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Mary Elizabeth Braddon

Mary Elizabeth Braddon (4 October 1835 – 4 February 1915) was an English popular novelist of the Victorian era. She is best known for her 1862 sensation novel Lady Audley's Secret, which has also been dramatised and filmed several times.

Biography
Born in Soho, London, Mary Elizabeth Braddon was privately educated. Her mother Fanny separated from her father Henry because of his infidelities in 1840, when Mary was five. When Mary was ten years old, her brother Edward Braddon left for India and later Australia, where he became Premier of Tasmania. Mary worked as an actress for three years, when she was befriended by Clara and Adelaide Biddle. They were only playing minor roles, but Braddon was able to support herself and her mother. Adelaide noted that Braddon's interest in acting waned as she began writing novels.

Mary met John Maxwell (1824–1895), a publisher of periodicals, in April 1861 and moved in with him in 1861. However, Maxwell was already married to Mary Ann Crowley, with whom he had five children. While Maxwell and Braddon were living as husband and wife, Crowley was living with her family. In 1864, Maxwell tried to legitimize their relationship by telling the newspapers that they were legally married; "however, Richard Brinsley Knowles wrote to these papers, informing them that his sister-in-law and true wife of Maxwell was still living, thereby exposing Braddon's 'wife' status as a façade". Mary acted as stepmother to his children until 1874, when Maxwell's wife died and they were able to get married at St. Bride's Church in Fleet Street. Braddon had six children by him: Gerald, Fanny, Francis, William, Winifred Rosalie, and Edward Herry Harrington.Her eldest daughter, Fanny Margaret Maxwell (1863–1955), married the naturalist Edmund Selous on 13 January 1886. In the 1920s, they were living in Wyke Castle, where Fanny founded a local branch of the Woman's Institute in 1923, of which she became the first president.

Their second eldest son was the novelist William Babington Maxwell (1866–1939).

Braddon died on 4 February 1915 in Richmond (then in Surrey) and is interred in Richmond Cemetery. Her home had been Lichfield House in the centre of the town, which was replaced by a block of flats in 1936, Lichfield Court. There is a plaque commemorating Braddon in Richmond parish church, which calls her simply "Miss Braddon". A number of nearby streets are named after characters in her novels – her husband was a property developer in the area.

Work
WritingBraddon was a prolific writer, producing more than 80 novels with inventive plots. The most famous is Lady Audley's Secret (1862), which won her recognition and a fortune as a bestseller. Braddon began publishing the first chapters of her novel serially in July, 1861, in Robin Goodfellow, a literary magazine owned by Maxwell, and then later Sixpenny Magazine. Lady Audley's Secret was then republished as a novel and sold through nine editions in its first year of publication. It has remained in print since its publication and been dramatised and filmed several times, with the first stage adaptation opening in London by the winter of 1863.

In addition to Lady Audley's Secret, Braddon's other best-known novel, Aurora Floyd, was published in 1863. Since it also featured a woman trapped in a bigamous relationship, Aurora Floyd and Lady Audley's Secret have been referred to as Braddon's "bigamy novels." Like Lady Audley, Aurora Floyd was first serialized in Temple Bar, a magazine, before appearing in novelized form.

R. D. Blackmore's anonymous sensation novel Clara Vaughan (1864) was wrongly attributed to Braddon by some critics.

Braddon wrote several works of supernatural fiction, including the pact with the devil story Gerard or The World, the Flesh, and the Devil (1891), and the ghost stories "The Cold Embrace", "Eveline's Visitant" and "At Chrighton Abbey". From the 1930s onwards, these stories were often anthologised in collections such as Montague Summers's The Supernatural Omnibus (1931) and Fifty Years of Ghost Stories (1935). Braddon also wrote historical fiction. In High Places depicts the youth of Charles I. London Pride focuses on Charles II. Mohawks is set during the reign of Queen Anne. Ishmael is set at the time of Napoleon III's rise to power.

Publishing

Braddon founded Belgravia magazine (1866), which presented readers with serialised sensation novels, poems, travel narratives and biographies, along with essays on fashion, history and science. It was accompanied by lavish illustrations and offered a source of literature at an affordable cost. She also edited Temple Bar magazine.

Legacy

There is a critical essay on Braddon's work in Michael Sadleir's book Things Past (1944). In 2014 the Mary Elizabeth Braddon Association was founded to pay tribute to Braddon's life and work.

Partial list of fiction
• The Trail of the Serpent (first published as Three Times Dead, 1860)

• The Octoroon (1861)

• The Black Band (1861)

• Lady Audley's Secret (1862) also at Project Gutenberg. French: Le Secret de Lady Audley (1863)

• Ralph the Bailiff and Other Tales (1862)

• John Marchmont's Legacy (1862–1863)

• The Captain of the Vulture (1863)

• Aurora Floyd (1863) also at Project Gutenberg (Vol.1), (Vol.2), (Vol.3)

• Eleanor's Victory (1863)

• Henry Dunbar: the story of an outcast (1864)

• The Doctor's Wife (1864)

• Only a Clod (1865)

• Sir Jasper's Tenant (1865)

• The Lady's Mile (1866). French: L'Allée des Dames (1868)

• Birds of Prey (1867). French: Oiseaux de proie (1874)

• Circe (1867)

• Rupert Godwin (1867)

• Run to Earth (1868). French: La Chanteuse des rues (1873)

• Dead-Sea Fruit (1868). French: Un Fruit de la Mer Morte (1874)

• Charlotte's Inheritance (1868). French: L'Héritage de Charlotte (1874)

• Fenton's Quest (1871)

• To the Bitter End (1872)

• Robert Ainsleigh (1872)

• Lucius Davoren; or, Publicans and Sinners (1873). French: Lucius Davoren (1878)

• Milly Darrell, and other tales (1873)

• Griselda (1873, drama)

• Lost For Love (1874)

• Taken at the Flood (1874)

• A Strange World (1875)

• Hostages to Fortune (1875)

• Joshua Haggard's Daughter (1876). French: Joshua Haggard (1879)

• Weavers and Weft, or, In Love's Nest (1876)

• Dead Men's Shoes (1876)

• An Open Verdict (1878)

• The Cloven Foot (1879), also at Project Gutenberg

• Vixen (1879) (Vol.1)

• Just as I am (1880)

• Asphodel (1881)

• Mount Royal (1882)

• Phantom Fortune (1883)

• The Golden Calf (1883)

• Ishmael. A novel (1884)

• Flower and Weed and other tales (1884)

• Wyllard's Weird (1885)

• Mohawks (1886)

• One Thing Needful (1886)

• The Good Hermione: A Story for the Jubilee Year (1886, as Aunt Belinda)

• Cut by the County (1887)

• The Fatal Three (1888)

• The Day Will Come (1889)

• One Life, One Love (1890)

• The World, the Flesh and the Devil (1891)

• The Venetians (1892)

• All Along the River (1893)

• The Christmas Hirelings (1894)

• Thou Art The Man (1894)

• Sons of Fire (1895)

• London Pride; or, When the World was Younger (1896)

• Rough Justice (1898)

• In High Places (1898)

• His Darling Sin (1899)

• The Infidel (1900)

• A Lost Eden (1904)

• The Rose of Life (1905)

• The White House (1906)

• Dead Love Has Chains (1907)

• During Her Majesty's Pleasure (1908)

• Our Adversary (1909)

• Beyond These Voices (1910) Some bibliographical material in this incomplete list comes from Jarndyce booksellers' catalogue ''Women's Writers 1795–1927. Part I: A–F'' (Summer 2017).

Dramatisations
Several of Braddon's works have been dramatised, including:
 * Aurora Floyd, by Colin Henry Hazlewood, first performed at Britannia Theatre Saloon, London, 1863.
 * "The Cold Embrace", starring Jonathan Firth, BBC Radio 4, 2009.
 * Lady Audley's Secret, by Colin Henry Hazlewood, first performed at the Victoria Theatre, London, 1863.
 * Lady Audley's Secret, starring Theda Bara, Fox Film Corp., 1915.
 * Lady Audley's Secret, starring Neve McIntosh, Kenneth Cranham, and Steven Mackintosh, PBS Mystery! 2000.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Mary Elizabeth Braddon


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Guar

The guar (from ग्वार : gvār) or  cluster bean, with the botanical name Cyamopsis tetragonoloba, is an annual legume and the source of guar gum. It is also known as gavar, gawar, or guvar bean. The genus name Cyamopsis means bean-like (from : kýamos "bean" +  : ópsis "view'). The specific name is from tetragōnoloba meaning four-lobed.

The origin of Cyamopsis tetragonoloba is unknown, since it has never been found in the wild. It is assumed to have developed from the African species Cyamopsis senegalensis. It was further domesticated in South Asia, where it has been cultivated for centuries. Guar grows well in semiarid areas, but frequent rainfall is necessary.

This legume is a valuable plant in a crop rotation cycle, as it lives in symbiosis with nitrogen-fixing bacteria. Agriculturists in semi-arid regions of Rajasthan follow crop-rotation and use guar to replenish the soil with essential fertilizers and nitrogen fixation, before the next crop. Guar has many functions for human and animal nutrition, but the gelling agent in its seeds (guar gum) is the most important use. Demand is rising due to the use of guar gum in hydraulic fracturing (oil shale gas). It is also a major ingredient of the toy Slime. About 80% of world production occurs in India, but due to strong demand, the plant is being introduced elsewhere.

Biology
Cyamopsis tetragonoloba grows upright, reaching a maximum height of up to 2–3 m. It has a main single stem with either basal branching or fine branching along the stem. Guar taproots can access soil moisture in low soil depths. This legume develops root nodules with nitrogen-fixing soil bacteria rhizobia in the surface part of its rooting system. Its leaves and stems are mostly hairy, depending on the cultivar. Its fine leaves have an elongated oval shape (5 to 10 cm) and of alternate position. Clusters of flowers grow in the plant axil and are white to blueish in color. The developing pods are rather flat and slim containing 5 to 12 small oval seeds of 5 mm length (TGW = 25-40 g). Usually mature seeds are white or gray, but with excess moisture they can turn black and lose germination capacity. The chromosome number of guar seeds is 2n=14. The seeds of guar beans have a remarkable characteristic. Its kernel consists of a protein-rich germ (43–46%) and a relatively large endosperm (34–40%), containing large amounts of the galactomannan. This is a polysaccharide containing polymers of mannose and galactose in a ratio of 2:1 with many branches. Thus, it exhibits a great hydrogen bonding activity having a viscosifying effect in liquids.

Climate requirements
Guar is drought-tolerant and sun-loving, but it is susceptible to frost. Although it can cope with little but regular rainfall, it requires sufficient soil moisture before planting and during maturation of seeds. Frequent drought periods can lead to delayed maturation. On the contrary, excessive moisture during the early growth phase and after maturation lead to lower seed quality. Guar is produced near to coastal areas in the Gandhidham region of Kutch, Gujarat, India.

Soil requirements
Cyamopsis tetragonoloba (L.) can grow on a wide range of soil types. Preferably in fertile, medium-textured and sandy loam soils that are well-drained, since waterlogging decreases plant performance. Guar grows best in moderate alkaline conditions (pH 7–8) and is tolerant of salinity. Its taproots are inoculated with rhizobia nodules and thus it produces nitrogen-rich biomass and improves soil quality.

Cultivation areas
Guar is grown principally in north-western India with smaller crops grown in the semiarid areas of the high plains of Texas in the US, Australia and Africa. The most important growing area centres on Jodhpur in Rajasthan, India, where demand for guar for fractionation produced an agricultural boom as in 2012. Currently [When? As of 2023?], India is the main producer of cluster bean, accounting for 80% production of the world's total, while the Rajasthan, Gujarat and Kutch regions occupy the largest areas (82.1% of total) dedicated to guar cultivation. In addition to its cultivation in India, the crop is also grown as a cash crop in other parts of the world. Several commercial growers have converted their crops to guar production to support the increasing demand for guar and other organic crops in the United States.

Varieties
Pusa Naubahar and Pusa Sadabahar. Seeds at the rate of 30 kilograms/hectare (9–11 lb/acre) are planted at a spacing of 45–60 × 20–30 cm (18–24 × 8–12 in) in February–March and June–July. During the rainy season, seeds are sown 2–3 cm (~1 in) deep on ridges and in furrows during summer months. FYM is applied at the rate of 25 tonnes/ha (11.1 tons/acre). N, P2O5 and K2O recommendation for the crop is 20:60:80 kg/ha (18:53:71 lb/acre). Average yield is 5 to 6 tonnes/ha (2.2–2.6 tons/acre). Meager information is available for genetic variability in cluster bean addressing the qualitative traits (Pathak et al. 2011).

Guar plant
Agriculture
 * Forage: Guar plants can be used as cattle feed, but due to hydrocyanic acid in its beans, only mature beans can be used.
 * Green manure: Guar plantings increase the yield of subsequent crops as this legume conserves soil nutrient content.

Domestic use
 * Vegetable: Guar leaves can be used like spinach, and the pods are prepared like salad or vegetables. Its beans are nutritious, but guar protein is not usable by humans unless toasted to destroy the trypsin inhibitor.

Guar gum
The seeds of the guar bean contain a large endosperm. This endosperm consists of a large polysaccharide of galactose and mannose. This polymer is water-soluble and exhibits a viscosifying effect in water. Guar gum has a multitude of different applications in food products, industrial products, and extractive industry.

Food
In several food and beverages guar gum is used as additive to change its viscosity or as fiber source.

Partially hydrolyzed guar gum (PHGG) is produced by the partial enzymatic hydrolysis of guaran, the galactomannan of the endosperm of guar seeds (guar gum). It is a neutral polysaccharide consisting of a mannose backbone chain with single galactose side units occurring on almost two out of every three mannose units. The average molecular weight is about 25,000 daltons. This gives a PHGG that still assays and functions as a soluble dietary fiber.

PHGG as sold commercially is completely soluble, acid and heat stable, unaffected by ions, and will not gel at high concentrations. Commercial PHGG is approximately 75% dietary fiber and has minimal effect on taste and texture in food and beverage items. PHGG is fully fermentable in the large bowel, with a high rate of volatile fatty acid formation. The pH of the feces is lowered along with an increase in fecal bulk that mainly consists of bacterial cell mass and water. Clinical studies have demonstrated a prebiotic effect of PHGG. Studies have shown that PHGG can be used to maintain regularity. PHGG is used in foods for particulate suspension, emulsification, antistaling, ice crystal control, and reduced fat baked goods.

Industry
Derivatives of guar gum that have been further reacted are used in industrial applications, such as the paper and textile industries, ore flotation, the manufacture of explosives and hydraulic fracturing (fracking) of oil and gas formations. Guar gum is often crosslinked with boron or chromium ions to make it more stable and heat-resistant. The crosslinking of guar with metal ions results in a gel that does not block the formation and helps efficiently in formation cleaning process. Guar and its derivatives make gel complexes with ions of aluminium, zirconium, titanium, chromium and boron. The borate–guar reaction is reversible, and depends on the pH (hydrogen ion concentration) of the solution. This reaction is used to give the toy "slime" its consistency. Crosslinking of guar with borate occurs at high pH (approximately 9–10) of the solution. Guar gum has proven as useful substitute for locust bean gum (made from carob seeds).

Feeds
Guar meal korma and guar meal churi are widely used as raw material for producing various kinds of cattle feeds, aqua feeds, fish feeds, poultry feeds, dairy feeds, swine feeds, etc.

Fracking agent
The use of guar gum in the hydraulic fracturing (fracking) extraction of oil and shale gas has increased demand substantially. Only 10% of Indian production is used domestically. The remaining 90% is exported for shale gas and oil industries. Consequently, many former cotton or wheat fields are converted into guar fields as production costs are lower. The increase of guar gum prices also has other reasons.

title: Guar


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User:Edolin

A bean and pulse fan, who I hope is using non-copyrighted source material. Leaving in phrases like "in this chapter" is a no-no.

Actually I am an agronomist with a particular interest in food crops/ food security issues. The material which I have contributed is non-copyright. The phrase "in this chapter" (see beans : talk) refers to the entry on beans which I contributed and not to a chapter in source material. - Edolin.

title: User:Edolin


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Lady Audley's Secret

Lady Audley's Secret is a sensation novel by Mary Elizabeth Braddon published on 26 May 1862. It was Braddon's most successful and well-known novel. Critic John Sutherland (1989) described the work as "the most sensationally successful of all the sensation novels". The plot centres on "accidental bigamy" which was in literary fashion in the early 1860s. The plot was summarised by literary critic Elaine Showalter (1982): "Braddon's bigamous heroine deserts her child, pushes husband number one down a well, thinks about poisoning husband number two and sets fire to a hotel in which her other male acquaintances are residing". Elements of the novel mirror themes of the real-life Constance Kent case of June 1860 which gripped the nation for years. Braddon's second 'bigamy' novel, Aurora Floyd, appeared in 1863. Braddon set the story in Ingatestone Hall, Essex, inspired by a visit there. There have been three silent film adaptations, one UK television version in 2000, and three minor stage adaptations.

History
Lady Audley's Secret was partly serialised in Robin Goodfellow magazine in July–September 1861, then entirely serialised in Sixpenny Magazine in January–December 1862 and once again serialised in The London Journal March–August 1863. It was published in 1862 in three volumes by William Tinsley.

Braddon initially sold the rights to the Irish publisher John Maxwell, with whom Braddon also lived and had children. Maxwell published it in his magazine Robin Goodfellow. Braddon wrote the final third in less than two weeks. It was published as a three-volume novel, and it became a success, allowing Braddon to be financially independent for the rest of her life. It was also a financial success for Tinsley, who went on to build a villa in Barnes, "Audley Lodge", with the profits.

Notably – given the theme of bigamy in the novel's plot – Maxwell himself was married to another woman, and so Braddon was unable to marry him until his wife died in 1874. When it became public that Maxwell and Braddon had been living in an "irregular" arrangement all those years, it caused a minor scandal during which all their servants gave notice.

In 1997 a Wordsworth Limited edition was released with an Introduction by Keith Carabine from the University of Kent in which he states, "In the latter half of the nineteenth century, everyone knew ''Lady Audley’s Secret."

Plot
The novel opens in June 1857 with the marriage of Lucy Graham and Sir Michael Audley. Lucy is a young, beautiful woman who enchants almost all who meet her. Sir Michael is a kindly, wealthy middle-aged widower. Lucy's past is unclear. Prior to marrying Sir Michael she had served as governess for the children of the local doctor, Mr. Dawson, and before that she was in service with Mrs. Vincent. Very little is known about her prior to that. Shortly after the marriage Sir Michael's nephew, the barrister Robert Audley, welcomes his old friend George Talboys back to England.

Three years before, though happily married, George's financial situation had been desperate. He left for Australia to seek a fortune in gold prospecting. Behind him in England he had left his young wife Helen, whom he is now anxious to get news of. He reads in the newspaper that she has died, and, after visiting her home to confirm this, he becomes despondent. Robert Audley cares for his friend, and, hoping to distract him, offers to take him to his wealthy uncle's country manor. George had a child, Georgey, who was left under the care of Lieutenant Maldon, George's father-in-law. Robert and George set off to visit Georgey, and George decides to make Robert little Georgey's guardian and trustee of £20,000 put into the boy's name. After settling the matter of the boy's guardianship, the two set off to visit Sir Michael.

While at the country manor Audley Court, Lady Audley avoids meeting George. When the two seek an audience with the new Lady Audley, she makes many excuses and avoids their visits. During her absence a thunder storm confines George and Robert to the interior of Audley Court, and the two are shown a portrait of Lady Audley. Looking back toward his friend, Robert notes that George seems disturbed, and attributes his disturbed mood to the storm. Shortly thereafter George disappears. Robert is perplexed. Unwilling to believe George simply left with no notice, Robert begins to look into the circumstances of his disappearance.

While searching for his friend, Robert takes note of the events surrounding George's disappearance. The name of Lady Audley repeatedly appears in these notes, and much to his distress, the evidence begins to collect against her. One night, he reveals his notes to Lady Audley, including that George was in possession of many letters of his former wife. Lady Audley sets off to London, where the letters were kept. Robert follows after her. However, by the time he arrives, he discovers that George's possessions have been broken into and the letters are missing. One possession, however, remains – a book with a note written by George's wife that matches Lady Audley's handwriting. This confirms Robert's suspicion that Lady Audley is implicated in George's disappearance; it also leads Robert to conclude that Lady Audley is actually George's supposedly dead wife.

Suspecting the worst of Lady Audley and being afraid for little Georgey's life, Robert travels to Lieutenant Maldon's house and demands possession of the boy. Once Robert has Georgey under his control, he places the boy in a school run by Mr. Marchmont. Afterwards, Robert visits George's father, Mr. Harcourt Talboys, and confronts the Squire with his son's death. Harcourt listens dispassionately to the story. In the course of his visit to the Talboys' manor, Robert is entranced by George's sister Clara, who looks startlingly like George. Clara's passion for finding her brother spurs Robert on.

In February 1859, Robert continues searching for evidence. He receives a notice that his uncle is ill, and he quickly returns to Audley Court. While there, Robert speaks with Mr. Dawson and receives a brief description of all that is known about Lucy's background. He hears that Lucy was employed by Mrs. Vincent at her school since 1852. To verify this claim, Robert tracks down Mrs. Vincent, who is in hiding because of debts. According to Miss Tonks, a teacher at Mrs. Vincent's school, Lucy actually arrived at the school in August 1854 and was secretive about her past. Miss Tonks gives Robert a travel box that used to belong to Lucy. Upon examining stickers on the box, Robert discovers both the name Lucy Graham and the name Helen Talboys.

Robert realizes that Helen Talboys faked her death before creating her new identity. When Robert confronts Lucy, she tells him that he has no proof. He leaves to find more evidence, heading to Castle Inn, which is run by Luke Marks. During the night, Lucy forces Luke's wife, Phoebe, to let her into the inn, then Lucy sets the place afire to kill Robert. However, Robert survives and returns to Audley Court and again confronts Lucy. This time, she says she is insane and confesses her life's story to Robert and Sir Michael, claiming that George abandoned her originally and she had no choice but to abandon her old life and child to find another, wealthier husband.

Sir Michael is unhappy and leaves with Alicia to travel through Europe. Robert invites a Dr. Mosgrave to make a more astute judgment regarding Lucy's sanity, and he proclaims that she is indeed victim to latent insanity, which overpowers her in times of stress and makes her very dangerous to any and all. Lucy, under the name of Madame Taylor, enters a mental institution located somewhere in Belgium along the route between Brussels and Paris. While being committed, Lucy confesses to Robert that she killed George by pushing him down a deserted well in the garden of Audley Court.

Robert grieves for his friend George until a dying Luke Marks contacts him. Before succumbing to injuries he suffered in the fire, Luke tells Robert that George survived Lady Audley's attempted murder. Luke then helped George escape, with George intending to return to Australia. Robert is overjoyed, and he asks Clara to marry him and go with him to Australia to find George. Clara accepts, but before they set out, George returns and reveals that he actually visited New York instead. The narrative ends with the death of Lucy abroad, and Clara and Robert happily married and living in a country cottage with George and his son. Robert's formerly infatuated cousin Alicia marries her once-spurned suitor, Sir Harry Towers, and Audley Court is left abandoned along with all of its unhappy memories.

Analysis and themes
Lady Audley's Secret plays on Victorian anxieties about the domestic sphere. The home was supposed to be a refuge from the dangers of the outside world, but in the novel, the seemingly perfect domestic lady turns out to be a violent criminal who has not only tried to commit murder but who has also committed bigamy and abandoned her child. This unsettled Victorian readers because it indicated that the concepts of "the perfect lady/mother" and "domestic bliss" were more idealistic than realistic. In addition, anxieties about the increasing urbanization of Britain abound; the city gives Lady Audley the power to change her identity because it renders its citizens effectively anonymous. The small town of Audley is no longer a refuge where everyone knows the life story of every neighbor; the residents of Audley must accept Lucy Graham's account of herself since they have no other information about her past. Other anxieties about unstable identity appear throughout the novel: Lady Audley's maid, Phoebe, resembles Lady Audley, thus banishing the idea of physical distinction between the upper and lower classes and therefore of any inherent superiority of the former.

Lady Audley's Secret is, furthermore, a story about gender and class, and Lady Audley's objectionable upward mobility suggests a threat to the paradigm of social class. Madness is also a key issue. Lady Audley and others often converse about the meaning of this word, but many readers believe that Lady Audley is not mad. In fact, many critics view Lady Audley's deception as a feminist act in which a woman takes control of the direction of her own life.

The novel mirrors many of the same themes from the real-life Constance Kent case of June 1860. The first instalment of Lady Audley's Secret came out almost exactly one year after the Kent murder. The novel, like the real-life case, featured a stepmother and former governess, a mysterious and brutal murder in a country manor house, a body thrown down a well, and characters fascinated by madness. Constance Kent can be seen in many of the female characters in the novel: the murderess Lady Audley, the tomboyish Alicia Audley, the restrained Phoebe Marks and the lonely Clara Talboys. Jack Whicher, the detective and case investigator, can be seen in the character of Robert Audley.

Adaptations

 * Films
 * Lady Audley's Secret, 1912 (USA, black and white, silent)
 * Lady Audley's Secret (aka Secrets of Society), 1915 (USA, black and white, silent, directed by Marshall Farnum)
 * Lady Audley's Secret, 1920 (UK, black and white, silent, directed by Jack Denton)
 * Lady Audley's Secret, 1949 (UK, TV, black and white)
 * Lady Audley's Secret (1978 film), 1978 (West Germany, TV, directed by Wilhelm Semmelroth)
 * Lady Audley's Secret, 2000 (UK, TV, directed by Betsan Morris Evans) – (In the USA part of the Mystery! series.)

 * Radio
 * Lady Audley's Secret, 2009 (UK, BBC Radio 4)

 * Stage
 * 1863 – adapted by Colin Henry Hazlewood, first performed at the Victoria Theatre, London, 1863. Hazlewood also dramatised Braddon's Aurora Floyd the same year.
 * 1930 – Cambridge Festival Theatre: a "melodramatized version" of the novel including a "birthday fete" and Rustic Ballet. The part of Lady Audley was played by (Dame) Flora Robson and the performance was produced by Tyrone Guthrie. It was preceded by a performance of Morton's Cox and Box.
 * 1971 – Chicago, Goodman Theatre, adaptation by Douglas Seale, music by George Goehring, and lyrics by John B. Kuntz.
 * 1972 – Off-Broadway, Seale adaptation, music by George Goehring, and lyrics by John B. Kuntz.

In popular culture
Lady Audley's Secret is involved in a subplot of Betsy and Tacy Go Downtown, the fourth book in the Betsy-Tacy series by Maud Hart Lovelace. Betsy has read it and other books in the same genre, and aspires to write similar works.

In the Agatha Christie short story Greenshaw's Folly Miss Greenshaw hides her will in a copy of Lady Audley's Secret remarking it was a "best seller in its day".

title: Lady Audley's Secret


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Cephalopod

A cephalopod is any member of the molluscan class Cephalopoda  (Greek plural κεφαλόποδες, ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles (muscular hydrostats) modified from the primitive molluscan foot. Fishers sometimes call cephalopods "inkfish", referring to their common ability to squirt ink. The study of cephalopods is a branch of malacology known as teuthology.

Cephalopods became dominant during the Ordovician period, represented by primitive nautiloids. The class now contains two, only distantly related, extant subclasses: Coleoidea, which includes octopuses, squid, and cuttlefish; and Nautiloidea, represented by Nautilus and Allonautilus. In the Coleoidea, the molluscan shell has been internalized or is absent, whereas in the Nautiloidea, the external shell remains. About 800 living species of cephalopods have been identified. Two important extinct taxa are the Ammonoidea (ammonites) and Belemnoidea (belemnites). Extant cephalopods range in size from the 10 mm (0.3 in) Idiosepius thailandicus to the 14 m (45.1 ft) colossal squid, the largest extant invertebrate.

Distribution
There are over 800 extant species of cephalopod, although new species continue to be described. An estimated 11,000 extinct taxa have been described, although the soft-bodied nature of cephalopods means they are not easily fossilised.

Cephalopods are found in all the oceans of Earth. None of them can tolerate fresh water, but the brief squid, Lolliguncula brevis, found in Chesapeake Bay, is a notable partial exception in that it tolerates brackish water. Cephalopods are thought to be unable to live in fresh water due to multiple biochemical constraints, and in their >400 million year existence have never ventured into fully freshwater habitats.

Cephalopods occupy most of the depth of the ocean, from the abyssal plains to the sea surface, and have also been found in the hadal zone. Their diversity is greatest near the equator (~40 species retrieved in nets at 11°N by a diversity study) and decreases towards the poles (~5 species captured at 60°N).

Nervous system and behavior
Cephalopods are widely regarded as the most intelligent of the invertebrates and have well developed senses and large brains (larger than those of gastropods). The nervous system of cephalopods is the most complex of the invertebrates and their brain-to-body-mass ratio falls between that of endothermic and ectothermic vertebrates. Captive cephalopods have also been known to climb out of their aquaria, maneuver a distance of the lab floor, enter another aquarium to feed on captive crabs, and return to their own aquarium.

The brain is protected in a cartilaginous cranium. The giant nerve fibers of the cephalopod mantle have been widely used for many years as experimental material in neurophysiology; their large diameter (due to lack of myelination) makes them relatively easy to study compared with other animals.

Many cephalopods are social creatures; when isolated from their own kind, some species have been observed shoaling with fish.

Some cephalopods are able to fly through the air for distances of up to 50 m. While cephalopods are not particularly aerodynamic, they achieve these impressive ranges by jet-propulsion; water continues to be expelled from the funnel while the organism is in the air. The animals spread their fins and tentacles to form wings and actively control lift force with body posture. One species, Todarodes pacificus, has been observed spreading tentacles in a flat fan shape with a mucus film between the individual tentacles, while another, Sepioteuthis sepioidea, has been observed putting the tentacles in a circular arrangement.

Senses
Cephalopods have advanced vision, can detect gravity with statocysts, and have a variety of chemical sense organs. Octopuses use their arms to explore their environment and can use them for depth perception.

Vision
Most cephalopods rely on vision to detect predators and prey and to communicate with one another. Consequently, cephalopod vision is acute: training experiments have shown that the common octopus can distinguish the brightness, size, shape, and horizontal or vertical orientation of objects. The morphological construction gives cephalopod eyes the same performance as shark eyes; however, their construction differs, as cephalopods lack a cornea and have an everted retina. Cephalopods' eyes are also sensitive to the plane of polarization of light. Unlike many other cephalopods, nautiluses do not have good vision; their eye structure is highly developed, but lacks a solid lens. They have a simple "pinhole" eye through which water can pass. Instead of vision, the animal is thought to use olfaction as the primary sense for foraging, as well as locating or identifying potential mates.

All octopuses and most cephalopods are considered to be color blind. Coleoid cephalopods (octopus, squid, cuttlefish) have a single photoreceptor type and lack the ability to determine color by comparing detected photon intensity across multiple spectral channels. When camouflaging themselves, they use their chromatophores to change brightness and pattern according to the background they see, but their ability to match the specific color of a background may come from cells such as iridophores and leucophores that reflect light from the environment. They also produce visual pigments throughout their body and may sense light levels directly from their body. Evidence of color vision has been found in the sparkling enope squid (Watasenia scintillans). It achieves color vision with three photoreceptors, which are based on the same opsin, but use distinct retinal molecules as chromophores: A1 (retinal), A3 (3-dehydroretinal), and A4 (4-hydroxyretinal). The A1-photoreceptor is most sensitive to green-blue (484 nm), the A2-photoreceptor to blue-green (500 nm), and the A4-photoreceptor to blue (470 nm) light.

In 2015, a novel mechanism for spectral discrimination in cephalopods was described. This relies on the exploitation of chromatic aberration (wavelength-dependence of focal length). Numerical modeling shows that chromatic aberration can yield useful chromatic information through the dependence of image acuity on accommodation. The unusual off-axis slit and annular pupil shapes in cephalopods enhance this ability by acting as prisms which are scattering white light in all directions.

Photoreception
In 2015, molecular evidence was published indicating that cephalopod chromatophores are photosensitive; reverse transcription polymerase chain reactions (RT-PCR) revealed transcripts encoding rhodopsin and retinochrome within the retinas and skin of the longfin inshore squid (Doryteuthis pealeii), and the common cuttlefish (Sepia officinalis) and broadclub cuttlefish (Sepia latimanus). The authors claim this is the first evidence that cephalopod dermal tissues may possess the required combination of molecules to respond to light.

Hearing
Some squids have been shown to detect sound using their statocysts, but, in general, cephalopods are deaf.

Use of light

Most cephalopods possess an assemblage of skin components that interact with light. These may include iridophores, leucophores, chromatophores and (in some species) photophores. Chromatophores are colored pigment cells that expand and contract in accordance to produce color and pattern which they can use in a startling array of fashions. As well as providing camouflage with their background, some cephalopods bioluminesce, shining light downwards to disguise their shadows from any predators that may lurk below. The bioluminescence is produced by bacterial symbionts; the host cephalopod is able to detect the light produced by these organisms. Bioluminescence may also be used to entice prey, and some species use colorful displays to impress mates, startle predators, or even communicate with one another.

Coloration
Cephalopods can change their colors and patterns in milliseconds, whether for signalling (both within the species and for warning) or active camouflage, as their chromatophores are expanded or contracted. Although color changes appear to rely primarily on vision input, there is evidence that skin cells, specifically chromatophores, can detect light and adjust to light conditions independently of the eyes. The octopus changes skin color and texture during quiet and active sleep cycles.

Cephalopods can use chromatophores like a muscle, which is why they can change their skin hue as rapidly as they do. Coloration is typically stronger in near-shore species than those living in the open ocean, whose functions tend to be restricted to disruptive camouflage. These chromatophores are found throughout the body of the octopus, however, they are controlled by the same part of the brain that controls elongation during jet propulsion to reduce drag. As such, jetting octopuses can turn pale because the brain is unable to achieve both controlling elongation and controlling the chromatophores. Most octopuses mimic select structures in their field of view rather than becoming a composite color of their full background.

Evidence of original coloration has been detected in cephalopod fossils dating as far back as the Silurian; these orthoconic individuals bore concentric stripes, which are thought to have served as camouflage. Devonian cephalopods bear more complex color patterns, of unknown function.

Chromatophores
Coleoids, a shell-less subclass of cephalopods (squid, cuttlefish, and octopuses), have complex pigment containing cells called chromatophores which are capable of producing rapidly changing color patterns. These cells store pigment within an elastic sac which produces the color seen from these cells. Coleoids can change the shape of this sac, called the cytoelastic sacculus, which then causes changes in the translucency and opacity of the cell. By rapidly changing multiple chromatophores of different colors, cephalopods are able to change the color of their skin at astonishing speeds, an adaptation that is especially notable in an organism that sees in black and white. Chromatophores are known to only contain three pigments, red, yellow, and brown, which cannot create the full color spectrum. However, cephalopods also have cells called iridophores, thin, layered protein cells that reflect light in ways that can produce colors chromatophores cannot. The mechanism of iridophore control is unknown, but chromatophores are under the control of neural pathways, allowing the cephalopod to coordinate elaborate displays. Together, chromatophores and iridophores are able to produce a large range of colors and pattern displays.

Adaptive value
Cephalopods utilize chromatophores' color changing ability in order to camouflage themselves. Chromatophores allow Coleoids to blend into many different environments, from coral reefs to the sandy sea floor. The color change of chromatophores works in concert with papillae, epithelial tissue which grows and deforms through hydrostatic motion to change skin texture. Chromatophores are able to perform two types of camouflage, mimicry and color matching. Mimicry is when an organism changes its appearance to appear like a different organism. The squid Sepioteuthis sepioide has been documented changing its appearance to appear as the non threatening herbivorous parrotfish to approach unaware prey. The octopus Thaumoctopus mimicus is known to mimic a number of different venomous organisms it cohabitates with to deter predators. While background matching, a cephalopod changes its appearance to resemble its surroundings, hiding from its predators or concealing itself from prey. The ability to both mimic other organisms and match the appearance of their surroundings is notable given that cephalopods' vision is monochromatic.

Cephalopods also use their fine control of body coloration and patterning to perform complex signaling displays for both conspecific and intraspecific communication. Coloration is used in concert with locomotion and texture to send signals to other organisms. Intraspecifically this can serve as a warning display to potential predators. For example, when the octopus Callistoctopus macropus is threatened, it will turn a bright red brown color speckled with white dots as a high contrast display to startle predators. Conspecifically, color change is used for both mating displays and social communication. Cuttlefish have intricate mating displays from males to females. There is also male to male signaling that occurs during competition over mates, all of which are the product of chromatophore coloration displays.

Origin
There are two hypotheses about the evolution of color change in cephalopods. One hypothesis is that the ability to change color may have evolved for social, sexual, and signaling functions. Another explanation is that it first evolved because of selective pressures encouraging predator avoidance and stealth hunting.

For color change to have evolved as the result of social selection the environment of cephalopods' ancestors would have to fit a number of criteria. One, there would need to be some kind of mating ritual that involved signaling. Two, they would have to experience demonstrably high levels of sexual selection. And three, the ancestor would need to communicate using sexual signals that are visible to a conspecific receiver. For color change to have evolved as the result of natural selection different parameters would have to be met. For one, you would need some phenotypic diversity in body patterning among the population. The species would also need to cohabitate with predators which rely on vision for prey identification. These predators should have a high range of visual sensitivity, detecting not just motion or contrast but also colors. The habitats they occupy would also need to display a diversity of backgrounds. Experiments done in Dwarf chameleons testing these hypotheses showed that chameleon taxa with greater capacity for color change had more visually conspicuous social signals but did not come from more visually diverse habitats, suggesting that color change ability likely evolved to facilitate social signaling, while camouflage is a useful byproduct. Because camouflage is used for multiple adaptive purposes in cephalopods, color change could have evolved for one use and the other developed later, or it evolved to regulate trade offs within both.

Convergent evolution
Color change is widespread in ectotherms including anoles, frogs, mollusks, many fish, insects, and spiders. The mechanism behind this color change can be either morphological or physiological. Morphological change is the result of a change in the density of pigment containing cells and tends to change over longer periods of time. Physiological change, the kind observed in cephalopod lineages, is typically the result of the movement of pigment within the chromatophore, changing where different pigments are localized within the cell. This physiological change typically occurs on much shorter timescales compared to morphological change. Cephalopods have a rare form of physiological color change which utilizes neural control of muscles to change the morphology of their chromatophores. This neural control of chromatophores has evolved convergently in both cephalopods and teleosts fishes.

Ink
With the exception of the Nautilidae and the species of octopus belonging to the suborder Cirrina, all known cephalopods have an ink sac, which can be used to expel a cloud of dark ink to confuse predators. This sac is a muscular bag which originated as an extension of the hindgut. It lies beneath the gut and opens into the anus, into which its contents – almost pure melanin – can be squirted; its proximity to the base of the funnel means the ink can be distributed by ejected water as the cephalopod uses its jet propulsion. The ejected cloud of melanin is usually mixed, upon expulsion, with mucus, produced elsewhere in the mantle, and therefore forms a thick cloud, resulting in visual (and possibly chemosensory) impairment of the predator, like a smokescreen. However, a more sophisticated behavior has been observed, in which the cephalopod releases a cloud, with a greater mucus content, that approximately resembles the cephalopod that released it (this decoy is referred to as a pseudomorph). This strategy often results in the predator attacking the pseudomorph, rather than its rapidly departing prey. For more information, see Inking behaviors.

The ink sac of cephalopods has led to a common name of "inkfish", formerly the pen-and-ink fish.

Circulatory system
Cephalopods are the only molluscs with a closed circulatory system. Coleoids have two gill hearts (also known as branchial hearts) that move blood through the capillaries of the gills. A single systemic heart then pumps the oxygenated blood through the rest of the body.

Like most molluscs, cephalopods use hemocyanin, a copper-containing protein, rather than hemoglobin, to transport oxygen. As a result, their blood is colorless when deoxygenated and turns blue when bonded to oxygen. In oxygen-rich environments and in acidic water, hemoglobin is more efficient, but in environments with little oxygen and in low temperatures, hemocyanin has the upper hand. The hemocyanin molecule is much larger than the hemoglobin molecule, allowing it to bond with 96 O2 or molecules, instead of the hemoglobin's just four. But unlike hemoglobin, which are attached in millions on the surface of a single red blood cell, hemocyanin molecules float freely in the bloodstream.

Respiration
Cephalopods exchange gases with the seawater by forcing water through their gills, which are attached to the roof of the organism. Water enters the mantle cavity on the outside of the gills, and the entrance of the mantle cavity closes. When the mantle contracts, water is forced through the gills, which lie between the mantle cavity and the funnel. The water's expulsion through the funnel can be used to power jet propulsion. If respiration is used concurrently with jet propulsion, large losses in speed or oxygen generation can be expected. The gills, which are much more efficient than those of other mollusks, are attached to the ventral surface of the mantle cavity. There is a trade-off with gill size regarding lifestyle. To achieve fast speeds, gills need to be small – water will be passed through them quickly when energy is needed, compensating for their small size. However, organisms which spend most of their time moving slowly along the bottom do not naturally pass much water through their cavity for locomotion; thus they have larger gills, along with complex systems to ensure that water is constantly washing through their gills, even when the organism is stationary. The water flow is controlled by contractions of the radial and circular mantle cavity muscles.

The gills of cephalopods are supported by a skeleton of robust fibrous proteins; the lack of mucopolysaccharides distinguishes this matrix from cartilage. The gills are also thought to be involved in excretion, with NH4+ being swapped with K+ from the seawater.

Locomotion and buoyancy
While most cephalopods can move by jet propulsion, this is a very energy-consuming way to travel compared to the tail propulsion used by fish. The efficiency of a propeller-driven waterjet (i.e. Froude efficiency) is greater than a rocket. The relative efficiency of jet propulsion decreases further as animal size increases; paralarvae are far more efficient than juvenile and adult individuals. Since the Paleozoic era, as competition with fish produced an environment where efficient motion was crucial to survival, jet propulsion has taken a back role, with fins and tentacles used to maintain a steady velocity. Whilst jet propulsion is never the sole mode of locomotion, the stop-start motion provided by the jets continues to be useful for providing bursts of high speed – not least when capturing prey or avoiding predators. Indeed, it makes cephalopods the fastest marine invertebrates, and they can out-accelerate most fish. The jet is supplemented with fin motion; in the squid, the fins flap each time that a jet is released, amplifying the thrust; they are then extended between jets (presumably to avoid sinking). Oxygenated water is taken into the mantle cavity to the gills and through muscular contraction of this cavity, the spent water is expelled through the hyponome, created by a fold in the mantle. The size difference between the posterior and anterior ends of this organ control the speed of the jet the organism can produce. The velocity of the organism can be accurately predicted for a given mass and morphology of animal. Motion of the cephalopods is usually backward as water is forced out anteriorly through the hyponome, but direction can be controlled somewhat by pointing it in different directions. Some cephalopods accompany this expulsion of water with a gunshot-like popping noise, thought to function to frighten away potential predators.

Cephalopods employ a similar method of propulsion despite their increasing size (as they grow) changing the dynamics of the water in which they find themselves. Thus their paralarvae do not extensively use their fins (which are less efficient at low Reynolds numbers) and primarily use their jets to propel themselves upwards, whereas large adult cephalopods tend to swim less efficiently and with more reliance on their fins.

Early cephalopods are thought to have produced jets by drawing their body into their shells, as Nautilus does today. Nautilus is also capable of creating a jet by undulations of its funnel; this slower flow of water is more suited to the extraction of oxygen from the water. When motionless, Nautilus can only extract 20% of oxygen from the water. The jet velocity in Nautilus is much slower than in coleoids, but less musculature and energy is involved in its production. Jet thrust in cephalopods is controlled primarily by the maximum diameter of the funnel orifice (or, perhaps, the average diameter of the funnel) and the diameter of the mantle cavity. Changes in the size of the orifice are used most at intermediate velocities. The absolute velocity achieved is limited by the cephalopod's requirement to inhale water for expulsion; this intake limits the maximum velocity to eight body-lengths per second, a speed which most cephalopods can attain after two funnel-blows. Water refills the cavity by entering not only through the orifices, but also through the funnel. Squid can expel up to 94% of the fluid within their cavity in a single jet thrust. To accommodate the rapid changes in water intake and expulsion, the orifices are highly flexible and can change their size by a factor of twenty; the funnel radius, conversely, changes only by a factor of around 1.5.

Some octopus species are also able to walk along the seabed. Squids and cuttlefish can move short distances in any direction by rippling of a flap of muscle around the mantle.

While most cephalopods float (i.e. are neutrally buoyant or nearly so; in fact most cephalopods are about 2–3% denser than seawater ), they achieve this in different ways. Some, such as Nautilus, allow gas to diffuse into the gap between the mantle and the shell; others allow purer water to ooze from their kidneys, forcing out denser salt water from the body cavity; others, like some fish, accumulate oils in the liver; and some octopuses have a gelatinous body with lighter chloride ions replacing sulfate in the body chemistry.

Squids are the primary sufferers of negative buoyancy in cephalopods. The negative buoyancy means that some squids, especially those whose habitat depths are rather shallow, have to actively regulate their vertical positions. This means that they must expend energy, often through jetting or undulations, in order to maintain the same depth. As such, the cost of transport of many squids are quite high. That being said, squid and other cephalopod that dwell in deep waters tend to be more neutrally buoyant which removes the need to regulate depth and increases their locomotory efficiency.

The Macrotritopus defilippi, or the sand-dwelling octopus, was seen mimicking both the coloration and the swimming movements of the sand-dwelling flounder Bothus lunatus to avoid predators. The octopuses were able to flatten their bodies and put their arms back to appear the same as the flounders as well as move with the same speed and movements.

Females of two species, Ocythoe tuberculata and Haliphron atlanticus, have evolved a true swim bladder.

Octopus vs. squid locomotion
Two of the categories of cephalopods, octopus and squid, are vastly different in their movements despite being of the same class. Octopuses are generally not seen as active swimmers; they are often found scavenging the sea floor instead of swimming long distances through the water. Squids, on the other hand, can be found to travel vast distances, with some moving as much as 2000 km in 2.5 months at an average pace of 0.9 body lengths per second. There is a major reason for the difference in movement type and efficiency: anatomy.

Both octopuses and squids have mantles (referenced above) which function towards respiration and locomotion in the form of jetting. The composition of these mantles differs between the two families, however. In octopuses, the mantle is made up of three muscle types: longitudinal, radial, and circular. The longitudinal muscles run parallel to the length of the octopus and they are used in order to keep the mantle the same length throughout the jetting process. Given that they are muscles, it can be noted that this means the octopus must actively flex the longitudinal muscles during jetting in order to keep the mantle at a constant length. The radial muscles run perpendicular to the longitudinal muscles and are used to thicken and thin the wall of the mantle. Finally, the circular muscles are used as the main activators in jetting. They are muscle bands that surround the mantle and expand/contract the cavity. All three muscle types work in unison to produce a jet as a propulsion mechanism.

Squids do not have the longitudinal muscles that octopus do. Instead, they have a tunic. This tunic is made of layers of collagen and it surrounds the top and the bottom of the mantle. Because they are made of collagen and not muscle, the tunics are rigid bodies that are much stronger than the muscle counterparts. This provides the squids some advantages for jet propulsion swimming. The stiffness means that there is no necessary muscle flexing to keep the mantle the same size. In addition, tunics take up only 1% of the squid mantle's wall thickness, whereas the longitudinal muscle fibers take up to 20% of the mantle wall thickness in octopuses. Also because of the rigidity of the tunic, the radial muscles in squid can contract more forcefully.

The mantle is not the only place where squids have collagen. Collagen fibers are located throughout the other muscle fibers in the mantle. These collagen fibers act as elastics and are sometimes named "collagen springs". As the name implies, these fibers act as springs. When the radial and circular muscles in the mantle contract, they reach a point where the contraction is no longer efficient to the forward motion of the creature. In such cases, the excess contraction is stored in the collagen which then efficiently begins or aids in the expansion of the mantle at the end of the jet. In some tests, the collagen has been shown to be able to begin raising mantle pressure up to 50ms before muscle activity is initiated.

These anatomical differences between squid and octopuses can help explain why squid can be found swimming comparably to fish while octopuses usually rely on other forms of locomotion on the sea floor such as bipedal walking, crawling, and non-jetting swimming.

Shell
Nautiluses are the only extant cephalopods with a true external shell. However, all molluscan shells are formed from the ectoderm (outer layer of the embryo); in cuttlefish (Sepia spp.), for example, an invagination of the ectoderm forms during the embryonic period, resulting in a shell (cuttlebone) that is internal in the adult. The same is true of the chitinous gladius of squid and octopuses. Cirrate octopods have arch-shaped cartilaginous fin supports, which are sometimes referred to as a "shell vestige" or "gladius". The Incirrina have either a pair of rod-shaped stylets or no vestige of an internal shell, and some squid also lack a gladius. The shelled coleoids do not form a clade or even a paraphyletic group. The Spirula shell begins as an organic structure, and is then very rapidly mineralized. Shells that are "lost" may be lost by resorption of the calcium carbonate component.

Females of the octopus genus Argonauta secrete a specialized paper-thin egg case in which they reside, and this is popularly regarded as a "shell", although it is not attached to the body of the animal and has a separate evolutionary origin.

The largest group of shelled cephalopods, the ammonites, are extinct, but their shells are very common as fossils.

The deposition of carbonate, leading to a mineralized shell, appears to be related to the acidity of the organic shell matrix (see Mollusc shell); shell-forming cephalopods have an acidic matrix, whereas the gladius of squid has a basic matrix. The basic arrangement of the cephalopod outer wall is: an outer (spherulitic) prismatic layer, a laminar (nacreous) layer and an inner prismatic layer. The thickness of every layer depends on the taxa. In modern cephalopods, the Ca carbonate is aragonite. As for other mollusc shells or coral skeletons, the smallest visible units are irregular rounded granules.

Head appendages
Cephalopods, as the name implies, have muscular appendages extending from their heads and surrounding their mouths. These are used in feeding, mobility, and even reproduction. In coleoids they number eight or ten. Decapods such as cuttlefish and squid have five pairs. The longer two, termed tentacles, are actively involved in capturing prey; they can lengthen rapidly (in as little as 15 milliseconds ). In giant squid they may reach a length of 8 metres. They may terminate in a broadened, sucker-coated club. The shorter four pairs are termed arms, and are involved in holding and manipulating the captured organism. They too have suckers, on the side closest to the mouth; these help to hold onto the prey. Octopods only have four pairs of sucker-coated arms, as the name suggests, though developmental abnormalities can modify the number of arms expressed.

The tentacle consists of a thick central nerve cord (which must be thick to allow each sucker to be controlled independently) surrounded by circular and radial muscles. Because the volume of the tentacle remains constant, contracting the circular muscles decreases the radius and permits the rapid increase in length. Typically a 70% lengthening is achieved by decreasing the width by 23%. The shorter arms lack this capability.

The size of the tentacle is related to the size of the buccal cavity; larger, stronger tentacles can hold prey as small bites are taken from it; with more numerous, smaller tentacles, prey is swallowed whole, so the mouth cavity must be larger.

Externally shelled nautilids (Nautilus and Allonautilus) have on the order of 90 finger-like appendages, termed tentacles, which lack suckers but are sticky instead, and are partly retractable.

Feeding
All living cephalopods have a two-part beak; most have a radula, although it is reduced in most octopus and absent altogether in Spirula. They feed by capturing prey with their tentacles, drawing it into their mouth and taking bites from it. They have a mixture of toxic digestive juices, some of which are manufactured by symbiotic algae, which they eject from their salivary glands onto their captured prey held in their mouths. These juices separate the flesh of their prey from the bone or shell. The salivary gland has a small tooth at its end which can be poked into an organism to digest it from within.

The digestive gland itself is rather short. It has four elements, with food passing through the crop, stomach and caecum before entering the intestine. Most digestion, as well as the absorption of nutrients, occurs in the digestive gland, sometimes called the liver. Nutrients and waste materials are exchanged between the gut and the digestive gland through a pair of connections linking the gland to the junction of the stomach and caecum. Cells in the digestive gland directly release pigmented excretory chemicals into the lumen of the gut, which are then bound with mucus passed through the anus as long dark strings, ejected with the aid of exhaled water from the funnel. Cephalopods tend to concentrate ingested heavy metals in their body tissue. However, octopus arms use a family of cephalopod-specific chemotactile receptors (CRs) to be their "taste by touch" system.

Radula
The cephalopod radula consists of multiple symmetrical rows of up to nine teeth – thirteen in fossil classes. The organ is reduced or even vestigial in certain octopus species and is absent in Spirula. The teeth may be homodont (i.e. similar in form across a row), heterodont (otherwise), or ctenodont (comb-like). Their height, width and number of cusps is variable between species. The pattern of teeth repeats, but each row may not be identical to the last; in the octopus, for instance, the sequence repeats every five rows.

Cephalopod radulae are known from fossil deposits dating back to the Ordovician. They are usually preserved within the cephalopod's body chamber, commonly in conjunction with the mandibles; but this need not always be the case; many radulae are preserved in a range of settings in the Mason Creek. Radulae are usually difficult to detect, even when they are preserved in fossils, as the rock must weather and crack in exactly the right fashion to expose them; for instance, radulae have only been found in nine of the 43 ammonite genera, and they are rarer still in non-ammonoid forms: only three pre-Mesozoic species possess one.

Excretory system
Most cephalopods possess a single pair of large nephridia. Filtered nitrogenous waste is produced in the pericardial cavity of the branchial hearts, each of which is connected to a nephridium by a narrow canal. The canal delivers the excreta to a bladder-like renal sac, and also resorbs excess water from the filtrate. Several outgrowths of the lateral vena cava project into the renal sac, continuously inflating and deflating as the branchial hearts beat. This action helps to pump the secreted waste into the sacs, to be released into the mantle cavity through a pore.

Nautilus, unusually, possesses four nephridia, none of which are connected to the pericardial cavities.

The incorporation of ammonia is important for shell formation in terrestrial molluscs and other non-molluscan lineages. Because protein (i.e. flesh) is a major constituent of the cephalopod diet, large amounts of ammonium ions are produced as waste. The main organs involved with the release of this excess ammonium are the gills. The rate of release is lowest in the shelled cephalopods Nautilus and Sepia as a result of their using nitrogen to fill their shells with gas to increase buoyancy. Other cephalopods use ammonium in a similar way, storing the ions (as ammonium chloride) to reduce their overall density and increase buoyancy.

Reproduction and life cycle

Cephalopods are a diverse group of species, but share common life history traits, for example, they have a rapid growth rate and short life spans. Stearns (1992) suggested that in order to produce the largest possible number of viable offspring, spawning events depend on the ecological environmental factors of the organism. The majority of cephalopods do not provide parental care to their offspring, except, for example, octopus, which helps this organism increase the survival rate of their offspring. Marine species' life cycles are affected by various environmental conditions. The development of a cephalopod embryo can be greatly affected by temperature, oxygen saturation, pollution, light intensity, and salinity. These factors are important to the rate of embryonic development and the success of hatching of the embryos. Food availability also plays an important role in the reproductive cycle of cephalopods. A limitation of food influences the timing of spawning along with their function and growth. Spawning time and spawning vary among marine species; it's correlated with temperature, though cephalopods in shallow water spawn in cold months so that the offspring would hatch at warmer temperatures. Breeding can last from several days to a month.

Sexual maturity
Cephalopods that are sexually mature and of adult size begin spawning and reproducing. After the transfer of genetic material to the following generation, the adult cephalopods in most species then die. Sexual maturation in male and female cephalopods can be observed internally by the enlargement of gonads and accessory glands. Mating would be a poor indicator of sexual maturation in females; they can receive sperm when not fully reproductively mature and store them until they are ready to fertilize the eggs. Males are more aggressive in their pre-mating competition when in the presence of immature females than when competing for a sexually mature female. Most cephalopod males develop a hectocotylus, an arm tip which is capable of transferring their spermatozoa into the female mantle cavity. Though not all species use a hectocotylus; for example, the adult nautilus releases a spadix. Some male squids, mainly deep-water species, have instead evolved a penis longer than their own body length, the longest penis in any free-living animals. It is assumed these males simply attach a spermatophore anywhere on a female's body. An indication of sexual maturity of females is the development of brachial photophores to attract mates.

Fertilization
Cephalopods are not broadcast spawners. During the process of fertilization, the females use sperm provided by the male via external fertilization. Internal fertilization is seen only in octopuses. The initiation of copulation begins when the male catches a female and wraps his arm around her, either in a "male to female neck" position or mouth to mouth position, depending on the species. The males then initiate the process of fertilization by contracting their mantle several times to release the spermatozoa. Cephalopods often mate several times, which influences males to mate longer with females that have previously, nearly tripling the number of contractions of the mantle. To ensure the fertilization of the eggs, female cephalopods release a sperm-attracting peptide through the gelatinous layers of the egg to direct the spermatozoa. Female cephalopods lay eggs in clutches; each egg is composed of a protective coat to ensure the safety of the developing embryo when released into the water column. Reproductive strategies differ between cephalopod species. In giant Pacific octopus, large eggs are laid in a den; it will often take several days to lay all of them. Once the eggs are released and normally attached to a sheltered substrate, the female usually die shortly after, but octopuses and a few squids will look after their eggs afterwards. Others, like the Japanese flying squid, will spawn neutrally buoyant egg masses which will float at the interface between water layers of slightly different densities, or the female will swim around while carrying the eggs with her. Most species are semelparous (only reproduce once before dying), the only known exceptions are the vampire squid, the lesser Pacific striped octopus and the nautilus, which are iteroparous. In some species of cephalopods, egg clutches are anchored to substrates by a mucilaginous adhesive substance. These eggs are swelled with perivitelline fluid (PVF), a hypertonic fluid that prevents premature hatching. Fertilized egg clusters are neutrally buoyant depending on the depth that they were laid, but can also be found in substrates such as sand, a matrix of corals, or seaweed. Because these species do not provide parental care for their offspring, egg capsules can be injected with ink by the female in order to camouflage the embryos from predators.

Male–male competition
Most cephalopods engage in aggressive sex: a protein in the male capsule sheath stimulates this behavior. They also engage in male–male aggression, where larger males tend to win the interactions. When a female is near, the males charge one another continuously and flail their arms. If neither male backs away, the arms extend to the back, exposing the mouth, followed by the biting of arm tips. During mate competition males also participate in a technique called flushing. This technique is used by the second male attempting to mate with a female. Flushing removes spermatophores in the buccal cavity that was placed there by the first mate by forcing water into the cavity. Another behavior that males engage in is sneaker mating or mimicry – smaller males adjust their behavior to that of a female in order to reduce aggression. By using this technique, they are able to fertilize the eggs while the larger male is distracted by a different male. During this process, the sneaker males quickly insert drop-like sperm into the seminal receptacle.

Mate choice
Mate choice is seen in cuttlefish species, where females prefer some males over others, though characteristics of the preferred males are unknown. A hypothesis states that females reject males by olfactory cues rather than visual cues. Several cephalopod species are polyandrous – accepting and storing multiple male spermatophores, which has been identified by DNA fingerprinting. Females are no longer receptive to mating attempts when holding their eggs in their arms. Females can store sperm in two places (1) the buccal cavity where recently mated males place their spermatophores, and (2) the internal sperm-storage receptacles where sperm packages from previous males are stored. Spermatophore storage results in sperm competition; which states that the female controls which mate fertilizes the eggs. In order to reduce this sort of competition, males develop agonistic behaviors like mate guarding and flushing. The Hapalochlaena lunulata, or the blue-ringed octopus, readily mates with both males and females.

Sexual dimorphism
In a variety of marine organisms, it is seen that females are larger in size compared to the males in some closely related species. In some lineages, such as the blanket octopus, males become structurally smaller and smaller resembling a term, "dwarfism" dwarf males usually occurs at low densities. The blanket octopus male is an example of sexual-evolutionary dwarfism; females grow 10,000 to 40,000 times larger than the males and the sex ratio between males and females can be distinguished right after hatching of the eggs.

Embryology
Cephalopod eggs span a large range of sizes, from 1 to 30 mm in diameter. The fertilised ovum initially divides to produce a disc of germinal cells at one pole, with the yolk remaining at the opposite pole. The germinal disc grows to envelop and eventually absorb the yolk, forming the embryo. The tentacles and arms first appear at the hind part of the body, where the foot would be in other molluscs, and only later migrate towards the head.

The funnel of cephalopods develops on the top of their head, whereas the mouth develops on the opposite surface. The early embryological stages are reminiscent of ancestral gastropods and extant Monoplacophora.

The shells develop from the ectoderm as an organic framework which is subsequently mineralized. In Sepia, which has an internal shell, the ectoderm forms an invagination whose pore is sealed off before this organic framework is deposited.

Development

The length of time before hatching is highly variable; smaller eggs in warmer waters are the fastest to hatch, and newborns can emerge after as little as a few days. Larger eggs in colder waters can develop for over a year before hatching.

The process from spawning to hatching follows a similar trajectory in all species, the main variable being the amount of yolk available to the young and when it is absorbed by the embryo.

Unlike most other molluscs, cephalopods do not have a morphologically distinct larval stage. Instead, the juveniles are known as paralarvae. They quickly learn how to hunt, using encounters with prey to refine their strategies.

Growth in juveniles is usually allometric, whilst adult growth is isometric.

Evolution
The traditional view of cephalopod evolution holds that they evolved in the Late Cambrian from a monoplacophoran-like ancestor with a curved, tapering shell, which was closely related to the gastropods (snails). The similarity of the early shelled cephalopod Plectronoceras to some gastropods was used in support of this view. The development of a siphuncle would have allowed the shells of these early forms to become gas-filled (thus buoyant) in order to support them and keep the shells upright while the animal crawled along the floor, and separated the true cephalopods from putative ancestors such as Knightoconus, which lacked a siphuncle. Neutral or positive buoyancy (i.e. the ability to float) would have come later, followed by swimming in the Plectronocerida and eventually jet propulsion in more derived cephalopods.

Possible early Cambrian remains have been found in the Avalon Peninsula, matching genetic data for a pre-Cambrian origin. However, this specimen is later shown that is a chimerical fossil.

In 2010, some researchers proposed that Nectocaris pteryx is the early cephalopod, which did not have a shell and appeared to possess jet propulsion in the manner of "derived" cephalopods, complicated the question of the order in which cephalopod features developed. However, most of other researchers do not agree that Nectocaris actually being a cephalopod or even mollusk.

Early cephalopods were likely predators near the top of the food chain. After the late Cambrian extinction led to the disappearance of many Radiodonts, predatory niches became available for other animals. During the Ordovician period the primitive cephalopods underwent pulses of diversification to become diverse and dominant in the Paleozoic and Mesozoic seas.

In the Early Palaeozoic, their range was far more restricted than today; they were mainly constrained to sublittoral regions of shallow shelves of the low latitudes, and usually occurred in association with thrombolites. A more pelagic habit was gradually adopted as the Ordovician progressed. Deep-water cephalopods, whilst rare, have been found in the Lower Ordovician – but only in high-latitude waters. The mid-Ordovician saw the first cephalopods with septa strong enough to cope with the pressures associated with deeper water, and could inhabit depths greater than 100–200 m. The direction of shell coiling would prove to be crucial to the future success of the lineages; endogastric coiling would only permit large size to be attained with a straight shell, whereas exogastric coiling – initially rather rare – permitted the spirals familiar from the fossil record to develop, with their corresponding large size and diversity. (Endogastric means the shell is curved so as the ventral or lower side is longitudinally concave (belly in); exogastric means the shell is curved so as the ventral side is longitudinally convex (belly out) allowing the funnel to be pointed backward beneath the shell.)

The ancestors of coleoids (including most modern cephalopods) and the ancestors of the modern nautilus, had diverged by the Floian Age of the Early Ordovician Period, over 470 million years ago. The Bactritida, a Devonian–Triassic group of orthocones, are widely held to be paraphyletic without the coleoids and ammonoids, that is, the latter groups arose from within the Bactritida. An increase in the diversity of the coleoids and ammonoids is observed around the start of the Devonian period and corresponds with a profound increase in fish diversity. This could represent the origin of the two derived groups.

Unlike most modern cephalopods, most ancient varieties had protective shells. These shells at first were conical but later developed into curved nautiloid shapes seen in modern nautilus species. Competitive pressure from fish is thought to have forced the shelled forms into deeper water, which provided an evolutionary pressure towards shell loss and gave rise to the modern coleoids, a change which led to greater metabolic costs associated with the loss of buoyancy, but which allowed them to recolonize shallow waters. However, some of the straight-shelled nautiloids evolved into belemnites, out of which some evolved into squid and cuttlefish. The loss of the shell may also have resulted from evolutionary pressure to increase maneuverability, resulting in a more fish-like habit.

There has been debate on the embryological origin of cephalopod appendages. Until the mid-twentieth century, the "Arms as Head" hypothesis was widely recognized. In this theory, the arms and tentacles of cephalopods look similar to the head appendages of gastropods, suggesting that they might be homologous structures. Cephalopod appendages surround the mouth, so logically they could be derived from embryonic head tissues. However, the "Arms as Foot" hypothesis, proposed by Adolf Naef in 1928, has increasingly been favoured; for example, fate mapping of limb buds in the chambered nautilus indicates that limb buds originate from "foot" embryonic tissues.

Genetics
The sequencing of a full Cephalopod genome has remained challenging to researchers due to the length and repetition of their DNA. The characteristics of Cephalopod genomes were initially hypothesized to be the result of entire genome duplications. Following the full sequencing of a California two-spot octopus, the genome showed similar patterns to other marine invertebrates with significant additions to the genome assumed to be unique to Cephalopods. No evidence of full genome duplication was found.

Within the California two-spot octopus genome there are substantial replications of two gene families. Significantly, the expanded gene families were only previously known to exhibit replicative behaviour within vertebrates. The first gene family was identified as the Protocadherins which are attributed to neuron development. Protocadherins function as cell adhesion molecules, essential for synaptic specificity. The mechanism for Protocadherin gene family replication in vertebrates is attributed to complex splicing, or cutting and pasting, from a locus. Following the sequencing of the California two-spot octopus, researchers found that the Prorocadherin gene family in Cephalopods has expanded in the genome due to tandem gene duplication. The different replication mechanisms for Protocadherin genes indicate an independent evolution of Protocadherin gene expansion in vertebrates and invertebrates. Analysis of individual Cephalopod Protocadherin genes indicate independent evolution between species of Cephalopod. A species of shore squid Doryteuthis pealeii with expanded Protocadherin gene families differ significantly from those of the California two-spot octopus suggesting gene expansion did not occur before speciation within Cephalopods. Despite different mechanisms for gene expansion, the two-spot octopus Protocadherin genes were more similar to vertebrates than squid, suggesting a convergent evolution mechanism. The second gene family known as C2H2 are small proteins that function as zinc transcription factors. C2H2 are understood to moderate DNA, RNA and protein functions within the cell.

The sequenced California two spot octopus genome also showed a significant presence of transposable elements as well as transposon expression. Although the role of transposable elements in marine vertebrates is still relatively unknown, significant expression of transposons in nervous system tissues have been observed. In a study conducted on vertebrates, the expression of transposons during development in the fruitfly Drosophila melanogaster activated genomic diversity between neurons. This diversity has been linked to increased memory and learning in mammals. The connection between transposons and increased neuron capability may provide insight into the observed intelligence, memory and function of Cephalopods.

Using long-read sequencing, researchers have decoded the cephalopod genomes and discovered they have been churned and scrambled. The genes were compared to those of thousands of other species and while blocks of three or more genes co-occurred between squid and octopus, the blocks of genes were not found together in any other animals'. Many of the groupings were in the nervous tissue, suggesting the course they adapted their intelligence.

Phylogeny
The approximate consensus of extant cephalopod phylogeny, after Whalen & Landman (2022), is shown in the cladogram. Mineralized taxa are in bold.

The internal phylogeny of the cephalopods is difficult to constrain; many molecular techniques have been adopted, but the results produced are conflicting. Nautilus tends to be considered an outgroup, with Vampyroteuthis forming an outgroup to other squid; however in one analysis the nautiloids, octopus and teuthids plot as a polytomy. Some molecular phylogenies do not recover the mineralized coleoids (Spirula, Sepia, and Metasepia) as a clade; however, others do recover this more parsimonious-seeming clade, with Spirula as a sister group to Sepia and Metasepia in a clade that had probably diverged before the end of the Triassic.

Molecular estimates for clade divergence vary. One 'statistically robust' estimate has Nautilus diverging from Octopus at.

Taxonomy
The classification presented here, for recent cephalopods, follows largely from Current Classification of Recent Cephalopoda (May 2001), for fossil cephalopods takes from Arkell et al. 1957, Teichert and Moore 1964, Teichert 1988, and others. The three subclasses are traditional, corresponding to the three orders of cephalopods recognized by Bather.

Class Cephalopoda († indicates extinct groups)
 * Subclass Nautiloidea: Fundamental ectocochliate cephalopods that provided the source for the Ammonoidea and Coleoidea.
 * Order † Plectronocerida: the ancestral cephalopods from the Cambrian Period
 * Order † Ellesmerocerida
 * Order † Endocerida
 * Order † Actinocerida
 * Order † Discosorida
 * Order † Pseudorthocerida
 * Order † Tarphycerida
 * Order † Oncocerida
 * Order Nautilida (extant; 410.5 Ma to present)
 * Order † Orthocerida
 * Order † Ascocerida
 * Order † Bactritida
 * Subclass † Ammonoidea: Ammonites
 * Order † Goniatitida
 * Order † Ceratitida
 * Order † Ammonitida
 * Subclass Coleoidea (410.0 Ma-Rec)
 * Cohort † Belemnoidea: Belemnites and kin
 * Genus † Jeletzkya
 * Order † Aulacocerida
 * Order † Phragmoteuthida
 * Order † Hematitida
 * Order † Belemnitida
 * Genus † Belemnoteuthis
 * Cohort Neocoleoidea
 * Superorder Decapodiformes (also known as Decabrachia or Decembranchiata)
 * Order Spirulida: Ram's horn squid
 * Order Sepiida: cuttlefish
 * Order Sepiolida: pygmy, bobtail and bottletail squid
 * Order Idiosepida
 * Order Oegopsida: neritic squid
 * Order Myopsida: coastal squid
 * Order Bathyteuthida
 * Superorder Octopodiformes (also known as Vampyropoda)
 * Family † Trachyteuthididae
 * Order Vampyromorphida: Vampire squid
 * Order Octopoda: octopus
 * Superorder † Palaeoteuthomorpha
 * Order † Boletzkyida

Other classifications differ, primarily in how the various decapod orders are related, and whether they should be orders or families.

Suprafamilial classification of the Treatise
This is the older classification that combines those found in parts K and L of the Treatise on Invertebrate Paleontology, which forms the basis for and is retained in large part by classifications that have come later.

Nautiloids in general (Teichert and Moore, 1964) sequence as given.

 * Subclass † Endoceratoidea. Not used by Flower, e.g. Flower and Kummel 1950, interjocerids included in the Endocerida.
 * Order † Endocerida
 * Order † Intejocerida

 * Subclass † Actinoceratoidea Not used by Flower, ibid
 * Order † Actinocerida

 * Subclass Nautiloidea Nautiloidea in the restricted sense.
 * Order † Ellesmerocerida Plectronocerida subsequently split off as separate order.
 * Order † Orthocerida Includes orthocerids and pseudorthocerids
 * Order † Ascocerida
 * Order † Oncocerida
 * Order † Discosorida
 * Order † Tarphycerida
 * Order † Barrandeocerida A polyphyletic group now included in the Tarphycerida
 * Order Nautilida

 * Subclass † Bactritoidea
 * Order † Bactritida

Paleozoic Ammonoidea (Miller, Furnish and Schindewolf, 1957)
 * Suborder † Anarcestina
 * Suborder † Clymeniina
 * Suborder † Goniatitina
 * Suborder † Prolecanitina

Mesozoic Ammonoidea (Arkel et al., 1957)
 * Suborder † Ceratitina
 * Suborder † Phylloceratina
 * Suborder † Lytoceratina
 * Suborder † Ammonitina

Subsequent revisions include the establishment of three Upper Cambrian orders, the Plectronocerida, Protactinocerida, and Yanhecerida; separation of the pseudorthocerids as the Pseudorthocerida, and elevating orthoceratid as the Subclass Orthoceratoidea.

Shevyrev classification
Shevyrev (2005) suggested a division into eight subclasses, mostly comprising the more diverse and numerous fossil forms, although this classification has been criticized as arbitrary, lacking evidence, and based on misinterpretations of other papers. Class Cephalopoda
 * Subclass † Ellesmeroceratoidea
 * Order † Plectronocerida
 * Order † Protactinocerida
 * Order † Yanhecerida
 * Order † Ellesmerocerida
 * Subclass † Endoceratoidea
 * Order † Endocerida
 * Order † Intejocerida
 * Subclass † Actinoceratoidea
 * Order † Actinocerida
 * Subclass Nautiloidea (490.0 Ma- Rec)
 * Order † Basslerocerida
 * Order † Tarphycerida
 * Order † Lituitida
 * Order † Discosorida
 * Order † Oncocerida
 * Order Nautilida (410.5 Ma-Rec)
 * Subclass † Orthoceratoidea
 * Order † Orthocerida
 * Order † Ascocerida
 * Order † Dissidocerida
 * Order † Bajkalocerida
 * Subclass † Bactritoidea
 * Subclass † Ammonoidea
 * Subclass Coleoidea (410.0 Ma-rec)

Cladistic classification
Another recent system divides all cephalopods into two clades. One includes nautilus and most fossil nautiloids. The other clade (Neocephalopoda or Angusteradulata) is closer to modern coleoids, and includes belemnoids, ammonoids, and many orthocerid families. There are also stem group cephalopods of the traditional Ellesmerocerida that belong to neither clade.

The coleoids, despite some doubts, appear from molecular data to be monophyletic.

In culture

Ancient seafaring people were aware of cephalopods, as evidenced by such artworks as a stone carving found in the archaeological recovery from Bronze Age Minoan Crete at Knossos (1900 – 1100 BC), which has a depiction of a fisherman carrying an octopus. The terrifyingly powerful Gorgon of Greek mythology may have been inspired by the octopus or squid, the octopus's body representing the severed head of Medusa, the beak as the protruding tongue and fangs, and its tentacles as the snakes.

The Kraken are legendary sea monsters of giant proportions said to dwell off the coasts of Norway and Greenland, usually portrayed in art as giant cephalopods attacking ships. Linnaeus included it in the first edition of his 1735 Systema Naturae. In a Hawaiian creation myth that says the present cosmos is the last of a series which arose in stages from the ruins of the previous universe, the octopus is the lone survivor of the previous, alien universe. The Akkorokamui is a gigantic tentacled monster from Ainu folklore.

A battle with an octopus plays a significant role in Victor Hugo's book Travailleurs de la mer (Toilers of the Sea), relating to his time in exile on Guernsey. Ian Fleming's 1966 short story collection Octopussy and The Living Daylights, and the 1983 James Bond film were partly inspired by Hugo's book.

Japanese erotic art, shunga, includes ukiyo-e woodblock prints such as Katsushika Hokusai's 1814 print Tako to ama (The Dream of the Fisherman's Wife), in which an ama diver is sexually intertwined with a large and a small octopus. The print is a forerunner of tentacle erotica.

Its many arms that emanate from a common center means that the octopus is sometimes used to symbolize a powerful and manipulative organization.

title: Cephalopod


text:
Signal reflection

In telecommunications, signal reflection occurs when a signal is transmitted along a transmission medium, such as a copper cable or an optical fiber. Some of the signal power may be reflected back to its origin rather than being carried all the way along the cable to the far end. This happens because imperfections in the cable cause impedance mismatches and non-linear changes in the cable characteristics. These abrupt changes in characteristics cause some of the transmitted signal to be reflected. In radio frequency (RF) practice this is often measured in a dimensionless ratio known as voltage standing wave ratio (VSWR) with a VSWR bridge. The ratio of energy bounced back depends on the impedance mismatch. Mathematically, it is defined using the reflection coefficient.

Because the principles are the same, this concept is perhaps easiest to understand when considering an optical fiber. Imperfections in the glass create mirrors that reflect the light back along the fiber.

Impedance discontinuities cause attenuation, attenuation distortion, standing waves, ringing and other effects because a portion of a transmitted signal will be reflected back to the transmitting device rather than continuing to the receiver, much like an echo. This effect is compounded if multiple discontinuities cause additional portions of the remaining signal to be reflected back to the transmitter. This is a fundamental problem with the daisy chain method of connecting electronic components.

When a returning reflection strikes another discontinuity, some of the signal rebounds in the original signal direction, creating multiple echo effects. These forward echoes strike the receiver at different intervals making it difficult for the receiver to accurately detect data values on the signal. The effects can resemble those of jitter.

Because damage to the cable can cause reflections, an instrument called an electrical time-domain reflectometer (ETDR; for electrical cables) or an optical time-domain reflectometer (OTDR; for optical cables) can be used to locate the damaged part of a cable. These instruments work by sending a short pulsed signal into the cable and measuring how long the reflection takes to return. If only reflection magnitudes are desired, however, and exact fault locations are not required, VSWR bridges perform a similar but lesser function for RF cables.

The combination of the effects of signal attenuation and impedance discontinuities on a communications link is called insertion loss. Proper network operation depends on constant characteristic impedance in all cables and connectors, with no impedance discontinuities in the entire cable system. When a sufficient degree of impedance matching is not practical, echo suppressors or echo cancellers, or both, can sometimes reduce the problems.

The Bergeron diagram method, valid for both linear and non-linear models, evaluates the reflection's effects in an electric line.

title: Signal reflection