And the definitive answer is:-

THE HEN

It's the very foolish theory Of some very foolish men
That the egg is just the hen's way To make another hen.
That's what I hear them say But I differ, sir, to beg;
The hen, sir, is the egg's way To make another egg.

The egg's the main event; the hen's A temporary mode;
An interim device to get The egg across the road.
No hen has never fathomed Why they cross the thoroughfare;
To the hen it's immaterial; The egg needs to be there.

Some folk will go through life And never have the slightest notion
That the egg makes the decision And the hen supplies the motion.
The chicken's rather stupid; It's the egg that really plans it;
And so I say to you A hen is just an egg in transit

Plaudits to the irrepressible Les