Pharyngula
Encyclopedia
In developmental biology
, the pharyngula is a stage in embryo
nic development. Named by William Ballard, the pharyngula stage follows the blastula
, gastrula and neurula
stages. At the pharyngula stage, all vertebrate
embryos show remarkable similarities, containing the following features:
The branchial grooves are matched on the inside by a series of paired gill pouches. In fish, the pouches and grooves eventually meet and form the gill slits, which allow water to pass from the pharynx
over the gills and out the body.
In the other vertebrates, the grooves and pouches disappear. In humans, the chief trace of their existence is the eustachian tube and auditory canal which (interrupted only by the eardrum) connect the pharynx with the outside of the head.
The existence of a common pharyngula stage for vertebrates was first proposed by German
biologist Ernst Haeckel
(1834–1919) in 1874.
Developmental biology
Developmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis", which is the process that gives rise to tissues, organs and anatomy.- Related fields of study...
, the pharyngula is a stage in embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
nic development. Named by William Ballard, the pharyngula stage follows the blastula
Blastula
The blastula is a hollow sphere of cells formed during an early stage of embryonic development in animals . The blastula is created when the zygote undergoes the cell division process known as cleavage. The blastula is preceded by the morula and is followed by the gastrula in the developmental...
, gastrula and neurula
Neurula
A Neurula is an embryo at the early stage of development in which neurulation occurs.Neurulation is the development of the nervous system in the vertebrates, at the thickened area above the notochord in ectoderms. The neural plate will fold to produce the neural tube which will develop into the...
stages. At the pharyngula stage, all vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
embryos show remarkable similarities, containing the following features:
- notochordNotochordThe notochord is a flexible, rod-shaped body found in embryos of all chordates. It is composed of cells derived from the mesoderm and defines the primitive axis of the embryo. In some chordates, it persists throughout life as the main axial support of the body, while in most vertebrates it becomes...
- dorsal hollow nerve cordNerve cordNerve cord may refer to the following structures:* in invertebrates, it refers to the ventral nerve cord, whereas* in chordates, it stands for the dorsal nerve cord....
- post-anal tail, and
- a series of paired branchial grooves.
The branchial grooves are matched on the inside by a series of paired gill pouches. In fish, the pouches and grooves eventually meet and form the gill slits, which allow water to pass from the pharynx
Pharynx
The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...
over the gills and out the body.
In the other vertebrates, the grooves and pouches disappear. In humans, the chief trace of their existence is the eustachian tube and auditory canal which (interrupted only by the eardrum) connect the pharynx with the outside of the head.
The existence of a common pharyngula stage for vertebrates was first proposed by German
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
biologist Ernst Haeckel
Ernst Haeckel
The "European War" became known as "The Great War", and it was not until 1920, in the book "The First World War 1914-1918" by Charles à Court Repington, that the term "First World War" was used as the official name for the conflict.-Research:...
(1834–1919) in 1874.
See also
- Evolutionary developmental biologyEvolutionary developmental biologyEvolutionary developmental biology is a field of biology that compares the developmental processes of different organisms to determine the ancestral relationship between them, and to discover how developmental processes evolved...
- EmbryogenesisEmbryogenesisEmbryogenesis is the process by which the embryo is formed and develops, until it develops into a fetus.Embryogenesis starts with the fertilization of the ovum by sperm. The fertilized ovum is referred to as a zygote...
- Embryo drawing
- Recapitulation theoryRecapitulation theoryThe theory of recapitulation, also called the biogenetic law or embryological parallelism—and often expressed as "ontogeny recapitulates phylogeny"—is a disproven hypothesis that in developing from embryo to adult, animals go through stages resembling or representing successive stages...