stages in chick development, starting from laying of the egg and ending with a newly hatched chick. It is named for its creators, Viktor Hamburger and Howard L. Hamilton.Chicken embryos are a useful model...

 in the chick
The chicken is a domesticated fowl, a subspecies of the Red Junglefowl. As one of the most common and widespread domestic animals, and with a population of more than 24 billion in 2003, there are more chickens in the world than any other species of bird...



Days are approximate, and reflect the days since the last ovulation
Ovulation is the process in a female's menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum . Ovulation also occurs in the estrous cycle of other female mammals, which differs in many fundamental ways from the menstrual cycle...

 before pregnancy
Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...

 ("Postovulatory age").

Stage 2: 2-3 days

  • cleavage
    Cleavage (embryo)
    In embryology, cleavage is the division of cells in the early embryo. The zygotes of many species undergo rapid cell cycles with no significant growth, producing a cluster of cells the same size as the original zygote. The different cells derived from cleavage are called blastomeres and form a...

  • morula
    A morula is an embryo at an early stage of embryonic development, consisting of cells in a solid ball contained within the zona pellucida....

  • compaction

Stage 5 (a-c): 7-12 days

  • implantation
  • embryonic disk
    Embryonic disk
    The floor of the amniotic cavity is formed by the embryonic disk composed of a layer of prismatic cells, the embryonic ectoderm, derived from the inner cell-mass and lying in apposition with the endoderm....

  • bilaminar germ disk
  • primary yolk sac
    Yolk sac
    The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...

  • amniotic cavity
    Amniotic cavity
    The amniotic cavity is the closed sac between the embryo and the amnion, containing the amniotic fluid. The amniotic cavity is formed by the fusion of the parts of the amniotic fold, which first makes its appearance at the cephalic extremity, and subsequently at the caudal end and sides of the embryo...

Stage 6: ca 17 days

  • primitive streak
    Primitive streak
    The primitive streak is a structure that forms during the early stages of avian, reptilian and mammalian embryonic development.-Introduction:...

  • primitive groove
    Primitive groove
    A shallow groove, the primitive groove, appears on the surface of the primitive streak, and the anterior end of this groove communicates by means of an aperture, the blastophore, with the yolk-sac....

  • chorionic villi
    Chorionic villi
    Chorionic villi are villi that sprout from the chorion in order to give a maximum area of contact with the maternal blood.Embryonic blood is carried to the villi by the branches of the umbilical arteries, and after circulating through the capillaries of the villi, is returned to the embryo by the...

  • secondary yolk sac
    Yolk sac
    The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...

Stage 7: ca 19 days

  • gastrulation
    Gastrulation is a phase early in the embryonic development of most animals, during which the single-layered blastula is reorganized into a trilaminar structure known as the gastrula. These three germ layers are known as the ectoderm, mesoderm, and endoderm.Gastrulation takes place after cleavage...

  • neural plate
    Neural plate
    In human embryology, formation of neural plate is the first step of neurulation. It is created by a flat thickening opposite to the primitive streak of the ectoderm.-Development:...

  • start of hematopoiesis
  • notochord
    The notochord is a flexible, rod-shaped body found in embryos of all chordates. It is composed of cells derived from the mesoderm and defines the primitive axis of the embryo. In some chordates, it persists throughout life as the main axial support of the body, while in most vertebrates it becomes...

Stage 9: ca 25 days

  • neural groove
    Neural groove
    The neural groove is a shallow median groove between the neural folds of an embryo. The neural folds are two longitudinal ridges that are caused by a folding up of the ectoderm in front of the primitive streak of the developing embryo...

  • neural folds
    Neural folds
    In front of the primitive streak two longitudinal ridges, caused by a folding up of the ectoderm, make their appearance, one on either side of the middle line...

  • septum transversum
    Septum transversum
    The septum transversum is a thick mass of cranial mesenchyme that gives rise to parts of the thoracic diaphragm and the ventral mesentery of the foregut in the developed human being.- Origins :...

  • placode
    A neurogenic placode is an area of thickening in the embryonic epithelial layer where some organ or structure later develops. The term usually refers to cranial placodes, peripheral nervous system structures associated with the special senses and cranial ganglia...

  • early heart
    The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...

Stage 10: ca 28 days

  • pharyngeal arches #1 and #2
  • cardiac loop
  • intermediate mesoderm
    Intermediate mesoderm
    Intermediate mesenchyme or intermediate mesoderm is a type of mesoderm that is located between the paraxial mesoderm and the lateral plate.It develops into the part of the urogenital system * forms of urogenital system...

External links

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