The hypoglossal nerve is the twelfth cranial nerve, innervates all the extrinsic and intrinsic muscles of the tongue, except for the palatoglossus, innervated by the vagus nerve. It is a nerve with a motor function; the nerve arises from the hypoglossal nucleus in the brain stem as a number of small rootlets, passes through the hypoglossal canal and down through the neck, passes up again over the tongue muscles it supplies into the tongue. There are two hypoglossal nerves in the body: one on the left, one on the right; the nerve is involved in controlling tongue movements required for speech and swallowing, including sticking out the tongue and moving it from side to side. Damage to the nerve or the neural pathways which control it can affect the ability of the tongue to move and its appearance, with the most common sources of damage being injury from trauma or surgery, motor neuron disease; the first recorded description of the nerve is by Herophilos in the third century BC. The name hypoglossus springs from the fact that its passage is below the tongue, from hypo and glossa.
The hypoglossal nerve arises as a number of small rootlets from the front of the medulla, the bottom part of the brainstem, in the preolivary sulcus, which separates the olive and the pyramid. The nerve passes through the subarachnoid space and pierces the dura mater near the hypoglossal canal, an opening in the occipital bone of the skull. After emerging from the hypoglossal canal, the hypoglossal nerve gives off a meningeal branch and picks up a branch from the anterior ramus of C1, it travels close to the vagus nerve and spinal division of the accessory nerve, spirals downwards behind the vagus nerve and passes between the internal carotid artery and internal jugular vein lying on the carotid sheath. At a point at the level of the angle of the mandible, the hypoglossal nerve emerges from behind the posterior belly of the digastric muscle, it loops around a branch of the occipital artery and travels forward into the region beneath the mandible. The hypoglossal nerve moves forward lateral to the hyoglossus and medial to the stylohyoid muscles and lingual nerve.
It continues forward to the tip of the tongue. It distributes branches to the intrinsic and extrinsic muscle of the tongue innervates as it passes in this direction, supplies several muscles that it passes; the rootlets of the hypoglossal nerve arise from the hypoglossal nucleus near the bottom of the brain stem. The hypoglossal nucleus receives input from both the motor cortices but the contralateral input is dominant. Signals from muscle spindles on the tongue travel through the hypoglossal nerve, moving onto the lingual nerve which synapses on the trigeminal mesencephalic nucleus; the hypoglossal nerve is derived from the first pair of occipital somites, collections of mesoderm that form next to the main axis of an embryo during development. The musculature it supplies develop as the hypoglossal cord from the myotomes of the first four pairs of occipital somites; the nerve is first visible as a series of roots in the fourth week of development, which have formed a single nerve and link to the tongue by the fifth week.
The hypoglossal nucleus is derived from the basal plate of the embryonic medulla oblongata. The hypoglossal nerve provides motor control of the extrinsic muscles of the tongue: genioglossus, hyoglossus and the intrinsic muscles of the tongue; these represent all muscles of the tongue except the palatoglossus muscle. The hypoglossal nerve is of a general somatic efferent type; these muscles are involved in manipulating the tongue. The left and right genioglossus muscles in particular are responsible for protruding the tongue; the muscles, attached to the underside of the top and back parts of the tongue, cause the tongue to protrude and deviate towards the opposite side. The hypoglossal nerve supplies movements including clearing the mouth of saliva and other involuntary activities; the hypoglossal nucleus interacts with the reticular formation, involved in the control of several reflexive or automatic motions, several corticonuclear originating fibers supply innervation aiding in unconscious movements relating to speech and articulation.
Reports of damage to the hypoglossal nerve are rare. The most common causes of injury in one case series were compression by tumours and gunshot wounds. A wide variety of other causes can lead to damage of the nerve; these include surgical damage, medullary stroke, multiple sclerosis, Guillain-Barre syndrome, infection and presence of an ectatic vessel in the hypoglossal canal. Damage can be on both sides, which will affect symptoms that the damage causes; because of the close proximity of the nerve to other structures including nerves and veins, it is rare for the nerve to be damaged in isolation. For example, damage to the left and right hypoglossal nerves may occur with damage to the facial and trigeminal nerves as a result of damage from a clot following arteriosclerosis of the vertebrobasilar artery; such a stroke may result in tight oral musculature, difficulty speaking and chewing. Progressive bulbar palsy, a form of motor neuron disease, is associated with combined lesions of the hypoglossal nucleus and nucleus ambiguus with wasting of the motor nerves of the pons and medulla.
This may cause difficulty with tongue movements, speech and swallowing caused by dysfunction of several cranial nerve nuclei. Motor neuron disease is the most common disease affecting the hypoglossal nerve; the hypoglossal nerve is tested by examining its movements. At rest, if the
Humans are the only extant members of the subtribe Hominina. Together with chimpanzees and orangutans, they are part of the family Hominidae. A terrestrial animal, humans are characterized by their erect bipedal locomotion. Early hominins—particularly the australopithecines, whose brains and anatomy are in many ways more similar to ancestral non-human apes—are less referred to as "human" than hominins of the genus Homo. Several of these hominins used fire, occupied much of Eurasia, gave rise to anatomically modern Homo sapiens in Africa about 315,000 years ago. Humans began to exhibit evidence of behavioral modernity around 50,000 years ago, in several waves of migration, they ventured out of Africa and populated most of the world; the spread of the large and increasing population of humans has profoundly affected much of the biosphere and millions of species worldwide. Advantages that explain this evolutionary success include a larger brain with a well-developed neocortex, prefrontal cortex and temporal lobes, which enable advanced abstract reasoning, problem solving and culture through social learning.
Humans use tools better than any other animal. Humans uniquely use such systems of symbolic communication as language and art to express themselves and exchange ideas, organize themselves into purposeful groups. Humans create complex social structures composed of many cooperating and competing groups, from families and kinship networks to political states. Social interactions between humans have established an wide variety of values, social norms, rituals, which together undergird human society. Curiosity and the human desire to understand and influence the environment and to explain and manipulate phenomena have motivated humanity's development of science, mythology, religion and numerous other fields of knowledge. Though most of human existence has been sustained by hunting and gathering in band societies many human societies transitioned to sedentary agriculture some 10,000 years ago, domesticating plants and animals, thus enabling the growth of civilization; these human societies subsequently expanded, establishing various forms of government and culture around the world, unifying people within regions to form states and empires.
The rapid advancement of scientific and medical understanding in the 19th and 20th centuries permitted the development of fuel-driven technologies and increased lifespans, causing the human population to rise exponentially. The global human population was estimated to be near 7.7 billion in 2015. In common usage, the word "human" refers to the only extant species of the genus Homo—anatomically and behaviorally modern Homo sapiens. In scientific terms, the meanings of "hominid" and "hominin" have changed during the recent decades with advances in the discovery and study of the fossil ancestors of modern humans; the clear boundary between humans and apes has blurred, resulting in now acknowledging the hominids as encompassing multiple species, Homo and close relatives since the split from chimpanzees as the only hominins. There is a distinction between anatomically modern humans and Archaic Homo sapiens, the earliest fossil members of the species; the English adjective human is a Middle English loanword from Old French humain from Latin hūmānus, the adjective form of homō "man."
The word's use as a noun dates to the 16th century. The native English term man can refer to the species as well as to human males, or individuals of either sex; the species binomial "Homo sapiens" was coined by Carl Linnaeus in his 18th-century work Systema Naturae. The generic name "Homo" is a learned 18th-century derivation from Latin homō "man," "earthly being"; the species-name "sapiens" means "wise" or "sapient". Note that the Latin word homo refers to humans of either gender, that "sapiens" is the singular form; the genus Homo evolved and diverged from other hominins in Africa, after the human clade split from the chimpanzee lineage of the hominids branch of the primates. Modern humans, defined as the species Homo sapiens or to the single extant subspecies Homo sapiens sapiens, proceeded to colonize all the continents and larger islands, arriving in Eurasia 125,000–60,000 years ago, Australia around 40,000 years ago, the Americas around 15,000 years ago, remote islands such as Hawaii, Easter Island and New Zealand between the years 300 and 1280.
The closest living relatives of humans are gorillas. With the sequencing of the human and chimpanzee genomes, current estimates of similarity between human and chimpanzee DNA sequences range between 95% and 99%. By using the technique called a molecular clock which estimates the time required for the number of divergent mutations to accumulate between two lineages, the approximate date for the split between lineages can be calculated; the gibbons and orangutans were the first groups to split from the line leading to the h
In human anatomy, the cribriform plate of the ethmoid bone is received into the ethmoidal notch of the frontal bone and roofs in the nasal cavities. The cribriform plate is narrow with deep grooves supporting the olfactory bulb, is perforated by foramina allowing the passage of the olfactory nerves; the foramina in the middle of the groove are small and allows the passing of the nerves to the roof of the nasal cavity. The foramina at the medial part of the groove allow the passage of the nerves to the upper part of the nasal septum while the foramina at the lateral part transmit the nerves to the superior nasal concha. A fractured cribriform plate can result in olfactory dysfunction, septal hematoma, Cerebrospinal fluid rhinorrhoea, infection which can lead to meningitis. CSF rhinorrhoea is serious and considered a medical emergency. Aging can cause the openings in the cribriform plate to close pinching olfactory nerve fibers. A reduction in olfactory receptors, loss of blood flow, thick nasal mucus can cause an impaired sense of smell.
Projecting upward from the middle line of this plate is a thick, triangular process, the crista galli, so called from its resemblance to a rooster's comb. The long thin posterior border of the crista galli serves for the attachment of the falx cerebri, its anterior border and thick, articulates with the frontal bone, presents two small projecting alae, which are received into corresponding depressions in the frontal bone and complete the foramen cecum. Its sides are smooth, sometimes bulging from presence of a small air sinus in the interior. On either side of the crista galli, the cribriform plate is narrow and grooved; the foramina in the middle of the groove are small and transmit the nerves to the roof of the nasal cavity. At the front part of the cribriform plate, on either side of the crista galli, is a small fissure, occupied by a process of dura mater. Lateral to this fissure is a foramen which transmits the nasociliary nerve. A fractured cribriform plate can result in leaking of cerebrospinal fluid into the nose and loss of sense of smell.
The tiny apertures of the plate transmitting the olfactory nerve become the route of ascent for a pathogen, Naegleria fowleri. This amoeba tends to destroy the olfactory bulb and the adjacent inferior surface of the frontal lobe of the brain; this surface becomes the site of proliferation of the trophozoites of Naegleria fowleri and their subsequent spread to the rest of the brain and CSF. Because of its initial involvement and trophozoite presence in early phases of Naegleria fowleri infection, flushing of this region with saline using a device, to obtain Naegleria fowleri for diagnostic PCR and microscopic viewing has been proposed for patients affected by Primary Amoebic Meningoencephalitis, by in a recent publication. Researchers have suggested the same route to administer drugs at an early phase of infection by using a " Transcribrial Device ", proposed to kill this pathogen at a place of its maximum proliferation. In a 2017 the inventor of the device has suggested that after slight modifications this method could be effective in delivery of stem cells to the brain as well A recent Australian study as shown that bacterium causing the tropical disease melioidosis, Burkholderia pseudomallei can invade the brain via the olfactory nerve within 24 h by transversing the cribriform plate.
The Keros classification is a method of classifying the depth of the olfactory fossa. The depth of the olfactory fossa is determined by the height of the lateral lamella of the cribriform plate. Keros in 1962, classified the depth into three categories. Type 1: has a depth of 1–3 mm type 2: has a depth of 4–7mm type 3: has a depth of 8–16mm From Latin cribrum + -form; this article incorporates text in the public domain from page 153 of the 20th edition of Gray's Anatomy Cross section image: skull/x-front—Plastination Laboratory at the Medical University of Vienna
Dove Medical Press
Dove Medical Press is an academic publisher of open access peer-reviewed scientific and medical journals, with offices in Manchester, Princeton, New Jersey, Auckland. In September 2017, Dove Medical Press was acquired by the Francis Group; as an open access publisher, Dove charges a publication fee to authors or their institutions or funders. This charge allows Dove to recover its editorial and production costs and to create a pool of funds that can be used to provide fee waivers for authors from lesser developed countries. Articles published are available via an interface following the Open Archives Initiative Protocol for Metadata Harvesting, a set of uniform standards promulgated by the Open Archives Initiative allowing metadata on archive holdings. Dove is a member of the Association of Learned and Professional Society Publishers, the Committee on Publication Ethics, the Open Archives Initiative; as of March 2019, it published a total of 135 journals. Dove Medical Press is a held company founded in 2003 by Tim Hill, a former managing director of Adis International and five other founders.
As of 11 April 2013, 42 of the 131 journals were indexed in PubMed, while 30 of the 131 journals had fewer than 10 articles. In 2012, the company was included on Beall's list of predatory open access publishers, but was removed. In 2013, the Dove Medical Press journal Drug Design and Therapy accepted a false and intentionally flawed paper created and submitted by an investigative journalist for Science as part of a "sting" to test the effectiveness of the peer-review processes of open access journals; the Open Access Scholarly Publishers Association terminated Dove's membership as a result of the incident. After satisfying The Open Access Scholarly Publishers Association Membership Committee that new editorial and peer review procedures were in place to address the concerns raised during its investigation, Dove Medical Press was reinstated as a full member of Open Access Scholarly Publishers Association in September 2015. In September 2017, Dove Medical Press was acquired by Francis Group. All articles, including meta-data and supplementary files, are published under the Creative Commons Attribution license.
List of Dove Medical Press academic journals Official website
Vestigiality is the retention during the process of evolution of genetically determined structures or attributes that have lost some or all of their ancestral function in a given species. Assessment of the vestigiality must rely on comparison with homologous features in related species; the emergence of vestigiality occurs by normal evolutionary processes by loss of function of a feature, no longer subject to positive selection pressures when it loses its value in a changing environment. The feature may be selected against more urgently when its function becomes definitively harmful, but if the lack of the feature provides no advantage, its presence provides no disadvantage, the feature may not be phased out by natural selection and persist across species. Examples of vestigial structures are the loss of functional wings in island-dwelling birds. Vestigial features may take various forms. Like most other physical features, however functional, vestigial features in a given species may successively appear and persist or disappear at various stages within the life cycle of the organism, ranging from early embryonic development to late adulthood.
Vestigiality, biologically speaking, refers to organisms retaining organs that have lost their original function. The issue is controversial and not without dispute. In addition, the term vestigiality is useful in referring to many genetically determined features, either morphological, behavioral, or physiological. A classic example at the level of gross anatomy is the human vermiform appendix—though vestigial in the sense of retaining no significant digestive function, the appendix still has immunological roles and is useful in maintaining gut flora. Similar concepts apply at the molecular level—some nucleic acid sequences in eukaryotic genomes have no known biological function; the simple fact that it is noncoding DNA does not establish. Furthermore if an extant DNA sequence is functionless, it does not follow that it has descended from an ancestral sequence of functional DNA. Logically such DNA would not be vestigial in the sense of being the vestige of a functional structure. In contrast pseudogenes have lost their protein-coding ability or are otherwise no longer expressed in the cell.
Whether they have any extant function or not, they have lost their former function and in that sense they do fit the definition of vestigiality. Vestigial structures are called vestigial organs, although many of them are not organs; such vestigial structures are degenerate, atrophied, or rudimentary, tend to be much more variable than homologous non-vestigial parts. Although structures regarded "vestigial" may have lost some or all of the functional roles that they had played in ancestral organisms, such structures may retain lesser functions or may have become adapted to new roles in extant populations, it is important to avoid confusion of the concept of vestigiality with that of exaptation. Both may occur together depending on the relevant point of view. In exaptation a structure used for one purpose is modified for a new one. For example, the wings of penguins would be exaptational in the sense of serving a substantial new purpose, but might still be regarded as vestigial in the sense of having lost the function of flight.
In contrast Darwin argued that the wings of emus would be vestigial, as they appear to have no major extant function. The ostrich uses its wings in displays and temperature control, though they are undoubtedly vestigial as structures for flight. Vestigial characters range from detrimental through neutral to favorable in terms of selection; some may be of some limited utility to an organism but still degenerate over time if they do not confer a significant enough advantage in terms of fitness to avoid the effects of genetic drift or competing selective pressures. Vestigiality in its various forms presents many examples of evidence for biological evolution. Vestigial structures have been noticed since ancient times, the reason for their existence was long speculated upon before Darwinian evolution provided a accepted explanation. In the 4th century BC, Aristotle was one of the earliest writers to comment, in his History of Animals, on the vestigial eyes of moles, calling them "stunted in development" due to the fact that moles can scarcely see.
However, only in recent centuries have anatomical vestiges become a subject of serious study. In 1798, Étienne Geoffroy Saint-Hilaire noted on vestigial structures: His colleague, Jean-Baptiste Lamarck, named a number of vestigial structures in his 1809 book Philosophie Zoologique. Lamarck noted "Olivier's Spalax, which lives underground like the mole, is exposed to daylight less than the mole, has altogether lost the use of sight: so that it shows nothing more than vestiges of this organ."Charles Darwin was familiar with the concept of vestigial structures, though the term for them did not yet exist. He listed a number of them in The Descent of Man, including the muscles of the ear, wisdom teeth, the appe
Dissection is the dismembering of the body of a deceased animal or plant to study its anatomical structure. Autopsy is used in forensic medicine to determine the cause of death in humans. Less extensive dissection of plants and smaller animals preserved in a formaldehyde solution is carried out or demonstrated in biology and natural science classes in middle school and high school, while extensive dissections of cadavers of adults and children, both fresh and preserved are carried out by medical students in medical schools as a part of the teaching in subjects such as anatomy and forensic medicine. Dissection is conducted in a morgue or in an anatomy lab. Dissection has been used for centuries to explore anatomy. Objections to the use of cadavers have led to the use of alternatives including virtual dissection of computer models. Plant and animal bodies are dissected to analyze the function of its components. Dissection is practised by students in courses of biology, botany and veterinary science, sometimes in arts studies.
In medical schools, students dissect human cadavers to learn anatomy. Dissection is used to help to determine the cause of death in autopsy and is an intrinsic part of forensic medicine. A key principle in the dissection of human cadavers is the prevention of human disease to the dissector. Prevention of transmission includes the wearing of protective gear, ensuring the environment is clean, dissection technique and pre-dissection tests to specimens for the presence of HIV and Hepatitis viruses. Specimens are dissected in morgues or anatomy labs; when provided, they are evaluated for use as a "fresh" or "prepared" specimen. A "fresh" specimen may be dissected within some days, retaining the characteristics of a living specimen, for the purposes of training. A "prepared" specimen may be preserved in solutions such as formalin and pre-dissected by an experienced anatomist, sometimes with the help of a diener; this preparation is sometimes called prosection. Most dissection involves the careful isolation and removal of individual organs, called the Virchow technique.
An alternative more cumbersome technique involves the removal of the entire organ body, called the Letulle technique. This technique allows a body to be sent to a funeral director without waiting for the sometimes time-consuming dissection of individual organs; the Rokitansky method involves an in situ dissection of the organ block, the technique of Ghon involves dissection of three separate blocks of organs - the thorax and cervical areas and abdominal organs, urogenital organs. Dissection of individual organs involves accessing the area in which the organ is situated, systematically removing the anatomical connections of that organ to its surroundings. For example, when removing the heart, connects such as the superior vena cava and inferior vena cava are separated. If pathological connections exist, such as a fibrous pericardium this may be deliberately dissected along with the organ. Human dissections were carried out by the Greek physicians Herophilus of Chalcedon and Erasistratus of Chios in the early part of the third century BC.
During this period, the first exploration into full human anatomy was performed rather than a base knowledge gained from'problem-solution' delving. While there was a deep taboo in Greek culture concerning human dissection, there was at the time a strong push by the Ptolemaic government to build Alexandria into a hub of scientific study. For a time, Roman law forbade dissection and autopsy of the human body, so physicians had to use other cadavers. Galen, for example, dissected the Barbary macaque and other primates, assuming their anatomy was the same as that of humans; the ancient societies that were rooted in India left behind artwork on how to kill animals during a hunt. The images showing how to kill most depending on the game being hunted relay an intimate knowledge of both external and internal anatomy as well as the relative importance of organs; the knowledge was gained through hunters preparing the captured prey. Once the roaming lifestyle was no longer necessary it was replaced in part by the civilization that formed in the Indus Valley.
There is little that remains from this time to indicate whether or not dissection occurred, the civilization was lost to the Aryan people migrating. Early in the history of India, the Arthashastra described the 4 ways that death can occur and their symptoms: drowning, strangling, or asphyxiation. According to that source, an autopsy should be performed in any case of untimely demise; the practice of dissection flourished during the 8th century. It was under their rule; this created a need to better understand human anatomy, so as to have educated surgeons. Dissection was limited by the religious taboo on cutting the human body; this changed the approach taken to accomplish the goal. The process involved the loosening of the tissues in streams of water before the outer layers were sloughed off with soft implements to reach the musculature. To perfect the technique of slicing, the prospective students used gourds and squash; these techniques of dissection gave rise to an advanced understanding of the anatomy and the enabled them to complete procedures used today, such as rhinoplasty.
During medieval times the anatomical teachings from India spread throughout the known world however the practice of dissection was stunted by Islam. The practice of dissection at a university level was not seen again until 1827, when it was performed by the student Pandit Madhusudan Gupta. Through the 1900s
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to impact the behavior of the receiving individuals. There are alarm pheromones, food trail pheromones, sex pheromones, many others that affect behavior or physiology. Pheromones are used from basic unicellular prokaryotes to complex multicellular eukaryotes, their use among insects has been well documented. In addition, some vertebrates and ciliates communicate by using pheromones; the portmanteau word "pheromone" was coined by Peter Karlson and Martin Lüscher in 1959, based on the Greek φερω pheroo and ὁρμων hormon. Pheromones are sometimes classified as ecto-hormones, they were researched earlier by various scientists, including Jean-Henri Fabre, Joseph A. Lintner, Adolf Butenandt, ethologist Karl von Frisch who called them various names, like for instance "alarm substances".
These chemical messengers are transported outside of the body and affect neurocircuits, including the autonomous nervous system with hormone or cytokine mediated physiological changes, inflammatory signaling, immune system changes and/or behavioral change in the recipient. They proposed the term to describe chemical signals from conspecifics that elicit innate behaviors soon after the German biochemist Adolf Butenandt had characterized the first such chemical, bombykol, a chemically well-characterized pheromone released by the female silkworm to attract mates. Aggregation pheromones function in mate selection, overcoming host resistance by mass attack, defense against predators. A group of individuals at one location is referred to as an aggregation, whether consisting of one sex or both sexes. Male-produced sex attractants have been called aggregation pheromones, because they result in the arrival of both sexes at a calling site and increase the density of conspecifics surrounding the pheromone source.
Most sex pheromones are produced by the females. Aggregation pheromones have been found in members of the Coleoptera, Hemiptera and Orthoptera. In recent decades, the importance of applying aggregation pheromones in the management of the boll weevil, stored product weevils, Sitophilus granarius, Sitophilus oryzae, pea and bean weevil has been demonstrated. Aggregation pheromones are among the most ecologically selective pest suppression methods, they are nontoxic and effective at low concentrations. Some species release a volatile substance when attacked by a predator that can trigger flight or aggression in members of the same species. For example, Vespula squamosa use alarm pheromones to alert others to a threat. In Polistes exclamans, alarm pheromones are used as an alert to incoming predators. Pheromones exist in plants: Certain plants emit alarm pheromones when grazed upon, resulting in tannin production in neighboring plants; these tannins make the plants less appetizing for the herbivore.
Epideictic pheromones are different from territory pheromones. Fabre observed and noted how "females who lay their eggs in these fruits deposit these mysterious substances in the vicinity of their clutch to signal to other females of the same species they should clutch elsewhere." It may be helpful to note that the word epideictic, having to do with display or show, has a different but related meaning in rhetoric, the human art of persuasion by means of words. Releaser pheromones are pheromones. For example, some organisms use powerful attractant molecules to attract mates from a distance of two miles or more. In general, this type of pheromone elicits a rapid response, but is degraded. In contrast, a primer pheromone has a longer duration. For example, rabbit release mammary pheromones that trigger immediate nursing behavior by their babies. Signal pheromones cause short-term changes, such as the neurotransmitter release that activates a response. For instance, GnRH molecule functions as a neurotransmitter in rats to elicit lordosis behavior.
Primer pheromones trigger a change of developmental events. Laid down in the environment, territorial pheromones mark the boundaries and identity of an organism's territory. In cats and dogs, these hormones are present in the urine, which they deposit on landmarks serving to mark the perimeter of the claimed territory. In social seabirds, the preen gland is used to mark nests, nuptial gifts, territory boundaries with behavior described as'displacement activity'. Social insects use trail pheromones. For example, ants mark their paths with pheromones consisting of volatile hydrocarbons. Certain ants lay down an initial trail of pheromones; this trail serves as a guide. As long as the food source remains available, visiting ants will continuously renew the pheromone trail; the pheromone requires continuous renewal. When the food supply begins to dwindle, the trail-making ceases. In at least one species of ant, trails that no longer lead to food are marked with a repellent pheromone; the Eciton burchellii species provides an example of using pheromones to mark and maintain foraging paths.
When species of wasps such as Polybia sericea found new nests, they use pheromones to lead the rest of the