Largely through the work of Paul Weiss, and it's wonderful work, on animal embryos - he was of the very strong opinion, and he liked to influence everybody else, including me, that chemotaxis was not something that you found in developing systems, but that it was what he called contact guidance, which it felt its way along. And although there was all… Anyhow that was the situation when I entered the battlefield. And so I tried to do all sorts of experiments, which would test this and I finally found one which I didn't have much faith in, but it turned out to be the answer. And that is that if you moved water around the central point of this aggregation that it carried something downstream which caused these amoebae downstream to orient up and crawl against it. And that kind of taxis is the same thing as if you have heat, if you had little heat spots. And so I had to look to be sure that it wasn't me. And I forget now exactly how we did it; it was a fairly simple experiment. And so the question that Paul Weiss had put before all of us was: a) did you have chemotaxis in development, yes; b) how can you demonstrate it so that you don't get a lot of arguments?