Ok, in truth, this was inspired by this post on Pharyngula, but that was not the whole point of PZ's post, so I was going to use some other source... but frankly, if you google "echidna penis" you get more than, perhaps, you were looking for. Anyway, go ahead and do an image search for an echidna's penis, and you will see that it has four heads. A little more looking into the available information about female echidnas, and you may understand why.
I count myself very grateful indeed that I am not an Echidna.
Two heads are better than one, so they say,
So four heads are better by far;
It took evolution to build this array,
And to humans, it still seems bizarre.
It never would work for a human male, though,
(Is it blessing, or is it a pity?)
See, men tend to think with their dicks, and we know
That nothing gets done by committee.