The theme is the alternative verses to a well known nursery rhyme.
The second line reads
'In & Out the Eagle' so it is necessary to add or remove ERNE from the solution before entry to the grid.
1d is therefore F ERNE RY
The third line reads-
'That's the way the money goes' so M (money) must be removed before entry.
37d is therefore HAW(m) - lounge about.
12a Everyman - the misprint in the clue changes Zero to Hero - Everyman --always an unknown number to follow my answer.