This aspect triggered the publica­ tion of this book, and in fact the various chapters emphasize that the funetional eomponents, expressed in the various epithelia, are not in­ finite in number, but they occur in epithelia which are separated in evolu­ tion by several hundred million years.

Assisted by: R. Bakker, G.A. Gerencser, R. Gilles, R. Greger, J.A. Groot, F. Lang, E.H. Larsen, W.S. Marshall, L.G. Palmer, A. Pequeux, E. Schlatter, M.J. Welsh