My dad used to sing this to us when we were kids. The main story was the same, but there was a different form to the song. I recall the last two verses were:

They rowed their boat across the lake,
Heigho, says Roly!
They rowed their boat across the lake,
And got swallowed up by a big black snake,
With a roly-poly, gammon and spinach,
Heigho, says Anthony Roly!

That was the end of him and her,
Heigho, says Roly!
That was the end of him and her,
Now we won't have tadpoles covered in fur,
With a roly-poly, gammon and spinach,
Heigho, says Anthony Roly!