Carnegie Stages

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Carnegie stages species comparison

Carnegie stages are named after the famous US Institute which began collecting and classifying embryos in the early 1900's. Stages are based on the external and/or internal morphological development of the embryo, and are not directly dependent on either age or size. The human embryonic period proper is divided into 23 Carnegie stages covering the first 8 weeks post-ovulation. Criteria beyond morphological features include ranges of age in days, number of somites present, and embryonic crown rump lengths (CRL).

Note that many photographs of staged (using Carnegie criteria) human embryos on this current site are from the Kyoto collection in collaboration with Prof Kohei Shiota and Prof Shigehito Yamada. Scanning electron micrographs are published in collaboration with Prof Kathy Sulik.

Links: Embryonic Development | Carnegie Stage Comparison | Carnegie Institution - Contributions to Embryology | Human Embryo Collections

Embryo Collections: Human Embryo Collections | Embryo Collections | Blechschmidt Collection | Carnegie Collection | Domenech-Mateu Collection | Harvard Collection | Hill Collection | Hinrichsen Collection | Hubrecht Collection | Kyoto Collection | Madrid Collection | Embryology Models | DEC Information | DEC
Carnegie Stages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | About Stages | Timeline

Carnegie Embryos

Human Carnegie stage 10-23.jpg

Embryo/Fetal Definition

The division of human development into an embryonic (embryo) and fetal (fetus) periods was an historically based arbitrary system. Defined by the probability that more than 90 percent of the identifiable structures of the adult body have appeared by Carnegie stage 23.

Streeter also defined the fetal period as beginning when the humerus cartilage was replaced by bone marrow.

There have been several other human systems of embryo categorisation developed, sometimes to establish a standard between species. To prevent confusion and consistency with the historic literature the Carnegie stages are used for human development on this site.


The following text and information about the collection is modifed from the original Carnegie Institute website.

Franklin Mall (1911)

Franklin Mall

Franklin P. Mall (1862-1917) is most remembered for his work done at the Department of Embryology at the Carnegie Institute of Washington. Mall began collecting human embryos while a postgraduate student in Lepzig with Wilhelm His, but didn't receive the first Carnegie specimen until his position at Johns Hopkins University. (More? Franklin Mall)

Franklin Mall Links: Franklin Mall | 1891 26 Day Human Embryo | 1905 Blood-Vessels of the Brain | 1906 Human Ossification | 1910 Manual of Human Embryology 1 | 1912 Manual of Human Embryology 2 | 1911 Mall Human Embryo Collection | 1912 Heart Development | 1915 Tubal Pregnancy | 1916 Human Magma in Normal and Pathological Development | 1917 Frequency Human Abnormalities | 1917 Human Embryo Cyclopia | 1918 Embryo Age | 1918 Appreciation | 1934 Franklin Mall biography PDF | Mall photograph | Mall painting | Mall painting | Carnegie Stages | Carnegie Embryos | Carnegie Collection | Category:Franklin Mall

Surprizingly age and size proves a poor way to organize embryos. It is very difficult to accurately age an embryo, and it could shrink a full 50% in the preserving fluids. Mall took it upon himself to find a better way. He had more success basing his "staging" scheme on morphological characteristics. To that end, Mall and his colleagues not only prepared and preserved serial sections of the embryos, they also made hundreds of three-dimensional models at different stages of growth. According to Adrianne Noe, who managed the collection at the National Museum of Health and Medicine, Mall gathered the most renowned scientists, scholars, artists, photographers, and craftspeople ever to apply their interests and skills to embryology.

Links: Franklin Mall

George Streeter

George Linius Streeter (1873-1948)

Began as an assistant professor at the Wistar Institute of Anatomy and Biology in Philadelphia, then went to the University of Michigan as professor of gross anatomy. In 1914, he became research professor in the department of embryology of the Carnegie Institution, at the Johns Hopkins Medical School under Franklin Mall and succeeded him as director of the Carnegie Institution.

Links: George Streeter

Collection Location

The embryo collection is now held at the National Museum of Health and Medicine, located at the Walter Reed Army Medical Center in Washington, D.C. the Carnegie collection is still available for use by researchers. The raw data, which will be copyright free, may be made available to all legitimate researchers and students. HDAC - Agreement Policies

Contributions to Embryology

The Contributions to Embryology are a historic series of papers published by the Carnegie Institution of Washington early in the 20th Century. Many of the collection embryos were first described and characterised in these papers and from serial sectioning of these embryos.

The 1920 volume (Volume IX) was prepared as a memorial by present and former members of the staff of the Institute to the late Professor Franklin Paine Mall.

Links: Carnegie Institution of Washington Series | Volume IX
Carnegie Institution logo

Carnegie Institute Staff 1935.jpg

Carnegie Institute Staff (1935)

James F. Didusch

James Didusch plate (1921)

James F. Didusch (1890 - 1955) was a medical illustrator in the Department of Art as Applied to Medicine, Johns Hopkins. He was the main illustrator for the Carnegie Institute of Embryology (1913-1955) with his drawings and plates forming the main visual component of many Carnegie publications. There has been a 1992 article on his artistic contribution to embryology[1] and his papers are held in the Alan Mason Chesney Medical Archives at Johns Hopkins.

Links: James Didusch

Osborne O. Heard

One of the first to be hired, in 1913, was modeler Osborne O. Heard, who spent 42 years at the department and made over 700 wax-based reconstructions.

The results of this team effort still stand as the international standard by which human embryos are described and classified.

The models were mainly made by the lost-wax casting process and his models were also more detailed than the earlier (1880's) Ziegler embryo models.

Osborne Heard (1891 – 1983) produced many embryo model reconstructions for the Carnegie Institute.

Links: Osborne Heard

Carnegie Collection Embryos

iBook - Carnegie Embryos  
link= iTunes link
  • iTunes link | iBook Store
  • Description - Imagine the excitement of seeing this incredible early period of human development for the first time. Now consider that much of our initial understanding of human development is based upon study of historic embryo collections. You can now look at these historic images of the first 8 weeks after fertilisation and explore for yourself the changes that occur in human development during this key period. This current book is designed as an atlas of the Carnegie embryo stages with some brief notes and additional information covering the first 8 weeks of development. These images are from from the beginning of last century and are one of the earliest documented series of human embryos collected for basic research and medical education on development. I hope you enjoy learning about the amazing early events that begin to make and shape us. This is the second book in a series of educational releases from UNSW Embryology.
  • Release: First Edition - Mar 12, 2012 ISBN 978-0-7334-3148-7 Print Length 82 Pages, 25.8 MB Language English.
  • PDF Preview version 3.87 MB (Read the associated information, this is an edited educational preview version with many features not functioning).
  • The current website also includes numerous embryo images from this textbook (see Embryonic Development and Carnegie Embryos).
Week: 1 2 3 4 5 6 7 8
Carnegie stage: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Stage 3

Stage 4

Stage 5

Stage 6

Stage 7

Stage 10

Stage 11

Stage 12

Stage 13

Stage 14

Stage 15

Stage 16

Stage 17

Stage 18

Stage 19

Stage 20

Stage 21

Stage 22

Stage 23

Carnegie Human Embryo Glossary


Postovulatory age is one criterion for the overall staging of embryos.

It is the length of time since the last ovulation before fertilization took place and is estimated by assigning an embryo to a developmental stage and then referring to a standard table of norms. A range of +/- 1 day is expected. Postovulatory age is stated in days or weeks.

Case Number

The basis of the Carnegie Collection of Embryos was Franklin P. Mall's personal collection of 813 embryos, which he began in 1887 with the first specimen. Carnegie Embryo No. 1. was acquired by Mall while he was an assistant in Pathology at the Johns Hopkins Hospital. All subsequent specimens in the Collection were numbered sequentially at the time of acquisition, i.e. case number.

Crown-Rump (C-R)

Crown Rump Length (CRL) Stage 13 embryo

One criterion for the overall classification of human embryonic development.

A measurement of prenatal length, from the vertex of the skull (crown), along the curvature of the spine to the midpoint between the apices of the buttocks (rump), of the developing embryo. This measurement was developed for smaller specimens, 35mm or less, so that their natural curved posture is not disturbed. C-R length is stated in millimeters.

An alternative measurement of prenatal length is the greatest length (G.L.), which some researchers find to be more useful in the assessment of length of an embryo. The G.L. is determined by measuring the embryo in a straight line, (i.e. caliper length) without any attempt to straighten the natural curvature of the specimen. G.L. is stated in millimeters.


Specimens in the Carnegie Collection have been graded Excellent, Good, Fair or Poor.

This reference is based on the total grade of the specimen, including both its original quality and the condition of the specimen.


Of the approximately 600 sectioned embryos in the Carnegie Collection assigned to the 23 stages, a majority have been classified as normal. However, variations in, and anomolies of, individual organs are known to occur.

Section Information

Plane of Section

The surface formed by extension through an axis of the embryo.

There are three primary descriptive terms referring to the planes of the embryo:

  1. Coronal A vertical plane dividing the body into anterior and posterior portions.
  2. Sagittal Any plane parallel to the median.
  3. Transverse A plane horizontal to the median.

Thinness of Section

The specified thinness of the cut embryonic section for mounting on a glass slide in serial order. Thinness is measured in micrometers. Some regions of a few of the specimens in the Collection were cut at various thinnesses; these instances are represented in the search results.


Total number of glass slides containing serial histologic sections of each specimen in the Collection.


Total number of serial histologic sections on any number of glass slides for each specimen in the Collection.


Gender identification, i.e. male or female, is noted where apparent. In the embryo, the gonads do not acquire male or female morphological characteristics until the 7th or 8th week of development (stages 18-23). Therefore, many specimens in the embryonic period are not identified by gender. This assignment applies mostly to very late embryonic period specimens in the Collection.


One criterion for the overall classification of human embryonic development.

Somites are paired segments of paraxial mesoderm appearing in longitudinal rows along the left and right side of the neural groove and notochord. They commence in the third or early fourth week of development (approximately the 20th day), appearing first in the cervical region of the embryo. Their formation proceeds in a craniocaudal direction. New somites appear approximately three per day, until at the end of the 5th week when 42 to 44 pairs are present. Differentiation of the somites leads to formation of the axial skeleton.

Stage of Development

The definitive classification of human embryos into developmental groups termed stages.

Stages are based on the external and/or internal morphological development of the embryo, and are not directly dependent on either age or size. The human embryonic period proper is divided into 23 Carnegie stages.

Criteria beyond morphological features include age in days, number of somites present, and embryonic length. This chart shows the relationship between Stage, Age and embryonic length.

Stain Type

The type of individual dye or staining substance, or combination of dyes and reagents, used in histologic technique to color the constituents of cells and tissues.

Carnegie Stage Table

Weeks shown in the table below are embryonic post ovulation age, for clinical Gestational Age (GA) measured from last menstrual period, add 2 weeks.

Days (approx)
(not to scale)
(week 1)
0.1 - 0.15
Human zygote two pronuclei 02.jpg
fertilized oocyte, zygote, pronuclei
2 - 3
0.1 - 0.2
Human embryo day 3.jpg
morula cell division with reduction in cytoplasmic volume, blastocyst formation of inner and outer cell mass
4 - 5
0.1 - 0.2
Human embryo day 5.jpg
loss of zona pellucida, free blastocyst
5 - 6
0.1 - 0.2
Week2 001 icon.jpg
attaching blastocyst
7 - 12
(week 2)
0.1 - 0.2
Stage5 bf11L.jpg
13 - 15
Stage6 bf03.jpg
extraembryonic mesoderm, primitive streak, gastrulation
15 - 17
(week 3)
Stage7 features.jpg
gastrulation, notochordal process
17 - 19
1.0 - 1.5
Stage8 bf4.jpg
primitive pit, notochordal canal
19 - 21
1.5 - 2.5
Stage9 dorsal.jpg
Somitogenesis Somite Number 1 - 3 neural folds, cardiac primordium, head fold
22 - 23
(week 4)
2 - 3.5
Stage10 bf4b.jpg
Somite Number 4 - 12 neural fold fuses
23 - 26
2.5 - 4.5
Stage11 bf7b.jpg
Somite Number 13 - 20 rostral neuropore closes
26 - 30
3 - 5
Stage12 bf5b.jpg
Somite Number 21 - 29 caudal neuropore closes
28 - 32
(week 5)
4 - 6
Stage13 bf2c.jpg
Somite Number 30 leg buds, lens placode, pharyngeal arches
Stage 13/14 shown in serial embryo sections series of Embryology Program
31 - 35
5 - 7
Stage14 bf2c.jpg
lens pit, optic cup
35 - 38
7 - 9
Stage15 bf1c.jpg
lens vesicle, nasal pit, hand plate
37 - 42
(week 6)
8 - 11
nasal pits moved ventrally, auricular hillocks, foot plate
42 - 44
11 - 14
Stage17 bf1c.jpg
finger rays
44 - 48
(week 7)
13 - 17
Stage18 bf1c.jpg
ossification commences
48 - 51
16 - 18
Stage19 bf1c.jpg
straightening of trunk
51 - 53
(week 8)
18 - 22
Stage20 bf1c.jpg
upper limbs longer and bent at elbow
53 - 54
22 - 24
Stage21 bf1c.jpg
hands and feet turned inward
Stage 22 shown in serial embryo sections series of Embryology Program
54 - 56
23 - 28
Stage22 bf1c.jpg
eyelids, external ears
56 - 60
27 - 31
Stage23 bf1c.jpg
rounded head, body and limbs
Following this stage Fetal Development occurs until birth (approx 37 weeks)

The embryos shown in the table are from the Kyoto and Carnegie collection and other sources.


  1. A R Altemus The life and work of James F. Didusch. J Biocommun: 1992, 19(2);8-21 PubMed 1624478

Carnegie Stages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | About Stages | Timeline

Glossary Links

Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link

Cite this page: Hill, M.A. (2018, December 12) Embryology Carnegie Stages. Retrieved from

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© Dr Mark Hill 2018, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G