Essential Embryology Terms and Definitions
Arquenteron
The primary digestive tract.
Blastocoele
The cavity within the blastula, located between the ectoderm and endoderm; also known as the segmentation cavity.
Blastoderm
A layer of cells (blastomeres) forming the wall of a blastula; also known as a blastodisc.
Blastodisc
A blastula where the blastomeres form a disk floating on an unsegmented yolk.
Blastomere
A cell of the embryo during the early stages of cell division.
Blastopore
The opening between the blastomeres of the blastula that leads into the interior of the embryo during gastrulation.
Blastula
An embryo that results from the segmentation (cleavage) of a fertilized egg.
Coelom
A fluid-filled cavity produced by the approximation of lateral mesoderm plates.
Neural Crest
Groups of cells on both sides of the neural tube, which will be the source of future nerves and related structures.
Ectoderm
The outermost germ layer of the vertebrate gastrula (one of the three primary germ layers).
Endoderm
The innermost germ layer of the vertebrate gastrula (one of the three primary germ layers).
Spermatogenesis
The process of sperm formation.
Spermiogenesis
The process of maturation of spermatids into spermatozoa.
Stomodeum
An epidermal invagination that forms the primitive mouth and anterior part of the digestive tract.
Fertilization
The fusion of a male gamete with a female gamete, producing a cell (zygote) with new genetic properties.
Fetus
An embryo that has acquired the general appearance of the mature organism.
Gastrula
An embryo that is formed after the process of gastrulation.
Gastrulation
A stage of embryogenesis characterized by a set of embryonic cell movements that reorganize the embryo into the three germ layers.
Gonads
The term designating the gamete-producing organs of animals.
Hypoblast
The inner layer of cells in the vertebrate blastodisc, contributing to extraembryonic membranes.
Larva
A free-living embryonic stage, capable of independent existence, often differing significantly in appearance from the adult animal.
Meiosis
Two successive cell divisions with the mission to produce four haploid cells from one diploid cell.
Mesoderm
The middle germ layer of the gastrula (one of the three primary germ layers).
Fertilization Membrane
An acellular membrane that forms around the egg during fertilization.
Zona Pellucida
An acellular membrane surrounding the mammalian egg.
Morula
An embryo in the course of segmentation, whose appearance is similar to a mulberry.
Myotome
A region of the somite that will differentiate into striated muscle.
Neuropore
The anterior or posterior opening of the neural tube.