Concept
Embryo
Overview
An embryo ( EM-bree-oh) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm cell. The resulting fusion of these two cells produces a single-celled zygote that undergoes many cell divisions that produce cells known as blastomeres. The blastomeres are arranged as a solid ball that when reaching a certain size, called a morula, takes in fluid to create a cavity called a blastocoel. The structure is then termed a blastula, or a blastocyst in mammals.
The mammalian blastocyst hatches before implantating into the endometrial lining of the womb. Once implanted the embryo will continue its development through the next stages of gastrulation, neurulation, and organogenesis. Gastrulation, possibly induced in part by paracrine signalling from the amnion, is the formation of the three germ layers that will form all of the different parts of the body. Neurulation forms the nervous system, and organogenesis is the development of all the various tissues and organs of the body.
A newly developing human is typically referred to as an embryo until the ninth week after conception, when it is then referred to as a fetus. In other multicellular organisms, the word embryo can be used more broadly to any early developmental or life cycle stage prior to birth or hatching.
Overview adapted from Wikipedia (CC BY-SA 4.0; see the article history for authors).
In the original texts
Passages from public-domain books where Embryo is discussed.
And in some whole groups of animals and in certain members of other groups, the embryo does not at any period differ widely from the adult: thus Owen has remarked in regard to cuttle-fish, “there is no metamorphosis; the cephalopodic character is manifested long before the parts of the embryo are completed;” and again in spiders, “there is nothing worthy to be called a metamorphosis.” The larvæ of insects, whether…
Charles Darwin, On the Origin of Species By Means of Natural Selection
names the idea; states what it is; opens on it
Plato says, that the embryo is an animal; for, being contained in the mother's womb, motion and aliment are imparted to it. The Stoics say that it is not an animal, but to be accounted part of the mother's belly; like as we see the fruit of trees is esteemed part of the trees, until it be full ripe; then it falls and ceaseth to belong to…
Plutarch, Complete Works of Plutarch — Volume 3
names the idea; states what it is; opens on it
We have a remarkable instance of substitution in the temporary appliances for respiration, which some embryos exhibit. During the first phase of its development, the mammalian embryo possesses a system of blood-vessels distributed over what is called the _area vasculosa_--a system of vessels homologous with one which, among fishes, serves for aërating the blood until the permanent respiratory organs come into play…
Herbert Spencer, The Principles of Biology, Volume 1
names the idea; states what it is; opens on it
With plants, hybridized embryos probably often perish in a like manner; at least it is known that hybrids raised from very distinct species are sometimes weak and dwarfed, and perish at an early age; of which fact Max Wichura has recently given some striking cases with hybrid willows.
Charles Darwin, The Origin of Species by Means of Natural Selection
states what it is; names the idea; opens on it
These changes through which the general structure of the embryo is marked out with slowly-increasing precision, are paralleled in the evolution of each organ. The heart is at first a mere aggregation of cells, of which the inner liquify to form the cavity, while the outer are transformed into the walls; and when thus sketched out, the heart is indefinite not only as being…
Herbert Spencer, First Principles
states what it is; names the idea
Related ideas
- Genetic engineering
- Ancient Greek
- Embryology
- Organism
- Nervous system
- Snake
- Cell (biology)
- Dinosaur
- Medieval Latin
Opposing perspectives
Place in the tradition
Part of Philosophy.