When was the embryo discovered

New Discoveries in Embryology. Human embryology in the 19th century began by using human embryo samples derived from maternal deaths, abortion, or surgery.

Nothing has been changed in the 21st century, because animal experimental biology developed in the 20th century could not and should not apply to human embryology on its ethical aspect. However, human embryology has progressed little during the last years, with only recently some limited molecular studies on small numbers of human material.

In contrast, recent studies using both nondestructive and destructive imaging techniques on existing collections have allowed many morphological measurements of these embryos using these novel imaging techniques.

Here we summarize the historic collections of embryos used in the study of human development, explain the criteria used for developmental staging, show sectioned and reconstructed images from newer three-dimensional 3D imaging in high resolution, and discuss the future directions for the analyses of the human embryo. During the history of human embryology the establishment and study of key human embryo collections has greatly contributed to our current understanding.

In this section we briefly summarize the history of some of these collections, such as the Carnegie Collection, the Kyoto Collection, the Blechschmidt Collection, and the Madrid Collection Table 1. Not included in this chapter will be descriptions of the smaller, less described human embryo collections, species comparative embryo collections, or collections that are of nonembryonic material, such as placenta.

An example of a mainly human placenta and early implanted uterus is the Hamilton-Boyd Collection in Cambridge. Note that many anatomy departments hold their own small collections of human material that are not covered here. A key factor in understanding the developmental morphological changes is the possession of human embryo samples at sequential developmental stages.

The following are the major historic collections used in most research and textbook publications that have aided our understanding of human development. Franklin P. Mall — began his human embryo at Johns Hopkins University in the early s; these formed the beginnings of the Carnegie collection. He and Franz Keibel — used these embryos in their textbook Manual of Human Embryology [ 1 , 2 ] and also in the Carnegie Institution of Washington Series Contributions to Embryology beginning in The same staging criteria have been subsequently applied in the organizing of the other major human embryo collections.

These stages will be described in detail from the Kyoto Collection later in this chapter. Reconstructions from histological sections of the collection embryos were the basis of the larger Carnegie models Figure 1 and this technique has also been used in the development of other collection models, as in the Blechschmidt Collection.

Mall received his medical degree at the University of Michigan in He traveled to Germany to receive a clinical training, where he met the German embryologist Wilhelm His — This initiated his interest in studying human embryology, and he began collecting human embryos in His collection had reached several hundreds of specimens by the time he returned to the Anatomy department of the Johns Hopkins School of Medicine in Baltimore, Maryland.

He received a Carnegie research grant in and became the first director of the Department of Embryology at the Carnegie Institution of Washington, in Baltimore, MD. The embryo collection grew at a rate of about specimens a year, donated by clinicians and researchers, and the number of samples reached over 8, by the early s. Researchers at the institute then began the complex task of organizing these embryos into a developmental sequence. Note that size alone was a difficult criterion due to the variable effects of fixation shrinkage.

Internal features were identified histologically from embryos that were serially sectioned, and also formed the basis of hundreds of 3D models and wax-based reconstructions.

George L. Streeter — and Franz J. Heard worked as an embryo modeler; and James D. Didusch as a scientific illustrator. Mall documented his research in a series of papers compiled in the Contributions to Embryology of the Carnegie Institution of Washington, published from to These articles even today are considered the core findings for studying human embryology.

Mall unexpectedly died in and was replaced as director by Streeter. Streeter was then the first to define the 23 Carnegie Stages currently used to classify the developmental stages of the human embryo see Table 2.

The collection continued to grow by hundreds of specimens every year and included rare, very young normal specimens. At the time, induced abortions were illegal in the United States and miscarriages usually resulted from embryo abnormalities. Streeter retired in and George W. Corner —] became the third departmental director. Corner was a former Johns Hopkins researcher who studied the menstrual cycle and identified the ovarian hormone progesterone.

During his direction until , many advances in human reproductive physiology were made and embryology research continued but came to an end with the succeeding director. Relocation of the collection began in to the University of California at Davis Medical School and was completed in At the retirement of the director in the collection was relocated again to its current location at the Walter Reed Army Medical Center in Washington, D.

In , preliminary work began with the current curator on establishing a partnership with the Digital Embryology Consortium to eventually digitize, preserve, and make more widely available this collection. Carnegie models located at the Carnegie Collection. Embryos shown in the bottom left-hand corner were laminated from individual layers and then painted. Originally collected by Charles Minot — , sometimes referred to as the Minot Collection, it now forms part of the larger Carnegie Collection.

By , the collection consisted of histologically sectioned embryos from human and other species Figure 2. Harvard Collection histology slide No. The human embryo collection is named after Erich Blechschmidt — , who directed the Anatomical Institute from until , and consists of two parts: firstly, a large histology collection of serial sections and, secondly, a model collection based upon these sections.

The histology collection is made up of about human embryos that have been cut in a range of anatomical planes into some , serial sections. In , some of the embryo serial section sets were temporarily incorporated into the Carnegie Collection and assigned Carnegie Nos.

The model collection Figure 3 "Human embryologische Dokumentations sammlung Blechschmidt" forms a permanent exhibition housed at the Centre of Anatomy and consists of 64 large models, generated from to The models are available for viewing upon request and are arranged in perspex cases that allow each model to be observed from all directions.

The models range from selected parts or systems of a specific embryo to whole embryos in surface view. Each model illustrates whole embryo surfaces, some organic systems including a circulatory organ, respiratory organs, a digestive organ, central nerve, and the skeletal system in precision, in addition to the right-side out.

The embryo collection has probably the largest number of excellently preserved specimens of the latter half of the embryonic period covering weeks 5—8 post conception.

Detailed documentation on individual specimens of the collection is sparse and some of the specimens are also depicted as color drawings in Blechschmidt [ 5 ]. The high quality and standard of the histology material was achieved by a combination of a "state-of-the-art" embryo collection gynecological practice mechanical curettage or hysterectomy from operations including termination of pregnancy and development of a special fixation procedure.

As a result, the quality of paraffin histological sections mounted on large glass microscope slides is unsurpassed and reveals valuable morphological detail of early organ development in the human embryo.

The Blechschmidt models and histology slides photo by Saki Ueno. Like many historic collections, even with optimal storage conditions, the slide histology has gradually deteriorated with evaporation of cover glass glue and bleaching of histological stains. Secondly, the large glass microscope slides are delicate and easily damaged during use. At that time, the only way to preserve for posterity morphological information contained in these specimens consisted in building large-scale polymer plastic reconstruction models.

These models were made from camera-lucida drawings at an intermediate magnification of regularly spaced histological sections [ 6 ]. Using the same series of serial sections several times over, Blechschmidt made reconstructions of the surface anatomy and the morphology of several organ systems of the same embryo, thereby enabling direct comparison of topographical characteristics and their dynamic changes during development, even though the cellular detail detectable at high magnification remained unexplored with this method.

Currently, the way to preserve the collection in its current condition lies with the scanning and digital preservation of the histological material with the Digital Embryology Consortium.

The Orts-Llorca Madrid Collection. Slides of serially sectioned embryos are stored in individual box sets. Photo by Mark Hill. The human embryo histology collection was started in by the Spanish embryologist Francisco Orts-Llorca — and is located at the Embryology Institute of Complutense University of Madrid [ 7 ].

The collection consists of histological serial sections of more than human embryos in thousands of serial sections covering the embryonic and fetal periods Figure 4. The collection includes both normal and abnormal embryos.

The sectioning is in a number of different anatomical planes and includes both normal and abnormal embryonic material. The collection has unfortunately suffered from the rigors of time, handling by many researchers, and fading of histological stains. Klaus V. Hinrichsen was a pupil of Blechschmidt and had the chair of Anatomy and Embryology at the Ruhr University Bochum in In the particular case of humans, development does not even stop at birth. Note that teeth continue to develop and sex glands with sexual differentiation mature long after birth.

For a number of years, many embryologists have referred to their discipline as developmental biology to escape from the need to confine their studies to earlier stages.

Embryology in the modern sense is the study of the life history of an animal and human embryology considers developmental aspects of life as a whole and not just the first eight weeks. The study of embryology, the science that deals with the formation and development of the embryo and fetus, can be traced back to the ancient Greek philosophers.

Originally, embryology was part of the field known as "generation," a term that also encompassed studies of reproduction, development and differentiation, regeneration of parts, and genetics. Generation described the means by which new animals or plants came into existence. The ancients believed that new organisms could arise through sexual reproduction , asexual reproduction , or spontaneous generation.

As early as the sixth century B. Aristotle — B. According to preformationist theories, an embryo or miniature individual preexists in either the mother's egg or the father's semen and begins to grow when properly stimulated. Some preformationists believed that all the embryos that would ever develop had been formed by God at the Creation. Aristotle actually favored the theory of epigenesis, which assumes that the embryo begins as an undifferentiated mass and that new parts are added during development.

Aristotle thought that the female parent contributed only unorganized matter to the embryo. He argued that semen from the male parent provided the "form," or soul, that guided development and that the first part of the new organism to be formed was the heart. Aristotle's theory of epigenetic development dominated the science of embryology until the work of physiologist William Harvey — raised doubts about A human two-cell embryo 24 hours after fertilization.

Photograph by Richard G. Custom Medical Stock Photo. Reproduced by permission. In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. For two tense weeks in mid, developmental biologist Magdalena Zernicka-Goetz was chasing a world record. She and her colleagues at the University of Cambridge, UK, were attempting to grow human embryos in the lab for longer than had ever been done before.

They wanted to glean insights into how a tiny blob of cells transforms itself into a complex, multipart structure. Previous efforts had stalled after about a week, but Zernicka-Goetz knew there was much more to learn about human development beyond that point.

The researchers started with embryos that had been donated by women who no longer needed them for in vitro fertilization IVF procedures. The team bathed the cells in a special medium and housed them in an incubator, using methods adapted from their previous work on mouse embryos.

Because the samples had to stay in a strictly controlled environment, the scientists could remove them only once or twice a day to track their progress under a microscope. The days ticked by — six, seven, eight. And still, the embryos continued to thrive and develop 1. Their advance, and a similar feat by a group based in New York City 2 , is one of a few achievements in the past five years to heat up the study of early human development.

But now, refinements in cell-culturing methods are enabling them to grow human embryos outside of the body for up to two weeks. Scientists are using gene-editing techniques, such as CRISPR, and building artificial embryo-like structures to explore the cellular signals and physical forces that shape the embryo and its supporting cast of tissues. And new high-resolution, digital images are revealing in fine detail how muscles and nerves grow a few weeks later in development.

Such discoveries could lead to a better understanding of how birth defects and developmental disorders arise, as well as why some pregnancies fail.

But alongside their promise, these new techniques are pushing researchers into uncharted ethical territory. Until now, the internationally recognized day rule has been a purely hypothetical limit. Many early developmental processes are surprisingly similar throughout the animal kingdom, with each species tweaking a few genes here or signals there. Among mammals, scientists have studied the mouse molecular instruction manual the most, disabling genes one by one to test what they do.

Mice are easy to obtain in the numbers often needed for experiments, and are considered a decent proxy for studying human embryonic development — many of the earliest cell types and components seem similar in both species.

But researchers are starting to question how far these similarities really go. With a limited supply of human tissue available, scientists have turned to highly efficient gene-editing technologies such as CRISPR—Cas9 to explore the early stages of embryo development.

In part owing to ethical sensitivities surrounding genetic modification of embryos, only a few groups have received authorization to perform such studies so far. At the Francis Crick Institute in London, developmental biologist Kathy Niakan led the first project of its kind to receive approval from national regulators. Human embryos with disruptions to this gene lacked a protein called OCT4 and failed to develop into blastocysts — balls of roughly cells.

By contrast, mouse embryos lacking the same gene formed blastocysts and faltered only later. The difference supports the growing idea that, even in very early development, some genetic details — such as when certain genes are active — might be specific to humans. The reasons for that are unclear. After blossoming into a cell ball, the little blastocyst must embed into the uterine wall to survive. But once this happens around day seven , scientists are largely unable to study its development.

Observing the implantation process itself is the first challenge: until recently, researchers lacked reliable methods for sustaining embryo development beyond the first week.

Now, scientists have opened that black box. Embryos that latch onto the dish are flatter than the real thing. Even the origin of amniotic fluid caused puzzlement during this time period. Two competing ideas were that amniotic fluid came from the sweat of the fetus or that it was secreted from the eyes and mouth of the crying and salivating fetus. Without sound experimental techniques these questions remained unsolved during the eighteenth century. Preformationism had become firmly established by the early s and Needham credits this to the writings of Malpighi, Swammerdam, and Charles Bonnet and to embryologists who proclaimed to see minute forms of men inside of gametes.

Among these animalculists a division arose between those who believed that preformed organisms existed in eggs ovists and those who believed that small adult organisms existed in sperm spermists. At this time preformationists outnumbered the number of epigeneticists those who believed that development proceeded progressively from unorganized matter , but there still remained many unanswered questions. Epigeneticists asked how embryonic monsters and regeneration of starfish arms fit into the preformation plan of a God that had made sure that all normal adult structures were in the egg or the semen , waiting to unfold.

Needham details how the preformation - epigenesis debate grew and culminated in a series of arguments between epigeneticist Caspar Friedrich Wolff and preformationist Albrecht von Haller. The folds eventually transform into a closed tube. Wolff argued that this observation proved that the intestine was not preformed and that organs appeared gradually. Wolff also examined embryonic monsters, declaring that they were formed by nature and stood as examples of epigenesis rather than preformationism.

Needham credits Hermann Boerhaave with having written the first detailed account of chemical embryology in his book Elementa Chemiae published in Boerhaave separated egg white from the yolk and added various acids and bases, heated them, shook them, and boiled them to see the chemical and physical effects that each procedure had on albumin.

This type of experimentation soon gave rise to the science of techniques and paved the way for later experimental work by such embryologists as Jacques Loeb and Hans Spemann.

Needham ends the fourth chapter by identifying several important embryological discoveries that occurred before the closing of the eighteenth century. The mammalian egg was finally seen and recognized as a single cell; the idea of the recapitulation theory began to take shape; and Scottish surgeon John Hunter showed that the maternal and fetal circulations were distinct physiologies. Needham argues that advancements in embryology rarely proceed with separate successions of geniuses but rather with embryologists who have inherited the observations and remarks of previous generations of scientists.

He argues that much of early embryology was descriptive in nature due to several limiting factors: social and political ruling ideas, cooperation or lack of cooperation of scholars, language barriers, and technology his examples include the introduction of hardening agents, especially alcohol and improvements in microscopy.

Needham argues that any modification of this balance acts as a powerful limiting factor itself. Keywords: History. A History of Embryology, by Joseph Needham In embryologist and historian Joseph Needham published a well-received three-volume treatise titled Chemical Embryology. Sources Bodemer, Charles W.