Embryonic Similarities

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Embryo Noun

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[em-bree-oh]

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Embryo

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An organism in its earliest stages of development, after fertilization but before birth, hatching, or germination.

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Example: This image shows a developing human embryo next to a ruler, demonstrating its small size (about 1.5 cm) and basic form.

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Zygote Noun

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[zy-goat]

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Zygote

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The initial single cell formed by the fusion of gametes at fertilization, which then develops into an embryo.

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Example: This diagram shows that a zygote is the single cell formed when a sperm cell fertilizes an egg cell, combining genetic material from both.

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Blastula Noun

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[blas-tyoo-luh]

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Blastula

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An early stage of embryonic development in animals, which consists of a hollow ball of cells surrounding a fluid-filled cavity.

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Example: This diagram shows a blastula, an early stage of an embryo. It is a hollow ball of cells with a fluid-filled cavity (blastocoel).

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Gastrula Noun

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[gas-troo-luh]

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Gastrula

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The embryonic stage following the blastula, when the embryo infolds to form the three primary germ layers.

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Example: The gastrula is an early embryo stage with distinct cell layers called the ectoderm and endoderm, which will later form different body parts.

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Germ Layers Noun

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[jurm lay-ers]

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Germ Layers

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The primary layers of cells that form during early embryonic development and differentiate to form all tissues and organs.

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Example: This diagram shows the three primary germ layers in an embryo's cross-section: the outer ectoderm (blue), middle mesoderm (green), and inner endoderm (orange).

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Notochord Noun

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[noh-tuh-kord]

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Notochord

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A flexible, rod-like structure that forms the main support of the body in early chordate embryos, providing a scaffold.

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Example: This diagram shows the notochord, a flexible rod-like structure (in red), located beneath the neural tube in an early embryo.

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Pharyngeal Arches Noun

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[fuh-rin-jee-uhl arch-es]

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Pharyngeal Arches

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A series of bulges in the neck region of a vertebrate embryo that develop into gills or other structures.

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Example: This diagram shows pharyngeal arches, which are structures in a developing embryo that form parts of the head, face, and neck.

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Post-Anal Tail Noun

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[post-ay-nuhl tayl]

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Post-Anal Tail

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A tail that extends beyond the anus, present in all vertebrate embryos at some stage of their development.

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Example: This fossil shows the skeleton of an ancient animal with a long tail extending past its main body, a clear example of a post-anal tail.

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Somite Noun

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[soh-myt]

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Somite

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One of a series of paired blocks of tissue that form along the main body axis in a developing embryo.

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Example: This diagram shows a somite, a block of tissue in an embryo, dividing into parts that will form the skeleton (sclerotome), muscles (myotome), and skin (dermatome).

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Limb Bud Noun

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[lim buhd]

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Limb Bud

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A small paddle-shaped protrusion on an embryo's body that develops into a limb like a leg, arm, or wing.

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Example: This diagram shows a limb bud, the initial structure that develops into an arm or leg, and labels the key zones that control its growth.