embryo: Quick Facts

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Last updated

Oct. 18, 2026

News •

Embryos harbor immune cells that already perform adult-like defense functions, study suggests • Oct. 19, 2026, 6:20 PM ET (Medical Xpress)

AI reveals a shared language guiding cell development • Oct. 16, 2026, 11:20 AM ET (Phys.org)

Photos and Videos

Diagram showing early human embryo development. The top row illustrates ovum cleavage from a single cell to a morula. The bottom row shows blastocyst formation and implantation, with labeled cell structures.

embryos of different animals

Labeled diagram of an amniotic egg showing the embryo surrounded by membranes including the amnion, chorion, yolk sac, and allantois, with albumin, amniotic fluid, yolk, and shell also identified.

Diagram showing the development of external genitalia in human embryos, with labeled illustrations comparing undifferentiated, female, and male stages at 12 and 36 weeks, highlighting anatomical changes during fetal growth.

Three labeled cross-section diagrams show the development of a human embryo implanted in the uterine lining at 7.5, 13, and 23 days, highlighting structures such as the embryonic disk, amniotic cavity, yolk sac, trophoblast, and chorion.

Two labeled diagrams show the human embryonic disk at 18 days: a three-quarter view and a cross-section, highlighting structures such as the amniotic cavity, yolk sac, embryonic shield, body stalk, and layers including ectoderm, mesoderm, and endoderm.

Diagram showing three stages in early human embryonic development: the growth of the amnion at 23 days, a back view of an embryo at 21 days with the amnion cut open revealing neural structures, and a side view at 23 days with the yolk sac and amnion cut open, highlighting the heart, brain, spinal cord, and umbilical blood vessels.

Diagram showing human embryological and fetal development in three stages: at six weeks, the embryo is enclosed within halved amnion, chorion, and uterus; another view at six weeks highlights the formation of the umbilical cord; at three months, the fetus is shown within the halved amnion, chorion, and uterus, with the placenta and umbilical cord labeled.

Cross-sectional medical illustration of a human uterus at seven weeks of pregnancy, showing the developing embryo inside the amniotic sac, placenta, umbilical cord, uterine wall layers, cervix, and vagina, with labeled anatomical structures related to gestation and embryology.

Follow the development of rice-paddy fish from fertilization to hatching in a laboratory setting

Close-up illustration of a human fetus inside the womb, showing the developing baby holding the umbilical cord in a warm, reddish environment.

See a movie illustrating wounded cells releasing signaling molecules causing a wave of calcium signaling

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Topics

sexual differentiation gestational age embryonic germ cell primordial germ cell embryonic stem cell bulbus aortae genital tubercle limb bud milk line placentation adolescence old age infancy puberty adulthood fetus zygote Larva childhood aging

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Key People

Hwang Woo Suk and Gerald Schatten

Hwang Woo-Suk

South Korean scientist

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Moon Shin Yong

South Korean obstetrician

Ohsumi, Yoshinori

Yoshinori Ohsumi

Japanese biologist

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Étienne Geoffroy Saint-Hilaire

French naturalist

Julian Huxley

Sir Julian Huxley

British biologist

Christiane Nüsslein-Volhard

Christiane Nüsslein-Volhard

German geneticist

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Sir John Graham Kerr

British biologist

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Eric F. Wieschaus

American developmental biologist

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C.H. Waddington

British embryologist

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Steen Willadsen

Danish embryologist

Belon, detail from an engraving

Pierre Belon

French naturalist

Fabricius ab Aquapendente, oil painting by an unknown artist

Hieronymus Fabricius ab Aquapendente

Italian surgeon

William Brooks

William Keith Brooks

American zoologist

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Aleksandr Onufriyevich Kovalevsky

Russian embryologist

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Martin H. Rathke

German anatomist