66 Sentences With "intromission" | Random Sentence Generator

Intromission, the meeting of penis and vagina, is crucial to reproduction.

Males use "prolonged intromission" to keep the female away from his competition while he impregnates her.

"Species with longer intromission periods [as in, the act of penetration] than three minutes tend to have longer baculums," Brindle responds.

With insufficient stiffness, intromission will not happen and the genes of the male will fail to make it into the next generation.

Third, there was a strong correlation between the length of the bone in a species, and the average length of time intromission lasted in that species.

Kit Opie, a postdoctoral research fellow at University College London who led the study, tells The Guardian that penis bone length was longer in males that engaged in "prolonged intromission"—meaning when species take more than three minutes to mate.

Matilda Brindle, the study's co-author, explains it like this on The Conversation:Far from simply being a nice way to spend an afternoon, prolonging intromission like this is a way for a male to prevent a female from sneaking off and mating with anyone else before his sperm have had a chance to work their magic.

The male then mounted, while balancing with outstretched wings. Intromission only lasted a few seconds.

In some species such as the ferret, the duration of intromission has no effect on the LH surge, whereas in other species such as the cat these are related and higher levels of LH were produced by mating multiple times. In many species, for a LH surge to occur, little intromission is required. The pathways in which information reaches the brain and causes GnRH release are not understood well; however, midbrain and brainstem noradrenergic neurones appear to be activated in response to intromission during mating. These neurones then go on to stimulate the mediobasal hypothalamic to release GnRH from the median eminence.

The mucus of this snail species contains species-specific signals that allow individual snails to identify others of the same species, but the causative mucus components decay within 10 to 30 min. The typically unilateral copulations are initiated when a male actor mounts the shell of a prospective mate. The male actor then moves towards the frontal left edge of the partner's shell, where he probes the female gonopore with his penis to subsequently achieve penis intromission. Following a typically 5–87 min penis intromission with usually successful sperm transfer, the male actor retracts to terminate copulation.

Langlois TH. The conjugal behavior of the introduced European giant garden slug, Limax maximus L., as observed on South Bass Island, Lake Erie. Ohio J Sci. 1965;65((5)):298-304. Evolutionary explanations for this behaviour are unclear. Belocaulus angustipes mating with intromission and internal sperm exchange.

The second theory, the intromission theory supported by Aristotle and his followers, had physical forms entering the eye from an object. Previous Islamic writers (such as al-Kindi) had argued essentially on Euclidean, Galenist, or Aristotelian lines. The strongest influence on the Book of Optics was from Ptolemy's Optics, while the description of the anatomy and physiology of the eye was based on Galen's account.. Alhazen's achievement was to come up with a theory that successfully combined parts of the mathematical ray arguments of Euclid, the medical tradition of Galen, and the intromission theories of Aristotle. Alhazen's intromission theory followed al- Kindi (and broke with Aristotle) in asserting that "from each point of every colored body, illuminated by any light, issue light and color along every straight line that can be drawn from that point".. This however left him with the problem of explaining how a coherent image was formed from many independent sources of radiation; in particular, every point of an object would send rays to every point on the eye.

In most mammals ejaculation occurs after multiple intromissions, but in most primates, copulation consists of one brief intromission. In most ruminant species, a single pelvic thrust occurs during copulation. In most deer species, a copulatory jump also occurs. During mating, a "copulatory tie" occurs in mammals such as fossas, canids and Japanese martens.

Males of some species are able to immobilize females and force copulation. In pigs and boars, males grab females and maneuver the pelvis to lift the vaginal opening and facilitate copulation. The stimulation following intromission causes the female to be immobilized. The male can then freely continue copulation without worrying about the female escaping.

These structures make it harder for males to achieve intromission. The clockwise coils are significant because the male phallus everts out of their body in a counter-clockwise spiral; therefore, a clockwise vaginal structure would impede forceful copulation. Studies have shown that the longer a male's phallus is, the more elaborate the vaginal structures were.

In alpaca, follicles ovulate approximately 26 hours after coital stimulation. Mounting accompanied by intromission is necessary to provide adequate stimulation for LH release and subsequent ovulation. Deposition of semen, which contains ovulation-inducing factor (OIF), has been shown to increase the chance of pregnancy. Prolonged copulation, causing abrasion and inflammation of the uterus, may enhance absorption of OIF.

Dixson demonstrated that increased baculum length is associated with primates who live in dispersed groups, while small bacula are found in primates who live in pairs. Those primates that have multi-male mating systems tend to have bacula that are larger in size, in addition to prolongation of post- ejaculatory intromission and larger relative testis size.

There are two types of induced pseudopregnancy; coitally induced pseudopregnancy and non-coitally induced pseudopregnancy. Rat The coitally induced pseudopregnancy is stimulated by the action of copulation. The copulation stimulation causes the nocturnal prolactin elevation which then activates the corpus luteum. The multiple intromission coital pattern initiates the neuroendocrine reflex which results in the sufficient progesterone secretion in pseudopregnancy.

Vicious intromission is a term of Scots law denoting the unauthorised assumption of ownership, or other interference with the rights of an estate. In 1771 James Boswell appeared before the Court of Session in Wilson vs Smith and Armour, arguing for a return to the principle that the punishment for vicious intromission should be restored to its traditional severity, of rendering the intromittor liable to pay all the debts of the estate. His attempt was unsuccessful, but led to an exchange with his friend Doctor Johnson in July 1772, recorded in his Life of Samuel Johnson, in which the latter wrote a paper on the legal principles involved, stating misera est servitus ubi jus est aut incognitum aut vagum ("miserable is that state of slavery in which the law is unknown or uncertain").

Intromission usually occurs in trees on horizontal limbs about off the ground. Frequently the same tree is used year after year, with remarkable precision as to the date the season commences. Trees are often near a water source, and have limbs strong enough and wide enough to support the mating pair, about wide. Some mating has been reported on the ground as well.

Domestic cats are often described as induced ovulators. During intromission, the penis probably causes distension of the posterior vagina and induces release of gonadotropin releasing hormone (GnRH) from the hypothalamus via neuroendocrine reflexes. A surge of luteinising hormone (LH) occurs within minutes of mating. With multiple matings, the LH surge is greater and lasts longer than when only one mating occurs.

She uses an advertising call to indicate her receptivity. Males approach and copulate repeatedly with the female and maintain intromission with the female for several hours. Mating patterns can be either monogamous or polygynous, often determined by the overlapping of host ranges and competing of males for best territories. Females typically give birth to 2 young, sometimes 1 or 3.

The front of a pronghorn's glans penis is relatively flat, while the back is relatively thick. The male pronghorn usually ejaculates immediately after intromission. The penis of a dromedary camel is covered by a triangular penile sheath opening backwards, and is about long. The camelmen often aid the male to enter his penis into the female's vulva, though the male is considered able to do it on his own.

The female will signal its readiness to mate by lifting its tail and staying still. The male will then coil itself around the posterior end of the female and align its tail ventrolaterally with the female's. Intromission may last longer than two hours and the pair remain motionless apart from occasional spasms from the male. The black mamba is oviparous; the female lays a clutch of 6–17 eggs.

These practical developments were followed by the development of theories of light and vision by ancient Greek and Indian philosophers, and the development of geometrical optics in the Greco-Roman world. The word optics comes from the ancient Greek word (optikē), meaning "appearance, look". Greek philosophy on optics broke down into two opposing theories on how vision worked, the intromission theory and the emission theory.A History Of The Eye . stanford.edu.

Even within the Vertebrata there are morphological variants with specific terminology, such as hemipenes. In most species of animals in which there is an organ that might reasonably be described as a penis, it has no major function other than intromission, or at least conveying the sperm to the female, but in the placental mammals the penis bears the distal part of the urethra, which discharges both urine during urination and semen during copulation.

ERα is similarly essential in the maturation and maintenance of the male reproductive phenotype, as male ERKO mice are infertile and present undersized testes. The integrity of testicular structures of ERKO mice, such as the seminiferous tubules of the testes and the seminiferous epithelium, declines over time. Furthermore, the reproductive performance of male ERKO mice is hindered abnormalities in sexual physiology and behavior, such as impaired spermatogenesis and loss of intromission and ejaculatory responses.

Adult males are slightly larger and more muscular than females, and have wider heads and necks. Visual sex determination can, however, be difficult, since the penis and testes are located internally between the rectum and urinary bladder in males and females have a single pair of mammae near the armpits. Fertilization occurs by contact transfer without intromission, similar to some lizards. Polygynous mating usually results in a single offspring; twins are possible but rare.

"How does light travel through transparent bodies? Light travels through transparent bodies in straight lines only.... We have explained this exhaustively in our Book of Optics." —Alhazen The Arab physicist Ibn al-Haytham (Alhazen) used experimentation to obtain the results in his Book of Optics (1021). He combined observations, experiments and rational arguments to support his intromission theory of vision, in which rays of light are emitted from objects rather than from the eyes.

"How does light travel through transparent bodies? Light travels through transparent bodies in straight lines only.... We have explained this exhaustively in our Book of Optics." —Alhazen The Arab physicist Ibn al- Haytham (Alhazen) used experimentation to obtain the results in his Book of Optics (1021). He combined observations, experiments and rational arguments to support his intromission theory of vision, in which rays of light are emitted from objects rather than from the eyes.

The front legs of the male hang loosely and intromission takes the form of a "copulatory jump". Gestation probably lasts around 8 months, although some studies suggest it may be slightly longer. Normally, only one calf is born at a time, although twins have been reported in up to 2% of births. Initially weighing , the calves are usually not spotted, although some subspecies have light spots which disappear not long after birth.

Estrous behavior in the female dog is usually indicated by her standing still with the tail held up, or to the side of the perineum, when the male sniffs the vulva and attempts to mount. This tail position is sometimes called “flagging”. The female dog may also turn, presenting the vulva to the male. The male dog mounts the female and is able to achieve intromission with a non-erect penis, which contains a bone called the os penis.

Carl Benjamin Boyer, The Rainbow: From Myth to Mathematics (1959) The work is also important for the early history of perception. Ptolemy combined the mathematical, philosophical and physiological traditions. He held an extramission-intromission theory of vision: the rays (or flux) from the eye formed a cone, the vertex being within the eye, and the base defining the visual field. The rays were sensitive, and conveyed information back to the observer's intellect about the distance and orientation of surfaces.

Retrieved 2012-06-10. The intromission approach saw vision as coming from objects casting off copies of themselves (called eidola) that were captured by the eye. With many propagators including Democritus, Epicurus, Aristotle and their followers, this theory seems to have some contact with modern theories of what vision really is, but it remained only speculation lacking any experimental foundation. Plato first articulated the emission theory, the idea that visual perception is accomplished by rays emitted by the eyes.

The German Angus was bred in the 1950s by cross- breeding imported Aberdeen Angus stock from the United Kingdom with local German breeds; these were the German Black Pied or Deutsches Schwarzbuntes Niederungsrind, the Deutsche Rotbunte or Rotbuntes Niederungsrind, and the Fleckvieh or German Simmental. Since 1960 there has been some intromission of North American Angus. In 1955 a breed society was established, and in 1956 a herd-book was started. In 2017 the population was recorded as 9603 cows and 454 bulls.

Mare and foal The Irish Sport Horse, or Irish Hunter, is an Irish breed of warmblood sporting horse, used mostly for dressage, eventing and show-jumping. It was bred from 1923 by cross-breeding of Irish Draught and Thoroughbred stock. There was some limited intromission of Hanoverian, Selle Français and Trakehner blood in the 1990s. It is a recognised true breed – foals may only be registered in the main section of the stud-book if both parents are registered in that section.

He used similar arguments to show that the ancient emission theory of vision supported by Ptolemy and Euclid (in which the eyes emit the rays of light used for seeing), and the ancient intromission theory supported by Aristotle (where objects emit physical particles to the eyes), were both wrong.D. C. Lindberg, Theories of Vision from al-Kindi to Kepler, (Chicago, Univ. of Chicago Pr., 1976), pp. 60–7. Al- Zahrawi, regarded by many as the greatest surgeon of the middle ages.

Cryptic female choice falls under the conflict in reproductive patterns. Cryptic female choice results from process that occurs after intromission which allows the female to preferentially fertilize or produce offspring with a particular male phenotype. It is thought that if the female's cryptic choice provides her with indirect genetic benefits in the form of more fit offspring, any male phenotype that limits female cryptic choice will induce a cost on the female. Often, cryptic female choice occurs in polyandrous or polygamous species.

Ibn al-Haytham is also regarded as the father of optics, especially for his empirical proof of the intromission theory of light. Some have also described Ibn al-Haytham as the "first scientist" for his development of the modern scientific method. In mathematics, the mathematician Muhammad ibn Musa al-Khwarizmi (c. 780–850) gave his name to the concept of the algorithm, while the term algebra is derived from al-jabr, the beginning of the title of one of his publications.Toomer, Gerald (1990).

This phallus everts out of the male body (when it's time to mate) in a counter-clockwise coil. As a response, females have developed vaginal structures called dead end sacs and clockwise coils to protect themselves from forceful intromission. Waterfowl females have evolved these “convoluted vaginal morphologies” to make it harder for males to insert themselves without the female's consent.Brennan, P. L. R., Clark, C. J. & Prum, R. O. Explosive eversion and functional morphology of the duck penis supports sexual conflict in waterfowl genitalia.

Florida mice breed throughout the year with a peak between July and December, a lesser peak in January and February, and a lull or cessation in April and May. Unlike most murids, copulatory behavior lacks intravaginal thrusting, the intromission thrust is more intense than the dismount, there is no lock, and ejaculation occurs with every thrust. Gestation is about 23 or 24 days. The mice dig side burrows off the main burrow of the gopher tortoise, line them with shredded plant material, and use them as nurseries.

Also, they may evolve shield over their genital openings to prevent intromission. Females of some species of water striders have evolved protection from forceful insemination, such as abdominal spines and downward-bent abdomens to make it harder for males to mate. In response, however, males have counter evolved, also changing the shape of their abdomens to those that would facilitate forceful mating. The male waterfowl (Aves: Anatidae) evolution of a phallus to forcefully copulate with females has led to counteradaptations in females in the form of vaginal structures called dead end sacs and clockwise coils.

Emission theory or extramission theory (variants: extromission) or extromissionism is the proposal that visual perception is accomplished by eye beams emitted by the eyes. This theory has been replaced by intromission theory (or intromissionism), which states that visual perception comes from something representative of the object (later established to be rays of light reflected from it) entering the eyes. Modern physics has confirmed that light is physically transmitted by photons from a light source, such as the sun, to visible objects, and finishing with the detector, such as a human eye or camera.

Ibn al- Haytham is also regarded as the father of optics, especially for his empirical proof of the intromission theory of light. Algebra was also pioneered by Persian Scientist Muhammad ibn Mūsā al-Khwārizmī during this time in his landmark text, Kitab al-Jabr wa-l-Muqabala, from which the term algebra is derived. He is thus considered to be the father of algebra. The terms algorism and algorithm are also derived from the name of al-Khwarizmi, who was responsible for introducing the Arabic numerals and Hindu-Arabic numeral system beyond the Indian Subcontinent.

After Mazinger's intromission, Gorgon goes down to the Mikene underworld to inform the General of Darkness about the situation. He finds him quite upset for the loss of some of his favorite beasts, and demands to know who is responsible for it. Gorgon reports that Mazinger had stopped the attacks and that Dr. Hell had had many troubles with him in the past. The Dark General then commands General Juuma to take some monsters of his choice to Japan to annihilate the enemy, so that finally, Mikene can see daylight once more.

In addition to Ariolimax species, autoapophallation (self- amputation) has been documented in Deroceras laeve. Here, it is a regular part of mating, although the penis does not get trapped in the other slug (as there is external sperm transfer), and may occur because the amputee's penis retraction ability has been inhibited by the partner by transfer of a secretion. As a result, these individuals can no longer mate, and are only able to reproduce uniparentally. Aphallic individuals of Ariolimax species are still able to mate, but only as females, as they have intromission and internal sperm exchange.

The Cornigliese breed was created in the mid-18th century by the Borboni of Parma by crossing the local Vissana breed with Spanish merinos to improve the quality of the wool, at that time the most important attribute of sheep. In the early 20th century, the weight was increased by intromission of Bergamasca blood. The Cornigliese is one of the forty-two autochthonous local sheep breeds of limited distribution for which a herdbook is kept by the Associazione Nazionale della Pastorizia, the Italian national association of sheep-breeders. The conservation status of the Cornigliese was listed as "endangered" by the FAO in 2007.

His work is considered instrumental in the development of science and astronomy. One of Al-Battani's best-known achievements in astronomy was the determination of the solar year as being 365 days, 5 hours, 46 minutes and 24 seconds which is only 2 minutes and 22 seconds off. Ibn al- Haytham (Alhazen) used experimentation to obtain the results in his Book of Optics (1021), an important development in the history of the scientific method. He combined observations, experiments and rational arguments to support his intromission theory of vision, in which rays of light are emitted from objects rather than from the eyes.

He used similar arguments to show that the ancient emission theory of vision supported by Ptolemy and Euclid (in which the eyes emit the rays of light used for seeing), and the ancient intromission theory supported by Aristotle (where objects emit physical particles to the eyes), were both wrong.D. C. Lindberg, Theories of Vision from al-Kindi to Kepler, (Chicago, Univ. of Chicago Pr., 1976), pp. 60–7. Experimental evidence supported most of the propositions in his Book of Optics and grounded his theories of vision, light and colour, as well as his research in catoptrics and dioptrics.

Japan was effectively isolated from the rest of the world from 1635 until 1854; there was no possibility of intromission of foreign genes to the cattle population during this time. Between 1868, the year of the Meiji Restoration, and 1887, some 2600 foreign cattle were imported. At first there was little interest in cross-breeding these with native stock, but from about 1900 it became widespread. It ceased abruptly in 1910, when it was realised that, while the cross-breeds might be larger and have better dairy qualities, their working capacity and meat quality was lower.

If an object was seen directly it was by 'means of rays' coming out of the eyes and again falling on the object. A refracted image was, however, seen by 'means of rays' as well, which came out of the eyes, traversed through the air, and after refraction, fell on the visible object which was sighted as the result of the movement of the rays from the eye. This theory was championed by scholars who were followers of Euclid's Optics and Ptolemy's Optics. The second school advocated the so-called 'intromission' approach which sees vision as coming from something entering the eyes representative of the object.

Cattle were brought to Japan from China at the same time as the cultivation of rice, in about the second century AD, in the Yayoi period. Until about the time of the Meiji Restoration in 1868, they were used only as draught animals, in agriculture, forestry, mining and for transport, and as a source of fertiliser. Milk consumption was unknown, and – for cultural and religious reasons – meat was not eaten. Cattle were highly prized and valuable, too expensive for a poor farmer to buy. Japan was effectively isolated from the rest of the world from 1635 until 1854; there was no possibility of intromission of foreign genes to the cattle population during this time.

Adherents of emission theory cited at least two lines of evidence for it. The custom of saluting is said by some to stem from the habit of Greek soldiers putting their hands up in front of their eyes to "shade" their eyes from the powerful "light" shining from the eyes of their commanders. The light from the eyes of some animals (such as cats, which modern science has determined have highly reflective eyes) could also be seen in "darkness". Adherents of intromission theory countered by saying that if emission theory were true, then someone with weak eyes should have his or her vision improved when someone with good eyes looks at the same objects.

Front page of the Latin Opticae Thesaurus, which included Alhazen's Book of Optics, showing rainbows, the use of parabolic mirrors to set ships on fire, distorted images caused by refraction in water, and other optical effects. The Book of Optics (; or Perspectiva; ) is a seven-volume treatise on optics and other fields of study composed by the medieval Arab scholar Ibn al-Haytham, known in the West as Alhazen or Alhacen (965–c. 1040 AD). The Book of Optics presented experimentally founded arguments against the widely held extramission theory of vision (as held by Euclid in his Optica), and proposed the modern intromission theory, the now accepted model that vision takes place by light entering the eye.

Ptolemy, in his treatise Optics, held an extramission-intromission theory of vision: the rays (or flux) from the eye formed a cone, the vertex being within the eye, and the base defining the visual field. The rays were sensitive, and conveyed information back to the observer's intellect about the distance and orientation of surfaces. He summarized much of Euclid and went on to describe a way to measure the angle of refraction, though he failed to notice the empirical relationship between it and the angle of incidence. Plutarch (1st–2nd century AD) described multiple reflections on spherical mirrors and discussed the creation of magnified and reduced images, both real and imaginary, including the case of chirality of the images.

Cattle were brought to Japan from China at the same time as the cultivation of rice, in about the second century AD, in the Yayoi period. Until about the time of the Meiji Restoration in 1868, they were used only as draught animals, in agriculture, forestry, mining and for transport, and as a source of fertiliser. Milk consumption was unknown, and – for cultural and religious reasons – meat was not eaten. Cattle were highly prized and valuable, too expensive for a poor farmer to buy. Japan was effectively isolated from the rest of the world from 1635 until 1854; there was no possibility of intromission of foreign genes to the cattle population during this time.

The Coolidge effect states that males typically will prefer novel mates every time the opportunity is present, however there is a physical limit to the sex drive. An experiment performed on rats showed that when left to reproduce to sexual satiety, the motor ejaculatory behavior, intromission, and dislodging seminal plugs were all possible after multiple mates, however little to no sperm would be produced during ejaculation. The experiment also concluded that males that reached satiety and non-satiety males both had the similar amounts of intromissions and time spent dislodging the seminal plug. Another study performed on rats showed the same results, but found data that concluded that reaching optimal chances of impregnating their mates happened after resting for 15 days.

Tajima cattle on a Hyōgo farm Tajima cattle on a Hyōgo farm Cattle were brought to Japan from China at the same time as the cultivation of rice, in about the second century AD, in the Yayoi period. Until about the time of the Meiji Restoration in 1868, they were used only as draught animals, in agriculture, forestry, mining and for transport, and as a source of fertiliser. Milk consumption was unknown, and – for cultural and religious reasons – meat was not eaten. Japan was effectively isolated from the rest of the world from 1635 until 1854; there was no possibility of intromission of foreign genes to the cattle population during this time. Between 1868, the year of the Meiji Restoration, and 1887, some 2,600 foreign cattle were imported, including Braunvieh, Shorthorn, and Devon.

Specific to the male hamster, his response to the female can be measured by mounting behaviour, intromission and ejaculation. Under semi-natural conditions, the mating behaviours of male and female hamsters were observed during the 4-day period of estrous. When they were allowed free interaction, females displayed lordosis in their own living area 93% of the time, where after 60 minutes of copulation the male would be driven out by the female while she retrieved his food supply and forced him into a corner farthest away from her nest via displays of aggressive behaviour. When a Syrian hamster is introduced to a stranger hamster in its own cage, they perform a standard sequence of acts and postures (also known as a fixed action pattern) that are agonistic by nature.

Sexual learning (a form of associative learning) occurs when an animal starts to associate bodily features, personality, contextual cues, and other stimuli with genitally-induced sexual pleasure. Once formed, these associations in turn impinge upon both sexual wanting and sexual liking. In most female mammals, the act of copulation is controlled by several innate neurobiological processes, including the motor sexual reflex of lordosis.PFAFF Donald W. , SCHWARTZ-GIBLIN Susan, MACCARTHY Margareth M. , KOW Lee-Ming : Cellular and molecular mechanisms of female reproductive behaviors, in KNOBIL Ernest, NEILL Jimmy D. : The physiology of reproduction, Raven Press, 2nd edition, 1994 In males, the act of copulation is more complex, because some learning is necessary, but the innate processes (retrocontrol of penis intromission in the vagina, rhythmic movement of the pelvis, detection of female pheromones) are specific to copulation.

Some horse dealers purchased young gray Poitevin horses, fed them heavily to make them larger and stronger, and then sold them at the age of four as Percherons. These "Percherons" were transported to areas such as Saintonge, Yonne, Nivernais and Gâtinais. Poitevin stallion in an engraving of 1877 In the nineteenth century the Poitevin received some intromission of other blood: early in the century, a few Percheron stallions were introduced to the breeding area; between 1860 and 1867, about ten Bourbourienne stallions were used; in the middle years of the century, more substantial use was made of Breton stallions, a practice supported by some breeders and criticised by others. The Breton influence tended to make the head more square and the ears shorter; the Poitevin lost weight without gaining anything else, the legs became too long and too thin, and gray became more common as a coat color.

With its main propagators Aristotle (De Sensu), Galen (De Usu Partium Corporis Humani) and their followers, this theory seems to have some contact with modern theories of what vision really is, but it remained only a speculation lacking any experimental foundation. (In eighteenth-century England, Isaac Newton, John Locke, and others, carried the intromission theory of vision forward by insisting that vision involved a process in which rays—composed of actual corporeal matter—emanated from seen objects and entered the seer's mind/sensorium through the eye's aperture.) Both schools of thought relied upon the principle that "like is only known by like", and thus upon the notion that the eye was composed of some "internal fire" which interacted with the "external fire" of visible light and made vision possible. Plato makes this assertion in his dialogue Timaeus (45b and 46b), as does Empedocles (as reported by Aristotle in his De Sensu, DK frag. B17). Leonardo da Vinci: The eye has a central line and everything that reaches the eye through this central line can be seen distinctly.