A male organism is the physiological sex that produces sperm. Each spermatozoon can fuse with ovum, in the process of fertilization. A male cannot reproduce sexually without access to at least one ovum from a female, but some organisms can reproduce both sexually and asexually. Most male mammals, including male humans, have a Y chromosome, which codes for the production of larger amounts of testosterone to develop male reproductive organs. Not all species share a common sex-determination system. In most animals, including humans, sex is determined genetically, but in some species it can be determined due to social, environmental, or other factors. For example, Cymothoa exigua changes sex depending on the number of females present in the vicinity; the existence of two sexes seems to have been selected independently across different evolutionary lineages. The repeated pattern is sexual reproduction in isogamous species with two or more mating types with gametes of identical form and behavior to anisogamous species with gametes of male and female types to oogamous species in which the female gamete is much larger than the male and has no ability to move.
There is a good argument that this pattern was driven by the physical constraints on the mechanisms by which two gametes get together as required for sexual reproduction. Accordingly, sex is defined operationally across species by the type of gametes produced and differences between males and females in one lineage are not always predictive of differences in another. Male/female dimorphism between organisms or reproductive organs of different sexes is not limited to animals. In land plants and male designate not only the female and male gamete-producing organisms and structures but the structures of the sporophytes that give rise to male and female plants. A common symbol used to represent the male sex is the Mars symbol, ♂ — a circle with an arrow pointing northeast; the symbol is identical to the planetary symbol of Mars. It was first used to denote sex by Carl Linnaeus in 1751; the symbol is called a stylized representation of the Roman god Mars' shield and spear. According to Stearn, all the historical evidence favours that it is derived from θρ, the contraction of the Greek name for the planet Mars, Thouros.
The sex of a particular organism may be determined by a number of factors. These may be genetic or environmental, or may change during the course of an organism's life. Although most species with male and female sexes have individuals that are either male or female, hermaphroditic animals, such as worms, have both male and female reproductive organs. Most mammals, including humans, are genetically determined as such by the XY sex-determination system where males have an XY sex chromosome, it is possible in a variety of species, including humans, to be XXY or have other intersex/hermaphroditic qualities, though one would still be considered genotypically male so long as one has a Y-chromosome. During reproduction, a male can give either an X sperm or a Y sperm, while a female can only give an X egg. A Y sperm and an X egg produce a male, while an X egg produce a female; the part of the Y-chromosome, responsible for maleness is the sex-determining region of the Y-chromosome, the SRY. The SRY activates Sox9, which forms feedforward loops with FGF9 and PGD2 in the gonads, allowing the levels of these genes to stay high enough in order to cause male development.
The ZW sex-determination system, where males have a ZZ sex chromosome may be found in birds and some insects and other organisms. Members of the insect order Hymenoptera, such as ants and bees, are determined by haplodiploidy, where most males are haploid and females and some sterile males are diploid. In some species of reptiles, such as alligators, sex is determined by the temperature at which the egg is incubated. Other species, such as some snails, practice sex change: adults start out male become female. In tropical clown fish, the dominant individual in a group becomes female while the other ones are male. In some arthropods, sex is determined by infection. Bacteria of the genus Wolbachia alter their sexuality. In those species with two sexes, males may differ from females in ways other than the production of spermatozoa. In many insects and fish, the male is smaller than the female. In seed plants, which exhibit alternation of generations, the female and male parts are both included within the sporophyte sex organ of a single organism.
In mammals, including humans, males are larger than females. In birds, the male exhibits a colorful plumage that attracts females. Boy Female Gender Male plant Male pregnancy Man Masculinity Gentleman Wedgwood, Hensleigh. "On False Etymologies". Transactions of the Philological Society: 68
Mammals are vertebrate animals constituting the class Mammalia, characterized by the presence of mammary glands which in females produce milk for feeding their young, a neocortex, fur or hair, three middle ear bones. These characteristics distinguish them from reptiles and birds, from which they diverged in the late Triassic, 201–227 million years ago. There are around 5,450 species of mammals; the largest orders are the rodents and Soricomorpha. The next three are the Primates, the Cetartiodactyla, the Carnivora. In cladistics, which reflect evolution, mammals are classified as endothermic amniotes, they are the only living Synapsida. The early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that produced the non-mammalian Dimetrodon. At the end of the Carboniferous period around 300 million years ago, this group diverged from the sauropsid line that led to today's reptiles and birds; the line following the stem group Sphenacodontia split off several diverse groups of non-mammalian synapsids—sometimes referred to as mammal-like reptiles—before giving rise to the proto-mammals in the early Mesozoic era.
The modern mammalian orders arose in the Paleogene and Neogene periods of the Cenozoic era, after the extinction of non-avian dinosaurs, have been among the dominant terrestrial animal groups from 66 million years ago to the present. The basic body type is quadruped, most mammals use their four extremities for terrestrial locomotion. Mammals range in size from the 30–40 mm bumblebee bat to the 30-meter blue whale—the largest animal on the planet. Maximum lifespan varies from two years for the shrew to 211 years for the bowhead whale. All modern mammals give birth to live young, except the five species of monotremes, which are egg-laying mammals; the most species-rich group of mammals, the cohort called placentals, have a placenta, which enables the feeding of the fetus during gestation. Most mammals are intelligent, with some possessing large brains, self-awareness, tool use. Mammals can communicate and vocalize in several different ways, including the production of ultrasound, scent-marking, alarm signals and echolocation.
Mammals can organize themselves into fission-fusion societies and hierarchies—but can be solitary and territorial. Most mammals are polygynous. Domestication of many types of mammals by humans played a major role in the Neolithic revolution, resulted in farming replacing hunting and gathering as the primary source of food for humans; this led to a major restructuring of human societies from nomadic to sedentary, with more co-operation among larger and larger groups, the development of the first civilizations. Domesticated mammals provided, continue to provide, power for transport and agriculture, as well as food and leather. Mammals are hunted and raced for sport, are used as model organisms in science. Mammals have been depicted in art since Palaeolithic times, appear in literature, film and religion. Decline in numbers and extinction of many mammals is driven by human poaching and habitat destruction deforestation. Mammal classification has been through several iterations since Carl Linnaeus defined the class.
No classification system is universally accepted. George Gaylord Simpson's "Principles of Classification and a Classification of Mammals" provides systematics of mammal origins and relationships that were universally taught until the end of the 20th century. Since Simpson's classification, the paleontological record has been recalibrated, the intervening years have seen much debate and progress concerning the theoretical underpinnings of systematization itself through the new concept of cladistics. Though field work made Simpson's classification outdated, it remains the closest thing to an official classification of mammals. Most mammals, including the six most species-rich orders, belong to the placental group; the three largest orders in numbers of species are Rodentia: mice, porcupines, beavers and other gnawing mammals. The next three biggest orders, depending on the biological classification scheme used, are the Primates including the apes and lemurs. According to Mammal Species of the World, 5,416 species were identified in 2006.
These were grouped into 153 families and 29 orders. In 2008, the International Union for Conservation of Nature completed a five-year Global Mammal Assessment for its IUCN Red List, which counted 5,488 species. According to a research published in the Journal of Mammalogy in 2018, the number of recognized mammal species is 6,495 species included 96 extinct; the word "mammal" is modern, from the scientific name Mammalia coined by Carl Linnaeus in 1758, derived from the Latin mamma. In an influential 1988 paper, Timothy Rowe defined Mammalia phylogenetically as the crown group of mammals, the clade consisting of the most recent common ancestor of living monotremes and therian m
The androgen receptor known as NR3C4, is a type of nuclear receptor, activated by binding any of the androgenic hormones, including testosterone and dihydrotestosterone in the cytoplasm and translocating into the nucleus. The androgen receptor is most related to the progesterone receptor, progestins in higher dosages can block the androgen receptor; the main function of the androgen receptor is as a DNA-binding transcription factor that regulates gene expression. Androgen regulated genes are critical for the development and maintenance of the male sexual phenotype. In some cell types, testosterone interacts directly with androgen receptors, whereas, in others, testosterone is converted by 5-alpha-reductase to dihydrotestosterone, an more potent agonist for androgen receptor activation. Testosterone appears to be the primary androgen receptor-activating hormone in the Wolffian duct, whereas dihydrotestosterone is the main androgenic hormone in the urogenital sinus, urogenital tubercle, hair follicles.
Testosterone is therefore responsible for the development of male primary sexual characteristics, whilst dihydrotestosterone is responsible for secondary male characteristics. Androgens cause slow epiphysis, or maturation of the bones, but more of the potent epiphysis effect comes from the estrogen produced by aromatization of androgens. Steroid users of teen age may find that their growth had been stunted by androgen and/or estrogen excess. People with too little sex hormones can be short during puberty but end up taller as adults as in androgen insensitivity syndrome or estrogen insensitivity syndrome. AR knockout-mice studies have shown that AR is essential for normal female fertility, being required for development and full functionality of the ovarian follicles and ovulation, working through both intra-ovarian and neuroendocrine mechanisms. Via the androgen receptor, androgens play a key role in the maintenance of male skeletal integrity; the regulation of this integrity by androgen receptor signaling can be attributed to both osteoblasts and osteocytes.
The primary mechanism of action for androgen receptors is direct regulation of gene transcription. The binding of an androgen to the androgen receptor results in a conformational change in the receptor that, in turn, causes dissociation of heat shock proteins, transport from the cytosol into the cell nucleus, dimerization; the androgen receptor dimer binds to a specific sequence of DNA known as a hormone response element. Androgen receptors interact with other proteins in the nucleus, resulting in up- or down-regulation of specific gene transcription. Up-regulation or activation of transcription results in increased synthesis of messenger RNA, which, in turn, is translated by ribosomes to produce specific proteins. One of the known target genes of androgen receptor activation is the insulin-like growth factor I receptor. Thus, changes in levels of specific proteins in cells is one way that androgen receptors control cell behavior. One function of androgen receptor, independent of direct binding to its target DNA sequence, is facilitated by recruitment via other DNA-binding proteins.
One example is serum response factor, a protein that activates several genes that cause muscle growth. Androgen receptor is modified by post translational modification through acetylation, which directly promotes AR mediated transactivation and contact independent growth of prostate cancer cells. AR acetylation determines recruitment into chromatin; the AR acetylation site is a key target of NAD-dependent and TSA-dependent histone deacetylases and long non coding RNA. More androgen receptors have been shown to have a second mode of action; as has been found for other steroid hormone receptors such as estrogen receptors, androgen receptors can have actions that are independent of their interactions with DNA. Androgen receptors interact with certain signal transduction proteins in the cytoplasm. Androgen binding to cytoplasmic androgen receptors can cause rapid changes in cell function independent of changes in gene transcription, such as changes in ion transport. Regulation of signal transduction pathways by cytoplasmic androgen receptors can indirectly lead to changes in gene transcription, for example, by leading to phosphorylation of other transcription factors.
In humans, the androgen receptor is encoded by the AR gene located on the X chromosome at Xq11-12. The androgen insensitivity syndrome known as testicular feminization, is caused by a mutation of the androgen receptor gene located on the X chromosome; the androgen receptor is defective in Kennedy's disease. In addition, point mutations and trinucleotide repeat polymorphisms has been linked to a number of additional disorders; the AR gene contains CAG repeats which affect receptor function, where fewer repeats leads to increased receptor sensitivity to circulating androgens and more repeats leads to decreased receptor sensitivity. Studies have shown that racial variation in CAG repeats exists, with African-Americans having fewer repeats than non-Hispanic white Americans; the racial trends in CAG repeats parallels the incidence and mortality of prostate cancer in these groups. Two isoforms of the androgen receptor have been identified: AR-A - 87 kDa - N-terminus truncated, which results from in vitro proteolysis.
AR-B - 110 kDa - full length Like other nuclear receptors, the androgen receptor is modular in structure and is composed of the following functional domains labeled A through F: A/B) - N-terminal regulatory domain contains:activa
Semen known as seminal fluid, is an organic fluid that may contain spermatozoa. It is secreted by the gonads and other sexual organs of male or hermaphroditic animals and can fertilize female ova. In humans, seminal fluid contains several components besides spermatozoa: proteolytic and other enzymes as well as fructose are elements of seminal fluid which promote the survival of spermatozoa, provide a medium through which they can move or "swim". Semen is produced and originates from the seminal vesicle, located in the pelvis; the process that results in the discharge of semen is called ejaculation. Semen is a form of genetic material. In animals, semen has been collected for cryoconservation. Cryoconservation of animal genetic resources is a practice that calls for the collection of genetic material in efforts for conservation of a particular breed. Depending on the species, spermatozoa can fertilize ova internally. In external fertilization, the spermatozoa fertilize the ova directly, outside of the female's sexual organs.
Female fish, for example, spawn ova into their aquatic environment, where they are fertilized by the semen of the male fish. During internal fertilization, fertilization occurs inside the female's sexual organs. Internal fertilization takes place after insemination of a female by a male through copulation. In most vertebrates, including amphibians, reptiles and monotreme mammals, copulation is achieved through the physical mating of the cloaca of the male and female. In marsupial and placental mammals, copulation occurs through the vagina. During the process of ejaculation, sperm passes through the ejaculatory ducts and mixes with fluids from the seminal vesicles, the prostate, the bulbourethral glands to form the semen; the seminal vesicles produce a yellowish viscous fluid rich in fructose and other substances that makes up about 70% of human semen. The prostatic secretion, influenced by dihydrotestosterone, is a whitish, thin fluid containing proteolytic enzymes, citric acid, acid phosphatase and lipids.
The bulbourethral glands secrete a clear secretion into the lumen of the urethra to lubricate it. Sertoli cells, which nurture and support developing spermatocytes, secrete a fluid into seminiferous tubules that helps transport sperm to the genital ducts; the ductuli efferentes possess cuboidal cells with microvilli and lysosomal granules that modify the ductal fluid by reabsorbing some fluid. Once the semen enters the ductus epididymis the principal cells, which contain pinocytotic vessels indicating fluid reabsorption, secrete glycerophosphocholine which most inhibits premature capacitation; the accessory genital ducts, the seminal vesicle, prostate glands, the bulbourethral glands, produce most of the seminal fluid. Seminal plasma of humans contains a complex range of inorganic constituents; the seminal plasma provides a nutritive and protective medium for the spermatozoa during their journey through the female reproductive tract. The normal environment of the vagina is a hostile one for sperm cells, as it is acidic and patrolled by immune cells.
The components in the seminal plasma attempt to compensate for this hostile environment. Basic amines such as putrescine, spermine and cadaverine are responsible for the smell and flavor of semen; these alkaline bases counteract and buffer the acidic environment of the vaginal canal, protect DNA inside the sperm from acidic denaturation. The components and contributions of semen are as follows: A 1992 World Health Organization report described normal human semen as having a volume of 2 ml or greater, pH of 7.2 to 8.0, sperm concentration of 20×106 spermatozoa/ml or more, sperm count of 40×106 spermatozoa per ejaculate or more, motility of 50% or more with forward progression of 25% or more with rapid progression within 60 minutes of ejaculation. A 2005 review of the literature found that the average reported physical and chemical properties of human semen were as follows: Semen is translucent with white, grey or yellowish tint. Blood in the semen can cause a pink or reddish colour, known as hematospermia, may indicate a medical problem which should be evaluated by a doctor if the symptom persists.
After ejaculation, the latter part of the ejaculated semen coagulates forming globules, while the earlier part of the ejaculate does not. After a period ranging from 15 – 30 minutes, prostate-specific antigen present in the semen causes the decoagulation of the seminal coagulum, it is postulated that the initial clotting helps keep the semen in the vagina, while liquefaction frees the sperm to make their journey to the ova. A 2005 review found that the average reported viscosity of human semen in the literature was 3–7 cP. Semen quality is a measure of the ability of semen to accomplish fertilization. Thus, it is a measure of fertility in a man, it is the sperm in the semen, the fertile component, therefore semen quality involves both sperm quantity and sperm quality. The volume of semen ejaculate varies but is about 1 teaspoonful or less. A review of 30 studies concluded that the average was around 3.4 milliliters, with some studies finding amounts as high as 5.0 ml or as low as 2.3 ml. In a study with Swedish and Danish men, a prolonged interval between ejaculations caused an increase of the sperm count in the semen but not an increase of its amount.
Some dietary supplements have been marketed with claims to increase seminal volume. Like other supplements, including so-called herbal viagra, these are not approved or regulated by the Food and Drug Administration
A thesis or dissertation is a document submitted in support of candidature for an academic degree or professional qualification presenting the author's research and findings. In some contexts, the word "thesis" or a cognate is used for part of a bachelor's or master's course, while "dissertation" is applied to a doctorate, while in other contexts, the reverse is true; the term graduate thesis is sometimes used to refer to both master's theses and doctoral dissertations. The required complexity or quality of research of a thesis or dissertation can vary by country, university, or program, the required minimum study period may thus vary in duration; the word "dissertation" can at times be used to describe a treatise without relation to obtaining an academic degree. The term "thesis" is used to refer to the general claim of an essay or similar work; the term "thesis" comes from the Greek θέσις, meaning "something put forth", refers to an intellectual proposition. "Dissertation" comes from the Latin dissertātiō, meaning "discussion".
Aristotle was the first philosopher to define the term thesis. "A'thesis' is a supposition of some eminent philosopher that conflicts with the general opinion...for to take notice when any ordinary person expresses views contrary to men's usual opinions would be silly". For Aristotle, a thesis would therefore be a supposition, stated in contradiction with general opinion or express disagreement with other philosophers. A supposition is a statement or opinion that may or may not be true depending on the evidence and/or proof, offered; the purpose of the dissertation is thus to outline the proofs of why the author disagrees with other philosophers or the general opinion. A thesis may be arranged as a thesis by publication or a monograph, with or without appended papers though many graduate programs allow candidates to submit a curated collection of published papers. An ordinary monograph has a title page, an abstract, a table of contents, comprising the various chapters, a bibliography or a references section.
They differ in their structure in accordance with the many different areas of study and the differences between them. In a thesis by publication, the chapters constitute an introductory and comprehensive review of the appended published and unpublished article documents. Dissertations report on a research project or study, or an extended analysis of a topic; the structure of a thesis or dissertation explains the purpose, the previous research literature impinging on the topic of the study, the methods used, the findings of the project. Most world universities use a multiple chapter format: a) an introduction, which introduces the research topic, the methodology, as well as its scope and significance. Degree-awarding institutions define their own house style that candidates have to follow when preparing a thesis document. In addition to institution-specific house styles, there exist a number of field-specific and international standards and recommendations for the presentation of theses, for instance ISO 7144.
Other applicable international standards include ISO 2145 on section numbers, ISO 690 on bibliographic references, ISO 31 on quantities or units. Some older house styles specify that front matter must use a separate page number sequence from the main text, using Roman numerals; the relevant international standard and many newer style guides recognize that this book design practice can cause confusion where electronic document viewers number all pages of a document continuously from the first page, independent of any printed page numbers. They, avoid the traditional separate number sequence for front matter and require a single sequence of Arabic numerals starting with 1 for the first printed page. Presentation requirements, including pagination, layout and color of paper, use of acid-free paper, paper size, order of components, citation style, will be checked page by page by the accepting officer before the thesis is accepted and a receipt is issued. However, strict standards are not always required.
Most Italian universities, for example, have only general requirements on the character size and the page formatting, leave much freedom for the actual typographic details. A thesis or dissertation committee is a committee. In the US, these committees consist of a primary supervisor or advisor and two or more committee members, who supervise the progress of the dissertation and may act as the examining committee, or jury, at the oral examination of the thesis. At most universities, the committee is chosen by the student in conjunction with his or her primary adviser after completion of the comprehensive examinations or prospectus meeting, may consist of members of the comps committee; the committee members are doctors in their field (whether a PhD or other des
Apoptosis is a form of programmed cell death that occurs in multicellular organisms. Biochemical events lead to death; these changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, chromosomal DNA fragmentation, global mRNA decay. The average adult human loses between 70 billion cells each day due to apoptosis. For an average human child between the ages of 8 to 14 year old 20 to 30 billion cells die per day. In contrast to necrosis, a form of traumatic cell death that results from acute cellular injury, apoptosis is a regulated and controlled process that confers advantages during an organism's lifecycle. For example, the separation of fingers and toes in a developing human embryo occurs because cells between the digits undergo apoptosis. Unlike necrosis, apoptosis produces cell fragments called apoptotic bodies that phagocytic cells are able to engulf and remove before the contents of the cell can spill out onto surrounding cells and cause damage to them; because apoptosis cannot stop once it has begun, it is a regulated process.
Apoptosis can be initiated through one of two pathways. In the intrinsic pathway the cell kills itself because it senses cell stress, while in the extrinsic pathway the cell kills itself because of signals from other cells. Weak external signals may activate the intrinsic pathway of apoptosis. Both pathways induce cell death by activating caspases, which are proteases, or enzymes that degrade proteins; the two pathways both activate initiator caspases, which activate executioner caspases, which kill the cell by degrading proteins indiscriminately. Research on apoptosis has increased since the early 1990s. In addition to its importance as a biological phenomenon, defective apoptotic processes have been implicated in a wide variety of diseases. Excessive apoptosis causes atrophy, whereas an insufficient amount results in uncontrolled cell proliferation, such as cancer; some factors like Fas receptors and caspases promote apoptosis, while some members of the Bcl-2 family of proteins inhibit apoptosis.
German scientist Karl Vogt was first to describe the principle of apoptosis in 1842. In 1885, anatomist Walther Flemming delivered a more precise description of the process of programmed cell death. However, it was not until 1965. While studying tissues using electron microscopy, John Foxton Ross Kerr at the University of Queensland was able to distinguish apoptosis from traumatic cell death. Following the publication of a paper describing the phenomenon, Kerr was invited to join Alastair R. Currie, as well as Andrew Wyllie, Currie's graduate student, at University of Aberdeen. In 1972, the trio published a seminal article in the British Journal of Cancer. Kerr had used the term programmed cell necrosis, but in the article, the process of natural cell death was called apoptosis. Kerr and Currie credited James Cormack, a professor of Greek language at University of Aberdeen, with suggesting the term apoptosis. Kerr received the Paul Ehrlich and Ludwig Darmstaedter Prize on March 14, 2000, for his description of apoptosis.
He shared the prize with Boston biologist H. Robert Horvitz. For many years, neither "apoptosis" nor "programmed cell death" was a cited term. Two discoveries brought cell death from obscurity to a major field of research: identification of components of the cell death control and effector mechanisms, linkage of abnormalities in cell death to human disease, in particular cancer; the 2002 Nobel Prize in Medicine was awarded to Sydney Brenner and John E. Sulston for their work identifying genes that control apoptosis; the genes were identified by studies in the nematode C. elegans and homologues of these genes function in humans to regulate apoptosis. In Greek, apoptosis translates to the "falling off" of leaves from a tree. Cormack, professor of Greek language, reintroduced the term for medical use as it had a medical meaning for the Greeks over two thousand years before. Hippocrates used the term to mean "the falling off of the bones". Galen extended its meaning to "the dropping of the scabs".
Cormack was no doubt aware of this usage. Debate continues over the correct pronunciation, with opinion divided between a pronunciation with the second p silent and the second p pronounced, as in the original Greek. In English, the p of the Greek -pt- consonant cluster is silent at the beginning of a word, but articulated when used in combining forms preceded by a vowel, as in helicopter or the orders of insects: diptera, etc. In the original Kerr, Wyllie & Currie paper, there is a footnote regarding the pronunciation: "We are most grateful to Professor James Cormack of the Department of Greek, University of Aberdeen, for suggesting this term; the word "apoptosis" is used in Greek to describe the "dropping off" or "falling off" of petals from flowers, or leaves from trees. To show the derivation we propose that the stress should be on the penultimate syllable, the second half of the word being pronounced like "ptosis", which comes from the same root "to fall", is used to describe the drooping of the upper eyelid."
The initiation of apoptosis is regulated by activation mechanisms, because once apoptosis has begun, it leads to the death of the cell. The two best-understood activation mechanisms are the extrinsic pathway; the intrinsic pathway is activated by intracellular signals generated when cells are stressed and depends on the release of proteins from th
The epoophoron or epoöphoron is a remnant of the mesonephric tubules that can be found next to the ovary and fallopian tube. It may contain 10–15 transverse small ducts or tubules that lead to the Gartner’s duct that represents the caudal remnant of the mesonephric duct and passes through the broad ligament and the lateral wall of the cervix and vagina; the epoophoron is a homologue to the epididymis in the male. While the epoophoron is located in the lateral portion of the mesosalpinx and mesovarium, the paroophoron lies more medially in the mesosalpinx, it has a unique histological profile. Clinically the organ may give rise to adenoma. List of homologues of the human reproductive system Vesicular appendages of epoophoron figures/chapter_35/35-8. HTM: Basic Human Anatomy at Dartmouth Medical School genital-016a—Embryo Images at University of North Carolina Swiss embryology ugenital/genitinterne05