where_away | Ram and Puss

'Brother, how tedious you can be, on occasion. I did hear some cries of "Jolly rogers - jolly rogers - we shall roger them." But in parenthesis, Jack, tell me about this word roger. I have often heard it aboard, but can make out no clear nautical signification.'
'Oh, it is no sea-term. They use it ashore much more than we do - a low cant expression meaning to swive or couple with.'
Stephen considered for a moment and then said, 'So roger joins bugger and that even coarser word; and they are all used in defiance and contempt, as though to an enemy; which seems to show a curious light on the lover's subjacent emotions. Conquest, rape, subjugation: have women a private language of the same nature, I wonder?"
Jack said, 'In some parts of the West Country rams are called Roger, as cats are called Puss; and of course that is their duty; though which came first, the deed or the doer, the goose or the egg, I am not learned enough to tell.'
'Would it not be the owl, at all?'
'Never in life, my poor Stephen. Who ever heard of a golden owl?

Why is it the duty of the rams to be called Roger, and of cats to be called Puss?