Well, during this period in the mid and late '60s, Francis had got very interested in gradients. The idea was – and it was one of the things that Lewis Wolpert had put forward as… a new idea in embryology – that cells took up their characteristics from their positions in a gradient field. Now the… the idea of gradients in development is very old. It goes back to the last years of the last century [sic], where in fact gradients were observed in eggs. But this idea was in fact, I think, very novel and Lewis didn't get much interest in this. I can remember finding Lewis in Woods Hole in the late '60s very depressed, saying that he'd given these lectures on gradients and no one had paid any attention to him. At that time I was teaching in Woods Hole and I can remember people discussing questions like, is differentiation a state or a process? And in fact, to try and explain the difference between these, I asked people the… what is the difference between laid-back and mellowing out? Some of… some people may remember these great words of the '60s. And, of course, that's exactly the difference between a state and a process. Mellowing out is a process, and laid-back is a state. Of course, by mellowing out you hope to reach the laid-back state. So this wasn't a… an academic question. However, what Francis got interested in was that the sizes of things – and that's the thing he noticed – were scaled about to what you would expect from a diffusion gradient. And so Francis began to do calculations on this, and indeed began to interest people in experiments.