Poem and song origins
In the Victorian Era children had to learn many moralizing poems by heart. Carroll altered some of these (once very familiar) verses for the Alice books, of course 
to the amusement of the Liddell sisters. Unfortunately these poems are hardly remembered nowadays, so the fun of the parody has disappeared for the greater part. Carroll also created new lyrics to famous melodies of the time.
The original poems and songs are being compared to Carroll’s parodies here, and you can read more about their origins.
`Let’s hear it,’ said Humpty Dumpty. `I can explain all the poems that were ever invented — and a good many that haven’t been invented just yet.’