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This page shows some key events of human development during the embryonic period of the first eight weeks (weeks 1 - 8) following fertilization. This period is also considered the organogenic period, when most organs within the embryo have begun to form. There are links to more detailed descriptions which can be viewed in a week by week format, by the Carnegie stages or integrated into a Timeline of human development. Online resources available include: individual images of all Carnegie stages, scanning electron micrographs of the earlier stages, cross-sections showing internal structures at mid- and late-embryonic, 3D reconstructions of internal structures, animations of processes, ultrasound scans and information about abnormalites of development.

Embryo Images Normal and Abnormal Mammalian Development is a tutorial that uses scanning electron micrographs (SEMs) as the primary resource to teach mammalian embryology. The 3-D like quality of the micrographs coupled with selected line drawings and minimal text allow relatively easy understanding of the complex morphological changes that occur in utero. Because early human embryos are not readily available and because embryogenesis is very similar across mammalian species, the majority of micrographs that are utilized in this tutorial are of mouse embryos. The remainder are human.

This case study was written for an introductory course for biology majors who are first learning about embryonic development. The case is composed of several parts and involves a storyline about a team of researchers who find frogs and eggs in bamboo plants during a field study. Students consider what these observations mean, learn basics about the stages of animal embryonic development, and make connections to phylogeny and natural selection. Students then apply their understanding of animal embryonic stage development to the chemical atrazine in the environment by examining data from several experiments. As a concluding activity students write a letter to an agency or newspaper of their choosing stating their opinion surrounding the use of atrazine in the environment. The case proceeds in a progressive disclosure format and involves a combination of class discussion, small group work, and homework. Because the case focuses on very basic animal embryonic development, it would also be a great start to a developmental biology course or an embryology course.

For years whale evolution was characterized by speculation and limited evidence. Evolution critics even focused on whales as a means to criticize evolutionary theory. Now whale evolution represents one of the best examples of "macroevolution." This "clicker case" uses this fascinating story of historical irony as a backdrop to the study of whale evolution. First, students study an array of whale fossils to learn how evolution is properly viewed as a branching, relationship-based process, not a linear, progressive, "chain-of-being." Using this view they learn how scientists seek to reconstruct past relationships and study transitional features, not search for "missing links." Students then learn that evidence for macroevolution relies on several lines of independent evidence from fossils, comparative anatomy, embryology, genetics, and paleoecology. With a focus on macroevolution, this case makes a critical contribution to evolution education. It could work well in a lower level undergraduate biology / evolution / paleontology course (non-majors or majors), or in an upper-level evolution course, perhaps early in the semester as a primer for related topics.

Fertization through early embryogenesis video 4:13

The Visible Embryo is a visual guide through fetal development from fertilization through pregnancy to birth. As the most profound physiologic changes occur in the "first trimester" of pregnancy, these Carnegie stages are given prominence on the birth spiral.

LifeMap Discovery® is a compendium of embryonic development for stem cell research and regenerative medicine, constructed by integrating extensive molecular, cellular, anatomical and medical data curated from scientific literature and high-throughput data sources.

Odyssey of life animations: human, pig, chicken, and fish embryos