Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
It is a common myth that an earthworm becomes two worms when cut in half. However, only a limited number of earthworm species are capable of anterior regeneration. When most earthworms are bisected, only the front half of the worm (where the mouth is located) can survive, while the other half dies. Also, species of the planaria family of flatworms actually do become two new planaria when bisected or split down the middle.

Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
The signing of the Declaration of Independence did not occur on July 4, 1776. The final language of the document was approved by the Second Continental Congress on that date, it was printed and distributed on July 4 and 5, but the actual signing occurred on August 2, 1776.

Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
The United States Constitution was written on parchment, not hemp paper. It is likely that drafts of the document were written on hemp, since a large portion of paper at the time was made from the material.

Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
Napoleon I (Napoleon Bonaparte) (pictured) was not particularly short, and did not have a Napoleon complex. After his death in 1821, the French emperor’s height was recorded as 5 feet 2 inches in French feet. This corresponds to 5 feet 6.5 inches in modern international feet, or 1.686 metres. There are competing explanations for why he was nicknamed le Petit Caporal (The Little Corporal), but few modern scholars believe it referred to his physical stature.

Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
Abraham Lincoln's Emancipation Proclamation of January 1863 did not immediately free all American slaves. The Proclamation pertained only to areas within rebelling states that were not under Union control. Since those states did not recognize the power of the federal government, most slaves were not immediately freed as a direct result of the Proclamation. Regions in the South that were under Confederate control when the Proclamation was issued ignored its dictum, so slave ownership persisted until Union troops captured further Southern territory. Immediately affected regions were Tennessee, southern Louisiana, and parts of Virginia. It was only with the adoption of the Thirteenth Amendment in 1865 that slavery was officially abolished in all of the United States. Thirty-six of the United States recognize June 19 as a holiday, Juneteenth, celebrating the anniversary of the day the abolition of slavery was announced in Texas in 1865.

Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
Italian dictator Benito Mussolini did not “make the trains run on time”. Much of the repair work had been performed before Mussolini and the Fascists came to power in 1922. Accounts from the era also suggest that the Italian railways’ legendary adherence to timetables was more myth than reality. Mussolini's trains were subject to frequent labour disruptions due to his conflict with labour unions.

Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
During the German Invasion of Poland in 1939, there is no evidence of Polish Cavalry mounting a brave but futile charge against German tanks using lances and sabres. This seems to have its origins in German propaganda efforts following the Charge at Krojanty in which a Polish cavalry brigade surprised German infantry in the open and charged with sabres until driven off by armoured cars. While Polish cavalry still carried the sabre for such opportunities, they were trained to fight as highly mobile, dismounted infantry and issued with light anti-tank weapons.

Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
During World War II, King Christian X of Denmark did not thwart Nazi attempts to identify Jews by wearing a yellow star himself. Jews in Denmark were never forced to wear the Star of David. The Danes did help most Jews flee the country before the end of the war.

Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
John F. Kennedy's words "Ich bin ein Berliner" are standard German for "I am a Berliner". An urban legend has it that due to his use of the indefinite article ein, Berliner is translated as jam doughnut, and that the population of Berlin was amused by the supposed mistake. The word Berliner is not commonly used in Berlin to refer to the Berliner Pfannkuchen; they are simply called Pfannkuchen. In other parts of Germany, though, the term "Berliner" actually also is used for the product in question, so there is a grain of truth in the myth.