It is of value to look at the other senses of "tit" that were current. The first sense the OED lists for "tit" is "One blow or stroke in return for another; ... retaliation." We still retain this usage in "tit for tat," one blow for another. Under this first sense are listed several variations on the meaning of "blow," with usage dating from 1556 up to years contemporary with the dictionary itself.
The second group of senses forms around the idea of "tit" as a diminutive or under-sized horse, person (especially girl), mouse or bird (among which see "tit-willow," below). For the person, the word seems mostly to have been used against girls or young women, as a derogatory term, especially a girl or woman, as the OED puts it, "of a loose character, a hussy, a minx."
(The third group of senses has to do with pulling or tugging, especially with force or with sudden force. Usages for this sense go back to the 1300s and continue, though apparently not particularly frequently, up to the time the dictionary was written.)
Some people believe that the "tit-willow," rather than being a patent fabrication Ko-Ko uses to enlist Katisha's sympathies, must be a real bird, and they find in it an American quail which they believe Sullivan must have heard on his trip to America in the early 1880s. If this is so, then the worm is inexact, as quail don't eat worms. No bird, obviously, could have "cold perspiration bespangl[ing] his brow," so it is all just nonsense, anyway, since Ko-Ko clearly expects Katisha to identify him with the bird.
Martyn Green (Green 442 n. 99) associates the song "Willow, Tit-Willow" with Nicholas Rowe's 17th-century poem:
This discussion is based on the definition of the word tit in the first edition of the Oxford English Dictionary, which requires a little explanation.
To Act I or Act II of Gilbert and Sullivan's The Mikado.
To the homepage of this Mikado website.
Suggestions, contributions, criticisms, questions? Email Sharon Cogdill.
College of Fine Arts and Humanities
This URL: http://web.stcloudstate.edu/scogdill/mikado/titipu.html.
Last update: 16 May 1998.