Twins

 are two produced by the same. Twins can be either monozygotic ("identical"), meaning that they develop from one, which splits and forms two embryos, or dizygotic ("fraternal"), meaning that they develop from two different eggs. In fraternal twins, each twin is fertilized by its own sperm cell.

Quotes

 * If you’ve ever sat in a room with twins, immediately you’re forced to deal with this confusion. You’re afraid to call them by name because you’re afraid you’re going to get it wrong. At first being a twin is a source of power, you can switch, you can fool people—but then it becomes a vulnerability because people confuse you when you don’t want them to. The famous story of the twins who were both spanked when either one of them did something wrong because the parents wanted to make sure they got the right twin. So that would immediately make each twin totally responsible for the other one’s actions and therefore would make you want to control the other twin’s actions. It gets quite twisted and the confusion of identities becomes quite intense.
 * David Cronenberg

καππεσέτην, ἐλάτῃσιν ἐοικότες ὑψηλῇσι. down they crashed like lofty pine trees axed.
 * Τοίω τὼ χείρεσσιν ὑπ' Αἰνείαο δαμέντε
 * So here the twins were laid low at ' hands,
 * Homer,  (c. 750 BC), Book V. 559–560 (tr. Robert Fagles).


 * More tears. Disgraceful. I was getting just like Kester, weeping at the drop of a hat, but of course I was Kester. I'd become him, and now there was just this other stranger who wrote me debonair notes and who sounded just like me.
 * Susan Howatch, The Wheel of Fortune


 * For one of us was born a twin And not a soul knew which.
 * , "The Twins", line 7, in Carols of Cockayne (London: John Camden Hotten, 1869) p. 9.